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.

Related recipe: Gougères (French Cheese Puffs); recipe: Dinner Rolls

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1. by sj.breeze on Apr 27, 2009 at 7:39 PM PDT

This information is really helpful--I’m a natural cook, struggling with learning how to bake. I don’t think it helps that most recipes measure by volume instead of weight! I’m just wondering, can melted butter be substituted for oil in recipes? I don’t like to use vegetable oil. And I read somewhere that butter for creaming should not be room temperature, rather it should be about 60 degrees--is that right? Any advice appreciated! :)

2. by Hank Sawtelle on Apr 29, 2009 at 11:47 AM PDT

Great article Kelly! You talked to all of the superstars. Regarding yeast, don’t forget about sourdough . . .

@sj.breeze - you can usually sub butter, but keep in mind that it’s about 80% fat and 20% water (by weight), so you may need to do some math and reduce the amount of liquid in the recipe accordingly. And I am totally with you on the annoyance of volume measures in baking recipes.

3. by helenrennie on Apr 29, 2009 at 12:00 PM PDT

Hi Kelly,

Great write up on the basics of baking! I am a cook at heart too, and one thing that made all the difference in my baking is weighing the flour. This will make WAY bigger difference than figuring out exactly how much protein your flour has. Get yourself a scale and try weighing a cup of flour 5 times. You’ll get different amount each time. Whatever you’ll get is likely not the amount the recipe writer had in mind either. A cup of flour can vary by as much as 25% from person to person. No one in US even agrees on what a cup is. Some say it’s 4.5 oz, some say it’s 5oz.

To avoid the protein content being all over the place for AP flour, Rose Levy Beranbaum suggests only using King Arthur, Pillsbury, and Gold Metal instead of generic brands. I find that her advice on baking gets me perfect results the first time around -- it boils down to being extremely precise with measurements, temperatures, and ingredients. Unfortunately, I can’t say the same for Reinhart. His book is great at explaining the theory, but the recipes need too much adjustment to work on the first try. The only way you’ll learn to adjust with baking is to make the same thing 20-30 times changing only one variable at a time (just like a proper science experiment). If your temperament is anything like mine, that’s never going to happen. That’s why I like meticulous recipes when it comes to baking -- I want something decent on the first try.

Cheers,
-Helen

4. by Caroline Cummins on Apr 29, 2009 at 7:25 PM PDT

Culinate columnist Matthew Amster-Burton also has two good takes on baking science: on yeast, and (like Helen, above) on why weighing ingredients is so much better than using volume measurements. Check ‘em out.

5. by dusksunset on Apr 30, 2009 at 11:44 AM PDT

I agree with Helen on using only King Arthur flour. At one of their seminars, the baker/instructor explained that they test the protein in their products to make sure it fits the description of the flour variety.

He also cautioned that flour should be loosely spooned into measuring cups and then gently leveled off, never packed in. Packing can add much more flour than what the recipe calls for.

6. by Linear Girl on May 4, 2009 at 12:29 PM PDT

I’m reminded of my grandmother today. She was born in 1898 and went to college for Home Economics. One of the first “adult” conversations we had was about the chemistry of baking and how and why ingredients interact. She would have loved to see a wider audience for knowledge of this kind. Thanks for the article.

7. by SDac on Apr 27, 2011 at 9:25 AM PDT

I am just starting to learn about Kitchen Chemistry to learn more about quick breads (since I have a sensitivity to yeast and am lactose intolerant - I am always on the search for bun and bread recipes that don’t require yeast). BUT....what does Milk have to do in kitchen chemistry - and can I substitute it for soy milk? will recipes work with soymilk? consequently, if you look at a popover recipe...the chemistry is basic, and apparently milk is needed for the sugars, so why can’t I add sugared water or sugary soy milk?
I would appreciate anyones comments. Thank you

8. by Caroline Cummins on May 4, 2011 at 5:20 PM PDT

SDac: Milk serves many purposes in baking, including browning, adding a richer flavor, and keeping crusts soft and crumbs fine. In general, you should be able to substitute soy milk for dairy milk, but the flavor may not be the same. (Don’t try this switch, however, in liquid-heavy puddings and baked custards/flans, because they won’t set properly.) As for a soy-milk popover recipe, try the one on the Silk website.

9. by anonymous on May 27, 2011 at 8:40 AM PDT

I just meant to get a little educated on the art of baking..but wound up with a great deal of information I find so helpful.I cant read all of it now but would like to add that it makes sense since I’ve been baking and cooking and do alot of it by feel..i couldn’t use a recipe even if i tried..I succeed mnost times with wonderful results.Thank you for sharing.

10. by anonymous on Oct 7, 2011 at 9:31 AM PDT

Thanks for the information. It has really helped me with understanding all of the properties of baking. I’m doing my junior project on the art and science of baking and cake decorating. I’m a natural baker and cook, but I only knew a part of the science of it. Thanks so much!

11. by anonymous on Oct 8, 2011 at 7:27 AM PDT

over 60 and have really never learned to bake or cook with medical background i am facinated by the science just made cream puff dough this week and wondered why still a bit custardy inside and gougeres tasted awful you cant believe how excited i was to hand whip a cup of heavy cream for the first time as a beginner this is very very helpful

12. by anonymous on Dec 5, 2011 at 8:34 PM PST

You can Clarify Butter before using it in baking recipes. Basically Clarifying butter just heats the butter over low heat until it stops bubbling and all the water has been removed. You can then store the butter in a jar where it will re-solidify. You can look for a videos of utube that will show you how.

13. by anonymous on Jan 19, 2012 at 9:07 AM PST

What about altitude? I live in Denver, a mile above sea level, and I don’t know how to adjust for that altitude in baking--or stovetop cooking, for that matter.

14. by Kristen on Feb 14, 2012 at 4:31 PM PST

Hi Kelly!

I am trying to understand the science/chemistry behind baking in order to successfully alter recipes for allergy purposes.

Right now I am struggling with how to effectively remove gluten and milk from baking products and still have it taste delicious.

Your above article is amazing in helping me to understand what role each of these plays in baking. Would you have any suggestions on how to maintain their role gluten and milk play after removing them from the baking process?

Are there other types of ingredients that can replace milk and gluten and still fulfill the role they play?

Thank you for your help!!!

15. by anonymous on Mar 22, 2012 at 1:47 PM PDT

Great article. I just made a cheese cake which required 5 eggs. It is delicious, but the cake itself is rather yellow which is even more noticable since it has a very white sour cream topping. I was wondering if I could just use egg whites and I think the article answers that question well .. should be ok since cheesecake is already quite moist.

Thanks

16. by anonymous on May 4, 2012 at 1:28 PM PDT

i like pie

17. by anonymous on May 16, 2012 at 4:05 AM PDT

great information!! This is a great review for my test that I have today at Le Cordon Bleu. Thanks!!!

18. by anonymous on Jun 6, 2012 at 1:43 PM PDT

This is a wonderful synopsis of the science of baking that a chef at the Homestead shared with me years ago and I found so fascinating. I am going to use this for one of our Cub Scout den meetings. It’s a wonderful way to tie in science, something most boys love, with cooking, which is one of their required achievements, and hopefully they’ll love that, too. Thanks for doing the research!

19. by anonymous on Jul 4, 2012 at 5:51 AM PDT

Bread is browned not so much by caramelization but more by the Maillard reaction between sugars and proteins when heat is applied.

20. by anonymous on Oct 21, 2013 at 6:39 PM PDT

Hi, I am doing a project and I have to have a magazine or journal so I thought that this is a online magazine but my teacher wants me to know the web address and magazine title.... if you could get back to me in a couple of days I would really appreciate it...

21. by anonymous on Oct 22, 2013 at 3:40 PM PDT

THANK U THANK U THANK U KELLY! I am doing science fair at my school and this was the best source I had. thank you

22. by Melanie on Oct 28, 2013 at 1:28 AM PDT

Im definitey a baker and not a cook and found this so interesting! I knew baking was all about science but never took uch interest in this aspect until now. Thank you for the wonderful insight Kelly!

23. by anonymous on Nov 17, 2013 at 9:34 PM PST

Hey thanks for the info I am using it for my food tech project, only thing is it would also have been helpful to know what vanilla essence and oil does to baking as I am stuck on that (if anyone can help me out that would be great!)Thanks though it was really helpful!

24. by Peggy on Nov 21, 2013 at 6:22 AM PST

I always knew you had to add salt but a friends cakes were not coming out the way they used to in her former country. I checked her recipe and the salt had been illimated and she was adding 2 to 3 teaspoons of baking powder. I am sending your info to her. Also the info about why use room temperature eggs and butter is always helpful . She is from the Caribbean and her eggs and butter were naturaly at room temp but here we need to leave them out for a bit before using them . Thank you for the info.

25. by Greg G. on Dec 19, 2013 at 4:33 AM PST

Great article. I have recently gotten into baking and the science behind it is right up my alley. Being a chemical laboratory technician, it’s like little science experiments in my kitchen! My son is a chef, and he said that one of the first things they learned in culinary school was the very thing your article touches upon.

26. by anonymous on Jun 24, 2014 at 12:51 PM PDT

realy helps.. keep up the great work!!!

27. by anonymous on Jun 28, 2014 at 6:07 AM PDT

love this post, thank you!

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