The Proofing Process

• Many recipes call for adding the yeast with the flour or other ingredients all at once, and that's all right if you're sure your yeast is fresh. You can verify this by checking the date on the packets, but if your yeast experienced any kind of temperature fluctuations during storage, this date could become a moot point. The best way to know if your yeast still packs its fungal punch is to proof it, which means exposing it to those elements that cause it to release its energy. These include moisture, warmth and food, and the yeast will let you know if it's good or if you should toss it out and start over.

To Toss or Not to Toss

• Yeast blooms best in a wet medium, usually water, that has a temperature between 80 to 120 degrees Fahrenheit. You can test the temperature with a candy thermometer or sprinkle some on your arm. If it feels comfortably warm, the yeast will cooperate. If it feels hot, cool it down before adding the yeast. At this point, a teaspoonful or so of granulated sugar should satisfy the yeast's sweet tooth. Stir it into the warm water until it dissolves, and then mix in the yeast. Blend well, and let it do its thing. The mixture should be slightly beige in color and lighten a little as the yeast develops. You'll know it's ready when you see a bubbly foam across the top of the liquid, which should take no longer than 15 minutes. If there is no foam by that time, the yeast is past its prime. Pour the liquid out, rinse the cup or bowl and test another packet.

Shopping for Yeast

• The yeast you're likely to find at the supermarket is dry yeast, which differs from the fresh moist type that professional bakers use and is typically sold in small cubes wrapped in foil. Dry yeast is sold in the familiar strips composed of three individual packets or in small jars. The two are interchangeable for use in the bread recipes and can be proofed in the same way. Be sure to check the expiration dates, which are listed on the edges of packets or on the jar label, since it can vary widely from packet to packet or jar to jar, and buy the freshest you can find.

Measuring Yeast

• Bread recipes call for a specific amount of yeast, but that may not always equal a full packet that can contain from 2 1/4 teaspoons to 1 tablespoon, depending upon the brand. Two loaves of bread made with all-purpose flour generally call for two packets, or 4 1/2 teaspoons, of yeast. If using dry yeast from a jar, simply measure out 2 1/4 teaspoons for every packet called for in the recipe, or less depending on the recipe's requirements. To prolong its life, store yeast in the refrigerator or freezer where it is less likely to experience drastic changes in temperature.