Malolactic fermentation
What is it?
Apart from alcoholic fermentation, there is another process of great importance in winemaking: which is called malolactic fermentation.
In this note we will see what it is about and why it is sometimes encouraged and other times their relationship is canceled.
In the process, malic acid is chemically transformed into lactic acid; by means of bacteria of lactic origin existing in the environment, or in the interior of the same fruit. The main effect is to reduce the acidity of the wine and this process if controlled can improve the quality of the wine. Malolactic conversion occurs in fermented beverages that come from fruit.
The formula of malolactic fermentation
Bacteria
The malolactic fermentation is carried out more generally in red wines after alcoholic fermentation and consists of the transformation of malic acid into lactic acid by means of bacteria that are naturally found in the grapes themselves and therefore also in the freshly fermented thin.
The number of lactic bacteria during alcoholic fermentation is usually very low, at most 102 per mL, since most are inhibited by ethanol and by SO2 added to the must to control the bacterial population, especially acetic ones. When the alcoholic ends and the yeast dies, some lactic bacteria can thrive and achieve some growth, sometimes up to 107 per mL. These lactic bacteria produce some transformations in wine, of which the most interesting is the so-called malolactic fermentation (MLF). The lactic bacteria that can be isolated in samples of musts and wines are of the genera Lactobacillus, Pediococcus, Leuconostoc, Weissella and, above all, of Oenococcus
Malolactic fermentation: conversion of malic to lactic by the malolactic enzyme (EML) of lactic acid bacteria cells such as Oenococcus oeni
Imagen de la bacteria Oenococcus oeni
Condition
- Limit sulphited musts to minimum values, thanks to a good sanitary status of the grapes and a strict general hygiene of the winery.
- Maintain the temperature of the wine after alcoholic fermentation at 20-22º C, without variations.
- Avoid acidities too strong, malolactic fermentation is much more complicated than useful in case of high acidities and a low pH. If necessary, it could be effective to slightly deacidify a lot, to facilitate the activity of lactic acid bacteria and then use them to plant the other lots.
- The best contribution of bacteria is formed by the natural "vat feet" isolated from vats in which a good malolactic fermentation has taken place. Cascade sowing is the best winemaker's tool, being enough most of the time.
- There are few operational malolactic ferments in constant evolution. Its practical effectiveness requires a strict implementation, according to the indications of the different suppliers increasingly oriented to direct sowings that bring together the already proven effectiveness of a few planting complexes after multiple reforestation.
generations. The direct sowing of the musts, before the alcoholic fermentation, seems to have been abandoned due to its uncertain efficacy and the existence of real risks