Malolactic fermentation (MLF) is a winemaking process involving a special bacterial strain that metabolizes the malic acid naturally found in grapes into lactic acid. Lactic acid is a weaker acid than malic acid so the effect of this conversion is a decrease in the wines acidity along with a corresponding raise in the wines pH. As an additional benefit, the bacteria also add mouthfeel and complexity to the wine. (Complete information on MLFs can be found in our Malolactic Fermentation Manual).
Malolactic Fermentation For All Wines?:
Completing a malolactic fermentation adds to the stability of a wine: once the malic acid is gone it is no longer available for any potential spoilage bacteria capable of metabolizing it to make undesirable flavors and aromas in our wine. However, it should be noted that as convenient as this stability is, malolactic fermentation does influence the fruit profile of a wine:
- For red wines this impact is most always beneficial, and we recommend an MLF for all red wines.
- For white wines, doing a malolactic fermentation may not always be desired: If you are looking for an opulent, fuller/fatter styled wine like many Californian Chardonnays and some styles of Sauvignon Blanc, then a complete MLF is recommended. However, if you are after a lighter, crisper styled white wine, then you probably do not want to change the fruit profile in any way. In this case, an MLF is not recommended.
- The winemaker also has the choice of doing a partial MLF; where an MLF is started for some complexity then stopped with SO2 before completion to maintain more of the original fruit profile.
Malolactic Chromatography Testing:
To monitor the progress and/or completion of a malolactic fermentation, we use a malolactic chromatography test kit. Using the kit is pretty straightforeward: sample wine is spotted onto a special piece of paper which is rolled into a cylinder and placed standing into a small amount of a developing solution. Over the next 8 hours the solution wicks up the paper and carries the acids in the wine sample up with it. Once finished, the paper is removed from the solution and allowed to dry. As it dries, the paper turns blue/green and the acid spots show yellow. You read the chromatography test by the presence and size of the malic acid spot as it relates to the lactic spot. That's it! (Complete instructions for prepping and reading a chromatography test can be found in MoreWine!s Chromatography Test Kit Instructions.)