26 STUDIES ON FERMENTATION. 



which are foreign to the composition of alcoholic ferment, 

 properly so called, the flavour of the beer is more or less un- 

 satisfactory, according to the abundance or nature of these 

 minute organisms. Moreover, when a finished beer of superior 

 qual'ty loses in the course of time its agreeable flavour, and 

 becomes sour, it may readily be shown that the alcoholic 

 ferment in the deposit existing in bottles or casks, although 

 originally pure, at least in appearance, becomes gradually 

 intermixed with these same filiform ferments or other ones. 

 These facts may be deduced from what precedes ; nevertheless, 

 some prejudiced minds might perhaps urge that these foreign 

 ferments are the consequence of some diseased condition, 

 produced by circumstances of which we know nothing. 



Although this gratuitous supposition may be difiicult to 

 sustain, we shall endeavour to corroborate our preceding obser- 

 vations by the method of experiment which will be seen to be 

 the more decisive. 



This method consists in proving that beer never possesses any 

 unpleasant flavour, so long as the alcoholic ferment, properly 

 so called, is not associated with foreign ferments ; that this also 

 holds good in the case of wort, and that wort, liable to change 

 as it is, may be preserved in a state of purity, if it is kept under 

 conditions that protect it from the invasion of microscopic 

 parasites, to which it presents not only favourable nutriment, 

 but also a field for development. 



By employing this second method we shall, moreover, have 

 the advantage of proving with certainty a proposition that we 

 just advanced, and showing that the germs of these organisms 

 proceed from the particles of dust which the common air wafts 

 about and deposits on every object, or which are spread over 

 the utensils and materials used in a brewer}-, materials that 

 are naturally charged with microscopic germs, which various 

 changes in the store-houses and maltings may multiply to an 

 indefinite extent.* 



* If we put a handful of germinating barley from a maltster's cistern into 

 a little water, and examine drops of the liquid, after it has become 



