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How to Adjust SO2 Levels In Must


Ron Rudnick — Liberty Lake, Washington asks,

Professional winemakers measure more data points because, having labs in-house or contracts with large wine laboratories, it’s cheaper and easier for them to get the information. We also have to anticipate and track the evolution of our wines for the larger commercial marketplace and for historical as well as quality control reasons naturally want and need more data. If you’re trying to save money, don’t feel like you have to be on the data geek squad with us; we get it.

I read in many publications to only add enough SO2 to bring the total must up to 50 ppm. I also read quite a bit about adjusting the wine (pre- or post-pressing?) based on the pH level. My question is — would it be best to add potassium metabisulfite based on the pH post-crushing or just go with the 50 ppm calculation?

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
Response by Alison Crowe.