The roots of Georgian viticulture have been traced back by archeology to when people of the South Caucasus discovered that wild grape juice turned into wine when it was left buried through the winter in a shallow pit. This knowledge was nourished by experience, and from 6000 BC inhabitants of the current Georgia were cultivating grapes and burying clay vessels, kvevris, in which to store their wine ready for serving at ground temperature. When filled with the fermented juice of the harvest, the kvevris are topped with a wooden lid and then covered and sealed with earth. Some may remain entombed for up to 50 years. Due to its diverse and unique microclimate, there are about 500 grape varieties in modern Georgia.