While scientists across the planet are delighting us with the speed of their Covid-19 vaccine development, a small team of researchers at the University of Bordeaux have come up with something to delight wine lovers: a way to reduce TCA (2,4,6-trichloroanisole) in wine. Even better, anyone who needs to remove the mouldy smell and taste can do so with a product from their kitchen cupboards.
The suggestion that ‘cling film’ – technically known as ‘alimentary plastic film’ – could do this has long been rumoured within the industry but not subjected to much scientific testing. Until now.
All is revealed in a paper entitled “Use of alimentary film for selective sorption of haloanisoles from contaminated red wine” published in November by Food Chemistry, which describes what María Reyes González-Centeno, Sophie Tempère, Pierre-Louis Teissedre and Kleopatra Chira set out to do with some 2013 red wine.
The wine in question was a Bordeaux-blend of 70% Cabernet Sauvignon and 30% Merlot that had spent two years in three 225-litre, medium-plus-toasted barrels dubbed A, B and C. Each of these had been contaminated with a specific level of TCA: one, three and nine nanograms per litre (ng/l) respectively. Human perception of TCA usually falls within the range of 1.5-3 ng/l, but even at low levels where no mustiness is apparent, wines often seem ‘muted’, especially to those who are familiar with the way they ought to taste.
The researchers immersed around 45 square metres, or the equivalent of three or four supermarket rolls, into each barrel, and measured TCA levels after eight, 24 and 48 hours. The effect over those periods was remarkable. Barrels B and C saw a reduction of 47% and 57% respectively after eight hours, which rose to around 82% after two days. In other words, a red wine with an undrinkable nine ng/l of TCA was transformed into one with around 2.75 – which most casual wine drinkers would probably find acceptable.
In the case of the mildly tainted Barrel A, the researchers reported that the precise “decontamination rate could not be quantified” because TCA levels fell below detectable limits.
If the film could remove taint, what impact did it have on the wine’s other flavours? This is where the story gets even more interesting. When the wines were analysed, “no significant effect on conventional enological parameters (pH, density, alcohol, total and volatile acidity, glucose/fructose ratio, malic, lactic and tartaric acid contents)” were found, The colour was unchanged, as was “the content of total phenolic compounds and total tannins in the treated wines, regardless of the duration of the treatment”.
These analyses only cover part of the picture, however. In removing TCA, the film inevitably has an effect on esters, and while levels of some of these remained unchanged, those of a few, such as the pear, pineapple, ethyl octanoate, fruity ethyl decanoate and floral ethyl dodecaoate, dropped by as much as 80%.
Unfortunately, the test did not include a TCA-free control, but one would imagine that it would be significantly more flavoursome and complex than any of the ‘cleaned-up’ samples. Even so, when the treated and untreated wines in the study were compared organoleptically in triangular tests, the examples of B and C with the film struck the tasters as being both oakier and fruitier. In other words, apart from adding its own unpleasant notes, TCA does indeed mute and flatten the flavours that make wine worth drinking.
This story reminded me of the days in the 1980s and 1990s when ‘flying winemakers’ contracted to make wines at – mostly – European cooperatives for big UK retailers used to carry copper in their suitcases with which, harmlessly but illegally, to treat mild cases of hydrogen sulphide (H2S). Cases of TCA infection within wineries are hardly rare, so it’s easy to imagine winemakers asking their nearest café where they can buy industrial quantities of cling film.
On the other hand, I’m not sure how to apply the technique to a corked bottle of Corton Charlemagne over 48-hours. But I’m sure I’ll learn.
All we need now is for some clever scientists to come up with a cheap, reliable way to remove smoke taint from wine, and the industry will have a lot to celebrate. Assuming, of course, the vaccines are going to get all the wine drinkers back into the restaurants where they will be buying and drinking our taint-free wines.
Robert Joseph
NB: As writer and Meininger's contributor Simon Woolf points out, the cling film needs to contain polyethylene to be effective. Check the box before dunking the cling film into your decanter.
