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SOME OP THE PRINCIPLES OF BREWING 



BREWING 

 By Samuel G. Prescott 



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. 



Briefly, 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, Saceharomyces eerevisim and Saceharomyees 

 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 : 



C((Hl206 



Sugar. 



= 2C02 -1- 2C2H5OH. 

 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 Munich or Bavarian type of lager beer 

 with dark color, malt flavor, and sweetish taste, 

 not with pronounced aroma and flavor of hops, usu- 

 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, 

 stout 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. 



We may now follow through the actual processes 

 comprehended in brewing. 



(1) Malting. 



This is the general name given to the process 

 whereby the starch of barley or other grain is 

 changed to maltose by the diastatic enzyme. The 

 product is known as " malt." The grain is carefully 

 selected and cleaned, and then is subjected to a 

 steeping process in " steep tanks," or big iron cylin- 

 drical hoppers with conical bottoms. The object of 

 steeping is to soften the outer coating and promote 

 rapid germination. When the steeping has been 

 sufficient, the grain is carried to the place where 

 germination takes place. 



Until comparatively recently, the malting took 



