Waiter, there’s a fly in my wine!
The semi-tropical humidity and frequent rain in Sydney this late summer has brought out the usual rash of vinegar flies. Otherwise known as fruit flies, correct name drosophela, these tiny flying insects about the size of the small ant can do terminal damage to a glass or open bottle of wine.
During my regular tastings, I always cover the open bottles to keep out flies of all descriptions, as they are strongly attracted to wine. Vinegar flies are the worst invaders: they are drawn to the aroma of wine and if one drowns in your glass, it can taint it irreparably. In such a case, the only place for the wine is down the sink. Even after you re-pour it, the smell of acetic acid can be so strong in the empty glass that a fresh one is required. Most surprisingly, if one fly simply alights on the rim of a glass, it can taint the glass so badly that acetic acid is all that can be smelled.
Vinegar flies are everywhere in nature. You’ll have seen them lingering around overripe or rotten fruit. They breed in rotting fruit and vegetable matter.
The flies carry acetic acid on their bodies, and this substance is so powerful that the flies can ruin wine just by touch. They don’t actually turn the wine to vinegar biochemically – that entails a reaction caused by acetic acid bacteria which takes days – the flies simply impart a taint, and it happens immediately.
Vinegar flies are one of the winemaker’s worst enemies. While red wines are actively fermenting in open-top fermenters, the carbon dioxide emitted is enough to keep flies at bay, but when fermentation ends and gas production subsides, flies in their thousands can land on the skins and taint the wine. Hence, protective gases like CO2, nitrogen and argon are used liberally in wineries, and wine is never left exposed to the open air.
If you’ve never experienced this taint, just leave a glass of wine, white or red, out for several hours and wait for a vinegar fly to fall in. Sniff the wine, and you will find the smell of vinegar. If in doubt, pour a fresh glass of the same wine and compare.