Different types of grapes are used for different things, but most growers have a plan before they plant grapes. Most produce is effectively sold before it’s planted, generally there are contracts that agree to price per bushel, delivery windows, and minimum quality. The price is based on commodity market trading generally. The other option is the farm is part of a winery, so they use the grapes to make their wine or juices.

Farmers don’t just grow things and hope to find buyers, they also don’t really care what the buyer does with their product.