big purple concord grapes grow wild in the US and are thick skinned and you squeeze or suck out the grape inside, skin significantly more tart than the sweet grape, pretty sure those are the tannins that you get in wine from skin contact even those those are different grape varieties.

I've visited a number of European winegrower family farms and they frequently also grow table grapes for their own consumption. The table grapes they eat are much much less sweet than vinifera grapes where the yeast consume all the sugar into alcohol and which are basically too sweet to enjoy.