The Chemistry of Baking

Inspired by Lessons in Chemistry by Bonnie Garmus

The chemistry of baking is important for any baker to understand. Elizabethe Zott was no stranger to that in Bonnie Garmus’ popular novel, Lessons in Chemistry. Although I found the book a bit trite, learning the chemistry behind baking is pretty interesting, and can actually help you elevate your culinary skills.

Lessons in Chemistry takes us back to the 1960’s, where Chemist, Elizabeth Zott, struggles to gain respect, be taken seriously, and generally do her work unencumbered at her all-male research institute. After being forced to resign, she is hired as a TV chef and host of the show Supper at Six. The only problem is – she’s not a TV personality …she’s a chemist.

Zott revolutionizes dinnertime by bringing scientific cooking instruction and feminist commentary to lives of housewives across the nation.

In This Post

The art of baking and its connection to chemistry
How understanding the role of each ingredient can elevate your culinary skills
What really happens during mixing and baking – and where you might be going wrong
Recommended reading for more info on the chemistry of baking

Chemical Changes

Baking is no doubt an art form — but it’s also a science.

After measuring, mixing, and heating raw ingredients, a chemical change occurs, resulting in something new that cannot revert to its original state.

The Role of Ingredients in Baking

There are four types of ingredients in baking, each serving an important role in the final product.

1. Tougheners (Structure Builders)

Ingredients that hold volume and shape, reinforcing the chemical structure of a mixture.

Examples – flour, eggs, cocoa powder, and starches

2. Tenderizers

The opposite of tougheners, tenderizers break chemical bonds and make baked goods soft and easier to chew.

Examples – Sugar, syrups, fats, oils, and leavening agents

A good balance of tougheners vs. tenderizers is necessary to ensure the bake is both edible and maintains shape.

3. Moisteners

AKA “wet ingredients”. This includes water and any ingredient that contains water.

Examples – Water, milk, cream, juice, fruit, liquid fats such as oil and melted butter

4. Driers

AKA “dry ingredients . Anything that absorbs moisture.

Examples – Flour, starch, dried powders such as spices, milk solids, cocoa, baking powder, baking soda

If substituting a moistener or a drier, use the same total amount that the recipe calls for, so that the overall texture of the bake is not affected. For example, I often substitute Greek yogurt in a one to one ratio in place of sour cream.

Mixing

1. Aeration

Mixing distributes ingredients evenly throughout a batter or dough. One main reason to mix ingredients is to incorporate air through a process called aeration. As a spoon or electric mixer beats air into a batter, pockets form to trap the air inside. The texture of the batter or dough can be altered by the tools and speed of mixing – compare slowly mixing a dough by hand vs. quickly whipping cream with an electric whisk.

Air pockets help create a sponge or foam – an open, porous structure. This is important for baking, as the air will expand when heated to create a beautiful, edible structure.

2. Dissolution

While mixing, water (and ingredients containing water) dissolve solutes such as sugar, salt, and baking powder. These solutes cannot be effective without first dissolving in water.

For example, when making a meringue, sugar (a solute) dissolves in egg whites (a solvent containing water) to sweeten and stabilize its chemical structure. Without incorporating into the egg whites’ structure, sugar cannot do it’s job.

3. Hydration

Instead of dissolving, larger molecules, such as proteins and starches, hydrate when mixed with water. That is, they attract and bond with water molecules. Proteins and starches absorb water and swell, as water surrounds and suspends them.

Proteins in flour must be hydrated in order to form gluten, which contributes to the crumb structure of baked goods. Mixing speeds up the formation of gluten by separating the proteins and exposing them to more water, thereby hydrating faster.

Clearly, the baker’s mixture is a key to success that shouldn’t be neglected.

Heat Transfer and Baking

Many changes occur when adding heat to a mixture, so I’m only including those most relevant for a home cook here.

Heat is transferred gradually from the outside of the bake towards the center. The rate of heat transfer depends on the temperature of the oven, type of heat (radiation, conduction, convection), and the type of baking pan used. All of these changes occur at different times throughout the baking process, so it’s important to allow the full baking time recommended in your recipe.

1. Melting, Evaporation, and Gas Expansion

During baking, ingredients transform from solids to liquids to gasses. Fat melts, water evaporates, and steam and carbon dioxide expand.

Take butter, for example – a solid fat that melts when heat is applied and releases water and air. If the butter is whipped or creamed, more air is trapped inside to be released in baking. The water evaporates into steam, which, along with the air, expands to create the volume and porous structure we see in bread, cakes, and pastries.

2. Safety and Structure

Safety first! Heating conveniently kills microorganisms like funguses, viruses, and bacteria. If your batter contains eggs, it should be baked to kill any possible salmonella before eating. Don’t eat raw cookie dough!

Heating also coagulates proteins in eggs and gluten, solidifying them so that they trap air and set the structure of the bake. When heat is applied, proteins denature and uncoil. Then, they bond together and create clusters that eventually dry out to form a rigid structure.

protein coagulation — Source: *How Baking Works, Third Edition* – Paula Figoni

The other key structure-builder, starch, also sets with heat. Around 200°F, starch gelatinizes as its molecules absorb and trap water. Solutes such as sugars and fats raise the temperature at which starch gelatinizes. So, be sure to use a strong high-gluten flour when making enriched doughs like brioche and sweet bread, or else extend the baking time.

3. Maillard Reaction

The Maillard reaction occurs when sugar breaks down in the presence of proteins. When water evaporates from the surface of a baked good, a dry crust forms on the outside. This exposes the sugars in the dough to high heat, causing sugars to break down. This reaction in the presence of gluten in flour causes Maillard browning, resulting is the delicious, toasty crust we all love.