Winemaking Terms 101: Malolactic Fermentation

I had a request recently to breakdown Malolactic Fermentation. What is ML, or MLF or Malo, as it goes by? Well, it’s a secondary fermentation that converts the harsher Malic Acid (think of a granny smith apple) to the softer Lactic Acid (think Milk) via Lactic Acid Bacteria (LAB). How? Well, you warm the wine and add the LAB (which consists of bacterium Lactobacillus, Pedioccocus, and Oenoccoccusoeni), ML is initiated. However, ML can occur spontaneously anytime during or after the initial alcoholic fermentation. The purpose of ML for red and white wines are similar. In reds, ML makes the wine more drinkable younger by lowering the overall acidity and making it softer on the palate. It is used in medium to full bodied reds where complexity is desired over fruitiness. ML in reds emphasizes fermentation aromas over fresh fruity aromas. And it makes the mouthfeel rounder, fuller, velvety, lusher as opposed to super tart (acidic) reds.

For whites, because it can mask fruity aromas, ML is really only desired for Chardonnay or other less ‘aromatic’ varietals. For example, ML would not be a great idea with a Sauvignon Blanc or Riesling with their very expressive fruit-driven notes. In Chardonnay it adds texture and flavors (complexity) to the wine.

When ML is not desired, to suppress it, a winemaker can filter and fine the yeasts out of the wine, or they can make sure the wine stays cool and add SO2 (Sulphur) the wine. Also, for ML to occur, the wine must have less than 14% alcohol and a PH of less than 3.3. Also grape pulp and yeast sediment is necessary to promote it’s growth in the wine.

So, the advantages to ML in reds and some whites is that it adds complexity to the wine. Flavors of butter (diacetyl), caramel, and a lush mouthfeel are the optimal results. Disadvantages to ML are that it can cause the PH to rise (which means lower acidity in a wine, which is problematic for warm climate wines that are naturally lower acid-wise). To counter this problem, winemakers add acidity to the wine. Another problem with low acid wines is that they are prone to bacterial infection and require more sulphiting. Also, Partial ML in a wine bottle can cause unintentional carbonation to occur, which would push up the cork and spoil the flavor of the wine. Take note the next time you order a bottle of wine and refermentation has will taste sparkling and lacking in clean flavors. Not cool. Another reason to store your wines at the proper temperature!! And it can take up to 2 months, and can start and stop and start and stop, which can be frustrating to the winemaker.

As you can see, there are profound advantages and disadvantages for ML. In my opinion, it should be done with caution and focus and only on certain wines.


Me, pushing down the cap to Fermenting Zinfandel!


winesmartiesWinemaking Terms 101: Malolactic Fermentation

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