Variation Of Yeast Assimilable Nitrogen In Wine Grapes And The Fermentation Process

Nitrogen is a type of macronutrient for wine yeast fermentation.Therefore,it is important to learn nitrogen levels exist in grape berries and the utilization of nitrogen nutrition by yeasts in controlling the fermentation.During the alcoholic fermentation,yeasts could absorb the free α-amino acids with the exception of praline,small molecular peptides and ammonium nitrogen,known as yeast assimilable nitrogen(YAN).The YAN contents of wine grapes in Rongzi vineyard,in modle wine fermentations,smaller container fermentations and pilot scale fermentations were investigated in this study.The results were as following:1.At the harvest time,YAN contents of all varieties were beyond 140 mg N/L,reaching the YAN amount of Saccharomyces cerevisiae required to complete the normal alcoholic fermentation.YAN contents showed decreased in three varieties of three vineyard plot and increased in only two varieties of two vineyard plot 5-15 days before harvest in 2011.2.In the modle wine fermentation,the relatively higher YAN could increase the starting rate of fermentation and reduce the time to complete the fermentation.The fermentation rate of different strains also varied at the same YAN concentration.3.In the modle wine fermentation,the utilization of amino nitrogen by the tested strains decreased with the increase of YAN concentration.The utilization rate of amino nitrogen in the same concentration of YAN was different:NX11424>RC212>NX8422>LFP525.4.In the modle wine fermentation,most of the ammonium ion nitrogen was absorbed in the early fermentation by the tested strains.With the increase in YAN concentration,ammonium ion nitrogen utilization rate was higher.5.The amount of H2S did not increased significantly with the rising concentration of YAN.YAN concentration and the H2S content in the final wine showed a negative correlation in majority of the fermentaions.6.The impact of YAN concentration on total acid content differed significantly in the modle wine fermentation.7.In small and pilot scale fermentation,YAN utilization by the tested strains mainly happened before vigorous stage.