Ask Wine Wizard

Acetobacter Problems


Mike Rodriguez — Fayetteville, North Carolina asks,

My dry Merlot has been aging in a carboy in my garage for about four months. I made a kit and have racked it two or three times now. The wine has recently changed and not for the better. I’m noticing a distinct vinegar aroma whenever I un-stop the carboy. What is this, can I fix it, and is there any way to prevent it happening again?

Well, it seems like you have been paid a visit by a colony of Acetobacter, aka acetic acid bacteria. They love air, eat alcohol, and turn it into carbon dioxide and vinegar. Not fun. The biggest issue is that no matter what, once you’ve got them and they’ve produced a certain amount of acetic acid, (aka “VA” or volatile acidity) there’s little you can do to remove it from your wine. Bigger commercial wineries can hire in reverse osmosis filters to remove some of the VA for you, but sadly home winemakers make far too little volume to make this kind of treatment worthwhile. The only option really available to you is to blend this carboy out with other wine to lessen the level of the vinegar smell. However, you and my loyal readers might know that I always advise you to never “blend a loser” i.e. don’t throw good money after bad. If you don’t love the new blend then you may be better off just tossing the offending Merlot batch and making a new one. That’s the beauty
Response by Alison Crowe.