lo Feb., 191 1.] Pure Yeasts or '' Levures." 109 



PURE YEASTS OK " LEVURES." 



F. dc Cdstella, Government Yiticulturist. 



Nearly forty years have elapsed since Pasteur's remarkable investigation 

 of alcoholic fermentation — the transformation of sugar into alcohol, which 

 is brought about through the agency of certain micro-organisms known to 

 science as saccharomyces and more generally as alcoholic ferments or 

 yeasts.* He showed that most of the diseases of wine and beer are 

 caused by bacteria. He also showed that several distinct varieties or races 

 of yeasts exist, some of which act in a more satisfactory manner than 

 others. In order to improve fermentation, two logical courses were open — 



1. To protect the yeast from the competition of injurious bacteria. 



2. To employ a variety of yeast capable of insuring a maximum of 



quality in the resulting product. 



The second of these brings us to the subject of the present article. 



Pasteur's discoveries and the research work conducted by his successors 

 have revolutionized the art of brewing to such an extent, that a properly 

 equipped bacteriological laboratory is now to be found in every up-to-date 

 brewery, and that the use of pure yeasts has become more and more 

 general in them. This is in marked contrast to what has, until quite 

 recently, obtained in the closely allied sister fermentation industry of 

 wine-making, in which spontaneous fermentation has been the almost 

 invariable rule. 



It is true that similar methods to those which proved of such value to 

 the brewer were attempted many years ago. The results, however, were 

 inconclusive and not up to expectations ; and in this we have the explanation 

 of the slow spread of the use of cultivated yeasts in the wine cellar. 

 Reasons for this contrast are not far to seek. The spontaneous nature 

 of grape juice fermentation renders the use of yeast unnecessary, and for 

 many centuries wines of the very highest quality have resulted from the 

 development of the ferment provided by Nature in the shape of the bloom 

 on the outside of the berry. In the case of beer, yeast of some kind 

 must be added, and it is easy to understand the difference in the results 

 to be obtained from the development of a good, as opposed to that of a 

 bad yeast, and the opportunity for improvement in the yeasts used. 



Another radical difference between wine and beer must also be remem- 

 bered. In the case of the latter, the yeast is added to a medium, sterilized 

 by heat, so that it has every opportunity of developing without interference 

 from organi.sms previously existing in it. With grape juice, preliminary 

 sterilization is of difficult application and the added yeast finds itself face 

 to face with all the germs naturally present in the bloom of the grape. 

 Some, at least, of these have a very good chance of finding in the juice 

 \ medium more suitable for their development, than for that of the 

 added yeast. 



Hence, it vcrv frciiiit'iith has li.ipi)(MU'd that the added yeast has 

 played little or no part in the fermentation it was intended that it should 

 i)ring alM)ut. The case is exactly similar to that of a cereal crop sown 

 in a verv dirty padrkKk, in which but little of the .seed which was .M>wn 

 may live to yield any grain at harvest time. It is true that the addition 

 of the cultivated yeast in a state of active growth should give it ;vn 



• Tlio FrPiicli word Irvure l)<"inK tho i-xnet oqiilviilont of tlip KiikHsIi " yen.xt," tliorp *cem* no nood 

 fur the retetitidii of tlic foninT in the Australinii vitiriiUuriil vi)i-nl)iiliiry. 



