Cooking FAQs

How to Proof Yeast

Test your yeast to see if it's still good

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Updated on 05/7/20

What Is Proofing?

When it comes to yeast, proofing means testing your yeast to see that it's still alive and able to start the fermentation process; the yeast needs to create the bubbles of gas that cause bread and other baked goods to rise. Yeast is a living organism, and if it is near its expiration date, or it hasn't been kept in ideal conditions, there may not be enough living yeast cells to create the gas needed to make your bread rise.

Do All Yeasts Need Proofing?

Not every type of yeast needs to be proofed. The two kinds of yeast you may want to test are active dry yeast and fresh active yeast (also called compressed yeast or cake yeast). You shouldn't proof rapid-rise yeast, instant yeast, or bread machine yeast. Those will lose their fast-rising ability if you dissolve them in liquid.

What Do You Need to Proof?

It is very simple to proof yeast, and the process only requires a few ingredients. You will need a packet of yeast plus 1/4 cup warm water and 1 teaspoon sugar. A bowl or 1-cup liquid measuring cup can be used to mix them together. The temperature of the warm water is crucial—it should feel lukewarm. If you want to measure its temperature, make sure it is between 100 to 110 F (40 C). If the water is too hot, it'll kill your yeast.

What Do You Do to Proof?

Combine the yeast, warm water, and sugar in a bowl or 1-cup liquid measuring cup. Let it sit for 10 minutes. During this time, if the yeast is alive, it will start eating the sugar and fermenting into alcohol and carbon dioxide.

After 10 minutes, you should see the yeast foaming up in the measuring cup to the half-cup line (doubling its height). If you used a bowl, you should see plenty of foam. Now you can add the yeast mixture to the rest of the ingredients, and continue with your recipe. It is important to check the amount of water and sugar called for in the recipe you are making before simply adding in the yeast mixture. Since you will be using 1/4 cup of water and 1 teaspoon of sugar to proof 1 packet of dry yeast (2 1/4 teaspoons), you will need to adjust the amount of water and sugar in the recipe accordingly. If your recipe doesn't call for sugar, add a small amount (1/8 teaspoon will do it) to the proofing mixture to give the yeast something to feed on.

If the mixture isn't bubbly, the yeast is no longer good. Dump out your mix, and start with fresh yeast. Unfortunately, there's no way to revive old yeast.

Tips

Dry active yeast usually has a shelf life of around 12 months. Once you open it, it's best to store it in the refrigerator. This will prolong its life. If you don't bake often, or you just want to keep your yeast fresh as long as possible, store it in the freezer. This will keep it fresh indefinitely. There's no need to thaw your yeast before you use it.
Be sure to check the expiration date before you buy yeast. Unless you're a prolific baker, you probably won't be able to use up a jar or packet close to the expiration date before it goes bad.
Store your yeast in an airtight container so it isn't inadvertently exposed to humidity or moisture that might activate it prematurely. Bulk yeast often comes in a vacuum-sealed foil pouch. If this is the way you buy your yeast, it's best to move it to a container that can be sealed tightly. This will help to keep it fresh and avoid messy spills.
If you have bought dry active yeast in bulk, you can proof the yeast using the above measurements to see if the whole container is still active. If the yeast is still alive, proceed with the recipe according to its instructions, using yeast from the remaining bulk amount rather than using the proofed yeast. If the rest of the bulk yeast is stored properly, you should not need to proof it again.