How would a winemaker prevent malolactic fermentation from taking place?

Dear Dr. Vinny,

How does a winemaker avoid or prevent malolactic fermentation from taking place? I read about a Chardonnay that was “barrel-fermented but non-malolactic.” What’s the process for this?

—Ryan, Sacramento, Calif.

Dear Ryan,

Malolactic fermentation (the cool kids call it “ML”) takes place after the primary fermentation, which converts sugar to alcohol. In ML, bacteria convert malic acid (think tart green apples) into lactic acid (think cream). (Strictly speaking, ML is a “conversion,” not a true “fermentation.”)

Most red wines and many whites are intentionally put through ML to enhance their stability and complexity. If a wine is put through ML intentionally, it also helps prevent it from taking place accidentally, in the bottle, which can turn a wine into a cloudy, smelly, fizzy mess.

If malolactic is stylistically undesired—if, for instance, those tart green apple flavors are just what a winemaker wants—ML can be prevented with one of three main methods: by adding sulfur dioxide to kill the bacteria that cause it, by filtering the wine to remove them, or by putting in a malolactic-inhibiting enzyme before bottling.

Plenty of delicious wines don’t go through ML, including some of my favorite crisp whites. For example, most Sauvignon Blancs never go through ML. I think you caught on that it is a bit unusual to barrel-ferment a wine but then prevent ML—after all, barrel fermenting and ML go very well together to create rich wines. But there are no fixed recipes. In the situation you describe, the winemaker might like the textural richness or flavor that barrel fermenting imparts, but still want to show the wine’s natural acidity.

—Dr. Vinny