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Malolactic fermentation: knowledge versus practice

Malolactic fermentation: knowledge versus practice

Maret du Toit

The whole process involving yeast and alcoholic fermentation (AF) has been greatly studied and is therefore largely understood.  However, many have realised the benefits that malolactic fermentation (MLF) can have, as well as playing a role in the final wine quality. In order to fully leverage the positive impact of the MLF process, it is important to understand the fundamentals: the chemical reactions and the microorganisms involved. It is also important to understand the role that various winemaking processes and decisions like timing of inoculation can play in determining the outcome.

MLF is a process that involves the conversion of malic acid to lactic acid and carbon dioxide. It is performed by lactic acid bacteria (LAB) that can either be naturally present in the matrix, or introduced via inoculation. In general, the impact of MLF in the wine can be grouped into three main categories: a reduction in acidity; an increase in the microbiological stability of the wine; the organoleptic impact on the wine.

These changes are brought on by LAB, mainly from the following genera: Oenococcus, Lactobacillus and Pediococcus. Commercial LAB cultures concentrate on Oenococcus oeni and Lactobacillus plantarum as the main species responsible for making positive contributions during MLF. Whereas commercial cultures were previously selected based on their ability to complete MLF, new research and developments have allowed for the selection of cultures that positively enhance the final wine sensory profile.

In order to fully optimise the quality improvement that MLF and LAB can have in your wine, it is imperative to understand the fundamentals of the process and the microorganisms involved. It is only with this understanding, that the winemaking process can be optimised in order to enhance the final wine quality.