Good for you for investing in a way to track your free SO2 (FSO2) levels. It’s one of the most important ways we can keep our wines safe. You can buy something like a Vinmetrica kit or send out samples monthly to a local wine analysis lab (like ETS here in Napa County), which is what I do for many of my own commercial wines, when the winery I’m working out of doesn’t have its own free-standing lab. Yes, you just read correctly — monthly. FSO2 gets bound up quickly and is essentially used up in the wine as it reacts with wine components, especially when the wine is young. It’s only a portion of the FSO2 that is doing our antimicrobial and antioxidant work, so depending on the pH of your wine (high-pH/lower-acid wines need more sulfur dioxide to be protected from oxidation and microbial spoilage), you’ll want to keep your FSO2 hovering between 25–35 ppm all the time. Like I said, it’s standard industry procedure for wineries to sample each lot for VA (volatile acidity) and FSO2 every
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