News of an early veraison is buzzing in the wine bulletins and newsletters! Our dry-then-wet-then-dry-and-warm Spring has led to the earliest veraison that we have experiences in quite a few year. This is good news to most of us! We hope that an early ripening will lead to more predictable harvest parameters and better phenolic development than we have seen in the past three years.
Veraison is the point at which grapes begin to ripen, usually 50 to 60 days after bud break. This event is signified by engustment, or the color changes from green to the color of the fruit near harvest. The pips are green and hard during a lag phase that precedes veraison, but begin to soften and enlarge at the onset of veraison. Depending on heat, canopy management, water restrictions, and crop load, grape clusters can complete engustment in one week or transpire over an entire month! In some years veraison is never completed which usually indicates an inappropriate varietal for the region, but often reflects a very cool season (remember 2010?).
The color changes in the fruit reflect anthocyanin replacement of chlorophyll. Anthocyanins are the color components in red wines, and carotenoids are the color components in whites. Both of these color factors are tannins produced by the vine to protect the fruit during the ripening stage, and perhaps become more appealing to birds and other foragers at ripeness. Of course, we like their colors, too!
Another huge factor that occurs during veraison is the beginning of hexose increase. Hexoses (glucose and fructose) begin to build in the fruit and engorge it, while the xylem in the vine decreases water allotment. The result is a rapid increase in berry size, sometimes up to 30 times the size of the pips, due to sugar accumulation with water restrictions. Most reds are harvested at 23% to 26% sugars by volume and whites at 19% to 23% sugars. I prefer lower alcohol wines, so I tend to harvest on the lower end of the spectrum (alcohol is roughly .52(x) the initial sugar content at harvest, depending on residual sugars and evaporation, etc.)
Acids decrease over time, too. After veraison the berries accumulate no more acids. The deacidification of the berries is due to a decrease in malic acid, and a dilution of the other dominant acid, tartaric acid, while the berry increases in size.
PH increases during ripening, along with sugar accumulation and deacidification. The pH of a lag phase pip is quite low. These pips are also very bitter and tart, completely inedible. I pay very close attention to the pH of grapes for harvest parameters, considering pH to be the most important indication of ripeness along with phenolic development. The rise in pH corresponds to the drop in acids, but they are not inversely proportional due to the natural buffer capacity in wine chemistry. Thus, often we might see a rise in pH while the acids remain static, or vice versa.
I have a vineyard tour set up in the next few weeks and I can’t wait to see how our grapes are doing!