Fleischmann’s Yeast, which was developed in 1868. During World War II Fleischmann's developed a granulated active dry yeast, which did not require refrigeration and had a longer shelf life than fresh yeast. The company created yeast that would rise twice as fast, cutting down on baking time. Baker's yeast is also sold as a fresh yeast compressed into a square "cake". This form perishes quickly, and must be used soon after production in order to maintain viability. A weak solution of water and sugar can be used to determine if yeast is expired. When dissolved in the solution, active yeast will foam and bubble as it ferments the sugar into ethanol and carbon dioxide.

When yeast is used for making bread, it is mixed with flour, salt, and warm water (or milk). The dough is kneaded until it is smooth, and then left to rise, sometimes until it has doubled in size. Some bread doughs are knocked back after one rising and left to rise again. A longer rising time gives a better flavour, but the yeast can fail to raise the bread in the final stages if it is left for too long initially. The dough is then shaped into loaves, left to rise until it is the correct size, and then baked. Dried yeast is always used for bread made in a bread machine.

It is not known when yeast was first used to bake bread. The first records that show this use came from Ancient Egypt.

Researchers speculate that a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of the flour caused it to ferment before baking. The resulting bread would have been lighter and more tasty than the normal flat, hard cake. (source

Compressed Yeast Active Dry Yeast
Weight Weight Measurement
1 oz 1/2 oz 1 1/2 Tbsp.
1 1/2 oz 3/4 oz 2 Tbsp.
2 oz 1 oz 3 Tbsp.
4 oz 2 oz 1/4 cup and Tbsp.
6 oz 3 oz 1/3 cup
8 oz 4 oz 1/3 cup and Tbsp.
10 oz 5 oz 1/2 cup and 2 1/2 Tbsp.
12 oz 6 oz 2/3 cup
1 lb 8 oz 3/4 cup and  3 1/2 Tbsp.
1 lb  8 oz 12 oz 1 1/3 cup
2 lb 1 lb 1 3/4 cup and Tbsp.

If the liquid is too cold, the yeast will either not activate or it will do so very slowly.

If too hot, it will cook the yeast and kill the life enzymes. Use a thermometer to take the guesswork out of determining the correct liquid temperature. An instant- read thermometer is best.

Unopened packages of dry yeast can be stored at room temperature.

Since yeast is very perishable when exposed to air, moisture and/or warmth, all opened packages of yeast must be refrigerated or frozen in an airtight container.

Under refrigeration, the life of yeast is about four months, and when frozen, six months.


Yeast, specifically Saccharomyces cerevisiae, is used in baking as a leavening agent, where it converts the fermentable sugars present in the dough into carbon dioxide. This causes the dough to expand or rise as the carbon dioxide forms pockets or bubbles. When the dough is baked it "sets" and the pockets remain, giving the baked product a soft and spongy texture. The use of potatoes, water from potato boiling, eggs, or sugar in a bread dough accelerates the growth of yeasts. Salt and fats such as butter slow down yeast growth. The majority of the yeast used in baking is of the same species common in alcoholic fermentation. Additionally, Saccharomyces exiguus (also known as S. minor) is a wild yeast found on plants, fruits, and grains that is occasionally used for baking.