New Parameters to Measure Ripeness

We have accomplished our primary goal of finding what phenolic components change as a result of ripening. We have developed new analytical methods to quantify grape tannins, in particular the skin tannins. The new method allows for the quantification of the polymeric tannins in grapes with a distinction between tannins of different sizes. Using this new method, our data shows that skin and seed tannins are very different, with skin tannins being of a larger size than seed. In addition, the average size of the grape seed tannins increases during the season, and this trend continues through the time of commercial harvest. Another result is that the seed tannins become harder to extract and thus a lower component in wines, while skin tannin levels increase. Thus wines made from more mature grapes should have lower levels of seed tannin and higher levels of skin tannins. While our methods cannot answer the question of “when” grapes are considered mature, as such a judgement requires an interpretation of data, it may be possible to use them to come up with guidelines for assessing relative grape maturity. In addition, it appears that water stress induces a slightly greater maturity based on our analysis.