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Troubleshooting Malolactic Fermentation


Donald Coustan — Jamestown, Rhode Island asks,


This year’s harvest from my 20 Cabernet Franc vines made 7 gallons (26.5 L), which I fermented in two plastic fermenters to a gravity of 1.000 and then started malolactic fermentation. I then transferred into two 3-gallon (11-L) carboys and a 1-gallon (3.8-L) carboy. It has now been just about 10 days and malolactic fermentation seems to be going well (slow bubbling) but one of the carboys has nice, fairly clear red wine while the other has cloudy wine. I checked pH and the cloudy wine was 3.77 while the clear wine was 3.57. Can you offer any explanation?

Well, it’s tough to say what would make one cloudy and the other clear, except for the fact that they may not have been identical coming from your fermenters. If you did blend/homogenize after pressing, then it’s possible you’re seeing the cloudy wine (pH 3.77) going through the MLF (malolactic fermentation) a little more quickly for whatever reason (is it stored in a slightly warmer place than the other one?), and, as MLF de-acidifies, it makes sense that the pH on the cloudy one is a little higher (high titers of microbes can cause cloudiness). Cabernet Franc isn’t necessarily more prone than other wines to having delayed MLF. Even if your post-press lots didn’t start out with the same acid levels, those are both perfectly fine pH levels to have healthy MLF. Most MLFs, no matter what the varietal, are finicky things. The ML bacteria are greatly affected by the following: Low pH, high alcohol, low storage temperature, or high sulfur dioxide levels (free SO2 above 10 ppm or a total SO2 above 60 ppm). ML bacteria (usually Oenococcus oeni
Response by Alison Crowe.