Bravo to you for doing bench trials! If you’ve read my columns over the years you know that doing bench trials — that is, testing a wine treatment on a small scale (“on the lab bench”) before performing it on your entire lot — is one of my most oft-repeated mantras. You also followed another of my key winemaking axioms — let your taste buds be your guide.
Yet another nugget of winemaking wizdom I often pass on to readers is to go slowly, do things in stages, and be conservative when making additions to wine that will dramatically change them. Adding acid, as it seems like you’ve found, is one of those things that will change many aspects of a wine, including taste balance, perceived tartness, color, pH, and microbial stability. Unlike Sauvignon Blanc and Pinot Grigio, Viognier tends to live in the “rounder” side of life for a white wine, a bit more like a Chardonnay than a higher-acid zinger. I think a 3.66 pH is probably right on the edge of stylistically too high . . . but I’d be careful of taking it down too far. If you can measure pH while you do your trials, I’d shoot for a pH around 3.50.
I’m glad that you’re aware that a high-pH wine is more susceptible to microbial spoilage and that acid can help a wine age gracefully. Just a little bit can go a long way, however. I would counsel you to try a much smaller dose, like a reduction on the order of ten, and try adding 0.2 g/100 mL to your bench trial and see if you like the taste. I would wager that just that little bit, which would raise your TA to 0.644 g/100 mL, might lower your pH down somewhere in the realm of 3.50–3.55, which is fine for long-term aging of a rounded style, malolactic-complete Viognier as long as you keep your free SO2 levels around 30 ppm. If you like a little bit more of a zingy style, also trial 0.3 g/100 mL or 0.4 g/100 mL, but always taste afterwards.
I wouldn’t count on the acid dissipating much. Since your malolactic fermentation is complete, the acid levels will be pretty stable. The only way you’re going to lose acid now is if you have some solid tartrate crystals fall out of solution, which will probably just move the TA by 0.02–0.05 g/100 mL, if that. I’ve never seen huge TA or pH shifts due to tartrate fallout during aging. That’s the beauty and the risk of adding tartaric after MLF is complete — once you add it, it’ll stick around, which is why you’ve got to be careful not to add too much and be stuck with a terribly tart wine forever.
