98 BACTERIA. 



drying the grain to kill the young plant and so prevent 

 further sprouting. To obtain a fermentable liquid, a solution 

 of the sugar and of the other soluble constituents of the 

 malt is made in hot water ; this is allowed to cool to a 

 temperature of about 16 C. A certain quantity of " high " 

 yeast is then added to the solution, and during the pro- 

 cess of fermentation the temperature may run up to 1 8 or 

 20 C. After a time little bubbles of carbonic acid gas are 

 seen to rise, the yeast increases in quantity and gradually 

 rises to the surface, whence it is skimmed off, and may be 

 again used to set up fermentation, if still pure. The fluid 

 becomes bright, clear, and sparkling (from the presence of 

 carbonic acid), and contains a certain proportion of alcohol ; 

 whilst the sugar, if the fermentation has been properly 

 carried on, has almost entirely disappeared. This is what 

 is known as " high yeast " fermentation. It goes on most 

 readily at a comparatively high temperature, and the yeast 

 rises to the surface as it is formed, bringing up with it 

 a certain proportion of the impurities contained in the 

 liquid, the heavier particles falling to the bottom. The 

 process goes on rapidly, but unless great care is taken it 

 is said that there is a danger that impurities may get in, 

 and that secondary fermentations may be set up, though this 

 is a position now scarcely tenable in these days of India Pale 

 Ales. 



The "low" fermentation is brought about by a ferment 

 which acts more slowly, at a much lower temperature, and 

 through the agency of yeast-cells that sink to the bottom as 

 they are formed. This fermentation of beer must be allowed 

 to go on at a temperature of from 4 to 5 C., and the fluid 

 is not completely ripened until the end of about fourteen 

 days. This low temperature is maintained in the small 

 breweries by inverted cones of metal, containing ice, which 

 are allowed to float in the fermenting liquid ; they are kept 

 constantly supplied with ice, and the number used is regulated 

 according to the temperature of the external air. In the larger 

 breweries the same results are obtained by passing currents 

 of purified cool air over the surface of the fermenting tanks, 

 which, as a rule, are underground, so as to allow of the 

 temperature being maintained at an extremely equable 

 level. Formerly all beer was made by the high fermenta- 

 tion process, a system that still prevails in this country, but 



