What is Leavening? | Home Ec

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What is leavening? You’ve heard the term, but what is it? In this lesson, I will briefly explain what leavening is and how it works in your recipes.

Very simply, leavening is the ingredient in your recipe that causes the baked good or food to “fluff up.” It makes the bread rise, the cookies airy, and the angel food cake the spongy, fluffy cake that it is.

These are the most common sources of leaven: Yeast, Baking Powder, Baking Soda, and Eggs. These are called “leavening agents.”


Yeast is a very small, single-celled fungus. There are several kinds of store-bought yeast out there to choose from:

Fresh yeast which comes in refrigerated blocks (compressed or cake.)

Dry yeast comes as active dry yeast, rapid rise yeast, or instant dry yeast.

Active Dry yeast must be dissolved in water prior to using and takes longer for your breads to rise.

Rapid rise or instant yeasts rise much faster (sometimes half the time of active dry yeast) and can be mixed right in with the rest of the ingredients, without prior dissolving.

When you bake with yeast, you essentially “wake up” the dormant yeast and create an environment for that yeast to live and grow in.

It requires liquid, warmth, and food. When working with yeast, it is important to make sure that your environment is warm, but not hot or cold. Cold yeast will not grow and a too hot environment will kill the yeast.

When you wake up the yeast, it begins to grow. As it grows, it produces gasses, which create the air in your bread.

Yeast is most commonly used in breads like sandwich bread or dinner rolls.

Some people find yeast to be very intimidating. I think it is simply because it does take a little more work and people envision all sorts of problems. Some things take a little practice to master and even a seasoned baker sometimes has a “flop” with a batch of bread. It happens to the best.

But once you get the hang of it, the possibilities are endless. There is nothing like fresh bread right out of the oven!

See this Article: What’s Wrong with my Bread!? | A Yeast Bread Troubleshooting Guide

When storing your yeast, it should be kept in a cold, dry, air-tight place. A container of yeast generally does not last a long time after opening, sometimes only two weeks.

The kind I use comes in a vacuum sealed, 1 pound bag. I can’t go through that much yeast in a timely manner.

When I open the large pack of yeast, I fill a small, dark glass jar and then use my vacuum-sealer to seal the original bag shut again. I store them both in the refrigerator.

As I empty the jar, I just re-fill it from the bag and re-vacuum seal it. This keeps both portions of the yeast fresh and keeps it from going to waste.

In the bible, there is often reference to leavening. In those days, “leavening” was the wild caught yeast that lives everywhere. It’s in the air, it’s on surfaces, it even lives on apple peels. We most often know of this wild yeast in reference to “sour dough.”

Sour dough starter is simply flour and water that has mixed together and allowed to ferment, which encourages that wild, natural yeast to grow. This mixture is called sour dough starter. The starter is fed every day with more flour and water to keep the natural yeast alive and thriving.

Then that starter is used to make sourdough bread and other goodies like pancakes.

In biblical times, they didn’t have grocery stores where they could purchase leavening agents or ingredients. Bread took time to make.

When the Israelites fled slavery in Egypt, they were told to eat their Passover meal with their coats and shoes on and to eat unleavened bread – Matzah.

Matzah is a flat bread, like a cracker, that is made very quickly with no leaven. They had to be ready to leave at any moment, as soon as the Pharaoh let them go.

Since then, the Feast of Unleavened Bread is kept every year in remembrance of this event.

Baking Soda

Baking soda is sodium bicarbonate.

Baking soda works by reacting with the liquids and the acid in a food to create carbon dioxide. It reacts immediately with these ingredients and must be baked immediately after mixing.

If you let a food sit a while, the reaction will have ended and the bubbles it created may dissipate, leaving you with a very flat bread.

This is why pre-heating your oven is very important in baking. The oven should be at the right temperature, waiting for you to put your goods in as soon as they are ready.

Baking Powder

Baking Powder is a combination of baking soda, two acids, and some cornstarch. The cornstarch keeps the acids from reacting to the baking soda in the container.

Most baking powder is what is called “double acting.” This means that the leavening agent reacts when it hits the liquid, creating air bubbles, and then it reacts again when it is exposed to the heat of cooking. So it “acts” twice.

Many brands of baking powder are out there and many of them actually contain aluminum. I’m not going to go into a health lesson here, but I try to avoid using anything aluminum, so I always read the label.

Baking soda and baking powder are most often used in quick breads, waffles, or cookies.

Finally, if you have a recipe that calls for baking powder and you have run out, here is an easy substitute if you ever find yourself in a pinch.

In recipes, 1 teaspoon of baking powder can be substituted with 1/2 teaspoon baking soda and 1/4 teaspoon cream of tartar (tartaric acid) if you find yourself in a pinch.


It may surprise you that eggs can also be a leavening ingredient. But eggs can be helpful as a leavening in two ways.

First, eggs can contribute as part of the liquid for the recipe, creating steam when the food is cooked or baked. That’s why scrambled eggs “puff up” in your skillet as they cook.

Secondly, whipped egg whites create thousands of little cells of air that are again filled with steam in the baking process. As the food item bakes, the steam expands inside those cells causing them to expand.

Whipped egg whites can expand or create a foam that is up to eight times their initial volume. When whipping the eggs, the proteins in the egg whites seal in the air bubbles.

Adding an acid, like cream of tartar or lemon juice can help to stabilize the egg white foam even further.

A great example is meringue cookies. They are nothing more than sweetened, whipped, and flavored egg whites.

In many baked goods, the proteins in the eggs work with the protein in the flour (gluten) and the starches which allows the structure of those cells to hold their shape after the baked good has cooled.

The best example of this that I can think if is an angel food cake. Angel food cake has no leavening other than whipped egg whites, yet it is one of the fluffiest cakes there is.

But the egg whites aren’t the only part of the egg that can create a leavening effect in cake batters or other baked goods. Cream puffs and eclairs (the Wisconsin State Fair staples that I grew up with) only rely on the leavening action from the liquid of the egg whites and yolks to create their airy, hollow shape.

Watch this Lesson in the Video below

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