Malolactic Fermentation is a bacterial conversion of harsher malic acid into softer lactic acid and carbon dioxide. This fermentation can occur in any wine that contains malic acid. There are many strains or genre of Pediococcus, Lactobacillus, Oenococcus and Leuconostoc bacteria that will perform the Malo-Lactic Conversion. This Malolactic fermentation will occur if the proper levels of PH and SO2 aren't maintained. The problem is that most of these bacteria will perform when they want to and not when it is most advantageous to the wine maker. They usually wait until the wine is bottled before working. Most also leave behind compounds that alter the aroma, flavor and sometimes color of the wine which are less than desirable. So they can do good work and they can also do harm. There are a few strains of Leuconostoc that have been used successfully to do Malo-Lactic fermentation because they leave behind few aroma and flavor altering compounds. Since Malolactic Fermentation is likely to occur anyway, why not control when it occurs and which strain of bacteria does the fermentation?
The preferred Malolactic culture is Oenococcus oeni (formerly Leuconostoc oenos). It includes strains Ey2d and Er1a.
What wines benefit from Malo-Lactic Fermentation.
Traditionally, red wines that are made to be aged and one of the two variations of Chardonnay wines benefit greatly from a Malolactic fermentation. Most white wines and fruity reds that are made to be consumed young do not benefit as much from Malolactic fermentation.
How to encourage Malo-Lactic Fermentation
Malo-Lactic bacteria work best when the wine or must has a pH above 3.3, free SO2 level below 15 ppm, temperatures between 55 & 75°F and alcohol content 13.5% or less. If the pH of your wine after yeast fermentation is 3.2 or lower we don't recommend inoculating. It's best to change to the fruiter Nouveux style than try to force the Malolactic fermentation. On the other hand if the pH is 3.3 or higher keep the SO2 additions very low until after Malo-Lactic Fermentation. Though Malo-Lactic fermentation can occur in temperatures of 55-75°F it occurs faster at temperatures at the high end of the range.
How to discourage Malo-Lactic Fermentation
To discourage Malolactic fermentation you must make sure the wine has a pH of 3.4 or less and make sure the free SO2 is 30-75 ppm, ferment and store the wine below 55°F or boost the alcohol above 14%. The lower the pH, the less free SO2 is required to protect the wine from Malolactic fermentation, thus as your pH goes up so must your SO2 additions.
When to inoculate.
While Malolactic fermentation culture can be added anytime after the onset of yeast fermentation, we believe it is best to wait until secondary fermentation is complete. Malo-Lactic bacteria like the temperature to be between 55 and 75°F., the pH to be above 3.3, the SO2 to be below 20 ppm and they work better if there is some sediment present. Since Malolactic fermentation may take up to three months to complete the sediment should contain mainly dormant yeast not fruit solids.
Pitch your active yeast starter into the crushed grapes or juice as usual.
If using grapes, rack the must off and press the skins (if you are not doing a second or false run).
Allow the racked must to complete fermentation and initial settling in glass.
If there is a heavy sediment (as usually occurs when pressing) rack into a clean carboy.
Add the Malolactic culture. (DO NOT ADD SULPHITE/CAMPDEN TABLETS)
Malo-Lactic fermentation is often slow. You may or may not see any visible signs of this fermentation. Be patient. Allow the wine to rest for 1 - 3 months depending on the amount of sediment. Heavy sedimented wines need to be racked after 1 month. If there is light sedimentation you can wait until 3 months have passed.
At the three month racking add 50 ppm SO2.
Wine may be fined, filtered, aged or bottled.