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This effected by allowing malt to act on the starch. This malt contains a certain chemical "ferment" or enzyme, called "diastase" ("I separate").

This is able under proper conditions to break up the gelatinized starch into simpler substances—the dextrins—and later into a fermentable sugar called maltose.

Fermentation.—The maltose or sugar in the "mash" is now to be converted into alcohol. This is accomplished by fermentation, a process of decomposition which converts the sugar into carbonic acid and alcohol. Fermentation is started by yeast, a fungus growth, which in the course of its life history produces a matter called zymose which chemically acts on the sugar to split it up into carbonic acid gas and alcohol.

Yeast may be either "wild" or cultivated. If the mash is left to stand under proper condition the wild yeast spores in the air, will soon settle in the mash and begin to multiply. This method of fermentation is bad because other organisms than yeast will also be developed,— organisms antagonistic to proper fermentation. As a consequence, pure or cultivated yeast is alone used.

This yeast is cultivated from a mother bed in a special yeast mash and when ripened is mixed with the mash in the fermenting vat. At a temperature between 50°F. and 86°F. the yeast induces fermentation, converting the sugar of the mash into carbon dioxid which escapes, and alcohol which remains in the decomposed mash, or "beer" as it is termed in the United States.

It now remains to separate the alcohol from the water of the beer with which it is mixed. This is accomplished by distillation and rectification, as will be fully described in the chapters following.

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