Oenococcus oeni is a species of lactic acid bacteria that is used in winemaking to perform malolactic fermentation, a conversion of malic acid to lactic acid. Not much is known about the impact of cell concentration and stage of growth on the ability of O. oeni to metabolize malic acid, but this information would be useful to winemakers who experience stuck malolactic fermentation. Corresponding optical absorbance at 650 nm and concentration data, based on viable cell plating, were collected for Alpha and MCW strains of O. oeni over time. This data was used to estimate viable cell concentrations and timing of growth phases for each strain using optical density measurements. Each stain was grown up to late stationary phase, washed and resuspended in buffer. Cells were then diluted to concentrations of 107 cells/mL, 106 cells/mL, 105 cells/mL, 104 cells/mL, 103 cells/mL, and 102 cells/mL and placed in a buffer that did not support growth. Malic acid was added, and samples were taken every half hour for four hours and analyzed for malic acid concentration by enzyme assay. This was repeated with cells that were harvested at the early exponential, mid exponential, late exponential/early stationary, and late stationary phases of growth adjusted to cell concentrations of 107 and 106 cells/mL. Results indicated that both strains performed malolactic fermentation from mid exponential to late stationary phase and that there was malolactic fermentation activity at both low and high concentrations (102 and 107 cells/mL). No conversion of malic acid occurred in cells harvested at the early stationary phase of growth.