Indeed, a pH of 2.9 is really low, even for a Sauvignon Blanc, and I think I would definitely de-acidify in that case. With deacidification you’ll always get some kind of precipitation; that’s totally normal. You just want to make sure it’s precipitating in your bulk-aging container (keg, carboy, drum, etc.) and not in the bottle! Who wants to strain crystals between their teeth when drinking a white wine?
Adjusting acidity is critical and so precipitation of solids just has to be put up with — though in whites you always want to make sure you cold stabilize in some way to retard precipitation in bottle. For home winemakers this can sometimes be hard to do the old-fashioned way, i.e. get the wine below 32 °F (0 °C) and then seed with potassium bitartrate crystals (cream of tartar) to force a precipitation. The wine is then filtered while cold to remove the solid crystals. As you might imagine, this can be really difficult for home winemakers to achieve.
If you just make a small amount of wine and have a spare “beer fridge” (my husband homebrews) like I do in my garage, pop your keg or carboy in there for a week or two. Even chilling to fridge temperature will help precipitate out excess tartrates in the wine though it may not take care of any and all crystals that might precipitate over time.
However, there is a new, legal, and safe wine additive that we all can use now to cold stabilize wines, without having to chill them down. Carboxy methylcellulose (CMC) is a new wine additive that basically forms colloids to help prevent crystallization in final bottled wine. All you do is add 1 mL/L to finished filtered white wines right before bottling. Well, to be more exact, to find out if your wine is a candidate for CMC (the wine has to be reasonably “unstable” as opposed to “very unstable”), you can send a sample to ETS Labs (www.etslabs.com) for an analysis called a “DITS” (Degree of Tartrate Instability). If the “Rate of Electrodialysis” is <24%, then your wine is a candidate for CMC use and you add 1 mL/L after final filtration, right before bottling. If your result is >24%, then you can try chilling your wine a bit, and see if that precipitates out some tartrates. Try re-testing for DITS after a few weeks of lower temperatures. For all of the wines I’ve bottled over the last five years, I’ve only ever had one wine not pass the DITS test, so it’s very likely that your wine will be fine. If you’d rather not pay for the DITS test (and hey, it’s home winemaking after all) you could probably get away with foregoing it.
Note that CMC does NOT work in reds or rosés, only whites. Most wine supply houses carry one of these products, for example the one sold by Laffort is called Celstab. It’s truly a game changer for home winemakers who want to cold stabilize their wines. No more worry about getting the wine cold enough and doing fiddly additions and filtrations.
