Oenococcus oeni is the lactic acid bacteria commonly used in malolactic fermentation (MLF). When grape sugars are available, O. oeni will ferment these sugars as their primary source of carbon for growth.
MLF is a survival mechanism that supplies energy to the bacteria when other nutrients become scarce. MLF converts naturally occurring malic acid to lactic acid, through the decarboxylation of L-malate to L-lactate.
Malolactic bacteria are present in low concentrations on grapes, approximately 100 cells/g, but then they increase to 104 cells/mL after crush and 107 cells/mL by the end of alcoholic fermentation when malolactic fermentation typically occurs. The metabolism of sugars and organic acids during malolactic fermentation can be divided into three phases:
- During the growth phase (Phase I), sugar catabolism occurs with little production of acetic and lactic acid; minimal citric and malic acid are metabolised in this phase
- As the bacterial cell numbers increase above 5 × 106 cfu/mL during Phase II, the catabolism of sugar ceases and malic acid metabolism proceeds accompanied by production of lactic acid; citric acid remains untouched at this stage, and there is no acetic acid produced during malic acid degradation.
- Phase III is characterized by the metabolism of citric acid accompanied by an increase in acetic acid. The increase of lactic acid content in the wine results in a softer mouth-feel and the acetic acid contributes to the volatile acidity of the wine
References:
1. Scott Laboratories Malolactic Bacteria.
2. Swiegers, Jan, Bartowsky, Eveline, Henschke, P.A. & Pretorius, I.S., Microbial modulation of wine aroma and flavour, Australian Journal of Grape and Wine Research, 2005, 11. 139 - 173. 10.1111/j.1755-0238.2005.tb00285.x.
3. Whitney Lysbeth Beaman, Effect of Cell Density and Growth Phase on Malolactic Fermentation by Oenococcus oeni, May, 2011.
3. The Australian Wine Research Institute, Achieving Successful Malolactic Fermentation
Other related blogs:
Malolactic Fermentation
Diacetyl Formation
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