166 MICKO-ORGANISMS AND FERMENTATION. 



siderable number of different species of yeast have been tried 

 on a large scale and under identical conditions, and where 

 the attenuation, taste, odour, time of clarifying, and permanence 

 as regards yeast turbidity, etc., etc., have been found to differ 

 for each individual species. 



HANSEN'S epoch-making work on the disease-yeasts (1883) 

 have shown, from another point of view, the marked differ- 

 ences amongst the Saccharomyces species in their action on the 

 nutritive liquid ; he discovered groups of the so-called wild 

 yeasts, which bring about detrimental changes in beer, whilst 

 others were found to be harmless. Amongst the former, again, 

 there are some which communicate a bitter taste and disagreeable 

 odour to the beer (Sacch. Pastorianus /.) without as a rule 

 producing turbidity ; whilst others only fully develop their 

 activity in a late stage of the secondary fermentation, and 

 cause the beer to become turbid (Sacch. Pastorianus III. and 

 Sacch. ellipsoideus II.). The latter effect is due to the abundant 

 yeast deposit formed in a comparatively short time after the 

 finished beer has been drawn off, which rises at the slightest 

 movement of the liquid. It is only when these species 

 Sacch. Pastorianus /., Sacch. Pastorianus III., and Sacch. 

 ellipsoideus II. are introduced into wort at the commencement 

 of fermentation that they are able to induce disease. The 

 addition of disease-yeast to beer in the store casks or to drawn 

 beer has no appreciable effect ; the inoculation of bottled beer 

 with Sacch. ellipsoideus II. will only take effect when the beer 

 has been very strongly infected. The main result of his work 

 is the proof that the danger of infection lies in the pitching-yeast. 

 These diseases have led to very great difficulties and have 

 caused considerable losses in breweries. HANSEN'S observations 

 on the disease-yeasts have been confirmed and extended by 

 the author, GRCENLUND, WILL, LASCH^. KOKOSINSKY, KRIEGER, 

 WINDISCH, and P. LINDNER. Wild yeasts can also bring about 

 disturbing effects in top-fermentation breweries. For instance, 

 the so-called " summer-cloud " of Australian beers is caused, 

 according to DE BAVAY, by a wild Saccharomyces species. 

 This organism causes turbidity and imparts an acid, bitter 

 taste to the beer. In English high-fermentation beers the 

 author found yeasts of the Saccharomyces anomalus type which 



