Changes in concentration of nitrogenous compounds during fermentation of white grape musts at pilot plant scale

Five vinifications were performed in 500 L tanks using two musts of the Malvar white grape variety. Four vinifications were carried out with or without the addition of sulphur dioxide by spontaneous fermentation and by a mixed culture of yeasts (Kloeckera apiculata, Torulaspora delbrueckii and Saccharomyces cerevisiae var ellipsoideus). A fifth experiment was performed with the addition of sulphur dioxide and the inoculation of a commercial active dry yeast (Saccharomyces cerevisiae 71B). The decrease in amino acids during fermentation was similar in all the experiments carried out on the same must in which there was no malolactic fermentation, regardless of the species of yeast conducting the fermentation, the free amino acid content of the corresponding must or whether sulphur dioxide was added to the musts or not. There was a smaller decrease in free amino acid concentration in wines where malolactic fermentation took place. This could be related to the release of amino acids from the wines' peptides by the peptidase activity of lactic acid bacteria.