Malolactic fermentation (MLF) is a secondary wine fermentation conducted by lactic acid bacteria (LAB). This fermentation is important in winemaking as it deacidifies the wine, converting L-malic acid into L-lactic acid and carbon dioxide, and it contributes to microbial stability. Wine pH is highly selective, and at pH below 3.5 generally only strains of O. oeni can survive and express malolactic activity, while under more favorable growth conditions above pH 3.5, species of Lactobacillus and Pediococcus may conduct the MLF. Among the LAB species Lactiplantibacillus plantarum strains have shown most interesting results under hot climate conditions, not only for their capacity to induce MLF, but also for their homo-fermentative properties towards hexose sugars, which makes them suitable for induction of MLF in high pH and high alcohol wines, when inoculated at the beginning of alcoholic fermentation.
Recently a highly concentrated L. plantarum starter culture proofed not only being able to induce and finish a malolactic fermentation before the end of alcoholic fermentation, when applied in co-inoculation in high pH red wines, but also to be a tool for high acidic white wines, characterized by a low pH (> pH 2.95) and high malic acid concentrations. Due to its good alcohol tolerance (up to 15 %vol) it can be applied in co-inoculation as well as in sequential inoculation.
An inoculation ratio could be used to control the amount of malic acid to be degraded to achieve both: a partial or a complete degradation of malic acid. Since this strain does not metabolize citric acid, no diacetyl is formed and thus the variety typicity is maintained and wine acidity is harmonized. With the partial or complete removal of the malic acid, the complex double salt or in some cases even necessary extended double salt deacidification could be circumvented. This also avoided calcium input and eliminated the resulting problems with tartar stabilization.
For use in sequential inoculation, a simple MLF pretest can be used to determine the success of an MLF with ML-Prime in a short time (maximum 7 days) and to provide exact information which amount of malic acid will be degraded. The results can be transferred directly into practice.
Author: Krieger-Weber Sibylle1
1Lallemand Office Korntal-Münchingen
*corresponding author: skrieger@lallemand.com
Keywords: Malolactic fermentation; Lactiplantibacillus plantarum; facultative hetero-fermentative; starter cultures; diacetyl.
