Yeast Freshness Test
Follow these steps if you are unsure of the freshness of your yeast (or just want to give it a 'good start').
Using a one-cup liquid measuring cup, dissolve 1 teaspoon of granulated sugar in 1/2 cup warm tap water at 110°F-115°F.
Using a thermometer is the most accurate way to determine the correct liquid temperature. Any thermometer will work as long as it measures temperatures between 75°F and 130°F.
If you don't have a thermometer, the tap water should be warm but NOT hot to the touch.
Stir in one 1/4 oz. packet (7g) or 2-1/4 tsp of dry yeast until there are no more dry yeast granules on top. Yeast should be at room temperature before using.
In three to four minutes, the yeast will have absorbed enough liquid to activate and start to rise.
After ten minutes, the foamy yeast mixture should have risen to the 1-cup mark and have a rounded top. It should look like the picture below.
If this is true, your yeast is very active and should be used in your recipe immediately.
Remember to deduct 1/2 cup liquid from the recipe to adjust for the water used in this test.
If the yeast did not rise to the 1-cup mark, your yeast has little or no activity. Discard this yeast.