Three kinds of yeast are in use for breadmaking, liquid
(home-made or baker's), dry, and compressed yeast. Liquid
yeast is prepared from potatoes, sometimes with the addi-
tion of a few hops, sugar, and enough yeast to start the
fermentation. It is used less than a few years ago, since
the convenient yeast cake has come into use. Dried yeast
finds its sale chiefly among those too far from market to
procure fresh yeast. It is possible to make good bread with
it, but not so easy as with fresh yeast.
In most general use, at least near the large centres of
population, is compressed yeast, a by-product in the manu-
facture of whiskey. It is prepared by skimming the masses
of yeast from the surface of the fermenting liquid, sifting it
to take out all coarse particles of material, and washing by
repeatedly adding and drawing off fresh water. Starch is
then added, and the whole mass is formed in large cakes
and sent to the point of distribution, where it is cut and
wrapped in tinfoil. One cake, sold for two cents, is said to
contain about sixty billion yeast cells. The advantage of
BREAD 243
this form of yeast is that it contains only one species of
yeast, and that, when it is fresh, there are fewer bacteria
present than in most home-made yeasts. A fresh cake is
essential for good results.
The property of yeast of which we make use in bread-
making is its power to change certain kinds of sugar into
alcohol and carbon dioxide; that is, to ferment sugar.
When yeast is added to the flour and liquid, which are the
essential ingredients of bread, and the whole is allowed to
stand at a temperature of from 70° to 80° F., complicated
chemical changes take place. The most important of these
are : first, the conversion of part of the starch of the flour
into sugar, accomplished by a ferment sent out by the yeast,
or perhaps by a ferment present in the flour itself ; second,
the change of the sugar into alcohol and carbon dioxide, a
direct result of the growth of the yeast. The chemical
reactions may be expressed as follows :
or,
starch Water Sugar
CeHioOs + H2O = CeHisOe (dextrose)
2 C6H10O5 + H2O = C12H20O11 (maltose)
Carbon
Dioxide
Dextrose Alcohol
CeHiaOe ( + yeast) = 2 CgHeO + 2 CO2
Maltose
C12H22O11 + H2O (+ yeast) = 4 C2H6O + 4 CO^
If bacteria are present, a further chemical change may take
place, and the alcohol be converted into acetic acid, thus
making the bread sour.
The reaction is
Alcohol Oxygen Acetic Acid Water
CaHeO -|- O = C2H4O2 + H2O
If perfectly pure yeast could be obtained, sour bread would
be unknown. Since this is not practicable at present, we
244 HANDBOOK OF DOMESTIC SCIENCE
must guard against the souring of tlie dough by stop]3ing
the fermentation at the right stage, and by avoiding a liigh
temperature, favorable to bacterial groAvth and deleterious
to the best development of the yeast.
Page 116
Presented as published in 1900. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
Three kinds of yeast are in use for breadmaking, liquid (home-made or baker's), dry, and compressed yeast. Liquid yeast is prepared from potatoes, sometimes with the addition of a few hops, sugar, and enough yeast to start the fermentation. It is used less than a few years ago, since the convenient yeast cake has come into use. Dried yeast finds its sale chiefly among those too far from market to procure fresh yeast. It is possible to make good bread with it, but not so easy as with fresh yeast.
In most general use, at least near the large centres of population, is compressed yeast, a by-product in the manufacture of whiskey. It is prepared by skimming the masses of yeast from the surface of the fermenting liquid, sifting it to take out all coarse particles of material, and washing by repeatedly adding and drawing off fresh water. Starch is then added, and the whole mass is formed in large cakes and sent to the point of distribution, where it is cut and wrapped in tinfoil. One cake, sold for two cents, is said to contain about sixty billion yeast cells. The advantage of
this form of yeast is that it contains only one species of yeast, and that, when it is fresh, there are fewer bacteria present than in most home-made yeasts. A fresh cake is essential for good results.
The property of yeast of which we make use in breadmaking is its power to change certain kinds of sugar into alcohol and carbon dioxide; that is, to ferment sugar. When yeast is added to the flour and liquid, which are the essential ingredients of bread, and the whole is allowed to stand at a temperature of from 70° to 80° F., complicated chemical changes take place. The most important of these are : first, the conversion of part of the starch of the flour into sugar, accomplished by a ferment sent out by the yeast, or perhaps by a ferment present in the flour itself ; second, the change of the sugar into alcohol and carbon dioxide, a direct result of the growth of the yeast. The chemical reactions may be expressed as follows :
or,
starch Water Sugar
CeHioOs + H2O = CeHisOe (dextrose) 2 C6H10O5 + H2O = C12H20O11 (maltose)
Carbon Dioxide
Dextrose Alcohol
CeHiaOe ( + yeast) = 2 CgHeO + 2 CO2
Maltose
C12H22O11 + H2O (+ yeast) = 4 C2H6O + 4 CO^
If bacteria are present, a further chemical change may take place, and the alcohol be converted into acetic acid, thus making the bread sour. The reaction is
Alcohol Oxygen Acetic Acid Water CaHeO -|- O = C2H4O2 + H2O
If perfectly pure yeast could be obtained, sour bread would be unknown. Since this is not practicable at present, we
must guard against the souring of tlie dough by stopping the fermentation at the right stage, and by avoiding a liigh temperature, favorable to bacterial growth and deleterious to the best development of the yeast.