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Malolactic Fermentation Timing


Paul Mazzeo — Osterville, Massachusetts asks,

I make 60 gallons (227 L) of Cabernet Sauvignon each year, which i press into glass carboys. My question is, when and to what container should I add the malolactic bacteria and nutrient? Should each be added to the primary fermenter before press, should I press and add small amounts of both to all (10) carboys, or press and after two days rack each carboy adding the bacteria and nutrient to each?


I’m a little old school when it comes to malolactic fermentation, but it’s always served me well. There are some winemakers who try to get a jump on malolactic (ML) completion and co-inoculate with ML bacteria and wine yeast at the same time, but in my mind this is a little risky. You see, yeast and bacteria actually “talk” to each other during fermentation and sometimes they don’t like what they hear. In fact, Dr. Linda Bisson’s lab at UC-Davis just published a really interesting study showing how wine bacteria “query” the environment to check for competitors and adjust their metabolic process accordingly. Too many mixed messages in some cases can cause problems with fermentation completion, higher volatile acids, and other non-optimal outcomes.

The take-away for me is that I like to let the yeast do their job eating sugar first (and making carbon dioxide and alcohol) undisturbed by too many outside competitors. Once they die off after primary fermentation (and the fermentation is hopefully dry), I press off my new wine and immediately add my ML bacteria and any ML nutrients together at the same time to the container holding the new wine. If you add your ML bacteria and ML nutrients before pressing off you’ll lose a lot of the dose (and those additives are expensive!) in the skins, which get discarded. Also, once you have the wine separated from the skins you know how much wine volume you have so you can measure your bacteria and nutrients accurately. It’s really hard to tell your final liquid yield when the wine is still sitting on the skins.

I would add your malolactic bugs and nutrients evenly into your carboys right away. This way you can also take advantage of any residual warmth carried over from the primary fermentation.

Response by Alison Crowe.