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The science of bakingKitchen chemistryBy Kelly StewartApril 27, 2009

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

Me, I’m definitely a cook. I enjoy the spontaneity of tweaking a recipe ormaking one up based on what’s in the fridge. But the downside to being acook is that, no matter how often I’ve prepared a particular bread or pastryrecipe, I can’t guarantee the same results every time. I envy mygrandmother, 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 asflat as cookies — I decided to become less of a cook and more of a baker. So I quizzed sixbaking experts about ingredients and techniques.

The secret to successful baking? It’s all in thechemistry. And here’s the scientific lowdown onhow each basic baking ingredient functions inthe kitchen.

Flour

I started my research with flour. After all, theprotein in flour lends structure to baked goods,from poufy popovers to crusty artisanal breads.As pastry chef Shuna Fish Lydon wrote recentlyon her Eggbeater blog, “In baking, proteinprovides the walls holding up roofs.” But youcan’t build walls of any kind without elbowgrease.

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

Gougères (FrenchCheese Puffs)Dinner Rolls

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

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“When you add water to the flour to hydrate the ingredients, these proteins are drawn toeach 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. Aformer Vanderbilt University biochemist, Corriher turned her kitchen into a laboratory ofsorts and published her experiments in two cookbooks, CookWise and BakeWise.

Kneading builds gluten networks, says Corriher, which in turn support bread. While doughrises, existing gluten threads touch and create more links. Later, inside the oven, theproteins 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 lowerprotein content in pastry, cake, and all-purpose flour creates a less rigid gluten networkand 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 abowl and stir it with a scant cup of water.

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

I tested the all-purpose white flour in my cupboard. Sure enough, I had made my top-heavycheese 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 offlour. Just check out the label on the flour in your pantry. The manufacturer has roundedthe protein weight to the nearest gram per quarter-cup. So one flour that contains 2.5grams of protein per quarter-cup, and a second flour that contains 3.4 grams, would bothround to 3 grams of protein for labeling purposes. That difference, however slight, canaffect 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’tprecision the whole point of baking?

“Every situation is different,” he says. “The instructions are a general guideline to get youinto 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 youcan start to improvise,” she says.

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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 — supplyairiness to bread and pastries.

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

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

It’s important to cream butter thoroughly to whip those bubbles of CO2 into the fat. “Startwith butter that’s soft, not runny,” advises Bloom, whose latest cookbook is Bite-SizeDesserts. “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 chocolateare all acidic — to produce carbon dioxide, which in turn puffs the batter.

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

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

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

Eggs

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

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

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

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Egg yolks, on the other hand, lend richness andmoisture to baked goods, says David Lebovitz, apastry chef whose books include Room forDessert. “If you were to make a cake with all eggyolks, it’d be moist, but also kind of wet,” heexplains.

And make sure to bring eggs to roomtemperature before mixing. “If you add cold eggsto butter and sugar, they won’t combinecorrectly,” Lebovitz warns.

Fats

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

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

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

Sugar and milk

Sugar gives pastries their addictive sweetness, but it also helps keep them moist. “If youthink of baked goods without sugar, it’s bread, because it’s not tender,” says Niall. Notsurprisingly, 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 offwith sugar, and you don’t get much gluten formed,” Corriher explains. And then your pastrywon’t have any structure.

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

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

Salt

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

Because it calls for lots of eggs, a Dutch babypancake puffs up in the oven and then deflates onceremoved from the heat.

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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 thathelps 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 sweetnessand 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, Idecided there was one more person I needed to quiz: my grandmother, the master bakerin my family. She didn’t have advice about science, but she did say that practice is the keyto 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 rollsin more than 2,000 baking sessions.

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

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

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

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