FERMENTATION
213. While baking powder is universally used for biscuits and cake,
it is seldom, if ever, used for bread, because it does not furnish
sufficient gas to lighten the tough heavy mass of bread dough. Then,
too, most people prefer the taste of yeast-raised bread. There is a
reason for this widespread preference, but to understand it, we must
go somewhat far afield, and must study not only the bread of to-day,
but the bread of antiquity, and the wines as well.
If grapes are crushed, they yield a liquid which tastes like the
grapes; but if the liquid is allowed to stand in a warm place, it
loses its original character, and begins to ferment, becoming, in the
course of a few weeks, a strongly intoxicating drink. This is true not
only of grape juice but also of the juice of all other sweet fruits;
apple juice ferments to cider, currant juice to currant wine, etc.
This phenomenon of fermentation is known to practically all races of
men, and there is scarcely a savage tribe without some kind of
fermented drink; in the tropics the fermented juice of the palm tree
serves for wine; in the desert regions, the fermented juice of the
century plant; and in still other regions, the root of the ginger
plant is pressed into service.
The fermentation which occurs in bread making is similar to that which
is responsible for the transformation of plant juices into
intoxicating drinks. The former process is not so old, however, since
the use of alcoholic beverages dates back to the very dawn of history,
and the authentic record of raised or leavened bread is but little
more than 3000 years old.
214. The Bread of Antiquity. The original method of bread making and
the method employed by savage tribes of to-day is to mix crushed grain
and water until a paste is formed, and then to bake this over a camp
fire. The result is a hard compact substance known as unleavened
bread. A considerable improvement over this tasteless mass is
self-raised bread. If dough is left standing in a warm place a number
of hours, it swells up with gas and becomes porous, and when baked, is
less compact and hard than the savage bread. Exposure to air and
warmth brings about changes in dough as well as in fruit juices, and
alters the character of the dough and the bread made from it. Bread
made in this way would not seem palatable to civilized man of the
present day, accustomed, as he is, to delicious bread made light and
porous by yeast; but to the ancients, the least softening and
lightening was welcome, and self-fermented bread, therefore,
supplanted the original unleavened bread.
Soon it was discovered that a pinch of this fermented dough acted as a
starter on a fresh batch of dough. Hence, a little of the fermented
dough was carefully saved from a batch, and when the next bread was
made, the fermented dough, or leaven, was worked into the fresh dough
and served to raise the mass more quickly and effectively than mere
exposure to air and warmth could do in the same length of time. This
use of leaven for raising bread has been practiced for ages.
Grape juice mixed with millet ferments quickly and strongly, and the
Romans learned to use this mixture for bread raising, kneading a very
small amount of it through the dough.
215. The Cause of Fermentation. Although alcoholic fermentation, and
the fermentation which goes on in raising dough, were known and
utilized for many years, the cause of the phenomenon was a sealed book
until the nineteenth century. About that time it was discovered,
through the use of the microscope, that fermenting liquids contain an
army of minute plant organisms which not only live there, but which
actually grow and multiply within the liquid. For growth and
multiplication, food is necessary, and this the tiny plants get in
abundance from the fruit juices; they feed upon the sugary matter and
as they feed, they ferment it, changing it into carbon dioxide and
alcohol. The carbon dioxide, in the form of small bubbles, passes off
from the fermenting mass, while the alcohol remains in the liquid,
giving the stimulating effect desired by imbibers of alcoholic drinks.
The unknown strange organisms were called yeast, and they were the
starting point of the yeast cakes and yeast brews manufactured to-day
on a large scale, not only for bread making but for the commercial
production of beer, ale, porter, and other intoxicating drinks.
The grains, rye, corn, rice, wheat, from which meal is made, contain
only a small quantity of sugar, but, on the other hand, they contain a
large quantity of starch which is easily convertible into sugar. Upon
this the tiny yeast plants in the dough feed, and, as in the case of
the wines, ferment the sugar, producing carbon dioxide and alcohol.
The dough is thick and sticky and the gas bubbles expand it into a
spongy mass. The tiny yeast plants multiply and continue to make
alcohol and gas, and in consequence, the dough becomes lighter and
lighter. When it has risen sufficiently, it is kneaded and placed in
an oven; the heat of the oven soon kills the yeast plants and drives
the alcohol out of the bread; at the same time it expands the
imprisoned gas bubbles and causes them to lighten and swell the bread
still more. Meanwhile, the dough has become stiff enough to support
itself. The result of the fermentation is a light, spongy loaf.
216. Where does Yeast come From? The microscopic plants which we
call yeast are widely distributed in the air, and float around there
until chance brings them in contact with a substance favorable to
their growth, such as fruit juices and moist warm batter. Under the
favorable conditions of abundant moisture, heat, and food, they grow
and multiply rapidly, and cause the phenomenon of fermentation. Wild
yeast settles on the skin of grapes and apples, but since it does not
have access to the fruit juices within, it remains inactive very much
as a seed does before it is planted. But when the fruit is crushed,
the yeast plants get into the juice, and feeding on it, grow and
multiply. The stray yeast plants which get into the sirup are
relatively few, and hence fermentation is slow; it requires several
weeks for currant wine to ferment, and several months for the juice of
grapes to be converted into wine.
Stray yeast finds a favorable soil for growth in the warmth and
moisture of a batter; but although the number of these stray plants is
very large, it is insufficient to cause rapid fermentation, and if we
depended upon wild yeast for bread raising, the result would not be to
our liking.
When our remote ancestors saved a pinch of dough as leaven for the
next baking, they were actually cultivating yeast, although they did
not know it. The reserved portion served as a favorable breeding place
to the yeast plants within it; they grew and reproduced amazingly, and
became so numerous, that the small mass of old dough in which they
were gathered served to leaven the entire batch at the next baking.
As soon as man learned that yeast plants caused fermentation in
liquors and bread, he realized that it would be to his advantage to
cultivate yeast and to add it to bread and to plant juices rather than
to depend upon accidental and slow fermentation from wild yeast.
Shortly after the discovery of yeast in the nineteenth century, man
commenced his attempt to cultivate the tiny organisms. Their
microscopic size added greatly to his trouble, and it was only after
years of careful and tedious investigation that he was able to perfect
the commercial yeast cakes and yeast brews universally used by bakers
and brewers. The well-known compressed yeast cake is simply a mass of
live and vigorous yeast plants, embedded in a soft, soggy material,
and ready to grow and multiply as soon as they are placed under proper
conditions of heat, moisture, and food. Seeds which remain on our
shelves do not germinate, but those which are planted in the soil do;
so it is with the yeast plants. While in the cake they are as lifeless
as the seed; when placed in dough, or fruit juice, or grain water,
they grow and multiply and cause fermentation.