YEAST
21. NATURE AND ACTION OF YEAST.--How yeast came to be discovered is not
definitely known, but its discovery is believed to have been purely
accidental. Some mixture of flour and liquid was probably allowed to
remain exposed to the air until it fermented and then when baked was
found to be light and porous. Whatever the origin of this discovery was,
it is certain that yeast was used hundreds of years ago and that its
action was not at that time understood. Even at the present time
everything concerning the action of yeast is not known; still continued
study and observation have brought to light enough information to show
that yeast is the agency that, under favorable conditions, produces
light, spongy bread out of a flour mixture.
22. It has been determined that yeast is a microscopic plant existing
everywhere in the air and in dust; consequently, it is found on all
things that are exposed to air or dust. In order that it may grow, this
plant requires the three things necessary for the growth of any plant,
namely, food, moisture, and warmth. Carbohydrate in the form of sugar
proves to be an ideal food for yeast, and 70 to 90 degrees Fahrenheit is
the temperature at which the most rapid growth occurs. When these
conditions exist and a sufficient amount of moisture is provided, yeast
grows very rapidly and produces fermentation.
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