Ripening of Lodi winegrapes continues this week as purple begins to show on the first individual berries throughout local vineyards.
The color change called "veraison" is the visual signal that sugars are starting to replace sour grape acids. In fact, glucose is a component of the red color.
"White" grapes are also changing from light lime green to a more golden yellow-green, but is harder to notice.
This period of color change is one of the last windows of effective field work. Workers out in the vineyards are now cutting loose bunches of grapes that aren't where they should be or aren't evenly developing - even more important in a cool growing season like 2010, which is still lagging perhaps a week and a half or more behind average.
You may also see green leaves littering the vine rows. These were pulled off the north or east side of rows to get more sun and air exposure to the grape bunches in the "fruiting zone." The right amount of sun helps to better ripen the grapes and build color.
Air flow helps to discourage mildew that is likely to form toward the end of ripening when we get a brief September sprinkle with shorter days.