How to Test Yeast: Testing Methods for Different Yeast Types

Yeast is a single-cell, living organism that converts sugar and starch into carbon dioxide through fermentation. In bread baking, yeast is a leavening agent—the yeast ferments and produces carbon dioxide gas, which expands the dough, giving it a rise. There are many different types of yeast, and they all have different rise times. For the longest shelf-life, store yeast in the refrigerator or another cool, dark place, like a pantry cabinet. Storing yeast at room temperature weakens its rise abilities and causes it to go bad faster. Note that yeast differs from both baking powder and baking soda—while yeast is a living organism, the latter are chemical leavening agents that will initiate chemical processes almost instantly.

Packages of yeast come with expiration dates, but there are no guarantees that the yeast will be good (still alive) before such a date or inactive (dead) after that same date. The shelf life varies, so unexpired yeast might fail to bloom whereas expired yeast might still bloom or ferment. If yeast is dead, it is unable to convert sugars into carbon dioxide and will not create the signature foam that appears when yeast is alive and blooming. Making bread with dead yeast results in a dense, under-proofed, and squat loaf of bread without a release of carbon dioxide gas to lift the dough. For these reasons, testing yeast, regardless of its expiration date, is crucial.

Yeast requires activation in order to benefit bread recipes, although different types of yeast require different proofing techniques to test their freshness.

1. 1. Active dry yeast: These yeast granules come in a jar or as a packet of yeast. To test active dry yeast, measure out one-fourth cup of warm water (ninety degrees to one hundred degrees Fahrenheit) in a glass measuring cup. Then stir in a teaspoon of sugar and two and a quarter teaspoons of yeast. Let that sit for about ten minutes. If the yeast mixture is foamy, it’s active; if it’s not, discard it.
2. 2. Fresh yeast: This type of yeast comes in cakes or blocks and smells yeasty and bread-like when it’s fresh. To test fresh yeast, combine the amount of yeast the recipe calls for with warm water (no hotter than one hundred degrees Fahrenheit) and sugar. Wait about ten minutes. By this point, the yeast mixture should be foamy and give off a bready aroma. If it does not, the yeast has gone bad.
3. 3. Instant yeast: Also known as bread machine yeast, quick-rise yeast, or rapid rise yeast, instant yeast comes in jars or packets. This type of yeast works similarly to active dry yeast but should take only a few minutes to start foaming if it’s fresh and active.

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