Direct inoculation cultures can be directly added to wine after being rehydrated. Quick build-up cultures require a simple 12-24 hour rehydration step using an acclimated culture of Oenococcus oeni and an energizer/activator (included in kits). Standard cultures must go through a build-up protocol prior to inoculation of the wine. The standard build-up process can take from 5 to 20 days to prepare.
ML should be inoculated at the end of primary fermentation. This helps avoid competition with the yeast that can lead to stuck fermentations. Bacteria can also produce large quantities of volatile acidity (VA) while fermentable sugars are present.
An optimum environment for malolactic bacteria includes a temperature between 20-25°C (68-77°F), alcohol below 13% (v/v), total SO2 below 25 ppm, pH above 3.4, little or no oxygen, low levels of short and medium chained fatty acids, low levels of organic acids and low levels of polyphenols.
If your wine is bordering the optimal limits for the bacteria environment, nutrients may be desired. Malolactic rehydration nutrients like Acti-ML can provide more surface area to keep bacteria in suspension, and can help strengthen the bacteria growth under difficult conditions. Other nutrients like Opti’Malo Plus can be useful to create an environment that promotes clean and quick MLF.
If your VA is creeping, you may already have lactic acid bacteria (LAB) present in your wine. Before inoculating first control the VA problem by assessing contamination and treating with lysozyme, SO2 or whatever is appropriate for the situation.
Air traps can be used to see if metabolism is occurring in the wine. Also paper chromatography can normally be used to monitor the production and reduction of lactic and malic acids. Another method is to listen for the small bubble “spritzing” usually found in these fermentations.
Traditionally SO2 has been used to control the rate and occurrence of MLF, however lysozyme can be used effectively to control the aspects of MLF and reduce the total amount of SO2 needed. Ultimately, sterile filtration is the best way to ensure complete removal of malolactic bacteria.
A bacteria culture will retain some of its viability even after being opened. Once opened, however, the bacteria media will become susceptible to contamination. Exposure to moisture in the air can encourage the bacteria to start growing in the package, thus reducing viability significantly. If you do decide to save your leftover bacteria, store in a dry, sealed container below 0°C and used within a short period of time (1-2 weeks).
For short periods of time, bacteria can be stored in the refrigerator at 40°F, however for longer viability store in a freezer below 32°F. Be sure to let the bacteria sit at room temperature before beginning rehydration.
Cultures are marked with production dates and expected viability under different temperatures. (12 months at 40°F and 18 months at 0°F.)
Diacetyl is the chemical responsible for the buttery character found in white wines that undergo MLF. Diacetyl is formed as a by-product of the catabolism of pyruvate, which is often derived after MLF from citric acid sources. Citrate and oxygen concentration will increase diacetyl levels while living yeast cells and SO2 levels in the wine will reduce concentrations. The ML strain used will also have an effect based on its catabolism of citric acid. Thus, there are multiple factors to think about when addressing the “butter issue”. The initial state of the wine, winemaking method (for example sur lies) and choice of bacteria strain all must be considered.