Production of SO2 Binding Compounds and SO2 by Saccharomyces during Alcoholic Fermentation and the Impact on Malolactic Fermentation

A. Wells, J.P. Osborne


The objective of this study was to investigate the production of SO2 and SO2 binding compounds by wine
yeast and the impact of the production of these compounds on the MLF at various time points during
alcoholic fermentation. Fermentations were observed for a number of commercial wine yeasts in a synthetic
grape juice and Pinot gris juice and SO2, acetaldehyde, pyruvic acid and α-ketoglutarate. Measurements
were taken at multiple time points during the fermentation. Samples were taken from the fermentations
at weekly intervals, sterile filtered, and inoculated with O. oeni strain VFO to induce MLF. Significant
differences between the amount of SO2, acetaldehyde and pyruvic acid produced by the various yeast
strains were noted. Some yeast strains such as FX10, CK S102, F15 and M69, produced significantly higher
SO2 concentrations than other yeast strains and MLF was inhibited in these wines. Insignificant free SO2
was measured, indicating that bound SO2 rather than free SO2 was responsible for inhibition. At almost
all time points of the alcoholic fermentation, acetaldehyde bound SO2 was determined to be the dominant
species of bound SO2 present, suggesting that MLF inhibition by bound SO2 was due to acetaldehyde
bound SO2.

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