Yeast is a living organism and baker's yeast is the species of yeast used in baking to leaven baked goods. Dry baker's yeast is granules of dormant yeast. Before using this yeast, bakers will often test it to make sure that it is still viable. The process of testing yeast to see if is still fresh and active is known as proofing and can be done in a few simple steps.
Check the expiration date on the package of yeast to ensure that it has not expired.
Pour 1/2 cup of warm water into a small bowl or cup. The water should be between 110 and 115 degrees Farenheit.
Dissolve 1 tsp sugar into the warm water.
Add 2 1/4 tsp yeast and stir until thoroughly dissolved.
Allow to sit 5 minutes.
Check to see if the yeast mixture is foamy and bubbly. If so, the yeast is active.
If you do not have an instant-read thermometer, you can approximate the temperature of the water by choosing water that feels comfortably warm if a few drops are placed on your wrist.
If the yeast mixture does not foam or bubble after 10 minutes, it is likely that the yeast is not good. Do not use this yeast.