Unless your family makes wine or you work at a vineyard, you probably don’t know that the best time to pick wine grapes is usually at night or early in the morning when temperatures are cooler. Cooler temperatures help preserve the grapes' natural acidity and enhance the wine's quality. They also help concentrate the grapes' aromas and flavors. The cooler temperatures help prevent the grapes from fermenting too early. In hot climates such as this one in Oak Park, California, picking at night or early morning can provide cooler conditions for the pickers.