624 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



As soon as the kilning is finished the radicles are removed by friction and screening 

 in special machines. 



WORK OF ENZYMES AND BACTERIA. The malt is first crushed by 

 pressing between rollers to facilitate the work of the enzymes and the 

 solvent action of the water. If unmalted grain is to be used as well, this 

 must be ground and the starch made soluble by heating under pressure 

 with three or four times its weight of water and a little malt to 8o-85 

 for about an hour. 



The methods of mashing are very various. They consist in general of mixing the 

 ground malt with warm water, bringing the mass to a temperature of 35 to 45 which 

 is gradually raised to 6o-65 by the addition of hotter water. When the action of 

 the enzymes commences, the heated decoction of unmalted grains is added in va- 

 rious ways, and the temperature controlled by additions of hot water or by heating 

 a portion of the mash. The whole mashing process requires from two to five hours 

 according to the methods used. 



During the mashing, the starch is transformed partly into maltose and partly into 

 dextrins. The ratio of these products will vary according to the amount of diastase 

 present and especially according to the temperature used. At about 60 the maxi- 

 mum amount of maltose is produced; at higher temperature (65 to 75) the 

 unfermentable dextrins increase. The amount of alcohol and the amount of extract 

 in the beer therefore depend to a great extent on the method of mashing. 



During the first part of the mashing, while the temperature is about 

 45, lactic bacteria develop. If their action is too intense they will 

 render the beer unpleasantly acid. If moderate, the acidity they com- 

 municate to the wort is useful in preventing the growth of the harmful 

 butyric bacteria which might develop. 



After mashing, the wort is separated from the solid matters by drawing off, 

 extracting the mash with hot water (sparging), and filtration. It is then boiled from 

 one to eight hours according to the result desired. 



Boiling sterilizes the wort, kills all bacteria and destroys any 

 enzymes which remain. These results are obtained almost instantane- 

 ously owing to the lactic acid present. Coagulation of protein sub- 

 stances is also brought about, effecting a clarification of the wort. 

 This requires one or more hours, according to the nature of the wort. 

 It is necessary also in some cases to concentrate the wort, which is 

 done by prolonged heating in open kettles. This may require several 

 hours. 



The Hopping of the wort takes place during the boiling. Sometimes 

 the hops are added just at the end of boiling; sometimes in two or three 



