Analysis of Sulfide-Off Odors Produced During Sur Lie Aging

The first goal of this project for the first year of funding was to validate the solid phase
microextraction (SPME) method developed in the Ebeler laboratory and to determine if
the method displayed the dynamic range of sensitivity needed to undertake an analysis of
the product-precursor relationships for the volatile S-containing compounds that appear
during aging on the yeast lees (sur lie). The SPME method has been validated and
displays the level of sensitivity needed to undertake the analysis of the chemistry of
formation of the S-volatiles under natural or un-spiked conditions. The method was used
to profile the appearance of S-volatiles in experimental samples and in wines acquired by
the University for analysis.

The second goal was to examine the impact of nutritional conditions of the primary
fermentation on the appearance of off-odors sur lie. The factors examined were: nitrogen
level, micronutrient level, nitrogen and micronutrient level, yeast strain, hydrogen sulfide
produced during the primary fermentation, supplementation with methionine and cysteine
at levels naturally occurring in juices, and sulfate level. To date none of these conditions
has resulted in the appearance of S-volatiles at the levels expected from the literature over
the five week time course used. Differences in the non-nutritional conditions could
explain the lack of appearance of S-volatiles in our study. A more likely explanation,
however, is the lowered levels of supplements used in our study done deliberately to
more accurately depict actual wine production conditions. The experiments will be repeated
using a longer time course as some of the samples did display low levels of Svolatiles,
detectable chemically but well below the sensory threshold of detection. Other variables
did appear to affect S-volatile formation such as pH and solids content, and these will
be explored more completely in the next year.