As a winemaker, the first thing I do during harvest is walk through vineyards where I know the grapes are starting to get close to ripeness. They are already delicious by that point but are not ready to be picked. I walk through a vineyard with a baggie and pick a random sample of the grapes, one berry at a time, until I have half a baggie full of grapes. In the meantime, as many grapes as I'm putting in the baggie, I'm eating to taste how ripe the grapes are. On any given day during harvest I eat hundreds of grapes.
At the winery, I squeeze the baggies of grapes and analyze the juice to see what the numbers say about the acidity and sweetness. I use those numbers as guidelines and when I'm in the range of the numbers I want, I spend the last few days in the vineyard just tasting grapes. When they taste right, it's time to pick them.
We pick the grapes on the day I feel they are ready. With white grapes, the first thing we do is get rid of the stems with a machine and then squeeze the grapes. We take just the white grape juice and it goes into either a tank or to a barrel. We then add yeast and start fermenting it.
With red grapes, again we take the stems away and this time we pump the grapes, skins and all into a tank. The juice of red grapes like Cabernet, Zinfandels and Pinot Noirs, is clear as water so we let the juice steep with the skins. With red grapes, it's the skins that have all the color and flavor. So the skins and juice steep together and then we add yeast to that and it ferments. When it's done fermenting, we drain the wine out of the tank and squeeze the grapes to get the last little bit of wine out. The harvest is pretty much over at that point. Of course there are a lot of little details in there but that's basically what we do.