Culinate

The science of baking

Kitchen chemistry

By
April 27, 2009

In the home kitchen, there are two kinds of people: cooks and bakers. For cooks, recipes are mere suggestions, flexible in their ingredients and proportions. For bakers, on the other hand, recipes are gospel truth, precise in their measurements and techniques.

Me, I’m definitely a cook. I enjoy the spontaneity of tweaking a recipe or making one up based on what’s in the fridge. But the downside to being a cook is that, no matter how often I’ve prepared a particular bread or pastry recipe, I can’t guarantee the same results every time. I envy my grandmother, who can whip together dough for dozens of dinner rolls without even measuring the flour. She just knows when the dough looks and feels “right.”

After a recent cheese-puff disaster — my typically lofty gougères came out of the oven as flat as cookies — I decided to become less of a cook and more of a baker. So I quizzed six baking experts about ingredients and techniques.

baking ingredients
Essential ingredients for baking, clockwise from top left: eggs, butter, milk, vegetable oil, baking powder, baking soda, salt, sugar, yeast, and flour.

The secret to successful baking? It’s all in the chemistry. And here’s the scientific lowdown on how each basic baking ingredient functions in the kitchen.

Flour

I started my research with flour. After all, the protein in flour lends structure to baked goods, from poufy popovers to crusty artisanal breads. As pastry chef Shuna Fish Lydon wrote recently on her Eggbeater blog, “In baking, protein provides the walls holding up roofs.” But you can’t build walls of any kind without elbow grease.

I coaxed Peter Reinhart — a baking instructor and the author of several books, including The Bread Baker’s Apprentice — into sharing the basics behind dough construction. He told me that two proteins — glutenin and gliadin — inhabit flour.

“When you add water to the flour to hydrate the ingredients, these proteins are drawn to each other and bond,” Reinhart says. “This new protein is gluten.”

Reinhart suggested I call Shirley Corriher for the nitty-gritty on the science of baking. A former Vanderbilt University biochemist, Corriher turned her kitchen into a laboratory of sorts and published her experiments in two cookbooks, CookWise and BakeWise.

Kneading builds gluten networks, says Corriher, which in turn support bread. While dough rises, existing gluten threads touch and create more links. Later, inside the oven, the proteins and starches in the flour transform into the sturdy webbing inside a loaf of bread.

Pastries, on the other hand, demand a more tender crumb. Corriher explains that the lower protein content in pastry, cake, and all-purpose flour creates a less rigid gluten network and a finer crumb.

But selecting the right flour for the job isn’t as easy as it seems. “The problem with all-purpose flour is that it is all over the place in protein content,” Corriher says.

So she shared a trick to help determine flour’s protein content: Measure two cups into a bowl and stir it with a scant cup of water.

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“If you have a high-protein flour, it’s going to suck in water like crazy” and form a dough, she says. Less protein-rich flour won’t come together unless you add more flour.

I tested the all-purpose white flour in my cupboard. Sure enough, I had made my top-heavy cheese puffs with a high-protein flour more appropriate for hearty bread.

Unfortunately, as Corriher says, there’s no easy way to determine the protein content of flour. Just check out the label on the flour in your pantry. The manufacturer has rounded the protein weight to the nearest gram per quarter-cup. So one flour that contains 2.5 grams of protein per quarter-cup, and a second flour that contains 3.4 grams, would both round to 3 grams of protein for labeling purposes. That difference, however slight, can affect how the rest of the ingredients play off each other.

Because there’s so much guesswork involved with flour and the other elements of baking, Reinhart suggests treating recipes as templates, not rigid rules. But wait a sec; isn’t precision the whole point of baking?

“Every situation is different,” he says. “The instructions are a general guideline to get you into the ballpark. You let the dough dictate to you what it needs.”

Bakers benefit from learning more about the reactions that happen in their mixing bowls, pastry chef Carole Bloom adds. “Once you know how ingredients work, that’s when you can start to improvise,” she says.

Leavening agents

I love peering through the oven window to watch as loaves and cakes puff up. Yeast, baking soda, and baking powder — combined with the extra oomph of steam — supply airiness to bread and pastries.

Reinhart reminded me that yeast literally brings bread to life. As yeast feeds on sugars in dough, it oozes a liquid that, when it touches an air pocket, lets loose carbon dioxide and alcohol. Or, in Reinhart’s words, “The yeast burps and sweats.” The elastic dough traps those tiny carbon-dioxide bubbles like a balloon.

Baking powder and baking soda, meanwhile, release carbon dioxide that “only enlarges bubbles that are already in the batter,” Corriher explains.

It’s important to cream butter thoroughly to whip those bubbles of CO2 into the fat. “Start with butter that’s soft, not runny,” advises Bloom, whose latest cookbook is Bite-Size Desserts. “If the butter is too firm, you’re not going to get it to that fluffy stage.”

Baking soda reacts with acids — citrus juice, buttermilk, molasses, honey, and chocolate are all acidic — to produce carbon dioxide, which in turn puffs the batter.

Double-acting baking powder, adds Corriher, releases carbon dioxide twice during the baking process: once when it reacts with liquids during mixing, and again when it’s exposed to higher temperatures in the oven.

Bakers struggling with heavy cakes and too-dense breads can often point to leavening agents as the culprit. Resist the temptation to add more leavener to compensate for a weak rise, warns Corriher: “If the recipe is overleavened, the bubbles run together, float to the top, and pop” — and your pastry sinks.

One teaspoon of baking powder — or just a quarter-teaspoon of baking soda — is enough to leaven one cup of flour, says Corriher.

Eggs

In pastry, eggs “help bind things together,” explains Mani Niall, a pastry chef and the author of the cookbook Sweet!.

Egg whites work as leavening agents. When heated, the proteins in egg whites uncoil and practically explode up the sides of the pan, just like Dutch baby pancakes.

dutch baby pancake
Because it calls for lots of eggs, a Dutch baby pancake puffs up in the oven and then deflates once removed from the heat.

Corriher has experimented with substituting egg whites for whole eggs to force a bigger rise out of cream puffs or gougères. But substitutions can be tricky, she cautions, because the proteins in egg whites force out moisture when they’re heated. The result: puffy but chalk-dry pastries.

Egg yolks, on the other hand, lend richness and moisture to baked goods, says David Lebovitz, a pastry chef whose books include Room for Dessert. “If you were to make a cake with all egg yolks, it’d be moist, but also kind of wet,” he explains.

And make sure to bring eggs to room temperature before mixing. “If you add cold eggs to butter and sugar, they won’t combine correctly,” Lebovitz warns.

Fats

As anyone who’s ever eaten a delicate, buttery croissant can attest, fats are incredible tenderizers. Fats coat the proteins in flour, says Corriher, preventing them from bonding with water and forming gluten.

“You don’t want a lot of gluten in muffins and scones, making them chewy in a breadlike way,” Niall says.

Oil coats flour’s proteins better than butter does, which explains why oil-based cakes are moister than butter-based cakes.

Sugar and milk

Sugar gives pastries their addictive sweetness, but it also helps keep them moist. “If you think of baked goods without sugar, it’s bread, because it’s not tender,” says Niall. Not surprisingly, there’s a scientific explanation behind sugar’s tenderizing properties.

“If you have a lot of sugar present, your glutenin runs off with sugar, your gliadin runs off with sugar, and you don’t get much gluten formed,” Corriher explains. And then your pastry won’t have any structure.

Likewise, adding milk to batter helps keep baked goods moist. Milk contains the sugar lactose, which bonds with flour proteins and hinders gluten formation.

Both sugar and milk promote browning, Corriher says. Essentially, bread crust is caramelized sugar.

Salt

Recipes for baked goods usually call for a pinch of salt because it helps conceal bitter tastes. But the mineral also plays a key role in gluten formation, says Patti Christie, a biochemist who teaches a series of popular kitchen-chemistry courses at the Massachusetts Institute of Technology.

“The reason you add salt to dough is to make dough more elastic,” Christie explains. “Charged amino acids in the flour are going to interact with the ions in the salt, and that helps line up the gluten fibers. Your bread is going to have better texture.”

As for sugary treats, a bit of salt added to batters and doughs helps to balance sweetness and enhance other flavors during baking. And if added as a finishing touch to, say, chocolate-chip cookies, salt provides a pleasing textural contrast.

Lab work

After talking with bakers and chemists about ingredients, methods, and reactions, I decided there was one more person I needed to quiz: my grandmother, the master baker in my family. She didn’t have advice about science, but she did say that practice is the key to good baking.

But just how much practice? Well, she’s baked four to six dozen dinner rolls for our big, hungry family every week or two for the past 58 years. That adds up to nearly 150,000 rolls in more than 2,000 baking sessions.

“After you’ve made bread for a while, you can tell just by feeling the dough how good a batch you’re going to get,” she says.

So even though I’m fresh out of my lessons on baking science, I still have lots of homework ahead of me. But with enough experimentation, I may be able to switch on my family baking genes after all.

Based in Portland, Oregon, Kelly Stewart is the editor of Roast magazine. Her writing about food has appeared in the Christian Science Monitor, Meatpaper, and Zagat Survey guidebooks.