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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
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Response by Alison Crowe.