| In this paper,the synthetic ice grape juice inoculated ST active dry yeast was used to ferment icewine.By determining the yeast density,the contents of reducing sugars,glycerol,assimilable nitrogen,acetaldehyde,ethanol,acetic acid,ethyl acetate,higher alcohols,biogenic amines and organic acids in the fermentation process,the effect of the types of nitrogen sources,inoculation rates and assimilable nitrogen concentrations on icewine fermentation were studied.The conclusions are as follows:Yeast powder and mixed amino acids were used as assimilable nitrogen sources for icewine fermentation.When the assimilable nitrogen supply was 180 mg/L,the assimilable nitrogen consumption of the two groups was basically the same.Compared with mixed amino acids,the fermentation using yeast powder consumed more reducing sugars and produced more ethanol,glycerol,acetic acid and ethyl acetate,increasd by 78.95%,90.38%,42.84%,99.35% and 23.8%,respectively.Higher alcohol production increased but not significant.It can be seen that yeast powder as a nitrogen source promotes the consumption of reducing sugars and the formation of various products in icewine fermentation to varying degrees.Therefore,yeast powder can be used as a nitrogen source for icewine fermentation,which will help speed up the fermentation at limited level and reduce icewine quality at higher level.In the icewine fermentation with different inoculation rates,yeast density,the content of glycerol,acetic acid,ethanol,total biogenic amines and total organic acids,and the consumption of reducing sugar and assimilable nitrogen increased with increasing inoculation rates.There was no significant difference in the contents of biogenic amine and organic acid among the groups with different inoculation rates.The maximum contents of acetaldehyde and ethyl acetate were reached at the inoculation rate of 0.4 g/L.The maximum content of total higher alcohol was reached at the inoculation rate of 0.5 g/L.The fermentation time to achieving alcohol content of 10% shortened while the inoculation rate increased,which was 15 days at the inoculation rate of 0.5 and 0.6 g/L,15-20 days at 0.3 and 0.4 g/L,and more than 20 days at 0.2 g/L.The results showed that fermentation with lower inoculation rate would extend the fermentation time and reduce the product contents;fermentation with higher inoculation rate would produce more substances harmful to the taste and quality of icewine.Therefore,the appropriate inoculation rate should be 0.4 or 0.5g/L for icewine fermentation.Assimilable nitrogen concentrations of 250,350,450 mg/L and inoculation rates of 0.25,0.5,0.75 g/L were used for the orthogonal experiment of icewine fermentation.Yeast density in the fermentation group with the same inoculation rate increased with increasing assimilable nitrogen concentration.The contents of glycerol,acetic acid,ethanol,ethyl acetate,total biogenic amine,total organic acid,and the consumption of reducing sugar and assimilable nitrogen increased with increasing assimilable nitrogen concentration and inoculation rate.Acetaldehyde and total higher alcohol content decreased with increasing assimilable nitrogen concentration and inoculation rate.The content of each product in the 250N+0.25 Y group was lower than that in the other groups,which indicated that the low nitrogen concentration at low inoculation rate could cause slow fermentation by slow down yeast growth,which was not suitable for icewine fermentation.To achieving alcohol content of 10%,both 250N+0.25 Y and 250N+0.5Y groups fermented for 30 days,both 450N+0.5Y and 450N+0.75 Y groups fermented for 15 days,and the rest groups fermented for 20 days.It can be concluded that the inoculation rate should be appropriately increased to shorten the fermentation process at insufficient initial nitrogen concentration,and should be appropriately reduced at excess initial nitrogen concentration to ensure icewine quality by reducing the content of acetic acid,ethyl acetate,biogenic amines and other substances. |
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