Effect Of Pre-Fermentation Cold Soak On The Chemical And Sensory Qualities Of Aromatic White Wines
The aroma profiles of Riesling, Gewürztraminer, and Traminette grapes are largely derived from monoterpenes found in grape pulp and skin. To optimize the extraction of monoterpenes and other volatile compounds, a winemaking technique called pre-fermentation cold soak (CS) is sometimes used. Unfortunately, CS may also allow for the extraction of undesirable bitter compounds, including monomeric phenolics. To address this concern, monomeric phenolic concentrations were measured in wines produced with varying CS durations. Among the compounds analyzed, (+)-catechin and (-)-epicatechin were most affected by CS duration. Because total monomeric phenolic concentrations tended to increase with increasing CS duration, wine bitterness intensity was quantified by a trained panel. Sensory evaluation results, however, suggest that CS duration and bitterness intensity are not directly related. Following the CS study, detection thresholds of (+)-catechin and (-)-epicatechin in model and commercial wines were determined in order to learn more about the contributions of these compounds to wine sensory characteristics. (+)-Catechin detection thresholds in model and commercial wines were 205 and 278 ppm, respectively. In contrast, the detection thresholds of (-)epicatechin were not found for the concentrations tested which went up to 501ppm. Threshold testing was selected as a starting point to understand how individuals perceive these compounds at sub- and suprathreshold levels. CS and other processing conditions can lead to color compound extraction or must oxidation, resulting in darker colored wines and potentially increasing bitterness intensity. The presence of an association between darker white wine color and bitterness intensity was investigated by having a panel of wine professionals rate the bitterness of color-modified white wine samples. The results did not indicate that wine professionals associate darker white wine color with bitterness. A final study investigated the possibility of differentiating Riesling clones through the analysis of juice monomeric phenolic and tannin profiles. The results did not show significant differences in the monomeric phenolic and tannin profiles among the clones analyzed. However, preliminary sensory results suggest that wine professionals can differentiate among monoclonal Riesling wines. If true, it may be possible to differentiate among Riesling clones through the analysis of other volatile and non-volatile compounds.
Enology; Pre-fermentation cold soak; Aromatic white wines
Cleland,Thomas A.; Sacks,Gavin Lavi
Food Science and Technology
Ph. D., Food Science and Technology
Doctor of Philosophy
dissertation or thesis