i82 CHEMISTRY OF THE YEAST CELL. 



mashed materials, and finally (in the case of hopped wort), 

 glutin substances and globules of hop resin, to v/hich latter 

 the disagreeable bitter flavour of the head is due. A permanent 

 head of the kind is peculiar to beer, and is not produced in the 

 fermentation of unhopped wort or on wine must ; and one must 

 therefore conclude that the presence of hop constituents is 

 indispensable to the structure of a normal head on beer. The 

 accuracy of this conclusion has been rendered more probable 

 by the results furnished by the experiments of E. Ehrich (L). 



The thickness of the head thrown up by the activity of yeast 

 in woi't, mash and wine must, is dependent — other conditions 

 being equal — on the available supply of the materials, by means 

 of which the initially naked gas bubbles are converted into 

 mucinous bubbles charged with gas. However, the amount of 

 these substances produced by different stocks of yeast, stands 

 in no definite relation to their fermentative activity, i.e. the 

 amount of carbon dioxide liberated in unit time. Hence it 

 will occasionally happen, in comparative fermentation experi- 

 ments, that a relatively high loss in weight {i.e. liberation of 

 carbon dioxide) is noticed in specimens which, from their 

 appeai-ance during fermentation, would seem to have fallen 

 behind considerably. Thus, for instance, in a set of experi- 

 ments conducted by Mueller-Thurgau (IY.) with 25 stocks 

 of fruit and wine yeasts, the one (a Waedensweil cider yeast) 

 that liberated the largest amount of gas fermented its nutrient 

 substratum without the slightest formation of head. So far, 

 no close attention has been devoted to the capacity of the wine 

 yeasts for depositing albuminoid mucinous substances, though, 

 in addition to the above named, other observations have been 

 recorded indicating the existence of this capacity. Thus, for 

 example, the well-known loss of colour in red wines when treated 

 with white-wine yeasts, seems attributable to the action of 

 similai' albuminoids. In contrast to the red-wine yeasts, which 

 are already saturated with colouring matter, the albuminoid 

 mucinous constituents of white-wine yeasts are still in a position 

 to take up tinctorial substances. The case is analogous to that 

 of browned wines when treated with yeast, this procedure, 

 according to Nessler (III.), affording a remedy for the malady 

 in qviestion. The combining and precipitating power of these 

 albuminoid excretions of yeast is probably the cause of the 

 phenomenon — well known in practice, and recommended for 

 vitilisation by H. Mueller-Thurgau (III). — that a wine 

 rendei'ed turbid by bacteria can be cured by pitching with a 

 small quantity of must in active fermentation. This must is 

 very rich in yeast cells, Mueller-Thurgau (Y.) having de- 

 tected about 3 milliards per litre. P. Lindner (XYI.) has 

 reported a similar instance of the cure of a sarcina-ropy white 

 beer by adding yeast and rousing. 



