Yeast: The Basics

What’s the difference between active dry, instant, and fresh yeast?

Sourdough Starter - Wheat

Photo by Robert Waters

Types of Yeast

Active Dry Yeast is the most commonly available form for home bakers. It’s available in ¼-oz packets or jars. The yeast is dormant, needs to be “proofed” and rehydrated before using.

  • To proof yeast, sprinkle the yeast over warm water (105-115 degrees F) and a pinch of sugar, and let it stand for 10 minutes until creamy and bubbly.
  • Dry yeast should be stored in a cool dry place; but do not use it after the expiration date on the package. Store open containers in the refrigerator.

Instant Yeast is a dry yeast developed in the past thirty years. It comes in smaller granules than active dry yeast, absorbs liquid rapidly, and doesn’t need to be hydrated or proofed before being mixed into flour.

  • Bread Machine Yeast and Rapid Rise Yeast is instant yeast that may include ascorbic acid, a dough conditioner.
  • Again, store the yeast in a cool dry place, or in the refrigerator once the package has been opened. Do not use yeast after the expiration date.

Fresh Yeast, also known as compressed or cake yeast, is active yeast. It’s sold in tiny cakes in the refrigerated section of many supermarkets.

  • Fresh yeast does not keep well; it will last about two weeks if refrigerated. The yeast should be pale gray-brown, fragrant, soft and crumbly–not hard, dark brown, or crusty. Any mold growing on the surface is an indication that the yeast should be discarded.
  • Fresh yeast should be proofed in tepid water (80-90 degrees F) without contact with salt or sugar. This yeast type is a good choice for breads requiring a long cool rise, or for breads made using the sponge method.

Wild Yeast and Starters

Before yeast was available in grocery stores, bakers kept colonies of yeast for making bread. These colonies were known as starters, and were sometimes passed on from generation to generation. You can make your own starter using commercial yeast, by using potato water (from boiled potatoes) to attract and feed wild yeasts present in the air around us, or by using the yeast found on the skins of organic grapes or organic raisins. Keep the starter in a one-quart crock, jar, or airtight container.

Learn about Sourdough Starters and how to use them.

Yeast Conversion Rates
In commercial baking, precise measurements are key. Home bakers generally don’t need to reduce or increase liquid amounts to compensate for the type of yeast used since the quantities are so small.

  • To substitute instant or bread machine yeast for active dry yeast, use 25% less instant yeast than active dry.
  • A .6-oz cube of cake yeast is roughly equivalent to 1½ to 2 teaspoons instant yeast or 2 to 2¼ teaspoons active dry yeast.

How Much Is That?
Each little .25-ounce packet of active dry yeast contains about 2 1/2 teaspoons of yeast.