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Why The Tiny Bubbles?

TroubleShooting

Tom DuKet — Topanga, California asks,
Q

I have a batch of white wine from grapes that I picked in heat, had crushed/ destemmed and bladder pressed. I took home juice in ice chests I have previously used (and cleaned) for several harvests. I transferred the juice to a 6.5-gallon (25-L) glass carboy as soon as I got home. I’m pretty careful about keeping it clean but I’m getting tiny bubbles that look like the wine is going through malolactic fermentation (MLF). I did not inoculate with lactic acid bacteria. My Brix is at -3 and I do not taste or smell Brettanomyces or any other funk but I worry I will. What bacteria can produce tiny bubbles in a dry must other than malolactic bacteria, and how concerned should I be that my wine is infected?

A
There are so many microbes that can produce tiny bubbles in new wines that perhaps your question should be, what microbes will not produce tiny bubbles in dry must? Everything from (of course) Lactobacilli (AKA LAB or lactic acid bacteria) to Acetobacter (which produce acetic acid) to spoilage yeasts like Brettanomyces will produce carbon dioxide gas as they go about their metabolic business. The very fact that these organisms can survive in a sugar-dry (no fermentable sugars left) environment means that they are at a special risk for stored and bottled wines. Before you finger one of these microbes, however, do be aware that lactic acid bacteria are generally present in the environment to some degree and even if you didn’t inoculate with them you may have a spontaneous malolactic fermentation happening in your wine. For this reason, unless you add sulfur dioxide immediately upon the halt of primary (sugar) fermentation, you may want to inoculate to make sure your malolactic fermentation goes to completion with the microbes of your choice. This way you know that there is no more
Response by Alison Crowe.