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What Could Lead To A Stalled MLF


Steven Mickelson — Chelan, Washington asks,

I have a small vineyard in the Chelan AVA (Washington state) and grow Merlot, Syrah, Malbec, Cabernet Sauvignon, and Cabernet Franc. This harvest season was late and ended prematurely (before full ripening) due to a hard freeze. The grapes other than the Merlot were only borderline ripe. Fermentation progressed nicely in all varieties, but only the Merlot successfully underwent MLF (malolactic fermentation). MLF in the others will not start despite re-inoculation attempts with three different commercial MLF strains (Wyeast 4007, Viniflora CH16, and Enoferm Alpha). Alcohol and pH are between 12.5–13.2% and 3.4–3.6, respectively, in the Syrah, Malbec, and Cabs. This has never been an issue in the past. Help!


Malolactic fermentations tend to stall, or not catch on at all, due to these seven most common factors:

  • High alcohol: Over 14.5% and most strains will go through slowly. Over 15.5% and most strains will completely balk at the prospect. You don’t seem to have this problem.
  • Low pH: Below 3.3 and strains will slow down and struggle. Below 3.2 sometimes won’t take off at all. At 3.4–3.6 range, your wines don’t seem to have this issue. Bacteria like a higher pH environment and your wines are right in their zone.
  • Cold temperatures: I like to keep my temperatures for MLF above 60 °F (16 °C) if possible. In colder climes, and especially during the “ML time of year” (late fall and winter) it’s tougher and tougher for home vintners to keep our ferments warm as so many of us use garages, basements, and outbuildings for our winemaking. Often our cellars are uninsulated.
  • Old/expired/dead strains: Since you’ve tried with three different commercial strains, I doubt this is your problem, but do make sure you are checking expiration dates and that you’re buying from a reputable supplier with high turnover. You want to buy only un-opened packets; sometimes a small fermentation supply store will un-bag dehydrated malolactic bacteria and parcel it out into smaller containers for their buyers. This is well-intentioned but ill advised as the moment the freeze-dried bacteria encounter air, their quality and potency would begin to deteriorate.
  • Choice of strain: In challenging conditions (low pH, high alcohol, etc.) you need a robust ML strain that’s up for the job. Wine-supply companies often sell different kinds so be sure to read the details. Some are bred especially for high alcohol, low pH conditions, or both. If you have any of those challenges be sure to buy accordingly.
  • Not following storage and use instructions: Once you purchase your ML strain for the year make sure you are following the storage instructions regarding temperature and conditions to the letter. Don’t forget — an open packet of ML bacteria cannot be used from one year to the next so please be sure you’re buying fresh strains every year. When inoculating your wine, make sure you’re also following instructions exactly and that you aren’t trying to spread too few bacteria over too much wine. Some of my winemaking buddies try to save money by first inoculating one batch and then trying to spread some of that batch to other lots . . . this can work if all the stars are in alignment (pH, temperature, alcohol, etc.) but is still risky if you have any historical difficulties with getting wines through ML fermentation.
  • Low nutrient base wine: Believe it or not, ML bacteria need good nutrition just like yeast cells, especially if environmental factors (high alcohol, low pH, or low temperatures) are going to be a factor. I know it sounds like one more thing to buy for an already expensive hobby, but purchasing ML bacteria micronutrients and stirring them into your wine before inoculation can really make a difference between a complete ML fermentation and an incomplete one. Most fermentation supply houses that sell ML bacteria can recommend a product. You only use very small amounts (less than a ¼ tsp. per 5-gallon/19-L carboy) so a little goes a long way.
Response by Alison Crowe.