A new chemical culprit can make wine taste musty.
A chemical leaching from flame-retardant chemicals and fungicides used in wine cellars can contaminate wine, French scientists have discovered. Even if old wood impregnated with the chemical is removed, the air in some cellars carries enough of the pollutants to make the wines made there taste musty.
Pascal Chatonnet at Laboratoire Excell, Bordeaux, looked at three French wineries, and found that most of the wine there contained enough of the chemical, called tribromoanisol (TBA), to taint the flavour1. Barrel-aged wine was hardest hit.
TBA could prove a huge headache for winemakers, says food scientist Fred Mellon of the Institute of Food Research in Norwich, Norfolk. "It should not be too tricky to test more wineries," he says. "But remedial action may be difficult and expensive, involving decontamination, replacement of equipment, and removal of wood."
The chemical is made when bacteria digest a commonly used flame retardant and fungicide called tribromophenol. This chemical was known to taint fruit packed in cases made from treated wood. But its affect on wine hadn't been quantified.
Chatonnet's team found TBA in the cellars' walls, barrels and corks. The wooden racks in one cellar contained 2,185 nanograms of TBA per gram of wood. In wine that had been stored in one-year-old barrels, concentrations were as high as 38 nanograms per litre.
This isn't a toxic level. But most people can taste TBA's musty flavour at concentrations as low as 4 nanograms per litre - about the same as one sugar cube dissolved in 100 Olympic swimming pools of water.
Tainting can still occur even if contaminated barrels have been removed, says Chatonnet. TBA released into the air from wood can settle on the cellars' clay walls. It is then re-released into the air, and into the wine.
"The effects on taste will depend on the wine," says Mellon. "Mustiness is more detectable in subtly flavoured whites," he says.
Many of Chatonnet's tasters described the wine as being corked. This usually refers to the effects of a similar chemical, trichloroanisole (TCA), produced by the breakdown of pesticides or disinfectants used in the cellar, or by mould in cork. About one in every twenty bottles of wine is affected.
“Mustiness is more detectable in subtly flavoured whites Fred Mellon , Institute of Food Research”
There are as yet no European restrictions on the use of tribromophenol, but Chatonnet says that it threatens to become a serious pollutant if it continues to be used as a flame retardant. Engineers are now moving away from chemical treatments, preferring heat-treated wood that doesn't burn, or sprinkler systems.
"Contamination like this is the number one issue for wine producers," says Julian Stevens, deputy manager of the London branch of vintners Berry Bros and Rudd. "They put all this time, energy and passion into making it, so having it spoiled at the end of the process is a real shame."
Chatonnet, P. et al. Identification and responsibility of 2, 4, 6-tribromoanisole in musty, corked odors in wine. Journal of Agricultural Food Chemistry, published online, doi:10.1021/jf030632f (2004).
Institute of Food Research