Ask Wine Wizard

Can I have some advice on malo-lactic fermentation and its impact on acidity?



Dear Wine Wizard,

I raised the TA of the must from 0.5 to 0.6 at the beginning of fermentation for my red wine. Should I still add malolatic bacteria to start MLF knowing that it will reduce the TA?

Tony Querio
Troy, Michigan

Wine Wizard replies: For most homemade red wines, actively encouraging the malo-lactic fermentation (MLF) is a good thing as it can add some flavor complexity and also stabilizes it against post-bottling MLF (always a fizzy catastrophe) by pre-emptively getting rid of the malic acid present in the wine. As opposed to starting MLF concurrent with fermentation, I suggest adjusting your acid pre-primary fermentation, see your wine healthily through primary and then check the acid again once primary is complete. Primary fermentation will typically lower a TA — be sure to de-gas your sample before you run the analysis!. If it’s not totally low (say, under 5.0 g/L, go ahead and put the wine through MLF and see where the acid comes out. If you need to adjust up to get it to that point, go ahead — you don’t want any “bad” bacteria (like acetobacter) taking advantage of a low-acid situation. Once you are through MLF, you can adjust the acid however you wish. The deal is that MLF bacteria are happier at a lower TA than yeast are, and what will make yeast (and your tastebuds) happy aren’t necessarily the same. For MLF bacteria — when we’re talking about typical wine TA and pH ranges — the lower that you are comfortable to go, the better.

MLF is a series of metabolic reactions carried out by a group of bacteria commonly called “the malo-lactic bacteria” in which the organism consumes malic acid (di-protic, or with 2 hydrogens and therefore more acidic) to lactic acid (mono-protic or with 1 hydrogen and therefore less acidic). The byproducts are CO2 and diacetyl. MLF can also contribute other more unhappy-smelling by-products which may spoil a bottle of finished wine. MLF can and often will happen spontaneously at any time during a wine’s life. By depleting the supply of malic acid early on, a winemaker lessens the chance of malo-lactic fermentative spoilage later, when a wine may be ready.