Malolactic fermentation is an integrated part of winemaking which cannot be ignored. It can however be beneficial or detrimental and it is important that winemakers are well informed about it in order to make the right decisions. The execution of the decisions is also important to ensure that the required results are obtained in the wines.
Three different MLF genera, Oenococcus, Pediococcus and Lactobacillus, can convert the malic acid in wine into lactic acid. Only one Oenococcus species, but different Pediococcusand Lactobacillus species occur. Oenococcus oeni usually dominates because it has a higher resistance against the conditions occurring in wine. It is also the most desirable bacteria for MLF in wine because it can develop pleasant characteristics in wine while other species can cause spoilage like mousiness, sweaty and sauerkraut characters.
The end result of MLF is the decrease of the fixed acid concentration and increase in pH of the wine. The pH can increase with 0.3 or more units. The pH increase can however create favourable conditions for undesirable malolactic bacteria. Desirable MLF is usually acceptable in cool regions with a high fixed acid concentration to create a better balance in wines. Seeing that nutrients in the wine are also utilised during the process, such wines will be more stable against potential spoilage bacteria. It is not only as result of the utilisation of the nutrients, but also possibly due to the formation of toxins by the lactic acid, which can inhibit the growth of the spoilage bacteria. As result of the formation of other compounds during MLF the flavour profile and mouth feel of wines can also change. Diacetyl, which exhibits a buttery character, is an important compound formed during MLF. Its formation is influenced by the bacteria species, inoculation concentration of the MLF pure cultures, duration of the MLF, temperature, oxygen, pH and yeast lees contact. Ester compounds which can influence the wine flavour positively can also be formed during MLF.