the microbiology of alcohol products 525 



Process oi' Brewing 



Outline. — ^The manufacture of beer takes place in four main stages. First, 

 a portion or all of the grain is soaked in water, allowed to germinate and then 

 dried. This produces the malt which contains the enzymes necessary for the 

 conversion of the starch into sugar and the disintegration of the tissues of the grain. 

 The malt is then crushed (and usually mixed with unmalted cereals or sugar) and 

 heated with water. This constitutes mashing. During this process, the starch 

 changes to maltose and dextrins which with other matters dissolve in the water; 

 then bacteria produce a small amount of lactic acid. The resulting solution con- 

 stitutes the wort. 



The wort, by the addition of yeast is fermented and changed to beer. The 

 fourth stage includes all manipulation of the fermented beer to prepare it for con- 

 sumption. 



Malting: Production of Enzymes. — The best malt is made from 

 barley, but for special beers may be made from wheat or other grains. 

 Steeping consists in soaking in water to start germination. This 

 requires from thirty-six to seventy-two hours and causes an increase in 

 weight of about 45 per cent. The temperature should be about 12.5°. 

 If higher, injurious molds will develop. If much lower, germination 

 will be retarded. The water should contain little organic matter or 

 chlorides, nitrates or iron salts. A little calcium sulphate is favor- 

 able. If it contains many microorganisms it should be sterilized by 

 boiling. A very little sulphite of lime or of potassium may be used to 

 discourage molds. 



During germination several enzymes appear, of which the most important to the 

 brewer are diastase which changes insoluble starch into soluble sugar, rendering it 

 available for the growth of the young plant; peptase, which performs a similar 

 function as regards nitrogenous matters; and cytase which helps in the disintegration 

 of the cellulose. All these are necessary to prepare for the work of the yeast. 

 When the plumule has grown to about two-thirds the length of the grain, sufficient 

 enzymes have been formed. This requires from about sixteen to twenty days. 



The growth of the sprouting seed is at this point stopped by careful drying with 

 artificial heat in a kiln. The kilning must be sufficiently rapid to kill the germinat- 

 ing seedling quickly, but not too rapid or at too high a temperature, otherwise the 

 enzymes will be weakened or destroyed. The enzymes are more sensitive when 

 moist, consequently the heat may be increased as drying proceeds. The process 

 commencing at a temperature between 30° and 35° is increased gradually to 

 50° and 55°. In twelve to twenty-four hours, the malt should appear dry. The 

 temperature is again raised gradually for another twelve to twenty-four hours to 

 8o°-ioo°. The lower the temperature the lighter the color of the malt. Higher 

 temperatures, especially while the malt is moist, produce dark malt. 



