Restarting A Stuck Malolactic Fermentation

Stuck Malolactic FermentationI have a Chilean Pinot Noir from fresh juice. I have a stuck malolactic fermentation. I’ve added malolactic culture when I inoculated my wine… Yesterdays MLF test read 75, pH 3.4, Free SO2 18-28, but my acid was .90%, too High?. Temp is 73 degrees. I’ve added malolactic culture twice. Should I try lowering the acid? Can I add sulfite and move on? Suggestions ? Thanks in advance

Name: John F.
State: Mass.
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Hello John,

I am assuming that the yeast fermentation has completed and you have an SG in the neighborhood of .996 on your hydrometer.

Going through the numbers, the only thing that concerns me is the SO2 (sulfite) level of the wine must. I would rather see it at around 10 to 15 ppm. I’m not saying this is what’s causing the stuck malolactic fermentation, but it very well could be contributing to it. Some experimentation may need to be done with aeration to lower the SO2. This could be as simple as racking the wine in a splashing manner. This alone could be all that is required for restarting your stuck malolactic fermentation.

Dropping some acid out may be helpful, as well, but I do not believe this is the root cause, either. At a total acidity of .90% you need to drop some acid for flavors sake, anyway, so go ahead and start this process to get it down to .80% for now. More readjusting may be needed after the MLF has completely run its course. Lowering the TA could also help with restarting a stuck malolactic fermentation.Shop Malolactic Culture

The temperature and pH of the wine are fine. I would not be concerned with them at all.

Realize, that an MLF can take months in some cases to finish. It is a function of how much malic acid there is to ferment. Each situation is different. Your malic is currently at 75 ppm, but this does not reflect how much has already been converted into lactic. Is this number lowering over time. That’s what’s important.

If you have not tasted the wine, I would do so now to see if too much lactic acid is starting to form. This will be noted as a sour-tang. If it is too noticeable or forward, then I would add sulfites such as potassium metabisulfite to the wine and move on. The rest of the excess acid can be reduced with neutralizers such as potassium bicarbonate.

If the wine does not have a forward sour-tang, then wait 3 weeks and take another malic reading. If it has dropped some, then you do not have a stuck malolactic fermentation. Just be patient. The wine will need to age anyway. What’s wrong with it aging while it’s doing its MLF?

As for the malolactic culture, I would not add any more. Too much, could set of an autolysis reaction that can add a bitter-nut to metallic flavor to the wine. This is something that is irreversible.Shop Wine Barrels

Restarting a stuck malolactic fermentation is something that very rarely needs to be done. It’s just that sometimes it can progress very slowly with time and patience being the only remedy. I you do have a stuck malolactic fermentation, just remember it is usually because of the environment the fermentation and not the lack of malolactic culture.

You can find more information on our website in the article: Malolactic Fermentation.

Happy Winemaking,
Ed Kraus
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Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.