Development of GC Olfactometry for the Analysis of Wines: Investigation of Sur Lie and Smoke Wine Taints
Summary of Major Research Accomplishments and Results: Chardonnay juice from grapes harvested in the UC Davis vineyard in the fall of 2009 was fermented in duplicate in 3 gallon carboys using three different yeast strains: 522, 940, 950. For each strain, three different levels of grape solids were evaluated: 0%, 6.25%, 12.5% by volume. At the end of the fermentation, samples were collected (day 0 samples) and the wines from the carboys were divided in two; one half was allowed to age sur lie and the other half was cold settled to separate the solids and used as controls. Samples were screened weekly, by project personnel, to identify samples that had veggie or other off aromas. Samples identified so far include: strain 950 with 6.25% and 12.5% solids at days 30 and 60 and strain 940 with 12.5% solids at day 50. The two wild isolates, UCD950 and UCD940, continued to show higher development of undesirable off-characters than did the commercial strain UCD522. Samples were taken at day 0 and at 3 months and stored in the freezer for further analysis. These samples were analyzed by gas chromatography with a sulfur chemilumenescence detector (GC-SCD) to specifically measure low molecular weight sulfur compounds in the samples. A second analysis using a GC attached to a mass spectrometer (GC-MS) and equipped with a sniff port was used for olfactometry measurements (GC-O) on the same samples. A panel of 5 volunteers (four female, one male) was identified to complete the GC-O analyses. The panel was trained to distinguish between fruity and veggie aromas, first by bench-sniffing solutions containing one standard of each aroma-type. The standards chosen were distinctively fruity or veggie; the veggie standards used were: dimethyl sulfide (DMS), dimethyl disulfide (DMDS), isobutyl methoxypyrazine (IMBP) and hexanal. The fruity standards were the ethyl esters of the valeric, caproic and caprylic acids.