Volatile Sulfur Compounds: Incidence and factors affecting their formation in Califomian Wines

In fermentations comparing the formation of volatile sulfur compounds in 1 -L and 10 gal fermentations using juice or crushed grapes without pressing, the fermentations conducted in the 10 gal lots with skins produced the highest levels of H2S during fermentation. Most probably this is attributable to the faster rate of fermentation due to higher temperature because of the cap or as a result of elemental sulfur on the skins. Little difference was seen in the levels of H2S among the other fermentations, suggesting that redox reactions etc do not differ between these two fermentation volumes. Analysis of 20 vintages of wine from one winery revealed an increase in dimethylsulfide (DMS) over the first eight vintages, with subsequent aging resulting in a slight decrease. Previous studies have claimed DMS increased with age, but had examined heterogeneous wines. Levels of H2S produced in a Pinot noir juice and in a vitamin-rich but nitrogen deficient synthetic medium were compared for 27 “strains” of Saccharomyces which have been characterized genetically by Dr. Mortimer of UCB. Some strains are high H2S producers in both Pinot noir and synthetic medium, some are low in both and some are high in one, but low in the other. This diverse set of genetically well-behaved strains offers the opportunity to finally determine the metabolic basis of the “strain differences” factor in hydrogen sulfide production. The GC used for analysis of sulfur volatiles is being recalibrated and flows adjusted to permit evaluation of the split effluent of the GC by sensory (sniff) evaluation and by flame photometry. Three papers have resulted from work funded by this AVF grant. A in-Press manuscript, summarizing our research was submitted with the February 1994 progress report. Attached are copies of two papers which were presented at a Symposium in Montpellier, France in February 1993 and which have just been published.