Twin taints in wine: Simultaneous determination of cork taint and Brett character

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  • Published: Feb 7, 2011
  • Author: Steve Down
  • Channels: Gas Chromatography
thumbnail image: Twin taints in wine: Simultaneous determination of cork taint and Brett character

Two unwelcome wine characteristics: cork taint and Brett character

Nothing takes the edge off a good restaurant meal more than being served a bottle of wine that has gone off. It's bad news for the restaurant as well as the customer because there is only one solution - pour the wine down the drain and open another. Unfortunately, tainted wine is not a trifling problem, with some estimates claiming that up to 15% of wines produced worldwide are affected.

Wine taints have several origins. Oxidation is induced by contact with the air, generally through a faulty cork. Storage at incorrect temperature, either too high or too low, will induce improper aging and affect the organoleptic conditions.

Two other common types of wine taint are cork taint and Brett character and they have been examined by a team of Spanish scientists from the University of La Rioja. Consuelo Pizarro and associates chose to study them both by GC/MS, since the factors responsible are all volatile compounds.

Cork taint is produced by the reaction of wine with the natural cork used as a stopper, although this source must be on the decrease with the widespread introduction of plastic stoppers and screw tops. It can also originate from contaminated winery equipment and airborne moulds.

The compounds responsible for cork taint have been identified as a series of haloanisoles, such as 2,4,6-trichloroanisole (TCA). It takes just a trace of TCA to have an effect because of its powerful odour of wet dog or mouldy newspaper, which can be detected in wine at just 2 ppt. The sensory thresholds of other taint haloanisoles are about 20 ppt.

Brett character was named after the yeast Brettanomyces bruxellensis, which thrives under warm cellar conditions to produce volatile phenols with unpleasant odours. 4-Ethylphenol (EP) has been described as smelling of antiseptic or horse stable, 4-ethylguaiacol EG) of smoked bacon or cloves and 4-vinylguaiacol (VG) and 4-vinylphenol (VG) have sweet, spicy odours.


Twin taints: GC with tandem MS gives excellent detection limits

Pizarro and colleagues devised a method for the simultaneous measurement of the principal components responsible for both taints. The compounds were spiked into a sample of wine for extraction by dispersive liquid-liquid microextraction method, with optimisation by a central composite design.

After comparing several extraction solvents and dispersers, the best recoveries were achieved with acetone as disperser and chloroform as extractant, using 1.43 mL and 173 µL, respectively, for 5 mL of wine. Extraction was conducted at room temperature in the absence of salt, to give recoveries higher than 80% for all of the compounds.

The extracts were spiked with p-cresol and 4-iodoanisole as internal standards for the phenols and haloanisoles, respectively, before analysis by GC/MS with electron ionisation. They were separated on a column with a polar polyethylene glycol mobile phase. The resulting chromatogram of four phenols, four haloanisoles and the internals standards showed good separation of all ten components within 20 minutes.

The compounds were quantified by tandem mass spectrometry to give detection limits near or below their olfactory thresholds and better than those from other published procedures. Those for the phenols and haloanisoles were in the ranges 0.005-0.012 and 0.017-0.041 µg/L, respectively.


Red and white wine: odourless samples contain taint compounds above their olfactory thresholds

The optimised procedure was used to test for the cork taint and Brett character components in two white wines and two red wines from different regions. A preliminary sensory analysis revealed that none of the wines had any organoleptic defects but the analysis told a different story.

Both red wines contained 2,3,4,6-tetrachloroanisole, EP and EG, the concentration of EG being slightly above its odour threshold. One red wine also contained TCA and pentachloroanisole above their odour thresholds, as well as VP and VG.

One white wine contained low levels of VG and VP but the other contained higher levels of these two compounds, as well as three haloanisoles each above their odour thresholds.

The results indicate that the GC-tandem-MS method is suitable for the analysis of taint compounds in wine, at detection levels down to their odour thresholds, and will provide a useful alternative to existing methods.

 


 


The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 
 
 
The compounds responsible for producing cork taint and Brett character in red and white wines have been determined by GC-tandem MS, following extraction by a novel dispersive liquid-liquid microextraction procedure

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