Every time you pick up the whisk or turn on the mixer, you are about to initiate a chemical reaction. Without realizing it, you combine acids and bases and heat them to initiate a chemical reaction.
So the next time your friends ask what you’re doing during your next night in, tell them chemistry!
Flour
Flour is made by milling or grinding wheat seeds into a fine powder. This powder is then sifted to isolate the endosperm, which contains many proteins necessary for baking. (more on this process here)
Gluten is the protein formed from gliadin and glutenin. Gliadin and glutenin are two essential monomeric proteins in flour, responsible for the strength and elasticity of dough. A monomer is a smaller molecule that can be joined with another molecule to create a larger, more complex molecule or polymer.
Gluten will not form until the flour or dough is wet, and the more the dough is mixed and kneaded the more gluten will be made. This is why many recipes advise against over-mixing; over-mixed dough will become too tough due to the excess gluten in the dough.
The gluten forms a sticky network of bonds within the dough to trap air bubbles (Carbon Dioxide or CO2) that rise to the surface of the dough. These trapped air bubbles cause the dough to rise and create its airy texture.
Leavening agents
Leavening agents are the substance(s) added to a dough that allows it to rise. The type of agent varies by recipe and is activated by different methods. Understanding the functionality of each allows you, the chemist, to decide which leavening agent will yield the best results.
Baking Soda
Baking soda is one ingredient; sodium (or sometimes potassium) bicarbonate. This base will react when exposed to high temperatures or around an acid in a wet environment.
When baking soda is incorporated into your dough it reacts with acidic compounds almost immediately. This reaction creates CO2 as the product which adds air to the dough. As previously mentioned, the gluten in the dough will capture the CO2 as it rises, causing the dough to expand.
Baking powder
Double-acting baking powder consists of one base and two acids; sodium bicarbonate, monocalcium phosphate, and either sodium acid pyrophosphate or sodium aluminum sulfate. It also contains cornstarch, which mainly serves as a buffer to prevent reactions between the base and acids.
Once the baking powder is added to the wet ingredients sodium bicarbonate and monocalcium phosphate will begin to react to form CO2. However, the second acid does not react with the sodium bicarbonate until it is wet and hot, meaning the rising process continues in the oven.
You may also come across single-acting baking powder. It is similar to double-acting baking powder in that sodium bicarbonate is combined with an acid, however, the acid is potassium bitartrate (cream of tartar) instead of monocalcium phosphate. A second acid is not added in single-acting baking powder and is typically available for commercial use only.
So, which should you use?
When you are choosing between baking powder or baking soda, it depends on the recipe. Baking soda is best used in recipes with acids already present, like snickerdoodles that use cream of tartar. Without an acid present, baking powder is best because it provides both an acid and a base.
Sometimes a recipe may require both baking soda and baking powder. Baking soda reacts quickly and may not fully leaven the dough as much as desired, so an extra pinch of baking powder creates a softer, airier result.
yeast
Yeast is a single-celled organism added to most bread recipes to make the dough rise. Starches in the flour provide the sugar for yeast to ferment, creating CO2.
Yeast also produces ethanol, which is useful when making alcohol. However, in baking the ethanol boils off and is removed from the dough; no need to worry about a bread-induced hangover!
Bread dough is left to develop for a few reasons. The yeast needs time to ferment the sugars in the dough to produce CO2. The CO2 makes the dough rise over time as it is trapped by gluten. Gluten also will further develop if given time which will trap more CO2, resulting in a better-developed loaf. The yeast also adds extra flavor to the dough as it ferments, deepening the flavor profile of your loaf.
butter
Butter is an emulsion of water and fats; on average it is about 80 to 82% fats and 16 to 17.5% water, the other 3.5% being salt and milkfat. When butter is heated to 92oF, the water and fats separate in the dough. Some of the water is caught by sugar while the rest of the water evaporates.
In cookies, this is when the dough flattens as the steam escapes and the fat becomes liquid.
eggs
When cooking an egg on the stove, the consistency turns from runny to solid and stiff with a deeper color. When introduced to high temperatures, the bonds holding each egg protein together break and the proteins begin to unfold. As the temperature rises, the proteins gain energy and form covalent bonds with surrounding proteins. These covalent bonds are stronger and create a solid egg after cooking.
This transition from liquid to solid occurs during the baking process as well. The proteins in the eggs create stronger bonds to support the dough’s structure as it bakes and then maintain its form as it cools out of the oven.
It is important to note that all eggs have salmonella, which can cause severe sickness if ingested. If you prefer to eat your cookies on the softer, doughier side always make sure your cookies reach at least 136oF. This is the temperature at which salmonella is killed and your cookies are safe to consume.
sugar
As mentioned with yeast, sugar is the food to jumpstart fermentation in bread recipes. Without it, the fuel for the yeast would be absent and you are left with a very deflated ball of dough.
In recipes without yeast, sugar is useful far beyond its sweet flavor. Sugar binds with water in a recipe, which captures moisture and prevents your cookies or cakes from immediately drying out. When butter melts in the oven the fats and water separate, it is the perfect chance for sugar to grab on.
The formation of gluten proteins is also inhibited by sugar, which maintains a soft and airy treat rather than a dense and tough dessert.
A deliciously sweet aroma drifts from the oven as the timer rings and the cookies are finished baking; this sweet aroma is a hallmark of the Maillard Reaction, which occurs when the cookies reach about 347oF (175oC). This is the temperature at which the sugar and proteins transform to create a golden hue on the top of your treats. This reaction is also the reason most recipes are baked at 350oF.
Vanilla
While vanilla smells delicious and adds a deeper flavor profile to many cookies and cakes, it does not heavily affect the overall chemical composition of the recipe. It arguably adds more liquid to an otherwise slightly dry recipe, but otherwise not crucial to the success of your recipe.
I hope you enjoyed the science of baking as much as I enjoyed researching information on the topic! Feel free to add a comment below with any thoughts or questions, and happy baking 🙂
References:
- Andy Brunning; Periodic Graphics: Baking soda versus baking powder
- Exploratorium; Bread Science 101
- ImperialSugar; The Science Behind Sugar
- Frank Graff; The Scientific Reason Why We Preheat at 350 Degrees
- Center for Dairy Research; Butter Science 101