436 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



OUTLINE OF THE PROCESSES OF BREWING. 



INTRODUCTION. 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 constitutes 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 consump- 

 tion. 



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 

 12.50. 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 favorable. 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 amylase 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 cellu- 

 lose. 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 germinating 

 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, conse- 

 quently the heat may be increased as drying proceeds. The process commencing at 

 a temperature of 30 to 35 is increased gradually to 50 or 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 80 or 100. The lower the temperature 

 the lighter the color of the malt. Higher temperatures, especially while the malt is 

 moist, produce dark malt. 



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

 in special machines. 



WORK or ENZYMES AND BACTERIA. The malt is first crushed by press- 

 ing between rollers to facilitate the work of the enzymes and the dissolving 

 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 



