Grape Harvest always begins 45 degrees (that is to say days) after the sun reaches zenith. When Sol comes out of solstice at Midsummer's Day, this is the traditional feast of Saint John the Baptist, who was born 6 months before Christ. And it's probably very close to Midsummer's Day that Christ was baptized in the Jordan River by John (if not literally on Midsummer's Day). It was a bit after the beginning of Wheat Harvest/Pentecost, so it's sometime very close to Solstice. After Jesus is baptized, he is tested for the 40 days of Fire until the beginning of Grape Harvest.

This year, Vine Harvest begins August 5th (Tu B'Av).