Ask Wine Wizard

What can I do to prevent my recurring problem of excess CO2 in my wines?


Laurie Hammack — via email asks,

I seem to be having a recurring problem of excess CO2 (bubbles) in my wines. The wines are bubbly long after fermentation is finished. They have all been racked at least once and are stored in glass carboys. What do you suggest I do to get the wines settled down prior to bottling?

Unless you artificially carbonate your still wines by kegging them, there is only one possible source of carbon dioxide in wines — microbes, specifically little bacteria and yeastie beasties that love to inhabit wine even after all of the fermentable sugar has been used up. If you’ve measured your wine for dryness by using a hydrometer — and it sounds like you have — you’re most likely experiencing the joys of a prolonged malolactic fermentation. Malolactic fermentations occur when certain strains of bacteria eat the malic acid naturally present in grapes and spit it out as lactic acid and carbon dioxide gas. Some strains are better for wine quality than others, but many common malolactic bacteria can be found just floating in the air around us. There are some less common spoilage microorganisms that produce carbon dioxide, but malolactic bacteria is likely your number-one culprit. In order to get the carbon dioxide to come out, I suggest you take the patient approach — wait. Eventually the malolactic bacteria will consume all of the malic acid and will no longer produce
Response by Alison Crowe.