In our last edition, Better, best, butter, we covered what butter is, how it’s made, and what it does in savory cooking. Today we turn to baking. Butter makes baked goods tender, moist, and rich. It holds air, extends shelf life, and helps dough rise. That makes it as indispensable to a pastry chef as to a cook.

Cookies show all of this at once. Shortbread, Viennese whirls, and a chewy chocolate chip cookie are built from the same ingredient, and how you work the butter into the dough decides the texture. First, a short detour through the Dutch cookie tradition.

One cookie with the coffee

The Netherlands is a true cookie country. Where others serve cake or pastry, a Dutch host puts out one koekje with the coffee. A koekje is small, precise, and carefully made. Koekje is even an export word: the English cookie comes straight from Dutch, from koekje, the diminutive of koek, “cake”. Etymonline dates the sweet, flat-cake sense to American English in 1808.

The Dutch cookie tradition took shape in the Golden Age, when sugar and spices arrived in the Netherlands in quantity. Bakers made their cookies from a shortbread-style dough of flour, butter, and sugar, with so little water that it bakes up crisp. Bakers call such a dough short: the butter coats the flour and keeps the gluten strands short, which leaves a tender, crumbly bite.

Today’s cookies are bigger, softer, and chewier, from New York style to brown butter, but they are still built on butter. Butter sets much of the structure, flavor, and aroma of every dough. How does that work?

1. Butter builds structure and texture

Butter shapes the texture of a cookie. The fat coats the flour particles with a thin film, so hardly any gluten forms. That makes the cookie crumbly instead of tough. During baking the butter melts and leaves small air pockets behind, which give the cookie its characteristic crisp structure.

The colder the butter when you mix, the coarser and crumblier the butter pieces in the dough, and the larger the pockets they leave behind. In practice, this means a crisper, more brittle cookie. Soft butter spreads more evenly through the dough and gives a finer structure. That is why the butter in our lemon short bread cookies (recipe follows) stays soft, but is deliberately never whipped.

2. Butter traps air

When you beat butter and sugar together, the sugar crystals punch thousands of tiny air bubbles into the fat. In the oven those bubbles expand, the dough rises, and it sets with a light, open structure. Butter temperature is critical here. Butter that is too cold won’t take up air, and butter that is too warm lets the bubbles collapse. Between the two lies a sweet spot of only a few degrees, and further on we pin it down to the degree.

It is the same principle as in a classic cake, where creaming is the engine of the whole bake. We went deep on it in our cake science edition. In cookie dough, more air means more expansion in the oven. Melted butter does the opposite. It holds no air, which gives a denser, chewier cookie that spreads instead of rising. Below, you’ll see why spritz cookies need the air, and why shortbread and brown butter cookies do without.

3. Butter carries aroma

Butter is a natural flavor enhancer. It contains hundreds of aroma compounds, and they become more complex in the oven. The milk fats and proteins form fragrant compounds such as diacetyl and lactones, which you recognize as the creamy, nutty smell of fresh-baked cookies.

It gets more intense with brown butter (beurre noisette), where the milk solids caramelize and give a full, nutty flavor. We show this in our brown butter chocolate chip cookies below. Butter also carries other aromas besides its own. You can capture them in infused butters, like the ones in Better, best, butter.

4. Butter builds color

Most of a cookie’s color comes from butter too. The milk sugars and proteins in butter react with each other during baking (the Maillard reaction), which gives that golden-brown tint and toasted flavor. Butterfat also conducts heat well, so cookies brown evenly and get crisp edges. It is also why we bake our brown butter cookies until the rim turns dark, while the center stays soft.

Time to bake

In the paid part of this edition we bake four recipes: lemon sablés (a sandy dough), a ginger Dutch butter cake, brown butter chocolate chip cookies, and orange-chocolate sablés made with orange butter. We also cover:

• working with cold, soft, and melted butter

• two cookie doughs, short dough and creamed dough, and when to use which

• resting and crystallization: when it helps and when it’s pointless

• the difference between dough and batter

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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I’m Eke Mariën, a curious chef and cookbook author based in Amsterdam, with a passion for the science of cooking. With a background in science, I threw myself into cooking. I ran a restaurant, a catering company and a delicatessen shop. Today I still write cookbooks and make food magazines at Het Kookkantoor, the culinary media studio I run with my wife, Annemarie. I also take all the photos myself. Since 2015 I have been writing about the science of cooking on Koken met Kennis, my Dutch-language newsletter and website. Kitchen Lab is its English edition, published every other week on Substack. (When an edition says “we”, that’s Annemarie and me.)

My motto:
if you understand what happens in your pan, you become a better cook.

My mission is to teach people to cook better and tastier, by explaining exactly what happens in the kitchen. Why flavors change, why vegetables turn soft and eggs turn firm, to name just a few things.

Is this cooking for nerds?

Yes and no. I wouldn’t call myself a nerd, but I can cook. What I am is curious. The more I understand about what happens in my pan or oven, the more I learn and the better I cook. I find that endlessly interesting, and I think many cooks will recognize it. And our food, our diets and our knowledge keep changing, so there is always something new to write about.

Five editions open to everyone

To help new readers find their way, I have opened five paid editions to everyone until 30 November. You already have all of them, plus the other 35 in the archive:

Why I’m telling you this

Kitchen Lab is more than a hobby to me. I put a lot of time and love into it, and your membership is what makes that possible. It lets me explain even more about the kitchen, and teach you all to cook even better. Thank you.

Know someone who would love this? Forward them one of the five editions above. This is a good moment.

Next week: butter, part 2

Next week it’s a regular edition again, and we dive back into the kitchen. Butter, part 2: what butter does in baking.

It makes bakes tender and moist, traps air and helps things rise. Think of crumbly Scottish shortbread, chewy American chocolate chip cookies and delicate French sablés. All butter, yet their textures couldn’t be more different. See you next week!

P.S. Hit reply and tell me: what question keeps popping up in your head while you cook? I read everything, and the best questions end up in a future edition.

Eke

I’m Eke Mariën, a curious chef and cookbook author based in Amsterdam, with a passion for the science of cooking. With a background in science, I threw myself into cooking. I ran a restaurant, a catering company and a delicatessen shop. Today I still write cookbooks and make food magazines at Het Kookkantoor, the culinary media studio I run with my wife, Annemarie. I also take all the photos myself.

Since 2015 I have been writing about the science of cooking on Koken met Kennis, my Dutch-language newsletter and website. Kitchen Lab is its English edition, published every other week on Substack. (When an edition says “we”, that’s Annemarie and me.)

My motto:
if you understand what happens in your pan, you become a better cook.

My mission is to teach people to cook better and tastier, by explaining exactly what happens in the kitchen. Why flavors change, why vegetables turn soft and eggs turn firm, to name just a few things.

Is this cooking for nerds?

Yes and no. I wouldn’t call myself a nerd, but I can cook. What I am is curious. The more I understand about what happens in my pan or oven, the more I learn and the better I cook. I find that endlessly interesting, and I think many cooks will recognize it. And our food, our diets and our knowledge keep changing, so there is always something new to write about.

Is Kitchen Lab for me?

That depends on you. Love science and cooking? Then it’s a definite yes. Just here for the recipes? You’ll still become a better cook. Not a fan of long reads? The Substack app can read editions aloud: tap the play icon. There’s a lot in between, so start by browsing. Five paid editions are now free for everyone until 30 November:

Is there more than newsletters?

Yes! Paying members get the complete archive, already 40 editions of around 3,000 words each. You’ll be busy for a while. You also get the Kitchen Lab Chat, where you can ask me and other members your questions. About cooking and food, preferably :-)

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You don’t have to. Every edition starts with an extensive free part: the theory behind the topic. Imagine an edition about fries: in the free part you read what makes them special, which potatoes to use and why, and what starch, sugar and water do in a potato. In the paid part we always go into the kitchen: the best techniques and the recipes, often with a video of the basic recipe.

Kitchen Lab is more than a hobby to me. I put a lot of time and love into it. If you want to support this, a paid membership is a great way. It lets me explain even more about the kitchen, and teach you all to cook even better.

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Next week: butter, part 2

Next week it’s a regular edition again, and we dive back into the kitchen. Butter, part 2: what butter does in baking.

It makes bakes tender and moist, traps air and helps things rise. Think of crumbly Scottish shortbread, chewy American chocolate chip cookies and delicate French sablés. All butter, yet their textures couldn’t be more different. See you next week!

P.S. Hit reply and tell me: what do you wonder about while you cook? Why does my sauce split? Why do my potatoes stay hard? Your question might become a future edition.

Butter enriches our lives. In flavor and energy (kcal), and in culinary applications. There’s so much to tell that it doesn’t fit in one newsletter. So it becomes two. In this first part, we tell you how butter is made, what the differences are between the many types in the supermarket, and about a dubious addition to cows’ diets that makes the milk fattier and our butter harder. We look at the savory applications of butter in the kitchen: as an emulsifier for making butter sauces (such as beurre blanc), as a flavor carrier for making compound and infused butters (such as herb and orange butter), and as a flavor intensifier in the form of beurre noisette. In the next newsletter, we explore the sweet side of butter in desserts and pastry.

What is butter?

Butter is made from the fat in milk: milk fat, also called butterfat. Butterfat consists mostly of saturated fat, which is why it’s firm at room temperature. Under European Union rules, butter must contain at least 80% butterfat, the rest is water, milk sugars, and proteins that stay trapped between the fat crystals during churning. The most common ratio in Dutch butter is about 82% milk fat, 16 to 17% water, and 1 to 2% milk components such as milk sugars and proteins. Exactly how that fat is composed ultimately determines the texture of the butter, more on that shortly.

How do you make butter?

Butter is nothing more than churned cream. When you let fresh milk stand, the fat slowly rises and forms a thick, yellowish layer on top of the milk: the cream. In the past, that cream was skimmed off by hand. By then whipping or churning the cream (a mechanical process in which the fat droplets collide with each other), the fat globules start clumping together. First you get whipped cream, the cream becomes thick and airy. If you keep whipping, the fat particles stick together so strongly that the water (the buttermilk) gets pushed out. You may know this from whipped cream that’s been whipped too far. The yellow butterfat has clumped together and sits in a puddle of water. You’ve accidentally made butter.

Sour milk

In the Netherlands, it used to be common to let the milk sour first, before skimming the cream off it. That gave a fresh, tangy flavor and slowed the growth of unwanted bacteria. These days, raw milk is no longer allowed to sour on its own: all milk is pasteurized, after which a bacterial culture is added for controlled souring. After about 24 hours, a thick, slightly sour cream forms.

Buttermilk

That cream is then churned: it’s tumbled around in large drums or vats (a kind of cement mixer), which separates the fat from the liquid. The liquid that’s left is called buttermilk and still contains very little fat, that fat is now in the butter. The fresh butter contains small amounts of water and milk components, which together give butter its typically creamy, slightly sour flavor.

Cultured versus sweet cream butter
In America, cream isn’t cultured before it’s churned into butter, it’s centrifuged straight from pasteurized milk. That gives so-called sweet cream butter a noticeably different flavor: no lactic acid bacteria, no tang. The standard varies by country: the Netherlands, Belgium, France, and Denmark culture their cream; England, Germany, and Australia mostly don’t.

That gap used to be much wider. In 1997, I worked at Charlie Trotter’s in Chicago. A French guest chef nearly despaired over American butter, it simply didn’t taste like home, and we scoured the city for something closer. These days, that search is easy: European-style and imported French butter are standard stock at most major supermarkets. That chef would have had a far easier night.

Butter and margarine

Margarine isn’t butter, but a fat emulsion based on vegetable oils that resembles butter in use and texture. The same 80% threshold that defines butter applies here too: in the US and the EU, a product only gets to call itself “margarine” above that fat percentage, anything leaner is sold as a ‘spread’ instead. Vegetable fats mainly contain unsaturated fatty acids, while animal fats such as milk fat are mostly saturated. That’s why saturated fat is solid at room temperature and unsaturated fat is liquid. To turn liquid oil into spreadable margarine, the fatty acids are partially transformed. In the past, harmful trans fats formed during this hardening process, but that problem has largely been solved by now. Modern margarines contain only trace amounts. Besides fat, margarine contains water, emulsifiers (such as lecithin), and sometimes small amounts of protein or milk components to blend the fat and water properly. So margarine is really something quite different from butter. And you can taste that too.

Grass-fed butter

Butter made from cows that also graze on grass (grass-fed butter) is usually softer. Their milk contains relatively more unsaturated fatty acids, which makes the butter creamier. The color also reveals something about the cow’s diet: butter from grass-fed cows is often more yellow because of the natural carotene in grass, while butter from barn-fed cows is lighter in color. That color difference isn’t always conclusive proof, though, season, breed, and processing play a role too. But if you need genuinely soft butter for a recipe, don’t go for the cheapest option, look closely at the color and the origin instead.

Cheap butter

So there are an enormous number of types of butter, with widely varying prices, packaging, and promises. Yet the production method is the same in most cases: all butter is made from cream. Butter is therefore automatically cream butter. During churning, the fats separate from the buttermilk. Cheap, then, doesn’t mean bad. Even cheap butter is simply real butter. Production is strictly monitored almost everywhere, whether that’s FDA and USDA oversight in the US or EU rules in Europe. Just as with wine and many other delicacies, the raw material determines the quality of the product. The difference is that with butter, that raw material isn’t so easy to read off the label. For that, you still have to trust your senses.

Getting into the kitchen with butter

In the paid section of this newsletter, we get to work with butter.

• How do you use butter as an emulsifier?

• How do you make the perfect beurre blanc and beurre bière?

• How do you use butter as a flavor carrier to lock in aromas?

• How do you clarify butter (with video)

• How do you make beurre noisette (with video), and how do you whip it up deliciously light?

• Five rich butter recipes!

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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I am excited to introduce you to Irina Totterman, who wrote today’s post. She teaches sourdough baking at sourdoughtalk.com and writes Sourdough Talk, where she digs into what works, what doesn’t, and what nobody actually knows yet. Irina is the first guest writer for Kitchen Lab. I plan to do this more often, on weekends between the regular Kitchen Lab editions. These guest posts are free for every reader, no paywall. Kitchen Lab is happy to give other chefs, bakers, and writers a stage when their work adds to a better understanding of what’s happening in our pots and pans. The motto stays the same: once you understand what’s happening in your pan, you become a better cook (or baker, in this case). Most of us think of cooking as a matter of time: thirty minutes in the oven, six hours on the counter, an hour at a simmer. Irina’s piece is a great example of why that’s the wrong way to think about it. What actually determines the result isn’t how long something cooks, it’s the temperature it reaches while doing it.

We often talk about temperature while in the kitchen. Preheat the oven to 400°F, heat the pan over medium heat, bake for thirty minutes, and cook until the center reaches a certain temperature. This is all about the environment we cook or bake in.

But we never remember that food itself has a temperature too. It sounds obvious until you start measuring it. And then, cooking starts to look different.

I learned this through sourdough, where I measure the temperature of water and flour, the dough temperature right after mixing, then during bulk fermentation, and finally the inside of the baked loaf. I started with sourdough, then began seeing the same idea in everything I cook and bake.

Time Is Not the Same as Progress

When a recipe tells you to bulk ferment sourdough for six hours, it gives you a time duration, but it doesn’t tell you how fast this is happening.

A dough at 78°F (26°C) and a dough at 70°F (21°C) behave differently, even if both have been fermented for exactly six hours. This is why sourdough bread recipes often confuse people. The recipe says six hours, and your dough either needs longer or was ready an hour ago. The reason is the difference in room temperature.

I started measuring the dough instead of trusting the recipe, and eventually I started doing the same with everything else I cook and bake.

Choosing a Temperature Instead of Discovering One

I’ve learned you can control your dough temperature from the start. Bakers call it Desired Dough Temperature (DDT). You choose a target, then adjust your water temperature based on how warm your flour and kitchen are that day. It’s especially useful when the seasons turn, because the recipe stays the same, but the environment changes.

The same idea works beyond bread. You start with the result you want and work backward instead of just following instructions.

Temperature Gives You Clues, Not Answers

The dough temperature I measure after mixing is a starting point. It doesn’t tell me when the bulk fermentation will be done.

During bulk, the dough can warm up or cool down depending on room temperature, the container, and how much dough I work with. Checking the dough temperature during bulk fermentation helps me understand why the dough behaves in the way it does.

But I can’t say that once the dough reaches 78°F (26°C), it is automatically ready for shaping. Bulk fermentation is a biological process. Temperature affects fermentation speed, but it doesn’t tell you when fermentation is finished.

I still use the visual cues: I look at how much the dough has risen, how it feels, how many bubbles are on the surface and sides of the bowl. The thermometer gives me the numbers, but I still need to read the dough. I developed this skill while baking.

Then There’s the Loaf Itself

Once the dough goes into the oven, the oven temperature comes into play. The oven might be at 450°F (232°C) for 20 minutes, but the internal bread temperature doesn’t correspond to that number. Heat moves inward as the crust dries and browns, the center slowly heats up, the bread gets its oven spring, and the dough’s structure changes.

For the loaves I bake, I usually aim for an internal temperature of 205°F to 210°F (96°C to 99°C), often targeting 207°F (97°C).

The Same Thinking Works Everywhere Else

Once you separate the oven temperature from the food temperature, you start seeing the difference everywhere.

Meat is a simple example. Your oven temperature doesn’t tell you whether a chicken breast is done, because the outside is usually much hotter than the center. For example, the USDA recommends cooking chicken breast to an internal temperature of 165°F (74°C), even when the oven is at 400°F (204°C) or higher. That difference is why you need to measure the internal temperature when food safety is the concern.

Note: These temperatures are based on USDA recommendations and may differ by country.

Cakes work the same way. Baking a cake in a 350°F (177°C) oven doesn’t mean it is ready. Most cakes are done when the inside reaches about 200°F to 210°F (93°C to 99°C), but we usually check by looking at the cake and its texture, and sometimes use a thermometer. The oven tells you about heat, but a toothpick and a thermometer inserted in the middle of the cake tell you what’s actually happening.

Custards are different because temperature helps create the texture. As the eggs heat, they thicken the custard. A stirred custard usually thickens around 170°F to 180°F (77°C to 82°C). If it does not get hot enough, the custard stays too thin. If it gets too hot, the eggs become too firm, and the custard turns unpleasant. So temperature not only tells you when the custard is done, but it also helps create the texture.

Chocolate. Tempering dark chocolate means melting it to around 115°F (46°C), cooling it to about 82°F (28°C), then bringing it back up to about 88°F to 90°F (31°C to 32°C). This lets the cocoa butter form the crystal structure you want. Reaching these numbers seems unnecessary, but they make a big difference. A thermometer doesn’t just check the end of the process; it’s the tool you use for proper chocolate tempering.

Fermented foods. Temperature affects how fast fermentation happens. It changes how quickly a starter ferments and rises and how it changes over time. A sourdough starter at 75°F (24°C) and one at 68°F (20°C) ferment at very different speeds, but temperature is only one part of the process. Flour type, strength, water quality, microbial community, acidity, hydration, and time also play a role.

What a Thermometer Actually Does

Measuring temperature has taught me a lot, but it’s also been a bit disappointing.

I’d love one perfect number that tells me when the bulk is done, but there are more questions to answer before the dough is ready for shaping. Sourdough works differently: you need to use your eyes to read the dough. No single magic temperature can tell you when bulk fermentation is done.

A thermometer tells you the temperature when you check it. It does not tell you what happened before or what will happen next. It also does not replace your eyes, hands, or experience. It simply gives you one more piece of information to help you understand what is happening.

It Changes How You Read a Recipe

This is where I noticed the biggest difference.

Instead of reading “bulk ferment for six hours” and setting a timer, you start asking what the dough temperature is and how it changes throughout bulk fermentation. Instead of reading “bake at 450°F for 20 minutes,” you start thinking about what is happening inside your loaf. Instead of “bake until done,” you measure the internal temperature to know when it is actually done.

It sounds like more work, but it usually makes things easier. When something goes wrong, you have more information on your hands, so you can figure out what happened instead of guessing.

I started measuring dough temperature because I wanted to bake more consistent bread. In the end, I started thinking differently about food.

Temperature is not just a setting on the oven. It affects fermentation, texture, structure, and other changes in the dough and food in general. Your dough has a temperature. So does your cake, steak, custard, chocolate, and yogurt.

I teach sourdough baking. If you’d like to learn and bake sourdough with me, that’s what I write about here: what happens in my kitchen, what works, what doesn’t, and what we still don’t have answers for.

Learn Sourdough With Me

Before we start, I want to share my enthusiasm about the enormous recent growth of Kitchen Lab, thanks to a note I posted last Tuesday, see below. It was actually a simple message saying that Kitchen Lab is here to explain what’s happening in your pots and pans, not just to share recipes. The counter jumped from nearly 13,000 to over 20,000 subscribers in just a few days, and it’s still climbing. To all those new curious cooks I want to say:

Welcome, all! Make yourself at home and dive deep with Kitchen Lab. To give you a better idea of what we do, I removed the paywall from three newsletters, so you can browse around and see what we’re up to.

1. Curry Part I. The flavor is in the fat: kitchenlab.substack.com…

2. Cheesecake. Soft. Creamy. Irresistible: kitchenlab.substack.com…

3. Fermentation. Cooking with life: kitchenlab.substack.com…

OK, back to this week’s deep dive: choux pastry.

This time we head into the pan and into the oven. Because choux pastry, also called a cooked dough, is first cooked and then baked. That makes it unique. On top of that it’s neutral in flavor, it triples in volume, and it forms the base for both sweet and savory pastries.

Nothing is more satisfying than baking beautiful choux buns (and nothing more frustrating when it fails). So we’ll tell you how the dough works and how to turn it, step by step, into perfect choux buns, such as airy éclairs, tiger puffs, and crisp little cheese puffs.

The choux pastry family

In the 16th century, the Italian baker Popelini experimented at the French court with a forerunner of this special dough. And from that grew a whole family of pastries: the elongated éclairs (filled with pastry cream and topped with fondant icing), profiteroles (little cream puffs with warm chocolate sauce), savory gougères or cheese puffs, and the Paris-Brest, a ring of choux pastry filled with praline cream. In the Netherlands, the choux bun got its own chocolate variant: the chocolate-glazed cream puff and its even bigger sibling, the Bossche bol, our national heroes. A Bossche bol, named after the city of ’s-Hertogenbosch, is a choux bun the size of a tennis ball, filled with whipped cream and dipped in chocolate glaze.

Cakes made of choux buns
Sometimes choux buns become the building blocks for spectacular cakes like the croquembouche: a pyramid of cream puffs glued together with caramel. The Saint-Honoré is a puff pastry base topped with a ring of cream puffs filled with light cream. The pastry is named after the French patron saint of bakers.

What is choux pastry?

Choux pastry (also called pâte à choux) is a cooked dough: you cook the base in the pan before anything goes into the oven. So with choux pastry, you already cook the base during preparation. The dough consists of four ingredients: liquid (often water + milk), butter, wheat flour, and eggs.

The magic of choux pastry

When you bake choux batter, several chemical processes work together. First the water in the dough evaporates, which makes the air bubbles in the dough expand and triples the volume. At the same time the starch in the flour gelatinizes: the granules absorb water, swell, and form a gel that reinforces the walls of the air bubbles. The proteins present (from flour and egg) denature and coagulate, which sets the structure of the dough. While the outside dries out, Maillard reactions and caramelization provide color and aroma. Milk proteins and lactose contribute to a golden-brown crust with nutty notes. This interplay of steam pressure, setting, and browning makes choux pastry unique: a dough that inflates itself and stays hollow inside, ready to be filled. That’s the perfect picture, but things regularly go wrong and the puffs collapse. That’s why we take a close look at the function of the ingredients and the steps of the process.

The ingredients

Flour

The gluten proteins in wheat flour form the network that captures the steam pressure. All-purpose flour (plain flour in the UK), which contains relatively few gluten proteins, gives a supple dough, but in combination with a stronger bread flour (for example French T65), you get more gluten and therefore a more elastic network. The result: taller, airier puffs.

Tip: use all-purpose flour for éclairs or small cream puffs, and half all-purpose flour with half bread flour for large cream puffs. Good to know if you’re in the US: American all-purpose flour usually contains a bit more protein than European plain flour, so it already sits somewhere between the two

In the paid part of this newsletter:

• Water, milk, butter, eggs, sugar, and salt: what role do the different ingredients play in choux batter?

• Step-by-step explanation plus a video for guaranteed airy choux buns

• Plant-based alternatives

• Gluten-free flour and how to bake choux buns with it

• Super tasty choux pastry recipes (see photos below)

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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Tempeh is a real retro meat substitute. You used to have to go to the health food store or the Asian supermarket for it. Now it’s just sitting on the supermarket shelf. That improved availability points to rising demand. Yet you rarely hear anyone truly enthusiastic about tempeh. People often say it “tastes like nothing.” But that mild flavor is exactly its strength. It makes tempeh the ideal meat-replacing chameleon in the kitchen. On top of that, tempeh is the most complete meat substitute. Reason enough to get started with it. In this newsletter, you’ll read how.

What is tempeh?

Tempeh is a block of fermented soybeans. They’re “grown” together by a parasitic mold that feeds on the carbohydrates and proteins in the soybeans. This mold, Rhizopus oligosporus, produces the enzyme protease during fermentation, which breaks down the proteins in the beans and makes them digestible. Tempeh originally comes from Indonesia, where this mold naturally floats through the air.

The flavor of tempeh

Some people taste a nutty flavor in tempeh and pick up a light mushroom aroma. That’s only true of truly fresh tempeh, and that’s hard to find. Most supermarket tempeh is slightly sour. That’s due to lactic acid that forms during fermentation, but also to the much sharper acetic acid that forms when tempeh oxidizes, for example from being stored too long or a damaged package. That lactic acid, by the way, is important for protecting the beans against other unwanted microorganisms that cause harmful spoilage. Tempeh contains little to no salt, because salt inhibits the growth of the tempeh mold. That’s why it’s bland, just like tofu.

Types of tempeh

The difference between types of tempeh isn’t, as with tofu, in the preparation method, but in the raw material. The fermentation starter, usually Rhizopus oligosporus (often combined with related species such as R. oryzae), can convert all kinds of legumes, seeds, and even grains into a firm block of tempeh, provided the right fermentation conditions (the rules of the game) are followed.

The most commonly produced type is soybean tempeh, which you’ll find everywhere in the Netherlands. But in Indonesia, the birthplace of tempeh, other raw materials are used too, such as peanuts (tempeh kacang tanah). Worldwide, there are also modern variants made from black beans, chickpeas, lentils, quinoa, or brown rice. Combinations are sometimes made too, for example legumes with nuts or seeds. These alternative types of tempeh are harder to find than regular soybean tempeh, but they’re definitely worth trying. Chickpea tempeh, for example, has a light nutty flavor, and lentils give a more earthy aroma.”

In the supermarket, you’ll also find processed tempeh products, such as seasoned tempeh cubes for stir-fries. In the end, it’s just tempeh with different flavorings, nothing you can’t make yourself at home. You can compare it to marinated chicken for the barbecue. Seasoning and marinating it yourself usually gives a better result and gives you control over flavor and texture. Smoked tempeh, however, is an interesting product. For this, the tempeh is first brined and then smoked. That produces a more pronounced, umami-rich flavor. We like to use smoked tempeh for crispy tempeh bacon: delicious on a burger or as a side dish.

Where to buy tempeh

A few good starting points:

• Regular supermarkets: tempeh has been steadily working its way into the mainstream chiller aisle, next to the tofu and the other meat substitutes. A chain like Whole Foods is a safe bet; elsewhere, check the vegetarian or vegan section of any large supermarket.

• Health food stores: still tempeh’s natural habitat, and usually the place with the widest range, including smoked and pre-seasoned versions. A store like Holland & Barrett is a good example.

• Asian grocery stores: worth checking too, especially if you want fresh, unpasteurized tempeh, often at a better price. The selection varies a lot from store to store, so don’t count on consistency.

A growing number of small, dedicated tempeh makers (Better Nature is one example) also sell directly through their own webshops, and increasingly ship internationally. Wherever you are: if your regular store doesn’t carry tempeh, ask. Its popularity is rising fast enough that more shops are adding it every year.

In the paid section of this newsletter

• why tempeh is so healthy (the most complete meat substitute)

• storing tempeh

• prepping tempeh (cutting, marinating, blanching, brining)

• cooking tempeh (pan-frying, deep-frying, air-frying, grilling, stir-frying)

• four delicious and easy recipes (see photos above)

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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Yes, another vegetable newsletter this week. Because it’s late summer, and that means harvest time. September is peak tomato season in the Netherlands: sun-ripened, aromatic, and available in dozens of varieties. Tomatoes are also the great connectors of the kitchen. They pair with almost anything, and they’re fascinating in their own right. Reason enough to dive into their flavor, texture, varieties, and cooking techniques. A newsletter packed with tomato power.

Flavor

In this newsletter, we already covered it: tomatoes are packed with umami. You don’t always taste that right away in a fresh tomato, where acidity dominates, along with sweetness if the tomato is properly ripe. Umami becomes more pronounced once you dry or concentrate the tomato. The ultimate expression is tomato powder, where the flavor is pushed to its peak.

Tomato Powder
Before you turn tomatoes into powder, they need to be completely dry. A dehydrator or a low oven works best for this. Slice the tomatoes thin and dry them at 120–140°F (50–60°C). Depending on the tomato, this typically takes 12 to 24 hours, until they’re bone-dry. Grind them fine in a blender, coffee grinder, or food processor, and you’re left with a concentrated flavor booster. Sprinkle the powder over pasta, salads, or into dressings. Tomato powder is a convenient, long-lasting umami booster in a compact form, and you can easily buy it online or at a restaurant supply store.

Umami

Umami flavor comes from glutamate and so-called nucleotides. MSG (monosodium glutamate) is the purest, synthesized form of glutamate. That compound has a reputation, literally and figuratively, but natural forms of glutamate work the same way: they amplify the flavor of a dish. No wonder tomatoes have a permanent place in nearly every cuisine on earth.

Sweet and Sour

A fully ripe tomato strikes the ideal balance between sweet and sour. That balance is delicate. Too much acid and the tomato tastes like nothing. Too much sugar and it feels mealy or overripe. The levels of sugar (glucose and fructose) and acid (citric acid and malic acid) depend on the variety and ripeness of the fruit, in other words, how much sun the plant received. Small tomatoes like cherry tomatoes contain relatively more sugar, which is why they often taste more intense.

Volatile Aromas

Beyond the basic tastes of sweet, sour, and umami, volatile aromas play a major role. Tomatoes contain hundreds of these compounds, but only a handful define their character. Aldehydes in particular, such as cis-3-hexenal, give raw tomatoes their grassy, fresh notes. Heat destroys these volatile compounds quickly, while carotenoids and Maillard reactions generate new ones. That’s why a cooked tomato tastes softer, sweeter, and rounder, but loses the fresh bite of a raw one.

Enzymes

Enzymes play a role too. Cutting a tomato triggers an enzymatic reaction that releases hexanal, the molecule responsible for that fresh-cut-grass smell. You can put this to use by cutting tomatoes for salsa a few hours ahead of time, which gives the salsa a fresher flavor. The same goes for gazpacho made with raw tomatoes: let it sit overnight and the flavor only improves. Once you heat tomatoes, this enzyme activity stops, and that green, fresh aroma disappears with it. We put this enzymatic process to work in our pico de gallo recipe.

Acid and pH

The acidity of tomatoes plays an important role in the kitchen, especially in stews. Tomato’s low pH slows down Maillard reactions, so a dish browns less and develops fewer savory aromas. That’s why tomato sauces often stay bright red instead of developing the same roasted flavors as, say, onions or bell peppers. For this reason, it’s a good idea to add tomatoes (fresh, boxed, or canned) later in the cooking process. Take a simple tomato pasta sauce as an example. If you want a deep savory flavor, sear the other vegetables first, onion, garlic, carrot, bell pepper, and celery, so the Maillard reactions generate plenty of umami. Only then add the tomatoes, and let the sauce simmer. The same principle applies to classic tomato-based stews like beef bourguignon. We used this same logic in this recipe for a meatless ragù in our newsletter on pasta sauces.

In the paid section of this newsletter, we cover cooking techniques, tomato varieties, and recipes, including:

• Structure and texture, and the effect of sugar, salt, and acid

• Peeling and seeding: when to bother, and when not to

• Raw, grilling, searing, roasting, drying, and reducing: how each technique transforms flavor

• From vine tomatoes to coeur de boeuf, from Green Zebra to San Marzano: which variety works best for what

• Four perfect (easy!) recipes with fresh tomatoes

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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In the past, cookbooks gave fennel just two options: boiling and braising. Vegetables clearly played a supporting role back then. Fortunately, that has changed, and vegetables now take a much more prominent place on the plate. So we’re putting fennel in the spotlight, showing you how to make it shine: roasted, grilled, confited, deliciously raw, or lightly pickled. Preparations that each bring out the best in this bulb.

The Flavor of Fennel

Fennel has a strong anise flavor, thanks to a compound called anethole, which is also found in anise seed and star anise. Some people find fennel’s flavor overpowering, but if you like that boldness (like we do), it opens up plenty of possibilities for giving character to a dish. Fennel seed and tarragon carry soft anise notes too, though tarragon contains somewhat less anethole.

Fennel also contains limonene, a terpene also found in citrus fruits. That compound gives fennel a light, fresh citrus note, which is exactly why you often see fennel paired with citrus. We like to turn that into a salad, for instance, combining fennel with bitter grapefruit, the richness of blue cheese, and the crunch of hazelnuts. You’ll find the recipe further down in the newsletter.

Not Actually a Bulb

We always talk about the fennel bulb, but that's not quite accurate. A true bulb, like onion or garlic, is a modified underground stem wrapped in fleshy, nutrient-storing leaves, built to help the plant survive winter and sprout again the next season. Fennel doesn't have that structure. What we call its 'bulb' is really a tightly packed cluster of overlapping leaf bases, sitting right at the surface rather than storing energy underground; leek is built the same way. Compare that to potato or celeriac, which really are underground storage organs.

Texture

Fresh fennel is crisp and crunchy, thanks to turgor pressure, the water pressure inside the cells. As long as the cells are full of moisture, they practically crackle under your teeth. But once the vegetable loses water, whether during storage or from overcooking, that pressure drops and the fennel turns tough, sometimes even fibrous. Enzymes play a role too: just like in other vegetables, they break down cell walls and pectin (the “glue” holding cells together) during storage. That makes fennel go limp, and in older bulbs, downright stringy. You can feel those fibers clearly, and suddenly you’re not enjoying the bite anymore, you’re mostly just chewing.

Storage

To keep your fennel fresh and crisp as long as possible, store it whole and unwashed in the crisper drawer of the fridge. Why unwashed? Tap water always leaves a thin film of moisture in the bulb’s crevices, and that standing water is a breeding ground for mold and bacteria; it speeds up spoilage. That said, a little moisture can actually help: wrap the fennel loosely in a damp kitchen towel, damp paper towel, or an open bag. That creates a slightly humid microclimate around the vegetable, keeping it from drying out in the fridge’s dry air and losing its crunch. Only cut or halve the fennel right before you use it, since once cut, it quickly loses moisture and aroma.

Freezing is an option too, but it changes the texture. Ice crystals puncture the cell walls, so after thawing, the fennel turns limp and watery. That makes it unsuitable for raw use, grilling, or sautéing, but it still works fine in stews, soups, or stocks. The aroma stays, even though the bite is gone.

In the paid section of the newsletter:

• 4 ways to cut fennel, explained in a clear video

• 5 cooking techniques for fennel: raw, grilled, caramelized, braised, and confit

• 4 recipes to get the most out of your fennel

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

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Few things in the kitchen feel as magical as a jar of vegetables that turns itself into something packed with flavor. No fire, no stove, just time, salt, and a little guidance. Fermentation is cooking without cooking: a technique where microorganisms such as bacteria, yeasts, and molds do the work. They don’t just make food last longer, they make it taste better, more complex, and sometimes even healthier.

In this newsletter, we dive into the technique of fermentation. What is fermentation, what actually happens, how do you steer the process, and how do you get started yourself? This fall, we’ll show you how to use fermented products smartly in the vegetarian kitchen, as a flavor booster, an umami boost, or a fermented twist. But first: the basics.

As old as the hills

Fermentation is an ancient, universal kitchen process where microorganisms, such as bacteria, yeasts, and molds, do the work for us. For thousands of years, people have used fermentation to preserve food, enrich its flavor, and even make it healthier. Many everyday treats owe their existence to fermentation: yogurt, beer, bread, sauerkraut, soy sauce, kimchi, and chocolate. With fermentation, food “spoils” under controlled conditions, in a good way. Pure magic in the kitchen.

Working closely with tiny life forms, milk becomes cheese and yogurt, grain becomes beer, cabbage becomes sauerkraut. The bacteria needed for this are often already on the food itself, doing their work. Take sauerkraut: green cabbage that transforms itself into a crunchy, sour treat that keeps for months. The trick? The lactic acid bacteria that naturally live on the cabbage. Without oxygen, these beneficial microbes multiply rapidly, crowding out the less friendly bacteria.

Why ferment?

What makes fermentation worth the effort, even in our modern kitchens full of refrigerators and freezers? Here are a few reasons.

Health

Fermented food is packed with probiotics: good, living bacteria that strengthen your gut flora. A daily bite of fermented food stimulates digestion and can support your immune system. Traditionally fermented products like kimchi, kefir, and kombucha are praised for their health benefits. Research even suggests that fermented foods contribute to a more diverse gut microbiome, which is linked to all kinds of positive effects, including a stronger immune system.

Flavor

Fermentation is a genuine flavor maker. During fermentation, microorganisms form countless new aroma and flavor compounds, from tangy sour to savory umami. That’s how soybeans become soy sauce after months of fermentation: salty, sweet, sour, and deeply umami. Bitter olives become complex, pleasant fruits through fermentation. Fermenting gets you deeper flavors than cooking alone. Think of the rich taste of a well-aged cheese or the bright, tingling bite of kimchi. Fermentation gives dishes new aromas and a depth that’s hard to match with regular cooking techniques.

Shelf life

Fermentation has long been an important preservation method. The process creates an environment where spoilage bacteria and molds can barely survive, thanks to the strong acid production in lactic acid fermentation. This keeps fermented food good for much longer, often months or more, without needing artificial preservatives. Before refrigerators and freezers existed, fermentation was the way to eat summer’s harvest well into winter. And the beautiful part is that nature does all the work. In a sealed jar of sauerkraut or pickles, bacteria acidify the mix and protect it from spoilage. That means a lot less food waste.

Sustainability

Fermentation is a low-tech, low-energy technique. You don’t need expensive equipment or electricity, just a few clean jars and some salt for lactic acid fermentation. Microbes do their work at room temperature. Fermentation extends shelf life efficiently and reduces the need for refrigeration or freezing, which saves energy and packaging material. It also lets you preserve seasonal vegetables at their peak for later, instead of letting them spoil. Think of turning a surplus of cucumbers into pickles, or a large cabbage into jars of sauerkraut. Fermentation contributes to a more sustainable kitchen this way: less waste, less energy use, and maximum use of what nature gives us.

In the paid section of this newsletter:

• How to direct your microbes: playing with salt, oxygen, time, and temperature

• Checklist for lactic acid fermentation: the four golden rules

• When has your ferment gone “far” enough?

• Two foolproof recipes: Latin American curtido and vegan Korean kimchi

• Plus: why fermentation isn’t rocket science, but is addictively fun and delicious

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat

How does fermentation work (in the kitchen)?

Fermentation works fundamentally differently from cooking. When you cook, you’re the active pilot: you chop, mix, and heat dead ingredients to change them chemically. When you ferment, you work with living organisms instead. You’re more like a coach, getting a team of microbes to perform. Instead of steering with fire and knives, you influence the process through environment and composition. The “art” of fermentation is setting the conditions so the microorganisms you want thrive, and the ones you don’t want disappear. You could call this playing with the dials on your chemical stove: composition (salt content, sugars), oxygen (exposed to air or not), temperature, and time. By turning those dials, you guide the fermentation process without stirring the pot yourself.

Another big difference from cooking is time. Where a pan on the stove gives results in minutes or hours, fermentation takes days to weeks. During that time, the microbes do their work slowly but steadily. As the cook, your main job is to not interfere, except for the occasional taste test and a small adjustment if needed (moving the jar to the fridge, for example, once the flavor is where you want it).

What is lactic acid fermentation?

The world of fermentation includes several different processes, like alcoholic fermentation (using yeasts) for beer and wine, or mold fermentation for cheese and miso, among others. In this newsletter, we focus specifically on lactic acid fermentation, because it’s easy to do at home. Lactic acid fermentation is the type behind sauerkraut, kimchi, and countless pickles. Lactic acid bacteria play the lead role here. So what actually happens during lactic acid fermentation?

Chop, salt, pack, and wait

In short: chop, salt, pack, and wait. You start with fresh vegetables that naturally carry plenty of lactic acid bacteria (on the cabbage leaves, the carrot skin, and so on). Slicing the vegetable finely increases the surface area, giving better access to the sugars locked inside the cells. Then you mix in salt.

How much salt?
Always use between 2 and 3% salt, calculated on the total weight of the vegetables and the liquid (so: vegetables plus brine).
- Less than 2% raises the risk that unwanted microorganisms, like molds or spoilage bacteria, take hold.
- More than 3% slows down the lactic acid bacteria. They can’t function well in a too-salty environment, which makes fermentation sluggish or causes it to fail.

Salt does three things: it draws moisture out of the vegetables through osmosis, it holds back unwanted bacteria, and it gives the lactic acid bacteria a head start. After a few minutes of kneading with salt, cabbage releases liquid, for example, and that liquid combines with the salt to form the brine you need. Make sure the vegetables stay fully submerged in that brine. This creates the oxygen-free (anaerobic) environment where lactic acid bacteria thrive.

During fermentation, these bacteria convert the sugars in the vegetables into lactic acid. That lowers the pH, preserves the product, and gives it that signature bright, sour taste. It also produces carbon dioxide (CO₂), which forms bubbles and helps push out any remaining oxygen. This further protects the ferment from spoilage.

Self-preserving

Once this groundwork is done, the lactic acid bacteria quickly take over. They feed on the natural sugars in the vegetables and convert them into lactic acid, plus a bit of carbon dioxide. The lactic acid lowers the pH, making the environment increasingly acidic. That works in your favor, because rising acidity preserves the product. Pathogens and molds don’t like that acidic environment and stay away. The jar of vegetables essentially makes its own preservative. The flavor shifts along with it: the more lactic acid, the more sour the vegetables taste. The process also produces carbon dioxide (CO₂) gas, which you’ll see as bubbles rising in your fermentation jar. That gas also pushes any remaining oxygen out of the jar, a double win.

Explosion risk

The carbon dioxide gas that builds up during lactic acid fermentation needs a way out. An airlock works well for this: a kind of gooseneck fitting you place on the jar and fill with water. The water in the airlock lets gas escape while keeping unwanted stuff from getting in. Using a glass jar instead? Don’t close the lid all the way. We like glass clip-top jars ourselves. During fermentation, we remove the rubber gasket so there’s enough space between the lid and the jar for the carbon dioxide to escape.

Flavor and texture

All kinds of new flavors develop during fermentation. Lactic acid gives a bright sourness. Countless aromas also form, often described as savory, that are unique to fermentation. What’s interesting is that the vegetable’s texture often stays crisp, or even improves. The acid firms up the pectin in the cell walls, which keeps something like cucumber or cauliflower pleasantly crunchy. The end result still resembles the original vegetable, but it’s more sour, often a bit saltier, nicely crunchy, and packed with new flavors. Even ingredients that taste bitter or harsh raw, like olives, can be transformed by fermentation into something deliciously complex.

Temperature and time

Temperature and time are key here. Lactic acid fermentation works best at room temperature, around 64-72°F (18-22°C). Things move fast in the first week: the bacteria multiply and produce acid at a high rate. After that, activity gradually slows as the environment acidifies. You can steer the sourness by timing your intervention. After about seven days, taste it to see if it’s sour enough for you. If so, move the jar to a cooler spot, max 50°F (10°C), or the fridge. The low temperature slows fermentation way down, so the flavor stops developing or intensifying further. This lets you pump the brakes and “park” the ferment at the point you like best. Always make sure the vegetables stay under the liquid; if they don’t, add extra saltwater (about 20 g salt per liter of water as a guideline). If the vegetables float up and touch air, mold can still form. That’s what you want to avoid.

A plastic bag as a weight

Sliced vegetables need to stay fully submerged in brine while they ferment. As soon as they poke above the liquid and touch oxygen, mold can form. A simple fix: a plastic freezer bag filled with water. Tie it shut tightly and set it on top of the vegetables as a weight, so they stay underwater. Don’t fill the jar all the way in that case; the bag needs room.

Fermentation stops on its own

The beautiful part of lactic acid fermentation is that it’s self-regulating: once the environment is acidic enough, the lactic acid bacteria stop on their own. They can’t survive in overly acidic conditions either. It’s a natural stopping point that keeps the product from turning inedibly sour. Always follow these basic rules for lactic acid fermentation:

• work with clean equipment

• use a minimum of 2% and a maximum of 3% salt of the total weight (brine plus vegetables)

• keep the vegetables under the brine

• keep track of what you do, in case something goes wrong, or turns out great

Get these four dials under control, and you’re already halfway to a successful ferment.

Sandor Katz, a well-known fermentation expert, calls lactic acid fermentation “the gateway to a world of fermentation.” In his book The Art of Fermentation, he teaches beginners to make sauerkraut like this: chop, salt, pack, and wait. Slice your cabbage, salt it well, pack it firmly into a jar, and wait. It can be that simple. Katz and other “fermentos” (the term for fermentation fans in the US) stress that you should just get started: this old craft is best learned by doing, and before you know it, you’re a proud fermento yourself.

Recipe
Curtido, spicy sauerkraut from Central America

An easy entry point into lactic acid fermentation. Curtido is a bright, sour cabbage slaw originally from El Salvador, made with carrot, onion, oregano, and chili. It’s just as approachable as sauerkraut, but with more kick and character. Delicious on a grilled cheese, in a taco, or alongside bean dishes.

Makes: one 1-quart (1-liter) jar Prep time: about 30 minutes Fermentation time: about 14 days

INGREDIENTS
1 green cabbage (about 800 g)
1 carrot (125 g)
1 red onion (75 g)
2 garlic cloves
2 jalapeños, or 1 tsp chili flakes
20 g salt (2% of the vegetable weight)
1 tsp dried oregano (or 1 tbsp fresh)

Extra: a clean, sealable 1-liter (1-quart) jar, a large bowl, a mandoline or sharp knife, a plastic bag (for the weight).

METHOD
Slice: Shred the cabbage very finely with a mandoline or slicer (the thinner, the faster the fermentation). Set one outer leaf aside. Coarsely grate the carrot, or cut it into thin strips. Slice the onion into half-moons and finely chop the garlic and jalapeños. Remove the seeds from the jalapeños for less heat.
Salt: Put all the vegetables in a bowl. Add the salt and oregano. Let sit for 5-10 minutes. The salt draws moisture out of the vegetables and makes them pliable.
Massage: Massage everything firmly with clean hands. Within a few minutes, liquid releases; this becomes your fermentation liquid (the brine). Keep massaging until the cabbage is nicely wet and pliable.
Pack: Spoon the vegetable mixture into the jar, pressing down firmly as you go to remove air pockets. Pour in the released liquid. Everything needs to stay submerged. If it doesn’t, top up with a 2% saltwater solution (20 g salt per liter of water). Cover with the reserved cabbage leaf. Place a clean bag of water on top as a weight.
Ferment: Close the jar loosely (or use an airlock). Let it sit for 10-14 days at room temperature, 64-72°F (18-22°C), out of direct sunlight. No airlock? Open the jar briefly each day to release pressure.
Finish: Taste after 10-14 days. If it tastes bright and sour, the curtido is ready. Remove the weight and cabbage leaf. Seal the jar well and store in the fridge; this stops or slows the fermentation.

Tips

• Not enough liquid? Make a brine with 20 g salt per liter of water and top up.

• A white yeast film (kahm) is harmless. Skim it off carefully.

• Always use clean utensils to keep the ferment from spoiling.

• It keeps in the fridge for up to a few months, as long as everything stays submerged.

• Flavor profile: bright, sour, crunchy, herby, and a touch spicy. Great with rich dishes, on a burger, or simply on a cracker.

Recipe video
Kimchi, Korea’s spicy flavor bomb

Kimchi is the classic among fermented vegetables. This Korean cabbage ferment is spicy, umami, sour, and crunchy, all at once. It’s a versatile flavor booster you can make in just a few days. We always make the vegan version, with miso instead of fish sauce.

Makes: one 1-quart (1-liter) jar Prep time: about 30 minutes Fermentation time: about 3-4 days

INGREDIENTS
1 napa cabbage (about 1 kg)
20 g salt (2%)
150 ml water
2 tbsp rice flour
3 garlic cloves
3 cm piece of ginger
1 small onion
1 tbsp miso (or soy sauce)
1 tbsp sugar
3-4 tsp gochugaru (or a mix of paprika powder and chili flakes)
1 carrot, coarsely grated
100 g daikon or white radish, coarsely grated
3 scallions, sliced into rings

Extra: a food processor or hand blender, a clean 1-liter (1-quart) jar, a large bowl.

METHOD
Salt the cabbage: Cut the cabbage into 1-inch (2-3 cm) pieces. Massage the salt in thoroughly. You’ll quickly feel the cabbage go limp and wet. Let it sit for about 30 minutes while you make the paste.
Make the spice paste: Cook the water with the rice flour into a thick paste, then let it cool slightly. Blend the rice paste with the garlic, ginger, onion, miso, sugar, and gochugaru until smooth.
Mix: Drain off any excess liquid from the cabbage. Combine the cabbage with the grated carrot, daikon, and scallions. Add the paste and massage everything together well. Kitchen gloves come in handy here. Everything should be coated in the red paste.
Pack: Spoon the mixture into a clean jar. Press down firmly to remove any air bubbles. There should be liquid above the vegetables; if not, add a splash of saltwater. A plastic bag filled with water works well as a weight, if needed. Cover loosely, or use an airlock.
Ferment: Let it sit for 2-4 days at room temperature. You’ll see bubbles and notice a sour smell. Taste after 2-3 days. If the kimchi is bright, sour, and spicy, it’s ready for the fridge. The flavors keep developing in the cold.

Tips

• Gochugaru is a coarse, mild chili powder. Don’t have any? Use a mix of paprika powder and mild chili flakes instead.

• No food processor? A hand blender works too.

• Always use clean utensils to keep the ferment from spoiling.

• You can eat the kimchi right away (it’s good!), but after 7 days in the fridge, the flavor really deepens.

• Gotten too sour? Perfect for kimchi pancakes, soup, or stew.

• Flavor profile: full, bright, sour, spicy, and umami. Great as a side dish, on a rice bowl, with grilled vegetables, in a sandwich, or on a grilled cheese.

With vegetables, fresher is almost always better. But sometimes you end up with more than you can eat. Preserving is the answer: as chutney, relish, jam, or pickled in a sweet-sour brine. A great way to keep seasonal vegetables going all winter. And preservation isn’t only about shelf life: the flavor and texture of preserved vegetables can be fantastic in their own right.

One more thing before we dive in. At the end of this issue you'll find a short poll. Kitchen Lab has always been vegetarian, and I'm considering whether to expand beyond that. Three quick questions, and your input genuinely shapes what comes next.

Knocking out bacteria

Most vegetables and fruits are designed by nature to be eaten quickly, so their seeds get spread. After harvest, decay sets in from the outside via bacteria and molds, and from the inside via enzymes in the plant cells. To preserve vegetables, you need to create an environment where the bacteria and molds responsible for spoilage can barely survive.

Drying out

The most efficient way to stop harmful microorganisms is to dry them out: simply deprive them of the water they need to survive. You can do this by drying vegetables, but also by adding large amounts of sugar or salt. Because the concentration of salt or sugar outside the plant is much higher than inside the plant cells, water flows outward through osmosis. Microorganisms can’t survive in high concentrations of salt or sugar because they dehydrate.

Lowering the pH

Another way to stop bacterial growth is to lower the acidity (pH) using vinegar. This is the essence of pickling. Many bacteria and molds can’t tolerate acid and die off. A popular combination is sweet and sour: it provides double protection, dehydration through sugar and an acidic environment. It’s also a great flavor match, since the sugar balances the sharpness of the vinegar.

Lactic acid fermentation is a preservation technique that uses the naturally occurring lactic acid bacteria on most plants. We’ll dedicate a separate issue to this technique in the future.

Then there’s texture

Every plant cell is surrounded by a cell wall that gives the plant its structure. The liquid inside the cell is under pressure, which is why biting into a fresh carrot is crisp: the cells don’t give way under pressure, they snap. Old carrots, on the other hand, lose moisture through evaporation. The pressure inside the cells drops, and with it, the crunch.

The same thing happens when you preserve vegetables in salt or sugar: they soften as they lose moisture. Acid (like vinegar) does the opposite: it firms up cell walls, which is why vegetables pickled in vinegar stay crisp. Calcium and magnesium ions also strengthen cell walls. Use unrefined salt (which contains these minerals) when preserving vegetables for a slightly crunchier result.

In the paid section:

• Flavor balance: the right ratios of salt, sugar, and vinegar

• Step-by-step: clean working, jars, sterilizing, filling, and cooling

• Pickling in vinegar: sweet-sour vegetables

• Chutney and relish: what’s the difference?

• Recipes: sweet-sour pickled vegetables, spicy pepper pickles, piccalilli, tomato chutney, zucchini jam

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat.

A question for you

When I started Kitchen Lab, I made a deliberate choice to focus exclusively on vegetarian cooking. I believe the world needs to move in that direction, and I still do.

But a 100% vegetarian world isn’t realistic, and it’s not what I’m asking of anyone. The principle I’ve come to embrace is 80% plant-based, 20% animal. And if you’re going to eat meat or fish, you might as well do it well. That’s the Kitchen Lab philosophy: understand what’s happening in your pan, and make every ingredient count.

Yes, I'm aware of the irony: I'm asking this question in a newsletter entirely dedicated to vegetables. But here we are. Three quick questions, and I'd love to hear what you think.

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Few things are as satisfying as a freshly baked tart loaded with summer fruit. Stone fruits like apricots, peaches, nectarines, plums, and cherries are perfect for this. And right now, they’re all in season. Capture the flavor of summer in a crisp crust with a rich filling. In this issue, we help you perfect your fruit tart. Which crusts work best, how do you keep them dry with all that juicy fruit, how do you make the most delicious fillings, and how do you prepare the fruit for the best result? Let’s bake.

Stone fruit basics

Stone fruits are fruits with a hard pit in the center, surrounded by juicy flesh. This group includes cherries, apricots, plums, peaches, and nectarines: all summer favorites from orchards close to home. The pit is botanically the seed, enclosed by a woody stone layer (endocarp), which is where the name comes from. Stone fruits are rich in aromatic esters, acids, and sugars that develop as the fruit ripens on the tree. Their balance of juiciness, brightness, and structure makes them ideal for tarts.

Cleaning and preparing

To peel or not to peel?

All stone fruits can be eaten with their skin on. The skin is rich in flavor compounds and dietary fiber. There are times when you’d want to remove it, though: peaches with their fuzzy skin, for instance, where a smooth filling or a clean glaze matters. And in fine patisserie, texture and appearance can play a role. Use the classic blanching technique: submerge the fruit in boiling water for 10 seconds, transfer immediately to ice water, and the skin slips right off. This only works with ripe fruit.

Removing the pit without damaging the fruit

How do you get the pit out cleanly?

Apricots and plums: halve the fruit along the natural seam and pop the pit out with your thumbs or a spoon.

Peaches and nectarines: cut around the pit and twist the two halves in opposite directions. The variety matters here. Freestone peaches release the pit easily and are ideal for halving cleanly, perfect for baking. Clingstone varieties hold tight to the pit. Removing it takes more effort and tends to bruise the flesh. You can’t tell from the outside, so ask at the market or test one fruit before buying a large batch for your tart.

Cherries: use a cherry pitter. No cherry pitter? Place the cherry (stem removed) over the opening of an empty bottle and push the pit out with a firm straw or chopstick. The cherry stays whole and you avoid splatter.

No precooking needed

Ripe fruit doesn’t need precooking; it’s soft enough to bake in the oven. Precooking can actually make it mushy. The key is to buy fruit that’s ripe but still firm enough to slice without falling apart.

If the fruit is too hard, you have a few options:

• Cut into pieces and briefly blanch (about 30 seconds in boiling water, then cool immediately).

• Cut into pieces and briefly microwave (start with 30 seconds at full power).

• Cut into pieces and roast in the oven. This concentrates the juice and deepens the flavor. Allow about 15 minutes at 320°F (160°C) convection.

Macerating: marinating fruit in sugar

Macerating is a smart technique for working with juicy fruit. You mix the fruit with sugar (and optionally some flavorings) and let it sit for a while. You’re essentially marinating the fruit in sugar. Through osmosis, the sugar draws moisture out of the fruit, similar to what salt does when brining vegetables, meat, or fish. Pastry chefs use this method often for tarts with peaches, nectarines, plums, or pears. It has two advantages: the fruit becomes slightly softer and more flavorful, and the juice is released before baking. You can drain that juice or cook it down into a syrup, so it doesn’t seep into the crust. The dough stays drier and crispier, and the filling holds together better.

How to do it:

• Mix the fruit with 5 to 10% sugar by weight. Use caster sugar or light brown sugar.

• Add cinnamon, vanilla, or lemon zest if you like.

• Let sit for 30 to 60 minutes.

• Drain off the released juice. You can reduce it to a syrup and brush it over the finished tart or stir it into the filling.

In the crostata recipe further on in this newsletter, we macerate fresh plums this way.

The European tart tradition

The idea of a fruit tart with a crisp crust, juicy filling, and a glossy finish is distinctly European. Outside Europe, fruit appears in desserts but rarely in this form. In the Middle East, fruit is mostly dried, candied, or used as syrup in pastries with nuts or semolina. In Asia, fruit tends to appear alongside puddings, jellies, or steamed cakes. In the US and UK, fruit desserts like pie, crumble, or cobbler are much looser and more rustic, with crumbly dough or biscuit-like toppings.

France, Germany, Austria, and Italy have developed fruit tarts into a refined genre within patisserie. In France, the clafoutis is the classic fruit bake, but it uses no dough at all. The batter is liquid, similar to a flan made with eggs, milk, sugar, and a little flour. You pour it over the fruit in the pan and bake; the batter turns custard-like as it sets. The moisture from the fruit is actually welcome here: it’s absorbed into the batter. A clafoutis is truly the simplest fruit tart you can make.

The Italian crostata is a proper tart with a crust. Italians use pasta frolla, a sweet dough very similar to pâte sucrée, sometimes with a little oil or baking powder added for extra crumbliness. The filling is usually jam, which avoids moisture problems. The dough is laid partly on top in a classic lattice pattern. Crostatas are robust, keep well, and tend to be slightly sweeter than French or British tarts. We made one with fresh plums.

In the paid section:

• Which dough to use when (and why)?

• Smart techniques to prevent a soggy bottom

• Which layer goes between dough and fruit for flavor and crunch?

• Recipes: apricot frangipane tart, cherry clafoutis, plum crostata, nectarine tart with meringue

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat.

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Most barbecues are meat festivals. That’s a shame, because grilled vegetables are actually much more interesting. The variety is greater, especially in summer. And grilled vegetables are incredibly versatile. You can fold them into a salad, turn them into a soup or starter, or serve them as a main course in their own right.

In this issue, we show you how to give vegetables the starring role on the grill. We start with a short masterclass in barbecue technique: how to control the fire, how to measure temperature, and why charcoal and briquettes behave differently. Then we walk through the best summer vegetables, with a technique guide for each. And of course we finish with recipes and flavor-boosting tips that will change how you think about the grill.

Why grilled vegetables taste so good

Barbecuing is cooking with fire, and that fundamentally changes the chemistry of vegetables. Above 300°F (150°C), Maillard reactions kick in: sugars and amino acids react with each other and produce hundreds of aromatic compounds (we wrote about this in an earlier issue). Caramelization plays a role too. Sugars concentrate at the surface of the vegetable, partially evaporate, and form a crispy, sweet crust.

On top of that, many vegetables naturally contain glutamate, inosinates, and other umami compounds. Think of leeks, mushrooms, or tomatoes. Grilling makes these compounds more pronounced, especially in combination with smoke.

The result: a deep, concentrated flavor that pairs beautifully with acids, fats, and bitters. A perfect foundation for modern, plant-forward barbecue cooking.

BBQ basics: the theory of temperature

Charcoal or briquettes?

Fire in a barbecue comes from burning charcoal or briquettes, and your menu should determine your fuel. Charcoal heats up faster, making it ideal for short, intense cooking where you want beautiful grill marks without losing crunch. Think green asparagus, sugar snaps, halved little gem lettuce, or spring onions. Briquettes burn longer and more evenly. They’re ideal for larger vegetables or indirect grilling (more on that below). Think roasted beets or thick slices of eggplant: vegetables that need more time to cook through.

If you use a kamado, for low and slow cooking with the lid closed, always use natural lump charcoal. The kamado’s closed ceramic construction already makes it perfectly suited for controlled, long cooking sessions. For open, high-heat grilling, briquettes can work fine.

Lids and oxygen: temperature control

If you’re serious about grilling vegetables, a barbecue with a lid is your best friend: a classic kettle grill or a kamado. They’re better insulated and give you far more control over temperature than an open grill or hibachi. With a lid, you regulate airflow through the vents. More oxygen means higher temperature. Less oxygen means slower cooking. That’s essential when you want to roast thick leeks, corn, fennel, or whole root vegetables without burning the outside.

A kamado is a ceramic barbecue with thick walls and a tight-fitting lid. The insulation lets you work at very stable temperatures, perfect for slowly cooking potato wedges, roasted beets, or celeriac at low heat, optionally with a little smoke.

Also keep an eye on ash buildup. As the coals burn, a grey layer forms that restricts airflow and drops the temperature by about 50°F (30°C) every fifteen minutes. Shaking the coals or removing ash helps keep the fire alive.

Measuring temperature

Fuel and oxygen determine how hot your barbecue gets. But how do you know if that temperature is right for what you’re cooking? Many barbecues have a built-in thermometer, but it measures the air under the lid, not the heat directly at your vegetables. And that’s where it actually matters.

A digital BBQ thermometer placed on the grate measures temperature at the right spot. For quick cooking with thin vegetables like sugar snaps, green asparagus, or baby corn, you want to be above 450°F (230°C). For thicker vegetables like slices of eggplant, zucchini, or bell pepper, slower grilling at 355–390°F (180–200°C) is ideal. For leeks, fennel, or whole root vegetables, you can go as low as 320°F (160°C), as long as you give them enough time.

A probe thermometer is also useful: it tells you when thick vegetables are fully cooked on the inside. Think roasted beets or celeriac. Depending on the vegetable, you’re aiming for an internal temperature of around 195°F (90°C).

The masochist’s method

No thermometer? There’s an ancient barbecue trick. Hold your hand just above the grate and count in your head, “one-Mississippi, two-Mississippi...”, until you can’t stand it anymore.

• 2–3 seconds: hot (450–680°F / 230–360°C)

• 6–8 seconds: medium (320–355°F / 160–180°C)

• 11–14 seconds: low (210–250°F / 100–120°C)

Slightly masochistic, but surprisingly effective.

Vegetables are the meat of the future

In the video below, Kitchen Lab chef Eke Mariën covers a few smart barbecue techniques for vegetables, including charring and roasting. The techniques and recipes are explained in detail further on in this newsletter.

In the paid section

• Smart grilling: how to use heat zones and timing to cook vegetables perfectly

• Spray or brush: controlling temperature and flavor with oil and infusions

• Charring: cooking directly in the fire for pure smoke flavor

• Fruit on the grill: tips for firm fruits with a caramelized crust

• New recipes: charred leeks with romesco, roasted root vegetables with salsa, summer salad with green beans and halloumi

• Technique guide: which vegetable, which method?

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, learn techniques, and cook better with real knowledge? Subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack, plus access to all our back issues and the Kitchen Lab Chat.

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Spring legumes don’t stick around. Fresh fava beans, peas, marrowfat peas, and snow peas are juicy and full of flavor, completely different from their dried, frozen, or canned counterparts. What makes them so special? How do you prepare them properly? And is a fava bean actually a bean? In this issue, everything about the flavor, structure, and origins of spring legumes, with practical tips and recipes from bean specialist and cookbook author Joeri Veul.

Why we forgot about beans

Joeri Veul was the number one BMX rider in the Netherlands when a stroke ended his career overnight. During his recovery, he threw himself into his second passion: cooking. That turned out to be the right move. He's now a cookbook author, food photographer, and one of the most followed food creators in the Netherlands (@joeri.veul on TikTok and Instagram). His mission hasn't changed since day one: make beans sexy.

According to Joeri, beans are the answer to many food challenges. They’re nutritious, can be grown locally, and actively improve soil health. Yet we eat very few of them. “People think beans are a hassle. They’ve forgotten how to soak or prepare them. Convincing people is a matter of seduction,” he says. His mission: make beans sexy again.

Pods, peas, beans: what’s what?

Legume is the umbrella term for all plants that develop their seeds in a pod. That includes fava beans, peas, lentils, chickpeas, lupins, and even peanuts: they’re all legumes.

In the kitchen, though, we make distinctions. Beans (such as green beans, black beans, and borlotti beans) are mostly species from Central and South America, which only arrived in Europe after the discovery of the New World. They belong to the genus Phaseolus. Peas, on the other hand, such as garden peas, snow peas, and sugar snaps, are of European origin. They grow on a different plant (Pisum sativum) and have been part of our diet since antiquity.

But as always, there are exceptions. The fava bean is botanically not a true bean at all, because it belongs not to Phaseolus (beans) or Pisum (peas), but to Vicia (Vicia faba). We still call it a bean simply because it looks like one. In short: every bean and every pea is a legume, but not every legume is a bean or a pea.

Spring-loaded

Unlike most edible fruits, beans don’t need animals to spread their seeds. Once the pods are ripe, they dry out and build up tension. A small touch is enough to make them snap open, shooting seeds several feet away. This is why they’re ideal to harvest when slightly dried: the seeds are collected before they spring from the pod on their own, then left to dry in a barn or shed. Dried this way, they keep for years.

Why they taste so good

The seeds of spring legumes are tiny energy factories. They store sugars, amino acids, minerals, and enzymes: everything needed to germinate. Those nutrients give fresh legumes their sweet flavor and snappy texture. They haven’t yet fully converted to starch (less sweet, more floury) or neutral proteins, as happens with dried beans.

For varieties with edible pods, like sugar snaps and snow peas, the pod itself contributes to the flavor. The pod photosynthesize and sends sugars to the seeds, even after harvest. That’s why fresh legumes are sweetest right after picking. The longer you wait, the more sugars convert to starch. That means flatter flavor and a mealier texture.

Joeri: “Fava beans are my favorite. Precisely because they’re a little bitter. That creates tension in sweet dishes, for example with raisins or saffron. And that velvety softness inside the pod, you don’t see that anywhere else.” On the debate between frozen and fresh: “Fresh peas are larger, crunchier, and visually more appealing. They work beautifully with pearl couscous: same size, same bite.” Try it in Joeri’s recipe below.

Recipe
Fresh peas with pearl couscous and grilled mushrooms

Serves: 3–4 Prep time: approx. 30 min. Resting time: minimum 15 min.

INGREDIENTS
2 organic lemons
15 g flat-leaf parsley
2½ tbsp olive oil
3 garlic cloves, pressed
½ tsp chili flakes
350 g (12 oz) small chestnut mushrooms
250 g (9 oz) pearl couscous
150 g (5 oz) fresh garden peas*
1 can (14 oz / 400 g) cannellini beans
10 g fresh dill, finely sliced
30 g (1 oz) toasted pine nuts

*Can’t find fresh? Use organic frozen peas instead.

METHOD
1. Finely grate 1½ tsp of zest from one of the lemons. Halve all the lemons and squeeze the juice from three halves. Cut the remaining half into 4 slices. Finely chop the parsley.
2. Mix 2 tbsp lemon juice, 1½ tbsp olive oil, 1/3 of the parsley, 2/3 of the garlic, the chili flakes, and ¼ tsp salt in a large bowl. Toss the mushrooms through the marinade and leave for at least 15 minutes (up to 3 hours).
3. Thread the mushrooms onto skewers, grouping similar sizes together.
4. Cook the pearl couscous in a large pan of generously salted water according to package instructions. Add the peas in the last 2 minutes, then drain.
5. Meanwhile, heat a grill pan or skillet over medium heat, or fire up the barbecue. Grill the mushrooms for 12–15 minutes, turning regularly. Grill the lemon slices for 4–5 minutes until they have grill marks or are golden brown.
6. Drain the cannellini beans, reserving the liquid. Blend the beans, 2 tbsp of the bean liquid, the lemon zest and 1½ tbsp lemon juice, 1 tbsp olive oil, the remaining garlic, ¾ of the dill, and ½ tsp salt in a food processor until smooth.
7. Spread the dill-lemon bean puree across the plates, smoothing with the back of a spoon. Stir the remaining parsley and plenty of pepper through the couscous and spoon over the puree. Place the mushroom skewers on top and garnish with pine nuts, lemon slices, and the remaining dill.

In the paid section:

• Fresh, frozen, or canned: what’s actually better?

• Why canned marrowfat peas taste completely different from fresh

• A preparation guide for each legume: cleaning, blanching, freezing

• Grilling, stir-frying, or raw: when to choose what

• More recipes with legumes in the lead role

• Extra tips from bean specialist Joeri Veul

Already a paying subscriber? Then just keep reading below. Not yet subscribed but want to read on, understand recipes better, and learn to cook with real knowledge? Take out a paid subscription. Tip: subscribe via our website for the best price (€60/year or €6/month). In the app you’ll pay €85/year due to Apple and Google service fees. As a subscriber you’ll receive the full Kitchen Lab newsletter every other Sunday, in your inbox or on Substack. You also get access to all our previous issues, including the archive. Members can also ask questions and share recipes or information in the Kitchen Lab Chat.

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This edition is all about the fresh spring vegetable spinach and its lesser-known relative Swiss chard. Why? Because they’re in season right now, and that’s when they taste best. We’ll show you that these fresh green leaves can go in almost any direction: raw, briefly blanched, stir-fried, or quickly braised. But first, we take you into the world of chlorophyll, the green leaf pigment that not only provides color but also brings some surprising cooking properties along with it. And of course we answer the question: can you reheat spinach or not?

Spring is green

Spring is a remarkable season. Everything turns green again, young leaves emerge, and photosynthesis kicks back into gear. Plants are preparing for a new growth cycle, with flowering, reproduction, and seed formation as the goal. Chlorophyll, the pigment that colors leaves green, plays a central role in this. It captures sunlight and converts that light energy, using water and carbon dioxide, into sugars: fuel for the plant’s cells. This makes plants fundamentally different from humans and animals. They produce their own energy and are, in a sense, self-sufficient.

The flavor of green

Green is not just a color; it also shapes flavor. Chlorophyll itself tastes fairly neutral, a bit like the smell of fresh grass. But the leaves that contain it have a distinctly pronounced flavor. Think of spinach and Swiss chard: both spring vegetables, both bright green, yet completely different. Spinach tastes earthier and more acidic; Swiss chard has something of cabbage to it. That difference comes from the fact that chlorophyll never occurs in plants on its own. It typically goes hand in hand with other substances characteristic of young, active leaves, such as oxalic acid, glucosinolates, and nitrate. Each one is a compound that protects the plant and delivers a clear flavor.

Why spinach sometimes tastes like chalk

Spinach, like rhubarb, can leave a gritty, almost chalky feeling on your teeth. That comes from oxalic acid, a plant acid that binds calcium in your mouth and forms tiny crystals (calcium oxalate). It’s like brushing your teeth with chalk. In the past, people would cook rhubarb with a copper coin to neutralize the acid. That helps a little, but more effective is adding something with calcium: milk, eggshell, chalk, or even a pinch of powdered plaster. This way the acid binds during cooking and spares your enamel. With Swiss chard the effect is less pronounced, because its oxalic acid content is lower than spinach.

In the paid section:

• Can you actually reheat spinach and Swiss chard, or combine them with fish?

• The best cooking techniques for leafy greens: blanching, stir-frying, braising, raw

• What varieties of spinach and Swiss chard are there?

• 5 exceptionally delicious spring recipes

Not a member yet? Join Kitchen Lab and get the full newsletter every other Fridaymorning, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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Some people fish every last chili out of a dish, others add a spoonful of hot sauce to just about every meal. How you experience heat is deeply personal. Why is that? And why do some people love spicy food so much? We explain what makes a pepper hot and look at the different types of heat (and the very different sensations they create). We also cover why chili is good for you and share tips for cooling down the burn. And of course: a few fiery recipes for a hot summer.

A flavor that isn’t a flavor

We often describe the sensation of spicy food as “hot,” but that’s not quite accurate. Heat isn’t a flavor the way sweet or salty are. What you feel when you eat a chili pepper is mild pain. Spicy compounds stimulate nerves that are normally designed to signal heat, cold, or physical damage. This form of perception is called chemesthesis: the sensing of chemical stimuli through the skin or mucous membranes. These nerves are also found on your tongue, lips, and in your throat. They respond to heat (like hot tea), cold (menthol), fizz (carbonation), and certain compounds in food. The most well-known example? Capsaicin, from chili peppers.

Why chili feels like fire

Capsaicin binds to a kind of “heat sensor” in your mouth: the TRPV1 receptor. This receptor sits on nociceptors (pain nerve fibers) and is designed to detect heat signals. Normally, TRPV1 is activated at temperatures above 107°F (42°C), such as when you take a sip of too-hot tea. But capsaicin does the same thing, without any actual heat involved. The result: an intense burning sensation in the mouth.

Why do people love spicy food?

Spicy food hurts, yet many people love it. Why? Part of the answer lies in the brain. Capsaicin activates the pain system, but causes no actual damage. This creates a paradox: you feel discomfort, but your body responds as if you’re in danger and releases a dose of endorphins. These natural painkillers produce a euphoric or relaxed feeling, similar to what you experience after exercise, sex, or a cold-water plunge. Dopamine, the reward hormone, is also released. The result: a mini-high at the dinner table.

This explains why spicy food feels exciting and can even be addictive. Like a roller coaster, it involves controlled stress: you know you’re safe, but your body reacts as if something is happening. That contrast between “panic” and “pleasure” is irresistibly appealing.

Some examples of this “delicious stress” in the kitchen:

• Thai tom yum soup with chili and kaffir lime leaf: hot and fresh, stress and relief. (see the recipe, for subscribers only)

• Sichuan mapo tofu: an almost “electric” tingle from sanshool (more on that below), burning from chili, mellowed by fermented bean paste. (see the recipe, for subscribers only)

• Mexican chipotle salsa: smoky heat that builds slowly and fades just as slowly.

There’s also the phenomenon of tolerance. The nerves in your mouth that register capsaicin (TRPV1 receptors) become less sensitive with repeated exposure. That’s why people who eat spicy food regularly can handle more and more, just like with coffee or alcohol. What’s unbearable for a beginner is a pleasant tingle for a seasoned chili eater. Culture plays a role too. In countries where spicy food is the norm (such as India, Mexico, and Thailand), people learn from a young age to handle heat. But it remains a learning process.

So we love spicy food not despite the discomfort, but because of it. It’s a controlled form of pain, rewarded with pleasure. And just like other thrilling experiences: the more you do it, the more you can handle, and the bigger the kick.

Why do pepper plants make capsaicin?

Pepper plants produce capsaicin as a defense mechanism: it keeps mammals away. Birds don’t experience that pain sensation, so they can spread the seeds without issue. Smart evolution. The amount of capsaicin varies between species (bell peppers have none; habaneros will torch your tongue), within species (supermarket chili vs. market chili: same variety, different heat), and depending on growing conditions (more sun often means more heat). Breeders can also deliberately select for more or less heat by choosing varieties with more capsaicin glands in the fruit wall. That’s how superhot varieties like the, in our view completely inedible, Carolina Reaper came to be.

But capsaicin isn’t the only thing that creates a peppery sensation. In the paid section of this newsletter, more on:

• Different types of heat (black and white pepper, mustard and wasabi, Sichuan pepper)

• How to cool down pepper heat

• Health benefits

• A quick pepper guide for the kitchen: which pepper goes in which dish?

• Four fiery recipes: tom yum soup, mapo tofu, Sichuan pepper chocolates, and toast with asparagus and wasabi cream

Not a member yet? Join Kitchen Lab and get the full newsletter every other Fridaymorning, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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Olive oil is indispensable in the kitchen, but choosing the right one from an overwhelming selection can be tricky. What should you look for? Which oil for which dish? Judith van Unen, certified olive oil taster and owner of olive oil wholesale and specialty shop Meeuwig and De Oliewinkel in Amsterdam, explains exactly how it works. We also answer the question of whether or not you can heat olive oil, and explain why it’s so good for you. Of course, we’ve also included a few flavorful, simple recipes where olive oil takes center stage.

Oil inside an olive

Olives are the fruit of the olive tree, and they’re exceptionally rich in oil. While apples and pears contain almost no fat, an olive consists of 11 to 15% oil. No wonder this fruit has been used as a plant-based oil source for thousands of years. Over the centuries, olive varieties have been selected for ever-higher oil yields. The methods used to extract the oil have also changed dramatically, and with them, the yield per olive.

What determines quality

Several factors determine the quality of the oil.

The method: pressing or extraction

Simply put, there are two ways to make oil from an olive: mechanically, by pressing or centrifuging, or chemically, through solvent extraction. Traditionally, olives were ground pit and all into a pulp, then pressed. Stone mills and wooden or metal lever presses were used, later replaced by screw presses. The pressed liquid, a mix of oil and water, was left to settle until the oil floated to the top, then poured off: the “first pressing.”

Today, presses have been replaced by stainless steel centrifuges that process olives continuously into oil. No more wooden barrels; modern technology with the same goal: separating oil from water and solids. The higher the pressure or centrifugal force, the higher the yield. This method produces extra virgin olive oil: the highest quality. The pulp left after centrifuging, called sansa or pomace, still contains some oil. This is extracted with solvents (such as hexane). The resulting oil can only be consumed after refining, and is sold under names like “light olive oil” or “pomace olive oil.”

You may still see the term “second pressing,” but it’s outdated: nearly all edible olive oil is now produced in a single pass. Whatever oil remains afterward isn’t pressed again; it’s chemically extracted.

Temperature

Processing temperature plays an important role in final oil quality. Olive oil may only carry the “cold extraction” label if production takes place at a maximum of 27°C (81°F). The higher the temperature, the more the oil’s flavor and aroma can change. Many reputable producers work at lower temperatures, often around 20°C (68°F), to preserve taste and aromatic properties at their best.

Acidity

Olive oil quality is also measured by acidity. Here, acidity doesn’t mean pH, but the percentage of free fatty acids in the oil, mainly oleic acid. Low acidity signals freshness and a careful production process where olives are processed quickly and without damage. According to EU regulations, extra virgin olive oil may have a maximum acidity of 0.8%. Virgin olive oil falls between 0.8% and 2%. Oil with higher acidity is classified as lampante oil and is only suitable for consumption after refining. Although acidity itself isn’t perceptible to the palate, low acidity typically goes hand in hand with better flavor, aroma, and shelf life.

Wonder oil is real

Extra virgin olive oil isn’t just a flavoring agent; it’s a proven healthy ingredient. Research shows that people who use olive oil daily have a lower risk of cardiovascular disease and death from dementia (the Mediterranean diet). One important detail: those benefits apply almost exclusively to extra virgin olive oil. Minimal processing preserves sensitive bioactive compounds like polyphenols and vitamin E. These antioxidants protect your blood vessels, reduce inflammation, and support healthy brain function.

One of the most studied polyphenols in olive oil is oleocanthal, known for the mild peppery sensation it causes at the back of the throat in fresh oil. Oleocanthal acts as a natural anti-inflammatory, comparable to a mild version of ibuprofen. So the spicier and more peppery an olive oil feels in the back of your throat, the more likely it is to be rich in oleocanthal. Hydroxytyrosol, a powerful antioxidant, also plays an important role in protecting cells from oxidative stress.

Refined olive oil undergoes heat and chemical processing, during which nearly all polyphenols are lost, along with most of the health benefits. In short: good-quality olive oil is an investment in both flavor and yourself.

It all starts with taste

According to Judith van Unen, certified olive oil taster and co-owner of Meeuwig and De Oliewinkel, two Amsterdam-based specialty shops for olive oil, vinegar, and Mediterranean delicacies, everything begins with your own palate. “Taste, taste, taste. That’s the only way to develop your sense of flavor. Customers are welcome to taste, especially with a new harvest. If you’re spending twenty, thirty euros on a bottle, you want to know what you’re getting.”

She emphasizes how diverse olive oil can be. “With wine, people understand that different grapes and regions produce different flavors. With olive oil, we’re still discovering that.” That’s why she prefers to import oils from the regions where the olive variety originates: Arbequina from northern Spain, Taggiasca from Liguria. “The chances of top quality are simply higher.”

Judith’s approach is refreshingly direct: you don’t need to know anything about olives or olive oil. You just need to know what you like. She never starts a consultation with technical terms, but always with the question: do you prefer mild and smooth, or bold and peppery?

She deliberately limits her range to oils from the Mediterranean basin. “I don’t want an oil with a plane ticket. But I do see opportunities for the future: enormous numbers of olive trees have been planted in Rajasthan, India. For bulk oil, the refined varieties, that could become quite interesting.”

For paid subscribers:
• Judith’s tips for choosing the right oil and her kitchen favorites
• Answers to pressing questions:

• How do you store olive oil?

• Can you heat it?

• How do you taste it?

• What does the oil color tell you?

• The best recipes, from classic to out-of-the-box, plus 4 additional recipe links

Not a member yet? Join Kitchen Lab and get the full newsletter every other Sunday, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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A well-cooked egg seems simple. It isn’t. In this newsletter, we dive into the molecular logic of proteins, coagulation, and temperature control. Why does an egg solidify when heated? Why is there a difference between the white and the yolk? And most importantly: why does your egg so often end up slightly too hard or too soft, even when you’ve done everything right? With the knowledge in this newsletter, you’ll serve a perfect boiled egg every time. And for extra creaminess, we take a detour into poaching. Also an art, but definitely not hard.

The science of setting

It’s remarkable that eggs become firm when heated. Vegetables soften, liquids evaporate, but egg proteins solidify. That’s due to the unique structure of the proteins in eggs. Both the white (90% water, 10% protein) and the yolk (17% protein) contain a mix of protein molecules that denature when heated. They unravel, form long strands, and bond with each other. This process is called coagulation. It creates a firm network that traps water, turning the egg from liquid to solid.

But here’s the catch: the white and yolk contain different proteins, each with its own setting temperature. The yolk starts to set at 144°F (62°C) and is firm at 158°F (70°C). The white doesn’t start to set until 145°F (63°C) and is fully set at 176°F (80°C). Serve an egg at 154°F (68°C) and you get a firm yolk with a soft white. A reverse soft-boiled egg, in other words.

For a proper soft-boiled egg, you need to keep the water at temperature long enough for the white to just set while the yolk stays warm and runny. That’s where the difficulty lies. The key to success is temperature control. So how do you do that?

Perfection in practice

Start hot. Always place eggs in boiling water. It’s more precise than starting in cold water. It also makes the eggs easier to peel, more on that later.

Know your egg. Size (S, M, L, or XL) and temperature affect cooking time. A cold egg straight from the fridge (39°F / 4°C) can easily cost you an extra minute. XL? Takes longer than S.

Cook smart. Cooking a lot of eggs at once? The water temperature drops when you add them. And with a weak heat source, it takes a while to return to a boil. Match the pan size and water quantity to the number of eggs. Make sure all the eggs fit in a single layer and that you have about 1 inch (2 to 3 cm) of water above them.

Be precise. The perfect time comes through trial and error. You know your pan, your heat source, and your eggs. Keep track and stay consistent.

Cooking time guide (for room-temperature eggs)

Soft: 5 minutes

Medium-soft: 6 minutes

Salad egg: 7 minutes

Hard: 10 minutes

Pierce or crack. The air pocket sits at the rounded end of the egg. As the egg heats up, the air expands. Piercing a small hole in the air pocket lets the air escape and prevents the shell from cracking. It also gives the egg a nicer, rounder shape. If the air pocket stays intact (in an unpierced egg), the white sets around the cavity and you get a dent or indent on one side.

Shock them. Cool your eggs in cold water immediately after cooking to stop the cooking process.

In the paid section of this newsletter:

• Does shocking really make a difference?

• Our recipe for the perfect boiled egg, with the nuances for an even better result.

• Recipes: egg-truffle salad and stuffed umami eggs.

• Poaching made easy, with a green spring shakshuka.

• Oil-poaching (the Chinese takeout egg) with a recipe for poached egg with chili crunch, kimchi, and avocado.

Not a member yet? Join Kitchen Lab and get the full newsletter every other Sunday, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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In this third and final part of our curry series, we dive into the magic of spices. We’re using Indonesian cuisine as our lens and handing the mic to guest chef Vanja van der Leeden. She’s a culinary author, cook, and expert in both Indonesian and Italian cuisine. Vanja is known for her rebellious style: she has no time for dogma and combines tradition with creativity. Her books Indorock, Indostok, and Italopop are a plea for boldness in the kitchen. She also writes on Substack (in Dutch). Highly recommended. You can find her here.

First, let’s clear up a misconception.

Vanja: ‘In Indonesia, you don’t say curry. You say gulai, kalio, semur, opor, or rendang.’

Yet all these dishes revolve around the same thing: a layered structure of spices. In this newsletter, we explore how spices like coriander and cumin work together, how to tame dominant spices like cloves or mace, and how to balance the heat of chile peppers (with fat, time, and technique).

Cumin and coriander seed

Vanja: ‘I always use coriander and sometimes cumin. And always more coriander than cumin.’ You’ll find cumin and coriander seed together in nasi kebuli (an Indonesian rice dish with Arabic influences), in semur (a soy sauce stew with meat, chicken, tempeh, or tofu), and in certain versions of bumbu bali. These spices reinforce each other and prevent any single flavor from dominating.

Coriander seed and cumin aren’t just a popular combination in Indonesian cooking. Across Asian cuisines, they form a classic pairing. Toasted and ground together (as in the Indian dhana-jeera mix), they create a broad, layered aroma. Coriander seed brings freshness thanks to its high linalool content, while cumin adds depth and warmth through the compound cuminaldehyde. The combination produces an aroma that is both light and earthy, without either one overpowering the other.

Toasting or frying

How you use spices and when you add them also affects flavor. Toasting or frying coriander and cumin together in oil triggers Maillard-like reactions that release new aromas. Maillard reactions also play a role when frying spice pastes (bumbu or curry pastes); more on that later in this newsletter. We covered the frying of spices in the previous newsletters as well. The oil absorbs the aromas from the spices, which then spread throughout the rest of the dish.

In the tempeh stew recipe below (semur in Indonesian), we use the combination of cumin and coriander seed. A small amount of cloves goes in as well for extra depth.

Recipe
Tempeh semur

Spiced tempeh in sweet soy sauce with coriander and cumin
Servings: 4
Prep time: 40 min.

INGREDIENTS
400 g (14 oz) tempeh
1 large onion
3 cloves garlic
1 piece ginger, about 1 inch (2 cm)
2 tsp ground coriander
1 tsp ground cumin
1/2 tsp ground cloves
1/2 tsp freshly grated nutmeg
3 tbsp kecap manis (sweet soy sauce)
2 tbsp kecap asin (or regular soy sauce)
2 tsp palm sugar or brown sugar
1 tbsp tamarind paste or 1 tbsp lime juice
250 ml (1 cup) vegetable broth
1 tbsp cornstarch
Sunflower oil
Serve with: rice and sweet-and-sour cucumber (or achar)

METHOD
1. Cut the tempeh into slices or triangles about 1/4 inch (1/2 cm) thick. Heat a generous layer of sunflower oil in a skillet. Fry the tempeh until golden brown and drain on paper towels.
2. Dice the onion. Finely chop the garlic and ginger. Heat 2 tbsp oil in a deep pan and fry the onion until light brown. Add garlic and ginger and cook for 1 min.
3. Add coriander, cumin, cloves, nutmeg, and optionally cinnamon or star anise. Fry for 30 seconds until fragrant.
4. Add the broth, kecap manis, kecap asin, sugar, and tamarind. Stir and simmer for 10 min. to reduce.
5. Mix the cornstarch with 2 tbsp cold water. Stir it in and let the sauce thicken briefly until it coats the tempeh.
6. Add the fried tempeh and simmer for 5 min.
7. Serve with rice. Great with fried shallots or red chile rings.
TIP: let a bruised stalk of lemongrass and/or a few lime leaves simmer along in the stew for a fresh note.

Garlic and ginger

A similar synergy to cumin and coriander seed often shows up in the combination of garlic and ginger. Raw, they’re sharp and pungent, but together, finely ground and fried in oil, they form a rounded, aromatic base. The sulfur compounds in garlic and the gingerols in ginger complement each other. The result is an umami-like foundation that appears in many Thai curry pastes and in many (though certainly not all) Indonesian bumbu.

The interplay of garlic and ginger isn’t a chemical reaction, but a matter of perception: one aroma influences how we experience the other. 1 + 1 = 3. A simple application of this can be found in a classic vegetable dish like sambal goreng beans (recipe below). The combination of garlic and ginger, together with onion, sambal, and a touch of kecap, forms the core of the flavor. You don’t taste individual spices, but a balanced, aromatic sauce where everything clicks. Simple and quick at the same time.

Vanja: ‘Garlic plus ginger plus oil is almost always a winner, but in Indonesian cooking, garlic and onion are really the foundation. Ginger is optional. Whether you use it depends on the dish. I often use galangal too, sometimes combined with ginger. It’s not always one or the other.’

In the paid section of this newsletter:`
-Vanja’s jackfruit rendang, with genuinely useful tips.
-Why fat, time, and technique are the key to a mild stew with 20 chile peppers.
-How to get maximum flavor from your bumbu in three steps.
-The difference between gulai, kalio, and rendang, and what that teaches you for vegetarian cooking.
-Tips from Vanja: how to maintain texture and build depth without meat.

Not a member yet? Join Kitchen Lab and get the full newsletter every other Sunday, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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In part 1 of this curry series, we wrote about the importance of oil and fat in Indian curries: the flavor is in the fat. In Thai curries, where fresh, vibrant flavors play a central role, other flavor carriers matter just as much. We’ll dive deeper into the techniques of extraction and infusion, zoom in on the secret of coconut milk, the impact of spices, and the importance of timing. All to improve the flavor of your curries, even in simple dishes. Want to go fully from scratch? We’ll give you a recipe for a homemade Thai curry paste.

What makes Thai curries so different

Thai curries may seem related to Indian curries, but they’re vastly different in preparation and flavor balance (with the exception of massaman curry). Indian curries are defined by deep flavors and long cooking times. Thai curries are all about freshness and speed. That’s what has made them popular worldwide. The traffic light curries (yellow, green, and red), massaman, and panang are on menus in Thai restaurants everywhere. In Thailand itself, you’ll find thousands of variations. Thai curries are usually thinner than Indian ones and served in a bowl, with the ingredients floating in the curry sauce.

The base: curry paste

Thai curries owe their intense flavor to a freshly ground curry paste combined with coconut milk. The hallmark is a balance of spicy, sweet, salty, and sour. Ingredients like lemongrass, makrut lime leaf, chile pepper, galangal, and Thai basil give those aromas their vibrant, recognizable character. You’ll find many of these spices in other Southeast Asian cuisines as well.

Homemade curry paste

Thai curries are known for their quick preparation, but that’s mainly true when you work with store-bought curry pastes. Making your own takes time, especially because you need to gather the right ingredients. Why bother? Because it’s fun. Because it gives you control over flavor. And because fresh ingredients deliver more aroma. Is it necessary? Not at all. There are perfectly good store-bought pastes available.

The advantage of store-bought pastes: they keep for a long time. But Kitchenlab wouldn’t be Kitchenlab if we didn’t also show you how to make your own. You’ll find the recipe at the bottom of this newsletter, plus tips like: freeze your ingredients first and they’ll be much easier to grind.

In the paid section of this newsletter:

• How do you extract and infuse aromas in your curry?

• What is the secret of coconut milk, and what types are there?

• The perfect timing: when do you add what?

• Making your own curry paste: ingredients explained.

• Four tested recipes + one recipe video.

Not a member yet? Join Kitchen Lab and get the full newsletter every other Friday, straight to your inbox. Plus access to our complete archive and the Kitchen Lab Chat, where you can ask questions and swap recipes with fellow food nerds. Subscribe at kitchenlab.substack.com/subscribe: €60/year or €6/month. To avoid app store fees (€85/€9), use the link above rather than subscribing through the Substack app.

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