Ask Wine Wizard

Testing For Free SO2


Paul Scott — Southfield, Michigan asks,

Last fall, I purchased a Vinmetrica Free SO2 tester and tested/adjusted the 10 kits that I had going. After I adjusted (based on pH) I’m bulk-aging all of them in 6-gallon (23-L) carboys. Is there any reason for me to “re-test” the free SO2 after 12–18 months, or can I rest assured that they’ll be fine? (I’m not a fan of blind faith, if there’s anything I can do about it!)

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
Response by Alison Crowe.