23° Journal of Agriculture. [lo April, 1909. 



organic nitrogenous compounds (albuminoi.l substances and others), must contains 

 small quantities of ammoniacal salts, and that, even in presence of readily assimil- 

 able organic nitrogen, yeast absorbs ammoniacal nitrogen with great ease, only 

 leaving a few milligrammes of ammonia in the wine, whereas the must contained 

 as much as 120 milligrammes per litre. 



In the same article he deals with the utility of organic nitrogen which, 

 though less readily absorbed, constitutes the greater part of the nitrogen 

 supply of the yeast — 



Nevertheless, experiments prove that organic nitrogen is unable to thoroughly 

 supplement the complete absence of ammonia under usual conditions of vinous fer- 

 mentation, and it is this that explains the almost invariably positive influence of 

 ammoniacal salts added to musts in order to increase the activity of fermentation. 



In concluding, Laborde further states— 



In a general way the ammonia naturally contained in must is greedily utilized 

 by yeast. 



In the Revue de Viticulture of 20th Julv. 1901, M. E. Kayser dealing 

 with the use of phosphate of lime in winemaking says — 



Furthermore, ammonium phosphate seemed to produce more marked eff^ects than 

 bicalcic phosphate; besides, we know from other experiments that ammonium phos- 

 phate produces an energetic action on the progress of the alcoholic ferment. M. 

 Martinand has shown us that a dose of 10 grammes per hectolitre (20Z. per 100 gallons) 

 of the latter salt was sufficient to invigorate a languishing alcoholic fermentation, 

 even at low temperature. It is also known that slight traces of this salt enable the 

 last traces of sugar in a wine to be transformed into alcohol. 



Semichon in his Traite dcs Maladies du ziti, p. 611, states that 

 amongst yeast stimulants, ammonia salts, especially phosphates, which 

 contain phosphoric acid as well as ammonia, hold first place. He describes 

 the tW'O principal phosphates of ammonia, viz., the mono-ammonia or 

 acid phosphate, and the bi-ammonia or crystallized form. The acid 

 reaction of the former is an advantage, in addition to its lower price ; it 

 is the one most frequently employed. 



From the above references it will be seen that yeast most easily absorbs 

 the nitrogen it requires in an ammoniacal form. The addition of an 

 ammonia salt, towards the close of fermentation, at a time when the vitality 

 of the yeast plant has diminished and when the proportion of ammonia 

 salts present has been considerably reduced has, therefore, a powerfully 

 stimulating action. 



Almost any ammonia salt may be used but, as yeast requires phosphatic 

 as well as nitrogenous food, phosphate of ammonium is to be preferred. 



The Effects of Excessive Aeration. 



Pasteur showed long ago that yeast behaves very differently in the 

 presence and in the absence of oxygen. In the former case it grows very 

 actively, producing a large weight of its own substance at the expense of 

 the sugar and other food substances at its disposal, but converting a rela- 

 tively small proportion of sugar into alcohol. Under these conditions its 

 vegetative growth is greater in proportion to its chemical activity. In the 

 absence of oxygen, its growth is less rapid, but its fermental power is far 

 greater. In other words, the quantity of sugar decomposed by a given 

 weight of yeast is very considerably increased. 



Excessive aeration, by bringing about the growth of a far larger crop 

 of yeast, leads to an increased consumption of the plant food substances 

 present pn the must. In the case of high gravity musts, where there is 

 much fermentati'c^i work to be done, this may result in the exhaustion 



