The Science Behind Baking

Few people acknowledge the chemistry that is involved in baking—we tend to rely on recipes and simply take them for granted. After all, they work! Most recipes tell you to put a certain amount of butter, flour, eggs, and sugar, stir them, then bake. What makes a cake different than a brownie or a cookie depends on how much of each ingredient you put relative to the others. It all sounds very simple… until you start to ask questions. Why do most recipes tell you to put your cookie dough in the fridge before baking it? Why do some deserts require baking soda, while others call for baking powder? How is it that whipping your butter too much can ruin the whole batch of brownies (and how on earth does butter turn into that semi-solid structure when whipped)? These are all questions of science: physics and chemistry. And for anyone who wants to become an expert at baking, knowing this science may be what takes your recipes from good to sensational?

Let’s start by understanding what happens to each of the ingredients when in the oven.

Fats

When you make your cookie, cake or brownie, often you will use a fair amount of butter. Butter provides fat, and these fats have an important role in the baking process. They melt. When the fats melt, they form a liquid, which evaporates and becomes steam. This steam rises, which is what causes cookies and brownies to rise when in the oven. It also explains why when you take them out and let them cool, you see them deflate.

That said, the type of butter you use is important.

Creamed butter — butter which has been beaten with sugar — has air pockets. As it is beaten, air is incorporated, making it light and fluffy. As a result, deserts using creamed butter will be lighter and fluffier, like in cakes. On the other hand, melted butter doesn’t allow the presence of air pockets, and results in a fudgier denser texture, like in brownies.

Proteins

When heat or mechanical force is applied to proteins, they coagulate. Coagulation is the process by which proteins turn from liquid to solid or semi solid. This happens when you cook eggs: they turn solid. It also happens when you boil milk: a layer forms on top, which is the result of proteins coagulating. You see this as well when cream is whipped and it turns from liquid to a fluffy semi-solid.

When you bake, proteins come from primarily from the eggs and milk. In the oven, they coagulate, turning solid. This is what provides structure to the desert. For that reason, recipes often tell you to put your cookie dough in the fridge for an hour before you bake it. You want your proteins to coagulate and give the cookie structure before the fats start to melt, otherwise you’ll end up with an uneven, badly shaped cookie. So, putting the dough in the fridge cools down the fat so that they take longer before they melt, letting the protein work its magic first.

Sugar

Believe it or not, sugar plays a bigger role than just making your dessert sweeter. Sugar is an acid, and there is an ingredient in your dough/batter which will only activate in the presence of an acid: baking soda. We will speak more about baking soda later, but for now, it’s important to understand that sugar is playing a crucial role in the chemical reactions going on in your oven. Without it, baking soda would not do its job.

Besides that, sugar also caramelises when heated, which is what creates the golden-brown color you want to see in your cookies and brownies.

Leavening agents

We said that baking soda needs sugar, or another acid, in order to do its job… but what is its job?

Baking soda and baking powder are leavening agents. They react with other substances and produce gas, mainly carbon dioxide. This gas causes the desert to rise.

Baking soda is a base (sodium bicarbonate) and so it is only activated when it reacts with an acid. This can be sugar, or other acidic ingredients like buttermilk, molasses or honey. On the other hand, baking powder contains both a base and an acid, meaning it activates immediately when in contact with moisture (it doesn’t specifically need an acid). For this reason, baking soda is used in deserts which only require a slight rise, like cookies and brownies, while baking powder is used in deserts that need a big rise, like cakes and muffins.

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So, it’s clear that a lot of things happen in the oven while you’re excitedly waiting for your sweet treat. Sugars caramelise, proteins coagulate, fats melt, carbon dioxide is released by leavening agents, and many more chemical reactions occur too. Knowing this might help you tweak your recipes and become an expert chef, and it might just make baking more fun next time because you know why everything happens. But in either case, baking is a science, a science many of us engage in, and it is a fascinatingly delicious one too.