20 PURE CULTURES OF 



from the open coolers brings contamination with bacteria and 

 wild yeasts, especially in the summer and autumn, and this is 

 also the case with the more or less impure air in the ferment- 

 ing cellars, especially where the air is not purified and no ice 

 machines are used ; infection is also readily introduced with 

 the utensils and by the workmen themselves. Even if a pure 

 yeast can be safely used for a longer time than an impure 

 yeast, other conditions being the same, a point is always 

 reached where it is necessary to introduce a fresh pure culture. 

 The time when this must be done can only be determined 

 by analysis. Local conditions and also the time of the year 

 play an important part in this connection ; no fixed rule can 

 be laid down for all breweries ; it must also be borne in mind 

 that different species of low-fermentation yeast do not possess ' 

 the same resistive power to contamination. 



My opponents have taken up this point and have exag- 

 gerated its importance. It has been stated, for instance, that 

 when the pure yeast has been added to the wort from the 

 cooler, it at once becomes reduced to its former impure state, 

 and that pure culture is therefore of no use. It is true that 

 it does again become infected, but it is not true that as a rule 

 it soon becomes contaminated to such an extent that it 

 cannot be used. Even under very unfavourable circumstances 

 the employment of pure yeast is always of advantage, and it 

 must always be preferred to impure yeast. As an example, 

 I may here state that the yeast which in Old Carlsberg we 

 call No. i, keeps sufficiently pure for six to eight months in 

 the brewery mentioned, and the No. 2 yeast (formerly used) 

 which is less resistive, two to four months. This was found 

 to be the case at the time when the whole of the wort was 

 cooled on the open coolers. In fact the conditions here 

 referred to were such as obtain in the great majority of 

 breweries; in the following pages, however, forms of appa- 

 ratus and plant will be mentioned by means of which all 

 infection, so to speak, is excluded. 



