In wines, Malolactic Fermentation is a little bit trickier than primary fermentation, the conversion of fructose and glucose to alcohol!
I recently spoke to an individual who had what appeared to be a lack of MLF in a Chardonnay. The pH was about 3.2, the temperature was 68 deg F, free SO2 was 10 ppm, and the total SO2 was 59 ppm. He didn’t know the alcohol level. What was up?
Initially I thought the problem was insufficient nutrients, but he had supplemented prior to inoculation. So I went back over the requirements for a reliable MLF.
First, it is important to match the MLF strain to the conditions of your wine!
A few MLF strains can successfully grow at a pH of 2.9 or higher, but most others must be above pH 3.2 or even above pH 3.4. For many strains the optimum pH is 4.0, but that is high for most popular wines. Also, higher pH levels facilitate the growth of some other types of lactic acid bacteria that can add off flavors.
Some MLF strains have minimum operating temperatures as low as 55 deg. F, but others require at least 65 deg. F. Note that there is a suggested maximum temperature also, which is usually 68 deg. F for white wines and 77 deg. F for red wines.
High alcohol levels can inhibit the MLF bacteria. Some essentially stop working at alcohol levels as low as 13.5%, while others can tolerate up to 17% alcohol.
SO2 management is extremely important when MLF is desired. Most malolactic cultures do not respond well if the Free SO2 level is above around 15 ppm. But unlike many of the nasty organisms we try to control in wine, MLF cultures are also sensitive to Total SO2. Some have maximum tolerance levels as low as 35 ppm Total SO2. Many can tolerate 60 ppm Total SO2, and a few can tolerate up to 80 ppm Total SO2. While few winemakers will add high levels of sulfite to a wine they are planning to undergo MLF, much of the early Total SO2 comes from yeast during primary fermentation. Yeast strains can produce between 10 and 80 ppm of SO2 during primary fermentation. Some of these strains also product high levels of the chemical acetaldehyde. This chemical binds strongly to sulfite, and keeps it from getting blown off or breaking down. If you are planning MLF, in addition to judiciously selecting an MLF strain, also carefully select a yeast strain that produces lower levels of both SO2 and acetaldehyde.
MLF bacteria require nutrients, just as yeast does. Consider adding a supplement designed for MLF bacteria. Also consider holding off on clarifying your wine until after MLF. Clarification eliminates yeast dregs which undergo autolysis, thus depriving the bacteria of growth factors (manno-proteins, vitamins) which can be liberated during this stage.
Monitor L-Lactic Acid levels to ensure that MLF has started; monitor the malolactic fermentation for completion (Malic Acid at 30 – 50 mg/L), then add appropriate SO2 for bacterial stability.
By the way, it looks like high Total SO2 was the culprit!