Malolactic Fermentation is the final step in making young wine. We cover it in the Cellar section because we manage it in the cellar. Following are key considerations
Decide whether to inoculate the wine in the settling tanks with malolactic bacteria and add nutrition or rely on indigenous bacteria in the wine to start the malolactic fermentation on its own. Alternatively, prevent the conversion of malic acids by killing the indigenous bacteria with SO2.
Monitor the progress of malolactic fermentation at every interaction with the cellar batch by measuring the concentration of malic and lactic acids. Malolactic bacteria require a minimum temperature of 63-65 dF, a bit higher than the average cellaring temperature; thus, the barrels will need to be heated.
Since the malolactic fermentation creates CO2, barrels with active malo-fermentation need to have a CO2 escape valve
Malolactic Fermentation
Malolactic Fermentation transforms malic acids into lactic acids. It reduces the acidity and harsh fruitiness of the young red wine and helps to create a rounder mouthfeel. This fermentation is not induced by yeasts (like the Primary Fermentation) but by lactic acid bacteria. These bacteria occur naturally in the vineyard on the outside of the grape skins and find their way into the must during crush. Specialized laboratories can provide commercial ML bacteria if an earlier SO2 addition has killed the indigenous bacteria. If the Primary Fermentation was done naturally (i.e., no SO2 was added at crush), then the Malolactic Fermentation is usually left to occur indigenously.
Malolactic Fermentations take one week to nine months, mainly depending on temperature. To track the progress, we measure the concentrations of malic and lactic acids. The ideal temperature for inoculated fast ML fermentations is close to 70°F. If we inoculate, we expect the fermentation to finish while the wine is still in the settlement tank. This is because the fermentation generates CO2, which must escape. Because our cellar is kept at 55-60 oF, we experimented with heated boxes for the barrels with wine undergoing an extended ML fermentation. A heating pad slides under the barrel on a tray. We control the heat with a temperature probe inserted through the bung. The CO2 generated must be released through a special valve in the bung. Otherwise, the pressure built up pushes the bung out. We used these heating boxes only for two vintages.
Example: 2020 vs. 2021 vintage
In 2020 we decided to inoculate the 2020CS fermentation batch at the end of the extended maceration period with CH Oenos 2.0 bacteria, as the Action tab in the REVIEW Fermentation Batch layout shows
Looking at the Acidity tab in the REVIEW Cellar Batch layout for the 2020CS1 barrel, we notice that the ML fermentation was completed before we filled the barrel; i.e., malic acids measured at 100 ppm, lactic acids at 1,000 ppm.
In 2021, we decided against inoculating with malolactic bacteria because we wanted to minimize interventions. Consequently, malic acids were measured still at 1,600 ppm at the beginning of the elevage. However, malolactic fermentation started on its own a few weeks later.
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Last updated: May 25, 2022