ALCOHOLIC FERMENTS. 187 



3. Species which attenuate strongly, clarify slowly, and 

 give a normal after-fermentation. The beer is 

 stable against yeast-turbidity. 



As a very significant result of practical experience, and 

 one which shows how pronounced are the characters of many 

 species of cultivated yeast, the fact may here be mentioned 

 that generally speaking the above grouping holds good, even 

 under the different practical conditions obtaining in widely 

 separated countries. For instance, the Carlsberg yeast No. 1 

 gives everywhere a beer which is very stable as regards yeast - 

 turbidity ; other species, which clarify more rapidly, have 

 been found to retain this property everywhere under normal 

 brewery-conditions. 



An example of the permanence of the specific properties 

 under very different external conditions has also been given 

 by Irmisch in a comparative examination of two bottom- 

 yeasts. One of the species gave a low attenuation and 

 multiplied to a very small extent in the wort, whilst 

 the other, on the contrary, gave a high attenuation and 

 possessed the power of multiplication in a high degree ; the 

 course of the fermentation in the two cases also showed 

 marked differences. These differences still obtain on varying 

 the concentration of the wort or the quantity of the yeast, at 

 very different temperatures, also when cultures are employed 

 which have been grown in wort containing diastase, under 

 various conditions of aeration with ordinary wort, and with 

 a specially prepared wort very poor in maltose, in the 

 presence of grains during fermentation, and in solutions of 

 cane-sugar. Likewise in fermentations which were carried 

 on for six months, an examination of the product showed 

 that the typical differences of the two species had not 

 disappeared. 



Besides the beer top-yeasts, there are also certain high- 

 fermentation species which are employed in distilleries and 

 in yeast factories. In recent years a number of distillery 

 yeasts have been prepared in the author's laboratory in 



