Various Influences of Harvest Date and Fruit Sugar Content on Different Wine Flavor and Aroma Compounds

Over the recent past a reduction of the time required for grapes to achieve sugar ripeness, possibly a result of climate change, has been observed in many countries, raising the issue of a potential disconnect between flavor ripeness and sugar accumulation. An experiment using Vitis vinifera L. cv. Riesling was conducted to test the relationship between sugar content of fruit and harvest date with changes in the abundances of wine volatile compounds. The Brix of individual berries was determined at four harvest dates and pooled in distinct sugar content categories before fermentation and analysis of headspace volatile compounds. Results showed a complex relationship for sugar content, harvest date, and wine volatile composition. The compounds that significantly changed in the wines could be grouped into six clusters depending on the accumulation patterns across both sugar content and harvest date. Positive impact varietal compounds, especially monoterpenes, generally increased in abundance in relation to increasing Brix, with less of an effect due to harvest date. Compounds that decreased in abundance in relation to Brix also seemed to be influenced by harvest date, with the concentration at the earliest sampling time point particularly high. Many of these compounds were acetate esters of higher alcohols as well as ketones and acetals. Results suggest that, overall, positive impact volatiles accumulate in a manner closely related to increasing Brix but that the loss of compounds in the fruit that may impart negative attributes to wine may be a passive process and require a certain amount of time on the vine.