93 



process being determined by the iodine test. The solution is then drawn oft' and 

 boiled, hops being added. The hops give to the beer a bitter taste, besides aid- 

 ing in its keeping; they also, by means of their tannic acid, facilitate the coagula- 

 io;i of the protein material, which is giing on by means of the boiling. The 

 wort is then cooled rapidly, after which it is ready for fermentation. 



There are diflerent methods used by manufacturers in the fermenting of the 

 wort, but l)y whatever method there are always three stages into which the fer- 

 mentation can be divided : the main fermentation, which begins in a short time 

 after the yeast is added, during which time the maltose is decomposed, new yeast 

 ceils are formed and a i-ise in temperature takes place; the after fermentation is the 

 next stage; maltose continues to be decomposed, the formation of yeast cells 

 nearly ceases, the yeast settles and the beer clears ; ihe last stage is the still fermen- 

 tation, maltose is still decomposed, dextrine is changed into maltose, but no new 

 yeast cells are formed. The main fermentation lasts from four to eight days; the 

 other stages vary in time, and are controlled by changing the conditions. 



In the experiments which I made the study was on the main fermentation, 

 and was to determine the ratio between the amount of alcohol and the number of 

 yeast cells formed. Wort, that was ready for fermenting, was obtained from one 

 ■of the breweries, filtered, then placed in flasks, and sterilized by the fractional 

 sterilization method. Two litres were used in a tlask. Pure yeast, which had 

 heen separated from a compressed cake by the Hansen orientation method, was 

 used ; a colony, which had been grown from a single cell, was placed in 5cc. of 

 wort in a test tube, and allowed to remain there twenty-four hours. This quan- 

 tity was then added to the wort in the flask. This corresponds to the method em- 

 ployed in breweries, where a quantity of yea^^t is first grown in a small amount of 

 wort; this quantity, called " j)itching yeast," then added to the main quantity 

 that is wanted for beer. After the addition of the pitching yeast, the flask was 

 shaken thoroughly, and 1 cc. taken out with a sterilized pipette, for the purpose 

 of counting the yeast cells. To the 1 cc^. was added 1 cc. dilute H ^ SO ^ for pre- 

 venting further growth of yeast, and also for dilution. The wort was kept in a 

 •constant temperature oven at 25°c., this being a temperature at which the yeast 

 grows vigorously. 



At the end of every twenty-four hours for seven days the flask containing the 

 wort was shaken vigorously for some time, so as to distribute the yeast cells thor- 

 oughly, then 1 cc. taken in the manner described, and also 200 cc. for determin- 

 ing the alcohol. The alcohol was estimated by direct distillation; 100 cc. was 

 ■distilled over, then an accurately tared pycnometer of 50 cc. capacity used for 

 the weighing. When the temperature varied from 15.5°c., Allen's formula for 



