Adaptation of Lactobacilli towards low ph and SO₂ to develop MLF in base musts for sparkling wines

Abstract

In some white wines, malolactic fermentation (MLF) is very interesting, and for low pH wines this process is particularly difficult. Although MLF is generally not recommended for sparkling white wine, some winemakers prefer to promote MLF to contribute to organoleptic complexity. Oenococcus oeni is generally the bacterium of choice for MLF. However, people’s interest in other species (such as Lactobacillus) is increasing. However, one disadvantage of lactobacilli is that they are more sensitive to low pH and SO2, and some producers of starters inoculate high doses of non-growing bacteria in grape musts. This work aims to grow some selected strains of Lactobacillus in grape juice and perform early MLF. With this strategy, beyond performing the MLF homolactic bacteria can contribute clearly to maintain or even decrease the final pH in wines by producing lactic acid from sugars; they also produce more complex wines, and prevent the spoilage of an undesired late MLF in bottles. 

To perform this selection, twelve Lactobacillus strains were successively inoculated after adapting to the lowering of pH and the increasing concentration of SO2. The cell concentration of the inoculum was in the order of x 106 CFU/mL to allow growth and synthesis of lactic acid. All Lactobacillus strains gradually adapted to low pH and SO2 and could grow at pH 3.2 and the highest SO2 concentration, thereby maintaining or even increasing their final biomass. After 7 days, all strains always underwent MLF. Malic acid consumption rate and lactic acid production depend on the strain. The final pH of wines was maintained or even decreased, even when complete MLF was achieved. This strategy helps in biological acidification of wines against the loss of acidity derived from climate change.