Effect of nitrogen nutrition on yeast ecology and alcoholic fermentation

Mestrado Vinifera Euromaster - Instituto Superior de Agronomia - UL

Wine is an alcoholic beverage obtained from the fermentation of grape juice. Alcoholic fermentation is the main process to obtain the final product but of course other reactions take place during the transformation of grape juice into wine. Yeasts are one of the fundamental microorganisms to realize the alcoholic fermentation, that leads sugars to be transformed in ethanol and to development of other compounds. Yeasts as known are living organisms so they need nutrients for their reproduction and often the lack of some important nutrients can lead to a stuck or slug in their metabolic activity. One of the most important nutrient for yeasts growth is Nitrogen, main component of aminoacids and proteins, that constitute the basic structures of the microorganism.In winemaking, both in the cellar and in the vineyards, the addition of nitrogen under different circumstances is a common practice. Nitrogen seems to influence not only fermentation rate and yeast growth but many of the fermentation product such as ethanol, acetic acid, glycerol, and of course residual sugars and the production of some off flavours,such as hydrogen sulphide. Although each yeast, species and strains,showed different behaviour both in the fermentation rates, growth and production of different metabolites. Not only the quantity and kind of Nitrogen source but also the timing of the addition seem to influence all these aspects in slightly different way between different strain. The nitrogen compounds especially apparently ammino acids showed also a particular relationship with the production of esters of higher alcohols and other compounds but the pattern of ester production is still uncertain. In this study there will be considered the main aspects of nitrogen nutrition, how it affects the yeasts ecology and the different conditions on which it is used and also different strains and species requirements