Rain and the Grape Harvest

  The Northern Hemisphere is in the midst of the wine grape harvest. One of the things you hear wine people worry about is rain. Why is that?

  Rain any time can be an issue, but during the harvest is especially troubling for winemakers. In order to find the right time to pick the fruit, they're looking for the optimal sugar-acid balance. This can be thrown out of whack by rain.

  Grapes will have a harder time ripening when it's overcast. Rain will be absorbed by the roots and make its way to the grapes, where it can dilute the flavors and upset that sugar-acid balance. Enough rain can cause the berries to swell and split open. With rain, or even high humidity, there are potential problems with spoilage as mold and mildew can set in. The spoilage can cause off-flavors in a wine.

  Grape clusters are more susceptible to these problems near harvest. Their size means less air circulation. Ripe fruit getting split open by birds, insects, hail, or too much rain leaving a breeding ground for problems

  Luckily, California generally has a dry growing season though rain near harvest can occasionally happen. When it does winemakers hope for dry, breezy weather afterwards. There are sprays and treatments for the different problems caused by late-season moisture. 

Botrytis bunch rot, a fungus