Examining Variations in Grape Phenolic Maturity and Ripeness at Harvest and How It Influences Wine Quality

Article published with permission on The Academic Wino

It is a well known fact that the phenolic maturity of grapes at harvest significantly impacts the overall quality of the finished wine. Specifically, the aroma, flavor, mouth feel, and astringency are all tied in with the composition of phenolic compounds in grapes and wine, thus are strongly influenced by grape ripeness or a lack thereof. Recent studies have shown that certain phenolics in the skins of unripe grapes are less extractable and certain phenolics in the seeds of unripe grapes are more extractable than those in the skins and seeds of fully matured grapes which results in altered flavor and aroma of the finished wine.

The demand at the moment for consumers in terms of ideal red wine characteristics are wines with a dark red color, full body, soft tannins, and ripe fruit flavors and aromas. To create wines with these characteristics, winemakers must use fully ripened grapes, specifically those grapes that have reached “phenolic maturity”. With this in mind there has been a lot of work done looking for a method to test grapes in the field to determine their ideal harvest date when phenolic maturity has been reached. There has been fair progress in this field of research whereby these methods rely on the average values of a sample of grapes in the vineyard, and don’t take into account the variability of the phenolic maturity of grapes within that sample. A large variability in grape phenolic maturities could mean problems for a winemaker attempting to create the “ideal wine” for consumers.

Each and every grape does not ripen at the exact same rate when ripening throughout the season. A lot of factors go into this variability, from weather to vineyard management practices and even to the specific location on the cluster. Because of this variability in ripening rates there is the potential for there to be a large variability in phenolic maturities of the grapes at harvest, even when the average values indicate it’s about time to pick. Apparently no one has ever looked at this variability (in other words, heterogeneity) of phenolic maturities in grapes, nor has it ever actually been quantified.

Thus, the goal of the study presented here was to evaluate the variability or heterogeneity of the degree of grape ripeness (degree of phenolic maturity) and how this variability affects wine quality and phenolic composition …