Utilization of nitrogen compounds in the fermentation of Must Garnacha and Chardonnay inoculated with different strains of Saccharomyces cerevisiae. Content of biogenic amines in the wines

In this Doctoral Thesis the influence of three Saccharomyces cerevisiae yeast strains (Na33, D47 and K1M) on the evolution of nitrogenous compounds during the fermentation of garnacha and chardonnay musts has been studied. In both cases the results are compared with non-inoculated fermentations which serve as a control. In the garnacha samples, independently of the inoculated yeast strain, the ammonium rapidly disappeared from the medium in all cases and the amino acids were consumed to a great extent and in a similar way at the beginning of fermentation. This was probably due to the fact that the indigenous flora made an important contribution at the initial process. During the second half of fermentation the amino acids were excreted in all cases except where the Na33 strain had been implanted. In this sample the nitrogenous compounds were consumed up to the end of fermentation. This evolution indicates a high tolerance of this strain to the toxic effects of ethanol. The excretion of amino acids was especially pronounced in the samples inoculated with the killer yeasts D47 and K1M. This was possibly due to the effects of the toxin killer which these yeasts excrete on sensitive strains present in the medium.; In the chardonnay samples differences in the nitrogen utilization were appreciated from the onset of fermentation. This was probably due to the fact that the contribution of the indigenous flora was less. In the sample inoculated with the D47 strain, the ammonium was consumed more slowly than in the samples inoculated with the Na33 and K1M strains; the amino acids were also consumed less and more slowly in the former sample than in the other two. In the control, the ammonium was not totally consumed and the amino acids were hardly assimilated during the fermentation, as the yeast population was probably very low. This control sample fermented very slowly, giving a wine with a great deal of residual sugar, a low alcohol concentration and high volatile acidity. None of the strains under study showed pronounced aminogenic activity. So, all the rosé and white wines showed levels of biogenic amines lower than those necessary to provoke toxicity or negative effects on the aroma.