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Control of the organoleptic quality of wines is essential to ensure a product free of sensory faults to the final consumer. Sensory analysis is a subjective technique under the influence of multiple external factors that also lacks measurement units. In addition, a sensory fault detected during the tasting, may result from synergy between various compounds considered as contaminants. It is very difficult to link a fault to its source without having a precise identification and quantification of pollutants involved in relation to their olfactory perception thresholds when taste the wine. For this reason, the laboratory has tried to find a chemical analysis method of high resolution for fine analysis allowing quantification, as is the case of gas chromatography and mass spectrometry used in the systematic method called Check list Excel®. The method developed by this laboratory allows simultaneous diagnosis and identification of the olfactory faults origin from very different backgrounds in a single analysis, taking a time of 60 minutes with a small sample of only 5 mL of wine. This technique can be used as quality control of wine post-fermentation process of wine; can help in the purchase and sale of wines, especially in warehouses dedicated to bottled wines. Especially this method is very interesting for developing coupages, as this method is always able to detect and quantify the defective compounds below the sensory detection.

In this study we present a rapid and simultaneous assay method using headspace (HS) solid-phase microextraction (SPME)/gas chromatography (GC)/electron impact (EI) mass spectrometry (MS) (selected ion monitoring) for contaminants causing the principal organoleptic defects of wine (2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, pentachloroanisole, 2,4,6-tribromoanisole, 1-octen-3-ol, geosmin, 2-methylisoborneol, 3-isopropyl-2-methoxypyrazine, fenchol, fenchone, 2-methoxy-3,5-dimethylpyrazine, 4-ethylphenol, 4-ethylguaiacol, 4-vinylphenol, 4-vinylguaiacol, 3-isobutyl-2-methoxypyrazine, guaiacol and ethyl acetate). The method was validated according to protocols NF ISO 5725-1, 2 and NF V03-110. Its characteristics (limit of detection (LOD), limit of quantification (LOQ), uncertainties) were determined after having optimised the SPME parameters. The target contaminants were quantified in the wines below their threshold of perception with a satisfactory relative standard deviation for all the analytes except ethyl acetate (RSD = 36%); for that, the assay method permits clear differentiation of the wines that are at risk of presenting an acescent character, i.e. containing more than 120 mg L −1 ethyl acetate. The target volatile and odorous substances were determined at concentrations significantly below their threshold of perception in a hydroalcoholic context and their threshold of recovery in wines.

The work we present in this article aims at optimizing and validating the assay technique based on SIDA-HSSPMEGC- MS/EI-SIM by means of intra-laboratory trials (NF V03-110 AFNOR 1998 and MA-F-AS1-06-PROVAL (OIV)) on several chloroanisoles (2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, 2,3,4,5,6-pentachloroanisole) likely to contaminate wine by direct or indirect contact, in order to define the precise characteristics and limitations of the method.We showed this technique to be a specific, accurate, linear, and repeatable method. Moreover, seeing the increasing reliance on this type of approach in scientific research and industrial monitoring laboratories (ISO/TC87/GT10) to assess the quality of cork stoppers and because of the important quantity of 2,4,6-Trichloroanisole present in this kind of material, we deemed appropriate to carry out an inter-laboratory study (ISO 5725-1,2,3,4 and 5) of TCA assays on dilute alcohol soaks of corks using the same method. Our results should make it easier to understand and interpret assay results obtained in different laboratories using the same technique. * : Stable Isotope Dilution Assay - Headspace Solid Phase Microextraction - Gas Chromatography - Mass Spectrometry / Electron Impact / Selected Ion Monitoring.

This study identifies a previously isolated bacterium as Rhizobium excellensis, a new species of proteobacteria able to form a large quantity of 2-methoxy-3,5-dimethylpyrazine (MDMP). R. excellensis actively synthesizes MDMP from L-alanine and L-leucine and, to a lesser extent, from L-phenylalanine and L-valine. MDMP is a volatile, strong-smelling substance detected in wines with cork stoppers that have an unpleasant "corky", "herbaceous" (potato, green hazelnut), or "dusty" odor that is very different from the typical "fungal" nose of a "corked" wine that is generally due to 2,4,6-trichloroanisole (TCA). The contamination of cork by MDMP is not correlated with the presence of TCA. It appears possible that R. excellensis is the microorganism mainly responsible for the presence of this molecule in cork bark. However, other observations suggest that MDMP might taint wine through other ways. Oak wood can also be contaminated and affect wines with which it comes into contact. Nevertheless, because 93% of the MDMP content in wood is destroyed after 10 min at 220 °C, sufficiently toasted oak barrels or alternatives probably do not represent a major source of MDMP in most of the cases. Due to MDMP's relatively low detection threshold estimated at 2.1 ng/L, its presence in about 40% of the untreated natural cork stoppers sampled at concentrations above 10 ng/cork suggests that this compound, if extracted from the stoppers, may pose a risk for wine producers.

Thanks to practical experience in various wineries in recent years, it is now clear that, similarly to the well-known phenomenon in corks, there are several sources of unpredictable contamination of oak wood by 2,4,6-trichloroanisole (TCA). TCA affects staves in the same barrel very sporadically, with extremely limited contaminated areas on the surface that may reach several millimeters in depth. The precise origin of the TCP and TCA in oak wood is not known at this stage. Available data indicate that the phase where stavewood is naturally dried and seasoned is the source of these undesirable organochlorine contaminants. The strictly chemical formation of 2,4,6-trichlorophenol (TCP), derived from organochlorine biocides, was demonstrated to be impossible under traditional cooperage conditions, and its accumulation remained highly improbable. Similarly to previous discoveries in corks, all the analyses of oak wood suggested that the TCP was of biochemical origin. The capacity to biomethylate chlorophenols is well-known and relatively widespread among the usual microflora in stavewood, but the precise origin of the intermediary leading to TCP formation is still unknown. One probable hypothesis is that this reaction involves chloroperoxidase (CPO). Several ideas have been proposed, but the microorganisms responsible for the formation of the TCA precursor in oak wood have not yet been identified. The extent of this problem is still severely underestimated by coopers and barrel-users, due to the extremely unpredictable, localized contamination of the staves.

In this work, gas phase chromatography analysis coupled with selective selected ion monitoring (SIM) identified 2,4,6-tribromoanisole (TBA) in wines found on tasting to have significant "musty or corked" character, although they did not contain noteworthy quantities of chloroanisoles or chlorophenols, the contaminants generally reported to cause this type of defect. The perception thresholds were studied, together with contamination conditions during winemaking, storage, and bottle-aging. A "musty" off-odor was perceptible on smelling wine containing as little as 4 ng L(-)(1) TBA, and spoilage may be detected by retro-olfaction at even lower concentrations. TBA, produced by O-methylation of its direct precursor, 2,4,6-tribromophenol, generally comes from sources in the winery environment. This paper is the first to identify the sources of a large number of cases of wines polluted during storage in premises where the atmosphere was contaminated with TBA used recently to treat wood, or originating from much older structural elements of the winery, or from used wooden containers. In certain cases, although the initial source had been eliminated, residual pollution adsorbed on walls could be sufficient to make a building unsuitable for storing wooden barrels and plastics, as well as corks, which have been found to be particularly susceptible to contamination by the TBA in the winery atmosphere.