by Andrew Chalk
I just spent a day in College Station in the most enjoyable way possible -- at a Texas A&M University course in “Wine Faults”. Almost everyone was either a winemaker or an academic taking a deep dive into the subject.
Wine Faults are important because, since wine is made (almost invariably) from grapes and the product of their fermentation and aging using universal techniques, all wines are subject to some degree or another to the same faults. Everyone in the industry can recite the names of the ‘Big Six’ but understanding their cause and amelioration is a totally different story. For example, it was brought home to me (as an outsider from the production process) how much ameliorating one fault is a compromise exacerbating another. The most headline-worthy finding was that you don’t need a cork to get cork taint!
The Big Six are: Oxidation, Brettanomyces, Hydrogen Sulfide (H2S), Cork Taint, Volatile Acidity, Malo-Lactic Fermentation in conjunction with high pH (low acid). In this series of articles I will report on each judged through the presentations by the faculty and graduate students who made them. Some of the findings are the results of primary research by the students themselves. The errors are all my own work.
HALOANISOLES/CORK TAINT - TCA/TBA
I once ordered a bottle of wine at a Dallas restaurant. On tasting it I immediately recognized that it was corked. I told the waitress, who looked at me as though she was offended. It was as though I had blamed her for some fault in the wine. She need not have worried, she was blameless. Cork taint, or a corked wine, occurs before the wine leaves the winery. By the time it is served the worst that can have happened is that a pre-existing condition has been exacerbated.
SYMPTOMS
The smell will be musty, like wet cardboard. Fruity aromas will be suppressed. It makes the wine less enjoyable, but is not dangerous. White wines seem more affected than reds due to more prominent flavors in reds masking cork taint. The amounts necessary to be noticed are extremely low. A level of 5 ppt (parts per trillion) mutes all aromas. A level of 25 ppt is like a musty, dank basement.
CAUSES
Cork taint is one of two compounds.
TCA (an abbreviation for 2,4,6 Trichloroanisole)
TBA (an abbreviation for 2,4,6 Tribromoanisole)
TCA occurs:
when corks are cleaned with bleach. Natural corks in the winery that had fungus on them mixed with the chlorine in bleach to produce TCA;
wood in the winery can also become affected with TCA;
TBA occurs:
When wood is treated with a bromine based fire retardant. That wood is used to create barrel, palets, structures, and the building itself. Fungus in the air mixes with the bromine creating TBA. The transmission channel is:
fungus (penicillium, aspergillus, actinomyces, or streptomyces)
+
chlorine/bromine
=
cork taint
TBA is much more prevalent than TCA nowadays.
Presenter Abby Keng (a masters student in the department) described some interesting case studies she came across in her research:
CASE 1:
A large winery in California found evidence of cork taint contamination in wines post fermentation but pre barrel/bottling. Testing via GCMS found the presence of TBA in wine. Common places were tested: barrels, atmosphere, drains, hoses, other wines in the same room. TBA was not found in these areas. Further investigation found that fining agents and other inputs were being stored in an unfinished room. The unfinished room had walls made from plywood! Plywood was coated in a fire retardant that contained bromine which produced TBA. TBA then infected their bentonite. When they fined with bentonite they were adding TBA to their wines!
CASE 2:
A large winery in California found 2 barrels of wine to be contaminated with TBA and TCA.
Wines in those barrels were very expensive and were insured. They filed a claim and their insurance carrier investigated.
They first looked at the barrels. Barrels scrapings were taken and found to have TBA in them.
Other barrels from the same lot in the winery were tested and found to be TBA free. Infected barrels were then taken apart stave by stave. One stave was found to have much higher concentrations of TBA and TCA on it. That stave was sectioned and tested. A dime size spot on one of the sectioned staves was found to have insane amounts of TBA (ppm). Where the dime-size spot was located in the winery, it was found that refrigerant fluid dripped onto it. That refrigerant was found to contain chlorine and bromine.
PREVENTION
Do not use chlorine-based cleaners;
Use corks from reputable sources;
Properly store inputs (e.g. bentonite);
No exposed plywood;
REMEDIATION
Believe it or not, mix a tainted wine with food grade PVC plastic wrap. TBA can be reduced with grape pomace.
DOES CORK TAINT NEED A CORK?
Clearly not, as several examples above demonstrate. So its curtains for that party humiliation where you ask an intoxicated friend "do you think this wine is corked?" when the wine had a screw cap. It still could be!
KEEPING UP TO DATE
Another faults workshop will take place mid spring 2023. For a definitive date and registration details keep an eye on their Facebook page (Texas Viticulture and Enology), where they post updates on upcoming educational programs.