SYSTEMATICALLY SELECTED YEASTS. 57 



fermenting cylinder is kept in use for a whole year. The 

 whole apparatus is cleaned before it is again set working. 

 / would emphasise this in mew of the incorrect opinions pre- 

 vailing in some breweries, namely that the fermenting cylinder 

 should be very frequently cleaned ; this is a complete mistake. 

 There is, indeed, nothing to prevent the fermenting cylinder 

 from being used for a much longer time than is the case 

 in Old Carlsberg ; yet, in my opinion, it is as well to clean 

 the apparatus once a year. With proper care the yeast 

 can be transferred to the wort cylinder, and kept there until 

 the fermenting cylinder has been cleaned and sterilised. 

 The arrangement of the apparatus is, in short, such that 

 the cylinder may be cleaned at any time, and as often as 

 required, without losing the pure yeast culture. If we have 

 a pure yeast which works well in practice, it should be em- 

 ployed as long as it keeps pure, i. e. free from infection. It 

 is a great mistake to imagine that a new pure culture should 

 be introduced into the fermenting cylinder at least once a 

 year. When the apparatus is handled with skill and no 

 accident is encountered whilst working with it, the yeast 

 will continually retain its purity. At New Carlsberg, the 

 fermenting cylinder at one time contained a pure culture 

 which was introduced into it more than five years previously. 

 As soon as any infection manifests itself, the yeast will, of 

 course, have to be renewed. As a rule, the brewer will not 

 be in a position to carry out the necessary analysis of the 

 yeast, and laboratories have, therefore, been appointed in 

 which this class of work is made a speciality. 



In using the apparatus, attention must be paid to two 

 main points : (i) that the steaming is sufficient, so that 

 thorough sterilisation is effected ; and (2) that during the 

 process of cooling and whilst the contents of the cylinder are 

 being drawn off, tJie pressure exerted by the sterile air within 

 the latter is in excess of the external atmospheric pressure. 

 When these two conditions are fulfilled, no infection and 



