220 "DISEASES" OF BEER, 



more and more plentiful from June to August, so that the 

 infection to which they gave rise reached its maximum in the 

 latter month. After that there was again a decrease. In 

 the years 1878 and 1880 the infection was greatest in August 

 and September, the maximum occurring at the beginning of 

 the latter month. At other times of the year yeast cells were 

 very scarce. August and September are, as regards infection 

 with wild yeasts, the two most dangerous months for breweries. 



The open coolers afford the means by which these harmful 

 organisms generally gain access to the brewery ; sometimes, 

 however, they can gain admission directly to the fermenting 

 cellar. More rarely they become introduced into the beer in 

 the lager casks ; but even when this occurs, the infection will, 

 under normal conditions, be of no consequence, as we have 

 seen above ; this at least holds good for the species which I 

 investigated. As long as the temperature of the wort on the 

 coolers is at its highest, the yeast cells are either killed, or, at 

 any rate, their further development is prevented. It is only 

 when the temperature falls that budding can commence. 

 When the aerated and cooled wort is run from the coolers 

 into the fermenting vessels, living yeast cells will become 

 deposited in the pipes, and will be able to multiply in the 

 small quantity of wort which remains in the latter. In this 

 manner a multitude of disease germs may be produced. The 

 next portion of wort will thus become more strongly infected 

 than the first, and the importance of a frequent and thorough 

 cleansing of the pipes and their unions is evident, and this, 

 also, of course applies to the coolers and filter bags. The 

 dangers of the latter have been clearly demonstrated by Will 

 in the ' Zeitschr. fur das ges. Brauwesen,' 1892. It is of 

 great importance to add the pitching yeast to the wort in 

 the fermenting vessels as soon as possible, in order that the 

 struggle with the dangerous foreign organisms may be com- 

 menced at once. 



The dust from fruit gardens is, however, not the only source 



