Nature Bulletin No. 175-A January 16, 1965
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation
Housewives who bake their own bread buy a cake of compressed yeast,
crumble it in a half-cup of warm water, mix it with a little flour and a
pinch of sugar, and put the cup in a warm place. Presently, little
bubbles begin to form and burst. The mixture swells and foams and
rises. It is fermenting.
-- the name is derived from a Latin word meaning "to
boil" -- has been known and used in making bread, beer and wine
since early times. Yeast, or leaven, was used in the days of the Hebrew
patriarchs. A portion of the uncooked dough was left from each baking
and allowed to sour. This dough "starter", mixed with fresh dough,
caused the whole to ferment, gas to form, and the bread raised or
from such a process, however, was deemed unfit for sacred
occasions. When two angels appeared to Lot at Sodom (Genesis XIX)
he "made them a feast, and did bake unleavened bread. " The
Congregation of Israel was sternly warred (Exodus XII) about the feast
marking the first month of the new year: "Seven days shall ye eat
unleavened bread; even the first day shall ye put away leaven out of
your houses; for whosoever eateth unleavened bread from the first day
until the seventh day, that soul shall be cut off from Israel. .
commonly called "the staff of life", has always been a staple
food. The preparation and baking of it is one of the oldest arts.
Perhaps the first bread was prepared from such fruits as ground-up
acorns and beechnuts, just as it was by our American Indians and
pioneers. In the sunken ruins of homes of the Swiss lake-dwellers who
lived in the Stone Age, 10, 000 or more years ago, has been found
hard little baked cakes made of coarsely-ground grains -- barley and a
kind of wheat. Apparently, they were spread on a hot stone, with hot
ashes piled on top to cook them.
The ancient Egyptians brought the art of baking to high perfection,
using flour made from wheat, barley, and a sorghum grain. Some of
their loaves were small and round, like muffins; others were elongated
rolls sprinkled with seeds, like Vienna bread. The rich ate a white
bread made from wheat. In ancient Greece and Rome there were
public bakeries at an early date.
Yeasts are tiny fungus plants related to bacteria, and to molds such as
the blue mold which grows on bread. There are hundreds of species.
Some kinds are carefully cultivated for special purposes such as
baking, brewing and wine making, but most kinds grow wild in
nature. A yeast plant is a single roundish or oval cell, from 1/25, C00
to 1/2500th inch in diameter, consisting of a transparent cell wall
enclosing a grayish watery jelly which is the living substance. Yeasts
multiply rapidly in warm sugary liquids, each cell producing new cells
by growing buds which increase in size until each breaks off from the
mother cell. Most yeasts produce a substance called "zymase" which
changes sugar into alcohol and carbon dioxide, a gas. This gas forms
bubbles. The process is called fermentation.
bread, the yeast mixture is added to flour, salt and water, and this
mixture is stirred and kneaded to form a thick dough. This dough is
then put away to "rise". The gluten in the flour makes the dough
gummy and elastic so that it can expand, puff up, and hold the bubbles
of gas generated by the yeast. When it is baked, the heat kills the yeast,
the alcohol evaporates, and we have the light porous food known as
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Update: June 2012