What is done with the thousands of tons of grape and grape skins that is left over when wine is made?
Much of it goes into silage for animal feed. In Italy, some of it is used to make Grappa, a liquor.
The winery I worked for during the 2006 harvest just dumpstered them up and sent them away as trash.
It depends of the winery.
It’s called pomace, and like beowulff said, it can be sent to silage for animal feed.
It is sometimes sold to processors as a source of grape seed oil.
Most of it is used as compost and goes right back out into the vineyards. It’s spread between the rows to help get the cover crops going during the dormant season.
My wife is a winemaker, in the thick of harvest right now. At her old winery (small) it was composted, and spread out in the vineyards in due time. At her current place, the volume is too great for composting, so a small portion is composted on site and the rest is dumpstered up and hauled away. I assume it is also composted (this being Oregon, and the winery’s owners being as green-minded as they are).