How to Test or Proof Yeast to See if it is Still Active

Yeast Bread

The expiration date on your yeast may say that it has expired, but if you have stored the yeast in the refrigerator, or better yet, in the freezer where it will remain active even longer, it may still be good beyond the expiration date. Here's an easy way to test the yeast to see if it is still active.

Difficulty:

Easy

Instructions

Things You'll Need

• Yeast
• Sugar

1. 

   Run 1/2 cup warm tap water into a measuring cup. To truly ensure accuracy, you can use a candy thermometer to check the temperature of the water. The temperature should be 110-115 degrees Fahrenheit.

2. 

   Stir in 1 teaspoon sugar and two teaspoons yeast (or one packet of yeast). You will see three almost equal levels: the bottom third with sugar and yeast, the middle third with cloudy water, and the top third with a film of yeast.

3. At 5 minutes

   If foam and bubbles form within 10 minutes, then the yeast is still active (alive). The mixture will be approximately half milky looking water and half foam.

Tips & Warnings

• Remember to wash your hands after handling yeast to avoid spreading the yeast, which is capable of causing a yeast infection.