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Visual Signs of MLF


Brian Testa — via email asks,

I’ve got about 5 gallons of Baco Noir that just finished fermentation. I live in the Finger Lakes region of New York and I understand that both the region and the grape I’m using means that high acid will be an issue. This is only my second attempt at winemaking, so I’m still learning the ropes. Given the higher acid content of this wine (0.8 after fermentation) I’m going to put it through MLF. I’m kind of fine with this, as there are many resources available on how to test for progress. However, none of the resources answer the simple question: Can I visually see MLF in action like I do with standard fermentation? Will there be any fizzing or bubbles? Is chromatography the only way to make sure that the bacteria have survived and are doing their job?

Great question. MLF (malolactic fermentation) can be a bit confusing for some because it’s called a “fermentation” but it’s certainly not as active, visible, smell-able and in your face as your primary sugar-to-alcohol fermentation. MLF happens when naturally-present (or artificially introduced) bacteria turn the malic acid in wine into lactic acid, producing a small amount of carbon dioxide gas and some aroma and mouthfeel components. I agree, you should put your Baco Noir through malolactic fermentation; it’ll de-acidify the wine a bit, round out flavors, and prevent MLF happening later in the bottle. MLF sometimes happens on its own, concurrently with the primary sugar fermentation, so it may go to completion without you noticing anything at all. After primary is over, most commercial winemakers will run an enzymatic assay that measures the level of malic acid in the wine — this way they can tell if MLF is complete or not. Most home winemakers don’t have access to the expensive equipment and reagents to do this kind of analysis, but luckily you can still send a sample of wine to
Response by Alison Crowe.