BREWING By the term brewing is generally comprehended the processes by which ale or beer is prepared from its raw materials. These processes are somewhat diversified in character, and as a result the brew ing industry is one of exceptional interest to the biologist and chemist.
Bristly, we may define brewing as the series of chemical changes by which barley or other grain or saccharine materials are prepared, subjected to alco holic fermentation by means of yeast, and made into a beverage of low or moderate alcoholic percentage. The brewing industry is dependent on two funda mental chemical changes: First, the transformation of starch to sugar by enzyme action, and second, the fermentation of the sugar thus formed.
The transformation of starch to sugar.
It has long been known that starch may be hydro lyzed or converted into sugar through the interven tion of certain digestive or fermentative enzymes.
In the germination of seeds, as barley, which have a large amount of stored-up starch, a similar action takes place, and the starch is changed by the action of enzymes secreted by the living cells of the seed into a sugar, maltose, which by the action of yeast is "fermented." Fermentation of sugars.
The alcoholic fermentation of sugars has been known and practiced for hundreds of years. Its true nature, and the exciting cause, and the char acter of the products were not thoroughly eluci dated until within comparatively recent years. Many theories of alcoholic fermentation have been current, but it remained for Traube, in 1858, to suggest what appears to be the true explanation of fermentation. According to his theory, fermenta tion is brought about by the action of substances secreted within the cells (ferments or enzymes) which act in a way analogous to that of digestive ferments, but in this case transfer oxygen from one group of atoms to another, thereby causing a breaking up of a complex sugar into simpler sub stances. Strangely enough, this theory did not gain general credence and support, and it was not until the discovery of zymase in yeast, by Buchner, in 1897, that the accuracy of Traube's theory became evident.
Many species of yeast are known, but those of industrial importance belong especially to the two species, Saceharomyees eerevisim and Saeeharomyces ellipsoideus. The former is the yeast employed in brewing, while the latter is the specific fermentation organism of wine.
The action of yeast on sugar may be expressed chemically by the equation : 2602 A- 'war. Carbon dioxid. Alcohol.
Types of beer.
While the fundamental chemical changes indi cated above are basic for the brewing industry, we may nevertheless recognize a number of types of the finished product as, for example : (1) The .ltunich or Bavarian type of lager beer with dark color, malt flavor, and sweetish taste, not with pronounced aroma and flavor of hops, in-u ally sparkling and lively, or bubbling with carbon dioxid gas.
(2) The Pilsen or Bohemian type of lager beer with light color, pronounced hop aroma and bitter taste, not particularly sweet, and also usually lively and sparkling.
(3) The American type of lager beer, brilliant, clear, lively and sparkling, light in color, pro nounced hop aroma, but less bitter than Bohemian.
(4) Ale, with light color, very marked bitter taste and aroma of hops, and with rather high per centage of alcohol and tart taste in the aged pro duct ; may be either lively or still, generally clear.
(5) Stout, with very dark color, sweet taste and malt flavor, heavier than ale, but generally con taining less alcohol ; usually lively and with tart taste in aged product.
(6) Weiss beer, very light in color, no marked hop or malt flavor ; pronouncedly tart and very lively, but generally turbid rather than brilliant.
(7) Common or steam beer, light in color, hop aroma and bitter taste, not very pronounced ; very lively, but not necessarily brilliant.
Beers may be further classified according to the kind of fermentation employed in their production. Certain types of yeast, known as "bottom yeast," and causing bottom fermentation," are employed in the preparation of the German lager beers and the American lager and steam beers. Ale, porter, stoat and Weiss beer, on the contrary, are fer mented by "top yeasts." Bottom fermentation differs from top fermentation in the temperature at which action takes place, the amount of acid formed, the amount of alcohol formed (generally) and in the behavior of the organisms, the bottom ferment developing especially in the depths of the liquid, while with top fermentation abundant masses of yeast are found at the surface of the solution. Certain differences in chemical and bio logical behavior have also been detected, but the organisms have been generally supposed to be of the same species (S. eerevisim). Of late, however, the question of species of yeast has been regarded with less certainty than in earlier years.