Monday, February 8, 2010

Are Italian wines more likely to be corked? A TCA primer.

Are Italian wines more likely to be corked than others? In our experience, yes. Over at Spume the question of corked Italian wines appeared too, confirming an old observation. But, this is not some funky Portuguese conspiracy because the manner in which these batches of wine are corked points to a slightly different offender.

TCA (2,4,6-Trichloroanisole) is well known as the primary perpetrator in corked wine. Or, should say, known to be. The "chloro" part gives away that it had to do with chlorine and it often originated in bleached corks. It was thought to be a good way to make those dark corks whiter and a good antimicrobial agent. Whoops. That problem is largely under control now as most corks are peroxided instead and usually subjected to some sort of steam cleaning, rinsing and heavy sulfuring. A bit of time in a wine shop though showed that indeed a truly abnormal number of Italian wines were corked - whole lots, not just individual bottles. Three bottles in a row come to mind of both very reputable Brunello  and Chianti Classico, and a high number of Alsatian whites also incidentally. Multiple bottles opened - all bad, though at slightly varying levels of corkiness.

The down and dirty truth is frightening. Basically, there are four related compounds all with similar effects if different sensory thresholds: TCA, TeCA, PCA and TBA. TCA is pretty clear in corks, but the frightening thing is that these compounds are alive and well in the wine cellar, TBA (2,4,6-tribromoanisole) in particular is more ubiquitous and just as potent. And, the sensory thresholds are in the parts per trillion (ppt) for the worst offenders - a few drops in an Olympic swimming pool sized. Observation shows that the sensory defects are similar but not exactly the same, and it seems that the threshold for recognition is more widely variable than for TCA. Long arguments have taken place over who can recognize it and who can't more than once.

For a long time everything was blamed on poor old TCA, which as a cork-based defect is isolatable and usually limited to a cork or a bale of corks. TBA is a taint that physically infects wine in the cellar, meaning large lots, like a tank or a barrel that inevitably is mixed in for bottling all at once. TBA is often used in wood treatment, ending up frequently in the lowly wooden pallet that necessarily appears everywhere. But wood pallets are not the only danger as TBA's precursor TBP is often present as a fire retardent ingredient in several carriers, in fungicides, paints, antiseptics, and bromine-containing detergents. No way, detergents unsafe? Yup, just like bleach. It can be in barrels, infect oak chips, it can show up in plastics, and it can be in the paint inside the cellar.

We have all experienced the flattened, fruitless bottle that does not seem corked or overtly musty and danky, but sure seems to suck. Chances are that the bad bottle was at 1-2 ppt TBA, just below threshold but clearly hurting quality. Sometimes it "blows off" a little, a curious thing that may indicates other problems as well - often a reduction issue. But when multiple bottles of the same wine show the same defect, TBA taint in the cellar is the suspect. These Italian wines are most likely not victims of bad corks, but either tainted wood or inappropriate cleaning compounds or paint in their cellars or coops.

1 comment:

Rooster Shamblin said...

http://roostershamblin.wordpress.com/ would you please spend a few minutes to read my blog. I have been raising more than 50 breeds of chickens 40 years