Ask Wine Wizard

Can MLF bacteria become airborne?


Joan Deacon — via email asks,

As the weather warmed in May, several of the wines in my basement started working again, similar in appearance to a MLF fermentation. I also noticed renewed fermentation in a few older (two-year old) carboys. I had blended a few wines, and wonder if that contributed to the problem. Can MLF bacteria become airborne? I have even considered sanitizing the area by burning some sulfur sticks. Help!

Spring and summer are ideal times for yeast and bacteria, who may have been mid-ferment when cold winter weather hit, to wake up after a long sleep and begin partying again! I’m sure many of our fellow readers experience this phenomena at some time. If this re-fermentation happens when the wine is in bulk storage, I wouldn’t worry because you have plenty of time for the microbes to settle down (i.e. die off) once they’ve finished eating up whatever food source (sugar, malic acid or something else) that you’ve got in your carboys, providing it doesn’t take so long that the wine gets oxidized. If all goes well, you can rack off the sediment when the wine falls bright; it helps to blanket your containers with carbon dioxide gas to retard oxidation if the fermentation isn’t producing enough of its own. Just don’t bottle up a wine before it’s done “finding itself” or you’ll have carbon dioxide, turbidity, popped corks and off-aromas. The fact that your older carboys have renewed some kind of fermentation is interesting and points to either
Response by Alison Crowe.