Malolactic fermentation (MLF) is a common processing technique used to biologically convert the malic acid to lactic acid and carbon dioxide (Krieger 2005). The conversion of malic to lactic acid is considered a deacidification technique. MLF is conducted through proliferation of native lactic acid bacteria (LAB), of which the three existing genera in wine are Lactobacillus, Oenococcus, and Pediococcus (Krieger 2005, Iland et al. 2007), or by inoculation of commercial LAB strains. The process of MLF has several chemical and sensory alterations to the wine (Waterhouse et al. 2016):

  • Decrease in titratable acidity (TA).
  • Increase in pH.
  • Decrease in sourness of the wine.
  • Potential development of the “buttery” aroma or flavor due to increased diacetyl production.

Commercial strains, Oenococcus oeni, are often preferred as this strain of LAB best conducts MLF (Waterhouse et al. 2016). O. oeni is relatively predictable in its ability to convert malic to lactic acid, and several commercial strains have various capabilities of producing the byproduct, diacetyl. Diacetyl gives rise to a buttery flavor or aroma that is desired in some styles of wine, such as oak aged Chardonnay.

When to Inoculate for MLF

LAB inoculation can be integrated into wine processing at several stages of production:

  • Before primary fermentation,
  • During primary fermentation,
  • Near the end of primary fermentation,
  • After primary fermentation is complete (Iland et al. 2007).

Each stage in which LAB can be added to the wine will offer a number of advantages and disadvantages to the winemaker. Ultimately, when LAB inoculation occurs can affect wine quality …