Diving into a relevant topic this month – as many of the wines in our cellar are currently undergoing this type of fermentation – it is a good time to demystify the term, which is often used in the context of winemaking, but not always understood.
First, some basic chemistry. In winemaking, primary fermentation is the process through which grape juice (or must) is turned into wine. Yeast (usually Saccharomyces cerevisiae) converts the sugar in the must to alcohol and CO2. Malolactic fermentation (also referred to as MLF or just ‘malo’) is a secondary fermentation, that can take place shortly after primary fermentation is complete. MLF is undertaken by a family of bacteria called lactic acid bacteria (Oenococcus oeni) but can also be done by species of Lactobacillus and Pediococcus. These bacteria convert the malic acid found in the wine to a different type of acid – namely lactic acid.
The main result of MLF is a change in mouthfeel. Malic acid is associated with a more tart, green apple taste, while lactic acid gives a more buttery, rich taste and mouthfeel. MLF in winemaking is not a necessary process, and the decision whether to allow a wine to convert malic acid to lactic acid depends on the style of wine desired. The climate of the area also plays a role. As MLF conversion causes a drop in acidity, it may typically be more desired in cooler areas (e.g. Elgin, or specific parts of Burgundy), where wines might show higher acidity. Conversely, warmer climate wines may have lower acidity to begin with, and MLF conversion might not be required or wanted.
At Oldenburg, Nic is selective in which of our white wines undergo MLF. Wines destined for <CL°, for example, aren’t put through MLF, allowing them to retain their fresh, fruity characteristics. He may choose partial MLF on some of the barrel components, but as excessive MLF can create an extremely buttery richness (think heavy-hitting California Chardonnay), it is important to monitor the progress of MLF through both tasting and analysis.
All the Oldenburg Vineyards red wines undergo MLF, and Nic inoculates with Oenococcus oeni to ensure the right strain of bacteria drives the fermentation. MLF can easily occur naturally (as the bacteria are already present), but the pH of the wine plays an important role in which specific strain dominates. If the wrong strain drives the active fermentation, the wine could be left with a faulty character (for example, the dreaded “mousiness”). Next time you enjoy a wine with a particularly full, rich mid-palate, you can thank the process of MLF.