Question Answered by Dr. Catherine Riddle, Radiochemist, INL
Have you ever baked a cake or a tray of biscuits in the oven? If so, congratulations, you are a scientist! Baking causes a chemical change in your ingredients from raw batter to cooked cakes, breads, cookies, or biscuits. A chemical change is when one or more substances is changed into a new substance (e.g. iron rusting, sodium and chloride combine to form salt, and baking a cake). Not only are you producing a specific series of chemical reactions, you are also following a recipe to bake a tasty treat allowing you to confirm a set of scientific principles. If you change a recipe to make the end result taste better, you have just made a hypothesis supported by experimental results (aka, baking your cake)! I have said baking is chemistry, but where’s the proof? Since there are multiple reactions depending on what you are baking (bread dough requires a little more chemistry) let’s keep it simple and look specifically at the chemistry that goes into baking a cake step by step.
- Boiling Water is one of the most fundamental chemical reactions. At 100°C (212°F), water boils and starts to evaporate from a liquid into a gaseous state. As the water turns to steam it leaves air pockets behind for a lighter, fluffier cake.
- Butter is not only tasty, but an emulsion – a combination of water, fat, and dairy solids that wouldn’t typically stay together under natural circumstances. When the oven reaches approx. 33°C (91°F), the butter begins to melt separating the components. The fat spreads out, causing the batter to fill the pan. The water heats and turns to steam, causing the batter to expand outwards as it tries to escape.
- Eggs are mostly made up of tangled proteins. Heating these proteins to around 60°C (140°F) causes the strings to start untangling and linking with one another into a more solid mass making our cake firm.
- Flour is a fine powder made from ground-up cereal grains. These grains contain the proteins glutenin and gliadin which form gluten. Once heated, the elastic bonds are solidified, giving the dessert its structure.
- Sugar not only sweetens our cake it also tenderizes and moistens it. When sugar dissolves in batter, it interferes with gluten formation, protein coagulation, and starch gelatinization, making the mixture softer. When sugar is heated above 160°C (320°F), it undergoes a Maillard reaction which we will discuss nest week.
- Baking Powder is a combination of sodium carbonate (baking soda) and acidic components like disodium pyrophosphate (Na2H2P2O7) which bring the strong alkalinity of baking soda to a neutral pH. When heated, the baking powder releases sodium carbonate, water, and carbon dioxide which helps our cake rise.
(We’ll continue to recipe next week.)
Without gluten, there would be nothing to hold the gas that makes bread rise. Think of gluten as the rubber of a balloon: The stronger it is, the more gas it can hold.
The following activity is a great way to get a feel for gluten.
You will need: flour (you can experiment with different kinds), water, bowl
- Into the bowl, measure 1 cup of flour.
- Slowly add about 1/2 to 3/4 cup water to the flour in the bowl, and knead the mixture until it forms a soft, rubbery ball of dough. Let the dough ball sit for about 10 minutes.
- In the sink, run cold water over the dough ball. Be careful not to let the dough disintegrate; try cupping your hands around the ball and squeezing gently to remove the starch.
- You’ll notice the water turning milky as it washes away the starch in the dough. Slowly, your dough ball will become a gummy, slimy network of gluten strands.
- When the water no longer becomes milky, you know there’s no more starch in the dough, leaving nearly pure gluten. Notice how much smaller your ball has become and how much more stretchy!
- Bake your gluten ball in the oven for about 15–30 minutes at 450° F. When you take it out of the oven, you’ll notice it has puffed up and hardened, which is exactly what happens to the gluten in a loaf of bread as it bakes.