Leavening Agents: The “Spies” That Make Baking Work

By: Eliana Zhang

If you’re a budding baker, you know whipped egg whites are the worst. What does the recipe mean by folding them “just the right amount and not a bit more?” You didn’t think that it would be that serious if you over-folded them, but now that you gave it two extra mixes, you’re beginning to worry if the cake will flop.

More seasoned bakers know the answers to these questions lie in the sponginess of the cake: do you want a thick, dense product or the fluffy cake you were promised? Two outcomes are possible because egg whites are an example of a leavening agent!

What is a leavening agent to begin with? If you’ve ever seen dough and batter expand, you’ve seen them at work. Leavening agents release gases in baked products. These gases, most commonly air or carbon dioxide, allow the products to rise and form porous structures. The most prominent examples of products with leavening agents are angel food, sponge cake, and bread, all of which have fluffy textures. Common leavening agents include egg whites, yeast, baking powder, and steam. These can be grouped into three categories based on their effect on the dough: air, steam, and chemical.

Air leavening agents require a batter that easily retains air bubbles and foams. The process of incorporating air leavening agents can involve vigorous mixing, like in the unfortunate case of egg whites mentioned previously. Egg whites become very foamy, and these air bubbles stay in the batter when baked. If you overfold batter with whipped egg whites, your product becomes dense because the air bubbles escape. If you don’t fold it enough, on the other hand, your final product will not be consistently porous due to the maldistribution of the air bubbles. Gluten is another example of an air leavening agent. After being whipped, it becomes similarly frothy and is used for certain types of biscuits. Both egg whites and gluten retain air bubbles in the batter. Since air expands when heated, the product rises and gains a fine and uniform internal structure as a result of the bubbles. Baked products that use air leavening agents include puff pastries, cake, and bread.

Steam leavening agents use a similar concept. They require more moisture in the batter, often coming from water, milk, or oil. When heated, these fluids approach their boiling point and evaporate. By exerting steam pressure on pre-existing bubbles in the batter, the gases cause the dough to rise. Steam leavening agents are less common than air or chemical agents but are frequently used for biscuits and puff pastries like napoleons and vol-au-vents.

Chemical leavening agents such as baking powder and baking soda decompose when heated, producing carbon dioxide. Because baking soda, or sodium bicarbonate (NaHCO3), needs an acid and a liquid to produce gas, it’s often added to batters already containing acidic ingredients like sour cream or cocoa. This is why using chocolate in place of cocoa usually doesn’t work—it wouldn’t provide the required acid. If the batter doesn’t have an acid, using baking soda would negatively alter the flavor and smell of the final product; the most common effects include a yellow tint and sour odor. Given how similar baking soda and baking powder sound, what’s the difference between them? Generally, baking powder is baking soda combined with an acid salt, so it only needs a liquid to produce carbon dioxide. When a liquid and acid are present, sodium bicarbonate (NaHCO3) reacts with the acid, producing CO2 and decomposing to sodium salt (Na+) and water (H2O). Inside the batter, the trapped carbon dioxide expands while baking, and causes the dough to rise, such as in cakes and brownies.

The technical aspects of cakes may be hard to follow for budding bakers, but when you break it down to a simple question like “what happens to folded egg whites in the batter?,” everything becomes much more understandable. Egg whites are just one example of leavening agents, which release gases in batter and let baked products rise. The ingredients in a cake often have more than one use, and even egg whites are there for more than porous structure, but it is great to know a bit about what’s going on behind the scenes of baking.

What did you learn?

What are leavening agents?

Leavening agents are substances that release gases when baked and cause baked products to rise. They make baked products as porous and airy as they are. Air leavening agents make air expand in the batter, steam leavening agents use steam pressure to expand pre-existing bubbles, and chemical leavening agents produce carbon dioxide bubbles when heated.

Why are leavening agents needed?

Bakers aim to make their cake, cookies, and bread light and airy. This result can only be obtained through leavening agents that make them rise. Without leavening agents, you would receive a thick, dense, and inedible product. If you mishandle leavening agents like baking soda, the flavor and smell of the final product would not be what you pictured, and if you mishandle air leavening agents like egg whites, your result would be dense or nonuniform.




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