On the winemaking front, things have been pretty quite as of late. My 200 lbs of Eaglepoint Ranch grenache has been destemmed, crushed, fermented, pressed and is presently undergoing malolactic fermentation or “ML”. This is an important part of the red (and sometimes white) winemaking process.
What exactly is Malolactic Fermentation?
ML or Malo is the process in which certain strains of bacteria (Lactobacillus, Leuconostoc and/or Pediococcus) metabolize the harsh malic acid (found in apples) present in the wine and transform it into the softer tasting and less acidic lactic acid (found in milk).
Although ML process is commonly referred to as a secondary fermentation (because CO2 is produced), in truth ML is not a true fermentation because no additional alcohol is being produced from the metabolism of sugars.
These bacteria are often naturally present in the fermenting wine, however you can purchase malo cultures, like the one from Whitelabs pictured above, to ensure a more timely start to the process.
What is the purpose of Malolactic Fermentation?
1. Helps to reduce harsh acidity
2. Increases complexity by generating additional flavor components (ketones like diacetyl)
3. Increases the stability of the wine by consuming bacterial nutrients
4. This increased stability is especially important in red wines, as added sulfur dioxide will bind to anthocyanins (coloring compounds).
When does ML generally start?
Malolactic fermentation can begin either during or after the primary fermentation. There are pros and cons to both times. The pros: An MLF which begins at the height of primary fermentation and before pressing will often proceed more quickly. Why? A higher temperature, and ML bacteria benefit from the presence of grapeskins. The cons: ML bateria and yeast often compete for the same nutrients during the active fermentation.
Like all bacteria, ML strains thrive in higher temperatures (70-75 degrees F) and have an aversion to sulfur dioxide. For this reason, during ML, it is important to monitor the temperature of your wine (or at the very least the cellar) and to NOT add sulfur dioxide. Failure to do so can result in a stuck ML.
Above is a closeup of the wine in full ML. Like primary fermentation, ML does generate a bit of carbon dioxide, however in much smaller quantities. Throughout the primary fermentation, considerable amounts of CO2 help to protect the wine against oxidation and wine spoilage bacteria.
However during ML, much less CO2 is generated. For this reason it is important to flush out any headspace with an inert gas (CO2, nitrogen or argon) and keep airlocks tightly secured on each carboy.
Once malo does start the entire process can take anywhere from two weeks (very fast) to 6+ months (very long). The average time is generally around 1-2 months.
In the next week or so, I will check in on the progress of ML by using a procedure called paper chromatography.