128 MOKPHOLOGY AND LIFE-HISTORY OF YEASTS. 



duction vessel, but must be first fi-eshened up by prepar- 

 ing a re-inoculation, which in turn is used to inoculate a 

 fresh nutrient solution as soon as development is in full swing. 

 The operation is several times repeated, according to circum- 

 stances, until one is able to assume that the film cells present 

 in the first inoculation of sedimental yeast have been entirely 

 suppressed. The beginner cannot be too strongly advised not to 

 regai'd the task of yeast cultivation as completed by the pre- 

 paration of the pure cultures, but rather to keep the latter 

 under constant supervision, examination and care. Neglect of 

 these precautions, and, in the case under consideration, the 

 use of sedimental yeast containing film cells, may, under certain 

 circumstances, lead to irregularities in the progress of fer- 

 mentation on the large scale, diminution in the quality (flavour, 

 &c.) of the product, and hence to unpleasant consequences for 

 the yeast cultivator. Cases in point have been recorded by 



A. JOERGEXSEN (YII.). 



This, however, must not be held to imply that the film cells 

 are the cause of all the unwelcome alterations that may appear in 

 beer yeasts. On the contr-ary, other forces are here in opera- 

 tion ; and from this side also, as already mentioned, we ari-ive 

 at the wide field of variation in the yeast cell, a domain in 

 which, as will be shown in a later chapter, Hansen, by his ex- 

 tensive experimental researches, has been our pioneer. More- 

 over, it should be recalled that Raymann and Kruis (I.) were 

 able, by means of yeast derived from old film cells, to produce 

 good beer that could not be distinguished from that obtained by 

 the aid of normal yeast. This harmonises with the results 

 obtained by Alb. Kloecker (privately communicated to the 

 authoi') with Carlsberg bottom-yeast No. I. and No. II., Sacch. 

 cerevisicB I. Hansen, Marienthal yeast, and Will's No. 2 stock 

 yeast. 



Will's observations bring to mind the flying yeast (Flughefe) 

 so dreaded by the brewer, i.e. yeast cells which are of smaller 

 size than those of the sedimental yeast, and, instead of settling, 

 continue to swim in the beer, and thus retard clarification. 

 This presumptive relation has not yet been more closely investi- 

 gated, but the researches of Hansen and others have placed 

 beyond doubt that this phenomenon is in many cases attributable 

 to the presence of wild yeasts. Another point that lequires 

 closer examination is the part played, in the maturing of beer, 

 by the film cells produced within the liquid. Finally, investi- 

 gation from this point of view is also desirable on the problem 

 of the cause of flocculence in the process of making pressed yeast 

 by the new, so-called aeration or wort process, which differs 

 chiefly from the Viennese method (§255) in the thick mash 

 being replaced by a clear mash as nutrient medium ; this, after 

 pitching, being well i-oused by aeration, whereby the reproduc- 



