In bread production, yeast
cells turn 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, 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.