Yeast (baking)
Yeast is a type of fungi used in baking and is known as Saccharomyces cerevisiae. This species is also used in fermentation of beer and wine.
Yeasts for leavening bread may be produced industrially or commercially or caught from the environment. Commercial yeast is prepared by taking one yeast cell, placing it in a test tube, and providing it with food and the moist, warm conditions it needs to thrive. Yeast undergo asexual reproduction, so it can reproduce itself rapidly, creating large numbers of cells.
In bread production, yeast cells convert carbohydrates into carbon dioxide, which causes the dough to expand or rise, and alcohol, most of which evaporates during baking. 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.
Baker's yeast comes in two forms. The first form 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.
Water can be used to determine if yeast is expired; it will foam if still active.
History
Yeast was first used to bake bread in Egypt in approximately the fourth millenium 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 and wine.
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.