Volatile acidity (acetic acid and ethyl acetate most commonly produced by Acetobacter aceti) can plague winemaking and, I suppose, home winemakers more than commercial ones. Even in the case of frequent and diligent punchdowns, Acetobacter can take up residence in a cap and wreak havoc in a wine.
Having this issue occur with both of my red ferments this year, I wondered what interventions are available to a home winemaker.
Acetobacter is not the only source of V.A., but it appears to be the most common culprit. Ethyl acetate can also form spontaneously when ethanol comes in contact with oxygen. Reportedly, stressed yeasts can also produce ethyl acetate. Additionally, other bacteria are also capable of producing V.A.
Anecdotal accounts from some commercial winemakers have it that V.A. is common and transient and can essentially “blow off”. It is not clear what the etiology of the V.A. in those cases.
When Acetobacter infects a cap and produces V.A., it can be killed off with healthy doses of SO2 and lysozyme. But when the wine is not even close to being finished with primary fermentation, this is not an option.
Reading up on Acetobacter, I surmised (correctly, or not – I’m not sure) that punchdowns seem to do the trick not because they keep the cap wet, but because they deprive A. aceti of oxygen. As an obligate aerobe, it cannot survive without oxygen.
It was this fact that led me to try an intervention which may or may not have been described in literature and may or may not be a routine practice: blanketing the cap with inert gases.
This bought some time, until the wines were dry or almost dry and I could rack them off the skins to further reduce (if not eliminate) the impact of Acetobacter.
Delaying racking and pressing a wine with an infected cap with the use of inert gas can be very useful in certain red ferments. This was more applicable to my Montepulciano, which is not a very tannic variety. More time on skins benefits the structure of the finished wine.
The Aglianico, by contrast, is very tannic. By racking tannic varieties off the skins and pressing around 4° Bx, one can tip the organoleptic balance in favor of fruit (rather than tannin) dominance – if that is desired.
I would like to hear about scientifically documented, or even anecdotal reports of success with eliminating A. aceti infection in a cap by creating an anaerobic environment in and around the cap.