28 PURE CULTURES OF 



practice. Nevertheless, nothing can be stated as regards 

 their properties until they have been investigated (see also 

 Chapter II). It must also be remembered that laboratory 

 experiments with small quantities give but imperfect informa- 

 tion in this direction ; the trial must be made in the brewery, 

 and under the conditions obtaining in practice. In such a 

 case, therefore, it will be several months before we can obtain 

 the result of the trials.* 



It will be remembered that we generally employ wort 

 gelatine in the preparation of our pure cultures, and that these 

 are grown at a temperature of 25 C. ; under these circum- 

 stances, varieties may sometimes be produced, and although 

 these are only of a temporary nature, they may, nevertheless, 

 now and then give rise to difficulties. Fortunately, this is only 

 rarely the case, and, when it does occur, my earlier method of 

 preparing pure cultures must be adopted that is to say, the 

 single cells must be introduced directly into flasks containing 

 wort, and not into gelatine ; and the growth must take place 

 at low-fermentation temperatures. Under these conditions it 

 is also advisable to introduce several pure cultures of the 

 same species into the same flask. In this way a pure culture 

 is obtained of a single species which, however, is not derived, 

 as is ordinarily the case, from one, but from several individual 

 cells, and it will, therefore, already in the first stage of its 

 development, possess all the peculiarities of the species. 

 There are only very few species and races which show an 

 exceptional tendency to form varieties, and which, therefore, 

 require this elaborate treatment. In most cases the ordinary 

 single-cell culture will at once give a normal fermentation. 



Assuming that we have succeeded with our pure culture, 

 and that we have a vigorous growth of the selected species in 



* The different laboratories in which pure yeast culture is undertaken on my 

 system possess large collections of yeasts which have been tested in practice, and 

 are able to furnish at once a suitable pitching yeast. It is, therefore, only in the 

 rarest cases that there is any occasion to undertake the tedious examination 

 mentioned above. 



