lo April, 1909.] The Nitrogen Food of Yeast. 229 



THE XITROGEN FOOD OF YEAST AND ITS BEARING 

 ON THE MAKING OF FULL-BODIED DRY WINES. 



F . de Castella, Government Viiiculturist. 



A new type of wine has been developed in Australia since the inception 

 of our export trade in wine to London. The full-bodied dry wines which 

 constitute the bulk of our shipments are different from, anything produced 

 in the wine countries of Europe, and in the making of them difficulties 

 have to be surmounted which do not occur in the fermentation of wines 

 of lower alcoholic strength. 



The chief of these is to insure the conversion into alcohol of the last 

 portions of the sugar contained in the must or grape juice. Yeast grows 

 with difficulty in the presence of much alcohol ; as the proportion of this 

 substance increases the conditions of life become more and more difficult 

 for its continued existence. Of recent years, the control of temperatures 

 during fermentation has received considerable attention with most bene- 

 ficial results to the quality of these full-bodied wines, but there is another 

 point which merits attention and in connexion with which material aid 

 can be given to the yeast plant. This is the amount of yeast food present 

 in the fermenting mass, the exhaustion of which is in some cases respon- 

 sible for the premature cessation of fermentation. 



Yeast is a vegetable organism and, in common with other plants, its 

 vital activitv is not possible, unless a sufficiency of food be available. Being 

 a fungus, it derives its carbon from the grape sugar instead of taking it 

 from the air like higher, green leaved plants. Like these, however, it 

 also requires a sufficiency of the three dominant plant food elements, nitro- 

 gen, phosphoric acid and potash. If any of these be deficient its growth must 

 cease and fermentation remain incomplete, even though the alcohol con- 

 tents are not sufficient to prevent a continuance of its life. Of these three 

 elements, nitrogen is the most important ; potash is present in ample 

 quantities in the shape of cream of tartar, whilst phosphoric acid appears 

 to be seldom deficient. Nitrogen, however, is not always abundant enough 

 and, what is more important, a sufficiency of it is not always present in a 

 form acceptable to the yeast plant, the requirements of which in this direc- 

 tion are peculiar. 



The Importance of Ammonia. 



In the must, nitrogen exists in several forms — chiefly as albuminoid sub- 

 stances, peptones, nitrates and ammonia salts. The last named is the 

 form in which it is most readily absorbed by yeast. As fermentation 

 advances, the amount of ammoniacal nitrogen present in the fermenting 

 mass shows a progressive diminution. Nitrates appear to be quite useless 

 to the yeast plant.* 



M. J. Laborde, in an article dealing with the nitrogen contents of wine 

 in the Revue de Viticulture of ist October, 1898, writes — 



Grape juice, like all natural sweet juices, contains nitrogen in a form essentially 

 assimilable for a large number of microscopic organisms and especially for the 

 yeasts of alcoholic fermentation. M. Duclauxf proved in 1866 that, apart from 



* Paccotet, Viiiijication, p. 49. 



t Sur Vabsorptioii d'animoniaque, &c., Annalcx de VEcole Normale Sitperigure, I., II., 1866. 



