What Is Yeast?

A Guide to Buying and Baking with Yeast

Place dough in bowl

​The Spruce Eats / Diana Chistruga

Yeast is a single-cell organism, called Saccharomyces cerevisiae, which needs food, warmth, and moisture to thrive. It converts its food—sugar and starch—through fermentation, into carbon dioxide and alcohol. It's the carbon dioxide that makes baked goods rise.

Fast Facts

  • Varieties: 500 plus species of yeast
  • Uses: Fermentation, for bread, alcohol, and more
  • Origins: Hundreds of millions of years ago

What Is Yeast?

Yeast is an egg-shaped single-cell fungus that is only visible with a microscope. It takes 20,000,000,000 (twenty billion) yeast cells to weigh one gram. To grow, yeast cells digest food and this allows them to obtain energy.

When baking yeast-leavened bread, the yeast ferments the sugars in the flour and releases carbon dioxide. Because the dough is elastic and stretchable, the carbon dioxide cannot escape. The expanding gas causes the dough to inflate or rise. Yeast is also an essential ingredient in brewing beer. The yeast eats the sugar in beer and produces carbon dioxide and alcohol.


There are two types of yeast available: Brewer's yeast, a wet yeast used primarily in beer making and baker's yeast, which is used as a leavening agent. There are then two types of baker's yeast—fresh yeast and active dry yeast.

Illustration With Facts About Yeast
The Spruce / Bailey Mariner

Fresh yeast, also called wet, cake, and compressed yeast comes in small square cakes that are made of fresh yeast cells. These blocks of fresh yeast, often used by professional bakers, are comprised of 70 percent moisture, and therefore are quite perishable.

There are two types of dry yeast: Active dry yeast and instant yeast. The only difference between the two is the size of the granules; active yeast has larger granules while instant has been ground into a finer texture. Instant is named as such because it can be added directly to other ingredients; it does not need to be dissolved in water before using as active dry yeast does. Active dry yeast is dormant until proofed, which occurs when it is dissolved in a small amount of lukewarm water (about 110 degrees Fahrenheit).

Instant yeast is also available as rapid or quick rising. This type of yeast includes enzymes and additives to help the dough rise faster. When using rapid-rise yeast, it will take half of the time to make bread rise, or if the recipe calls for two sets of rising times, you can skip one of them and proceed to kneading and shaping the loaves.

Yeast Uses

Yeast is used in baking bread. There are a few dessert recipes that call for yeast such as Christmas bread, sweet rolls, and bee sting cake. It's also essential for beer production.

How to Cook With Yeast

If you are unsure if your yeast is still alive, you can easily test it. Pour about 1/2 cup lukewarm water into a bowl and sprinkle over the yeast along with a pinch of sugar. Stir, and let sit for a few minutes; if it completely dissolves and the liquid bubbles, it means the yeast is active.

Yeast needs warm temperatures to activate, so when placing the dough to rise, make sure it is sitting in a place that is 70 to 80 degrees Fahrenheit. And if your recipe includes a lot of eggs, butter, sugar, and milk, you may need a little more patience; these ingredients slow down the leavening process. If not used right away, fresh yeast can be stored in the refrigerator for up to only three days, so it should be bought in amounts that will be used quickly.

The fresh yeast cake has a stronger smell than dry yeast. It is light beige in color and soft and crumbly in texture. Since it is highly perishable, fresh yeast cakes are stored in the dairy case near the butter, but may not be available in your local supermarket. Depending on the manufacturer, such as Fleischmann’s, one cake of fresh yeast equals one envelope of dry yeast. Otherwise, the conversion is 2/3 ounce of fresh yeast equals 2 1/4 teaspoons dry yeast. Fresh yeast is often more expensive than active dry yeast.

What Does Yeast Taste Like?

Fresh yeast has a specific taste. It smells ripe and tastes almost bready and rich. It tastes a bit sour and raw.

Yeast Substitute

You can use baking soda as a substitute for yeast. To do this, you need to add an acid to the mixture. Use equal parts baking soda and lemon juice to equal the amount of yeast used in the recipe.

Yeast Recipes

Yeast is present in a wide variety of baked goods. Try these:

Where to Buy Yeast

The three most common brands of yeast you may find in your local supermarket are Fleischmann's Yeast, Red Star, and SAF Perfect Rise Yeast. Dry yeast is granulated and comes in little 1/4-ounce packets (approximately 2 1/4 teaspoons) or loose in a jar. Fresh yeast can be found in the refrigerated section of the grocery store. The packages may look a bit like foil-wrapped butter.


Once exposed to the air, the yeast should be stored in the refrigerator. You can store yeast in the freezer, which will pause its activity and prolong its shelf life. Just be sure to place it in a well-sealed container before freezing.