Chapter 7

Malolactic Fermentation in Wine

Completion of Malolactic Fermentation

Generally, it is best to aim for a malic acid result of not detected, which is usually less than 50 mg/L by enzymatic analysis (Coulter, 2012). However, a result of 100 mg/L or less is low enough for the MLF to be considered virtually complete and to minimize the risk of spoilage (Osmond, 2016). Regardless, it is essential to ensure malolactic fermentation has completed and that it does not occur too late in the life of a wine, especially when it is in the bottle.

Change in Titratable Acid and pH after MLF

It is a well-established fact that malolactic fermentation causes acid reduction. The extent of acid reduction will depend on the amount of malic and citric acid in the must; but generally, the reduction in titratable acidity (TA) varies between 0.1 to 0.3 percent, with subsequent rise in pH of 0.1 to 0.3 units.

Post-Malolactic Fermentation Operations

When malolactic fermentation is complete, the wine is racked and subjected to different clarification and stabilization treatments and/or is stored in oak barrels or tanks for maturation for a variable period of time. The wine is racked to eliminate a fraction of the bacteria with the coarse sediment.

Preventing Malolactic Fermentation

Although malolactic fermentation is occasionally difficult to induce, the prevention of lactic acid bacteria can also be difficult. The results are often disastrous when malolactic fermentation occurs in bottled wine because it results in bottle deposits, off-odors, bad tastes, and petillance (from the released carbon dioxide trapped in the bottle). So, winemakers must take specific steps to improve long-term stability before any wine containing both malic acid and lactic bacteria can be bottled.

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