Used mostly for red wines, it’s often done partially, meaning, say, 25 percent of the crop is left in bunches. The result is that the wine’s tannins are a bit firmer, the acid is zippier, and there is a touch of noticeable carbon dioxide, as well as a slightly vegetal aroma. The tannins come from the stems—it’s key that they’re mature, not green and the tannins give the wine a little more structure,
