STUDIES ON FERMENTATION. 15 



is derived, a diflferent and inferior variety is accidentally 

 mixed with that which we intend to use ; in such a case, 

 the inferior variety, the product of which will possess an inferior 

 quality, will exercise such an influence on the brewing as to 

 induce the belief that disease must be present. The microscope, 

 if consulted, will reveal no special organism, nor any of those 

 diseased ferments of which we have given specimens. It is in 

 the study of yeast that we must endeavour to find the cause of 

 the results we observe. This point, which is of the greatest 

 importance to brewers, will become clearer as we proceed. 



If we examine the practices of the beer trade, in its 

 retail as well as in its export branches, we shall find that 

 many of them aftbrd evidence of the liability of the beer to 

 deteriorate. We may cite some of these. When taken out of 

 the ice-cellars, the beer is kept in casks of small capacity, that 

 it may be the sooner consumed ; when exposed to a high tem- 

 perature, the beer will not keep sound for any length of time, 

 but will speedily effloresce with mycoderma vini or mycoderma 

 aceti. 



Beer which is intended for bottling should not be kept for 

 more than a month or six weeks. Even in bottling we may 

 perceive the tendency of the liquid to deteriorate.* It is neces- 

 sary that the bottles, immediately after being filled, should be 

 laid on their sides for twenty-four or forty-eight hours ; they 

 ma}'- then be placed upright ; the reason for this is that the air 



* To preserve bottled beer from deterioration, some bottlers employ, 

 at the moment of filling, a small quantity of bisiilpliite of lime. Others 

 heat the bottles to a temperature of bb° 0. (131° F.) In the north of Ger- 

 many and in Bavaria, this practice has been widely adopted since the 

 publication of the author's " Studies on Wine," and some of M. Velten's 

 writings. The process has been termed pasteurizaiion in recognition of the 

 author's discovery of the causes of deterioration in fermented liquors, and 

 of the means of preserving such liquors by the application of heat. Unfor- 

 tunately this process is less successful in the case of beer than in that of 

 wine, for the delicacy of flavour which distinguishes beer is affected by 

 heat, especially when the beer has been manufactured by the ordinary 

 process. This effect would be less felt in beer manufactured by the 

 process which is advocated in this work. 



