Research Accomplishments: As previously suggested, nitrogen-deficient grape juices produced higher concentration of hydrogen sulfide. However, despite the examination of musts reported to have produced serious sulfur spoilage problems and which were shown to be nitrogen deficient, no wines were produced which contained serious volatile sulfur spoilage problems as shown in these two studies by the absence of mercaptans. The role of nitrogen deficiency in musts or of different yeast strains in the production of sulfur compounds, despite very rigorous analytical analyses of precisely controlled fermentations is still unclear. As demonstrated by the results of the last two years, no simple relationship between must composition and production of sulfur off-flavors exists. Complex factors which require painstaking and systematic study appear to regulate the production of these compounds.
Spoilage organisms: Zygosaccharomvces and Kloeckera, whose presence in wines seems to be increasing as use of sulfur dioxide is decreasing, were found to be reticent to control at levels which controlled all other spoilage organisms. Studies carried out during this year show that both of these organisms can be efficiently controlled by carbon monoxide but at much higher levels than those employed to control Brettanomyces, Dekkera, and Hansenula.