Interactions between Commercial Wine Yeast and Malolactic Bacteria

Commercial yeast and lactic acid bacteria (LAB) starter cultures are commonly used to promote the alcoholic and malolactic fermentations (MLF) in winemaking. MLF is especially important in cool climate grape growing regions (e.g. New Zealand) where high acid wines are produced. MLF reduces acidity, as malic acid is decarboxylated to the weaker lactic acid. Wine yeast and LAB are not necessarily neutral in association and can interact in vinifications. For example, the yeast can cause inhibition or stimulation of the LAB which may result in delay or promotion of MLF. The aim of this research was to screen commercial yeast strains for their inhibitory or stimulatory action on wine LAB using an agar diffusion assay. Subsequently, observed interactions were confirmed in actual grape juice fermentations, and the timing and mechanism of inhibition/stimulation during a fermentation was investigated.