Malolactic Fermentation is the final step in making young wine. We cover it in the Cellar section because it is managed in the cellar. There are three steps

  • Racking the pressed or free-flowed wine: We let the sediments settle, then rack the barrels, the variable capacity steel tank or the mixing tank into the barrels and keep the remainder in a fresh topup tank.
  • Initiate the Malolactic Fermentation: we may inoculate with malolactic bacteria and add nutrients. Then we maintain the temperature at around 70°F until it the fermentation is completed (this may take 1-6 months)
  • Rack the wine: We let the sediments settle, then rack the barrels and the steel tank, top up the barrels from the steel tank, and protect all wine with SO2


Racking is about removing sediments from the bottom of the barrels or the steel mixing tank. At this juncture, the sediments consist mostly of dead yeast cells and other remanents of the fermentation.


Malolactic Fermentation

In the Malolactic Fermentation malic acids are transformed into lactic acids. This 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.  If they have been killed by an earlier SO2 addition, they may be purchased from specialised laboratories/providers and added back in. If the Primary Fermentation was done naturally (i.e. no SO2 was added at crush), then the Malolactic Fermentation is usually also left to occur on its own. Here is a more detailed discussion of the process and potential pitfalls from

Barrel Boxes for Temp Control.jpg

Malolactic Fermentations takes between 2 and 9 months, and its progress should be measured by tracking the concentrations of malic and lactic acids. During ML fermentation, the temperature should be kept at around 70°F, and it can help to stir up the sediments bi-weekly, at least in the beginning. Because the cellar is kept at 55-60 oF the barrels with wine undergoing ML fermentation, need to be kept in a separate compartment and slightly heated. We built insulated warming boxes shown in the picture, open on the left, closed on the right. A heating pad slides under the barrel on a tray. The heating pad is controlled by a temperature controller. The temperature is monitored with a probe inserted through the bung

Thus following inoculation with lactic bacteria, we have a monthly process (which coincides with the regular cellar monitoring process of the older wine still in barrels – as described in the Barrel Ageing page):

  • Open the vessels and stir the lees (dead yeast cells and other sediments)
  • Take samples and top up the barrels with wine from the topup tank
  • Taste and measure temperature, chemical properties and spectra for phenolics.

In the past, we used a paper chromatography test every month, or two confirm completion of the malolactic fermentation. This proved to be too time-consuming. Since 2017, Malic and lactic acid measurements are part of the OenoFoss analysis.


Rack & SO2

Once the  Malolactic fermentation is completed we rack again in the cellar where ambient temperatures are stable at around 55-60 °F. Next, we protect the young wine by adding SO2. How this is done is described in the Laboratory Section on page Measuring and Adding SO2.


Data Management

We enter actions regarding Malolactic Fermentation in the Cellar Actions table. This screenshot shows the cellar actions on Jan 31, 2018, when we inoculated the 2017 barrels with malolactic bacteria (samples # 6 & 7)

DataM ML Input.png


Last harvest: 2017 vintage

In 2017 we decided free-flow the juice directly into barrels rather than into a temporary holding tank. We removed the rough lees, seeds and few skins by running the freeflow through a sieve.

Since we had not used any SO2 yet, we hoped for an indigenous  ML fermentation. However, when we could not measure any conversion after a month, we decided to inoculate with malolactic bacteria (Viniflora CH16).

The following screenshots show the detail for the two barrels

DataM Cellar Batch Review wb1.png
DataM Cellar Batch Review wb2.png




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Last updated: February 26, 2018