from which it derives its flavour and aroma, and, in a word, everything which gives it a value in the eyes of the consumer. It very often happens, especially in badly-managed breweries, and more particularly in those in which several beers are manufactured, that the yeast is a mixture of different ferments. The evil effects of such a mixture are experienced in the course of manufacture, and still more so in the beer after manufacture. Brewers in good “low” fermentation breweries, who brew what is called _stock_ beer, during the winter months, for consumption in summer, up to August and September, are very anxious to prevent the development of a _vinous_ flavour in beers of this kind. According to our observations, this vinous flavour seems to be principally due to an intermixture with the pitching yeast of _saccharomyces pastorianus_ or its varieties, one of the peculiarities of which ferment is that in the course of time it imparts a decided vinous flavour to beer. If this ferment were not present amongst the yeast-cells—and here we are speaking of an absolute, so to say, mathematically absolute absence—the beer produced would gradually grow old in the store cellars, without ever acquiring any vinous flavour, properly so called. This vinous flavour develops more especially in English beers when these are kept. It is an easy matter to show that in English beers, after their manufacture, _saccharomyces pastorianus_ and the ferment which we have termed _caseous_, which also imparts a peculiar flavour, form almost exclusively, notwithstanding the fact that the yeast used in the manufacture of English beer is a ferment essentially distinct from _saccharomyces pastorianus_. The secondary fermentation which takes place in “high” and “low” beers stored in cask after manufacture, is very often due to this same ferment, which may be recognized by elongated jointed cells, at times more or less ramified, as well as by the influence which it exercises upon the flavour of the beer.