A novel culture medium for Oenococcus oeni malolactic starter production

- OPM has been improved to grow O. oeni at high cell densities, able to survive in wine and perform MLF.
- The composition of OPM medium permits to reach a population of O. oeni of CFU = 1 × 109 mL−1 in 6 d.
- Scale-up of the process generates 80 L of O. oeni starter culture (CFU = 1 × 109 mL−1) in 22 d.
- OPM allows bacteria to adapt to wine conditions, consuming all the malic acid in 7 d.
- Cells grown in OPM can be efficiently preserved at 4 °C, −20 °C, or freeze-dried.

Malolactic fermentation is essential in wine quality. One of the strategies used to control this fermentation involves the inoculation of selected lactic acid bacteria, mainly Oenococcus oeni. Laboratory media usually produce large amounts of biomass, but with little or no adaptability to wine. We propose a culture medium to grow and pre-adapt O. oeni cells, and the steps to scale-up production. To achieve this objective, 27 different media were tested. All contained grape must and wine, and nutritional supplements in order to benefit bacterial growth. Those media contained different ethanol levels, pH values, and grape must concentrations. The optimized culture medium named Oenococcus Production Medium (OPM) contained diluted commercial 4X concentrate white must (1:6), ASv = 4%, and a pH of 3.8. The total time to obtain 80 L of an O. oeni liquid starter culture from the stock culture at the laboratory, with a final population of CFU = 1 × 109 mL−1, was 22 d. The starter culture was efficiently scaled-up, and preserved at 4 °C, −20 °C, or freeze-dried. This new culture medium also allowed adaptation of bacteria to the wine conditions, consuming all malic acid (3 g/L) in 7 d with an inoculum of CFU = 1 × 106 mL−1.