Yeast

Baker's yeast comes in two forms. The first form, compressed yeast, is fresh yeast pressed into a square cake. This form perishes quickly, and must be used soon after production in order to maintain the desired effects. Dry yeast is granulated and has a longer shelf life than fresh yeast. In the production of beer or wine, sugar is converted into alcohol by yeast.

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 digests the sugar and converts it into carbon dioxide.

Yeast was first used to bake bread in Egypt in approximately the fourth millennium BC. Artifacts have been found that are associated with bread making, as well as drawings that depict bakeries. Prior to the use of yeast in baking, breads were typically unleavened. During this time, bread was seen as a luxury.

Some theories state that yeast was discovered simply by being in the air and coming in contact with the unleavened bread being prepared. Another theory states that ale was used instead of water, and the yeast from the ale caused the bread to rise.

In 1859, Louis Pasteur discovered how yeast worked and explained fermentation in the making of beer.

Today there are several retailers of baker's yeast, one of the best-known being Fleischmann’s Yeast, which was developed in 1868. During World War II Fleischmann's developed active dry yeast, which did not require refrigeration. The company created yeast that would rise twice as fast, cutting down on baking time.