DISEASES OF BEER 111 



organisms able to produce the diseases. The demonstration by- 

 experiment of the cause of these diseases was worked out by Pasteur, 

 who, as we have seen, estabUshed the fact that there are different 

 micro-organisms inducing different kinds of fermentation, and there- 

 fore if it be desired to procure a pure fermentation, a pure and 

 not a mixed ferment must be used at the commencement; and 

 immediately after the primary fermentation the wine must be 

 " pasteurised " to destroy the disease-producing organisms. In short, 

 disease-producing organisms must either be excluded from, or killed 

 in, the wine. 



By carrying out a large number of experiments, partly with 

 single species of yeast, and partly with mixtures, Hansen was able to 

 declare that many of these diseases were due to particular yeasts. 

 The number of such yeasts is by no means small. Hence we have 

 two groups of yeasts, namely, " culture " or " brewery yeasts," those 

 that are employed in brewing ; and " wild yeasts," occurring widely 

 distributed in nature, and which on gaining entrance to breweries set 

 up diseases in the fermentations. The development of wild yeasts is 

 promoted by vigorous aeration of the beer whilst it is being drawn 

 off, and also through the bottles being badly corked. Beer which has 

 undergone a feeble fermentation, and which has a high extract, is 

 more subject to contamination than a beer which has not. When 

 beer which has remained sound in the larger casks is attacked after 

 it has been drawn off, it is clear that the agent of the disease 

 obtained entrance into the beer from the surrounding air or from 

 unclean vessels. If the infection is not great in amount, it may, 

 particularly in a good beer, have practically no effect. There can be 

 no doubt that some of the Saccharomycetes can live for months in soil 

 and dust, even atmospheric dust, and amongst these may be various 

 disease-yeasts. 



The diseases of wines and beers are various. Generally speaking, 

 the chief forms are comprised in the following simple classifica- 

 tion : — 



1. Turbidities. — (a) Gluten turbidities, or albunainous scud, due 

 to precipitation of albuminoids. 



(6) Chemical suspension and deposits, e.g. calcium tartrate, 

 reduced sulphur scud, resins, essential oils, etc. 



(c) Starch turbidity, due to the presence of unsaccharified starch. 



(d) Yeast turbidity, due to a high content of yeast cells. 



(e) Bacterial turbidity, brought about by fission fungi. 



2. Ropiness, which may be thus classified separately, although 

 doubtless frequently due to a high degree of turbidity. This con- 

 dition of ropiness in wine, formerly attributed to a coagulation of the 

 albuminoids, was traced by Pasteur to a number of organisms 

 of which he described two chief forms, namely, a streptococcus and 



