Okay so calling chemical reactions “techniques” isn’t exactly the most accurate category. After typing up this category I thought about changing it to leavening (which is also not technically a technique) but I realized down the road I may add more here that would have to do with reactions that occur during baking that are not about leavening. If you’ve ever wondered how leavening works in baking then read on!
Sources: The New Food Lover’s Companion
Physical Leavening
Chemical Leavening
Biological Leavening
Physical leavening is the process of leavening a baked good using air or steam. Physical leavening is commonly used in sponge cakes, puff pastry, and pate a choux. There are several examples of physical leavening:
1. A meringue and pate a bombe that is folded into a cake leavens it. Each of these has air cells created in it which adds volume.
2. When a fat melts in the oven at a high temperature it release steam and air. Butter has water as well as air cells trapped inside of it. These air cells are enhanced during the mixing process. As the butter melts the super hot air and super hot steam expand the air cells leavening the product.
3. In the case of pate a choux, the moisture in the eggs (as well as the milk and water) turns into super hot steam, expanding the entire product. If your éclairs and cream puffs aren’t puffing up, add another egg.
Air’s Primary Role: Paula Figoni’s How Baking Works
Chemical leavening is the use of a chemical to leaven a baked good, such as baking soda or baking powder.
Baking soda (sodium bicarbonate) is an alkaline that needs to be mixed with an acid to produce carbon dioxide in order to leaven a product. Acids include chocolate, buttermilk, yogurt, sour cream, brown sugar, molasses, and honey as well the more commonly known acids like juice and vinegar. Recipes that use baking soda must be baked right away so the baking soda doesn’t get all used up and lose its strength. Baking soda commonly makes products spread rather than rise – which is why it’s used in cookies (especially chocolate chip cookies).
Baking powder is a combination of baking soda, cornstarch, and dry powdery acids. The most common acid used is cream of tartar but other acids exist. Since baking powder has the acid built in it isn’t necessary to add an acid for it to produce carbon dioxide – all you need is water.
Baking powder used to be classified as single acting and double acting though double acting baking powder is essentially the only kind you can find, whether you are a home baker or work in a commercial kitchen. Single acting baking powder releases carbon dioxide once – during the mixing process. It reacts with water in the batter to release carbon dioxide. Double acting baking powder releases carbon dioxide twice – once in the mixing process and once during the baking process. It reacts to the liquids in the batter but also to the heat of the oven. Some of the acids are treated (or coated) so that they do not react when liquids are added and the coating is dissolved in the heat of the oven.
Nowadays baking powder is described as fast acting or slow acting. Typically fast acting is the only kind available to home bakers. Bake shops will prefer to use slow acting since their batches are usually larger and will sit out longer before being baked. Fast acting refers to baking powders that release their carbon dioxide early on when being added – meaning most of the carbon dioxide is released during the mixing process. Slow acting is the opposite, releasing some carbon dioxide during mixing while releasing most during the baking process. You do want some gas released during the mixing process as it helps in the creation of air cells.
Baking powder helps leaven products because it helps with the timing of the egg proteins and starches forming the structure of the baked good. If the gas is released too early the gas will just come out of the batter and no leavening will take place. If the gas is released too late the proteins and starches will have gotten hard and the product won’t leaven as much but will crack and form holes in the surface instead. Baking powder is perfect because it releases the gas when the heat of the oven is just starting to set the proteins so the air cells will expand without breaking but are also strong enough that they don’t lose their shape.
Keep in mind though that even though baking powder is used to leaven products, the most important leavener of all is liquid/steam.
Chemical leaveners have functions other than leavening. They, like all leaveners, tenderize product by stretching the air cells and thinning them out. They also adjust the pH of the product (alkalis like baking soda increase pH while acids like cream of tartar reduce it) which affects flavor and weakens gluten.
Biological leavening refers to the use of yeast to leaven baked goods – most commonly sweet breads, breads, and laminated doughs. Yeast is referred to as biological leavening because yeast is a living micro organism. There are three forms of yeast available:
Fresh/compressed/cake yeast is the type of yeast used mainly in bakeshops. It is difficult to find for home baking. It is dissolved right in the water used in the recipe. Active dry yeast is the most commonly available form of yeast for home bakers. Yeast has been dried through a harsh process which creates granules that consist of dead yeast cells on the outside and living yeast on the inside.
Active dry yeast is not typically used commercially because the high amount of dead yeast cells (25% by volume!) produce a substance that negatively affects the development of gluten. Active dry yeast needs to be warmed in a warm liquid (between 100 and 115 degrees F) for about 5-10 minutes before being used. Use half as much active dry yeast when substituting active dry yeast for cake yeast.
Instant yeast is similar to active dry yeast in that it’s yeast that has been dried out to help extend its shelf life. Instant yeast is a little more desirable than active dry yeast though because the drying out process is more gentle than the process used on active dry yeast so there are not as many dead yeast cells (if any) on the surface of the granules. However, instant yeast is more active than active dry yeast so you can risk over proofing doughs easily. Instant yeast can be added directly to the dough without being dissolved in water first. Use ¼ to ½ as much instant yeast when substituting it for fresh cake yeast.
Unlike other leaveners, yeast ferments bread. When making bread and sweet bread it is very common to leave dough out to rest for 1 – 2 hours. This process allows the yeast to ferment the bread. Fermentation is the name of the process of yeast breaking down sugar for energy. The ideal temperature of the dough to maximize fermentation is between 78-82 degrees F. Generally speaking, yeast cannot break down starch into sugar the same way we can so many bread recipes add sugar to the dough to promote yeast fermentation. Yeast fermentation produces carbon dioxide gas and alcohol (as well as energy for itself and other by products sometimes referred to as flavor molecules). The carbon dioxide helps create air cells during the mixing process and helps expand and tenderize the dough during resting. The alcohol produced helps give the dough its sour yeasty flavor. When the bread is baked it immediately rises rapidly which is referred to as oven spring. During oven spring yeast is very warm and highly active producing lots of carbon dioxide but also the alcohol they produced vaporizes into steam which contributes to leavening just as much as carbon dioxide. Once the internal temperature reaches about 120 degrees F yeast fermentation slows down since it is starting to be killed, and at 140 degrees F all of the yeast has been killed.
