For harvest purposes, when adding SO2 to grapes in order to knock down feral yeast and bacteria (with the goal of reducing VA and letting your yeast of choice get a foothold), I tend to add 35 ppm total SO2 (calculate based on 1 ton of grapes = 170 gallons wine/1 metric ton = 710 liters). 50 ppm seems a bit much unless your fruit is compromised by mold, rot, or Botrytis, etc. That being said, if I know I’ve got high pH fruit to begin with, like a hillside Syrah I know will land post-crush over 3.7 pH, then I might up it to 40 ppm. In the fruit stage, I don’t sweat it so much and neither do many winemakers. This addition is a theoretical target as well. It is a bit of an over kill if a winemaker was taking sulfite readings to make sure they’ve hit their target at this stage in the game. Adding a little over or under won’t hurt too badly because much of the excess free SO2 will get bound up during
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