The (easy to understand) Science of Baking-Leavening Agents

The (easy to understand) Science of Baking-Leavening Agents

So let’s dabble into baking for a bit, specifically the science of leavening agents. It may sound like it will be complicated but don’t leave yet!!! It’s actually really easy to understand if it’s explained in the right way (which I believe that I can). So with baking, It’s often said that the difference between cooking and baking is that cooking is an art and baking is a science. Grumping and grumbling about how there is plenty of room for creativity in baking aside, there is truth to this. With baking, the ‘essential ingredients’ often work together in a very specific way to give a very specific product. Of course you can add some things in, create toppings and shape the base how you’d like. BUT, if you go messing around with the sort of ‘base recipe’ you may quickly find that you could ruin the dish. This is the first in an eventual series that will cover all of the essential ingredients in baking. We are going to start with the most…active piece (and I’d say interesting) ingredient, leavening Agents.

What Even is a ‘Leavening Agent’?

Well, as intimidating as it sounds, a leavening agent is simply an ingredient that makes your baked good rise. By rise I mean that it ‘grows’ or puffs up either before or while going through the cooking process. You probably have heard of yeast, baking soda and baking powders. Those three are the most popular leavening agents. To some extent you can use them interchangeably but yeast is usually used when you want the dough to grow a lot (or for flavor). So on the opposite end you have baking powder/baking soda when you want things to sort of puff up but not grow substantially. We’ll dive into that a little more later, but mainly what I want to introduce here is that there are three types of leavening agents. You have your chemical (baking soda and powder), Biological (yeast), and physical (eggs). Let’s look at each a little more closely.

Chemical Leavening

Chemical leavening is caused by a chemical reaction in which gas is released to cause the puffing of the dough. Let’s break that down some more. You often have two common types of chemical leavening, Baking soda and Baking powder. Baking soda, has the chemical term: sodium bicarbonate and it is a base. Without getting things too complicated a base is a category of chemicals with the important property of ‘canceling out’ acids. Basically if you take something that is a base and something that is an acid then mix them together in water then a chemical reaction occurs. A perfect example of this is the baking soda and vinegar volcano you probably did for an elementary school experiment. You have baking soda (the base) and vinegar (the acid and water) when mixed together create a bunch of bubbles that overflow the volcano.

Cookies, Chocolate Chips, Crackers and Baking Soda

Hopefully you are still with me. Because that experiment is exactly what happens when you are baking with baking powder or soda. Those bubbles that form happen in your dough while it’s cooking. As the outside of your bread begins to cook and harden, it traps those little bubbles inside, creating pockets of air that then make your soon-to-be baked goods rise and ‘grow’.

The reaction often starts as soon as you introduce the dry ingredients into the wet ingredients step in a recipe. This is why it’s usually one of the last steps before baking. While the heat from the oven really kicks the reaction into gear, if you wait too long to put your dough/batter into the oven the reaction will mostly be over and your dish will fall flat (no pun intended).

Last stop before we move onto yeast and ‘biological’ leavener. What exactly is the difference between baking soda and baking powder. Also, if you mixed them up, you can definitely tell something is wrong with the dish. Baking soda is just the base, sodium bicarbonate. Baking soda is both the base and the acid mixed together. So, when a recipe is acidic enough on it’s own for the chemical reaction to occur, baking soda is used. If you need both the acid and base then baking powder is your guy. Then, if you mix them up and they taste awful it’s because the reaction didn’t occur correctly, causing an awful taste.

Biological Leavening

Next up here is the famous biological leavener, yeast! Yeast is the go to leavener for all things bread. Of course these things can be jerry rigged for chemical leaveners to save time, but yeast is actually one of the key sources of flavor for breads. So what is yeast? I’ve heard a lot of times yeast is said to be a type of bacteria, which is incorrect. Yeast is a micro-organism but it is actually a fungus more so than bacteria. I know it sounds strange that something alive is in your food but by the time you eat any bread all of the yeast is killed off. Besides, it is completely harmless either way.

Bread, Pretzels and Yeast

So how does yeast work? It’s actually somewhat similar to how chemical leavening works in that we get trapped bubbles that create those airy pockets to make our dough nice, light and airy. So, how is the gas formed then? Well consider that yeast is alive, and alive things need to eat. Then once the food goes through their system, whatever is left over is released as ‘waste’. Well, yeast eats sugar and wastes a gas (carbon dioxide) and alcohol. With breads though you never ferment enough to get a substantial amount of alcohol but you get plenty of gas.  This gas is, again, what rises the dough and gives us the texture we want. Yeast is also very good at developing flavor. It’s what gives bread its characteristic ‘bread’ taste. If you’ve ever smelled a home or factory that’s baking bread, then you have smelled yeast.

There are a few types of yeast to consider while baking as well. The most common yeasts are the dry yeast. This can include active dry yeast and rapid rise yeast. Active dry often is what gives the most flavor. Rapid rise yeast still can give good flavor but takes less time to rise overall. Both of these suffer from the problem of having a high percentage of ‘dead’ yeast that doesn’t come back to life when you activate it (often in warm water). That’s where you might consider fresh, wet or ‘cake’ yeast. This is yeast that has a much higher percentage of live yeast and often leads to more effective rising. That said, it’s not always very easy to find in your everyday supermarket.

One last type of yeast would be a sourdough starter. This is actually how bread was made long before we could buy convenient little packets of yeast in stores. You see, all flour contains ‘wild’ yeast inside of it (as does virtually everything on earth). If you add water, and sugar and help grow and ferment the yeast some. You end up with a sourdough starter that can then be used with a recipe to create sourdough bread.

Physical Leavening

Lastly, let’s talk about the physical leavener, eggs. This type of leavening is neither a chemical reaction or the product of something being alive. It’s still a very interesting process because of how it works. What occurs when you use egg as a leavening agent is that you essential beat air into the batter by stirring vigorously.  So you essentially have a lot of tiny little air bubbles mixed into your batter. You then place the batter in a very hot oven that rapidly cooks the batter. You may know that air expands and contracts with the temperature, like how a balloon shrinks up if it would be left outside in the middle of winter. Well, when placed in such a hot oven, the air beat inside of the batter rapidly expands while the outside hardens and cooks. The once small air bubbles are now very large and cause the batter to expand quickly.

Whisking Egg and Egg Yolk

The end result is an interesting type of baked product. You will get a hardened shell with a nearly hollow center. This is how cream puffs and similar pastries/baked goods are made. The eggs main role in this is that, as a protein, they will both hold the air thats beat into them as well as quickly cook in the hot oven, thus hardening an outer layer that traps all the air inside. Just don’t go waiting very long once the eggs are beat in because the air can escape!


Leavening agents are definitely a huge part of what makes cooking such a ‘science’ but don’t let that thought get to your head. We will definitely explore how baking can be just as much an art as anything else on another day. Hopefully that was a pretty digestible introduction to leavening agents.  If you had some confusion in any part of this let me know and I’ll let you know and alter the post accordingly! Thanks for reading!


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