Troubleshooting Your Wine
The faults and flaws and their analysis and resolution presented below are from my latest book, Modern Home Winemaking, where you can find additional information should you wish to explore these further.
STUCK MALOLACTIC FERMENTATION (MLF)
DESCRIPTION
When lactic acid bacteria (LAB) prematurely and unexpectedly stop converting malic acid into lactic acid where there is no sign of activity or progress judging from chromatography analysis, the condition is termed a stuck MLF. If LAB are still working but the MLF is taking an unusual amount of time, more than a couple of months, the condition is termed a sluggish MLF. Here we will treat both conditions as a stuck MLF for the purpose of implementing a restart protocol.
A stuck MLF that takes several months to complete can open the door to spoilage microorganisms that can cause undesirable organoleptic deviations or outright spoilage as the wine is not yet protected with SO2.
CAUSES
The most common causes of a stuck MLF are usually related to environmental and wine chemistry conditions outside the specifications of the LAB, for example, the temperature might be too cold, pH is too low, ethanol level is very high, there is too much SO2, or from a lack of nutrients.
To maximize your chances of a successful MLF, observe the following recommendations (or as per your LAB’s specifications) to the extent possible:
- Alcohol level (% ABV) below 15%, which means a SG of 1.110 (26 Brix)
- pH above 3.2
- Maximum total SO2 level around 40–50 mg/L
- Temperature in the range 18–22 °C (64–72 °F)
High TA (total acidity) due to high malic acid can also be a problem as the acid is converted into inhibitory levels of lactic acid.
High levels of DO (dissolved oxygen) can also inhibit (anaerobic) LAB; avoid racking prior to or during MLF.
ASSESSMENT
It can be very difficult to relaunch a stuck MLF depending on the cause and the amount of malic acid available.
Unless pH has dropped below the LAB’s critical level during MLF, wine pH is seldom the problem, unless combined with an addition of SO2. And if you had started with a high-SG/Brix must, it was recommended to initiate the MLF as early as possible to avoid the LAB having to work in a high-alcohol environment. Trying to relaunch an MLF in a high-alcohol wine — greater than 16% ABV — may be a futile exercise.
REMEDIAL ACTIONS
You have to try and complete the MLF, or else, you will have to stabilize the wine with SO2 and lysozyme or chitosan to avoid a renewed MLF in bottles.
Measure total SO2, if so equipped, to make sure that it is not beyond the LAB’s specification. This would only happen if you added excessive amounts of potassium metabisulfite (KMS) prior to the MLF or if the yeast strain used for the AF has produced large amounts of SO2. Adding KMS post AF, but pre MLF, is a common mistake with beginners. Removing SO2 is not simple, and if this is the problem, your best bet is to stabilize the wine with lysozyme or chitosan.
If all looks good, try increasing the temperature towards the upper range of the LAB’s specification, and if that does not work, you will need to implement a restart protocol.
Go the RESTART PROTOCOL.
PREVENTIVE ACTIONS
Follow the recommendations in the ASSESSMENT section above.