Absorption of chloroanisoles from wine by corks and by other materials

Sixty 750 mL bottles of a white wine were each spiked with deuterium-labelled 2,4,6-trichloroanisole (d₅ TCA) and then sealed with a variety of wine corks. Thirty months later, approximately half of the d_5-TCA had been absorbed by each of the corks, regardless of supplier, bleaching treatment or whether the corks were natural or agglomerate. In addition to the added labelled TCA, every one of these corks also contained endogenous (i.e. unlabelled) TCA. Fifteen of the corks, mostly agglomerates, imparted some of their endogenous TCA into the wines. There was no direct relationship between the amount of endogenous TCA in the corks and that found in wines. The high variability in the distribution of endogenous TCA between wine and cork contrasts with the relatively uniform distribution of the d₅-_-TCA. This contrasting behaviour distinguishes between wines tainted prior to closure and wine tainted by corks. Natural bark corks in wine bottles can also absorb 2,3,4,6-tetrachloroanisole (TeCA) and pentachloro-anisole (PCA) from bottled wine. Bottle storage of commercial wines that had become tainted with TeCA and PCA during production resulted in the corks absorbing most of these two compounds, so that the wines were no longer tainted to a significant extent. Soaking whole corks in wine spiked with chloroanisoles, under conditions typically employed in the wine industry to test batches of corks for possible taint, resulted in most of the TCA in the wine being absorbed by the corks. Thus, if five corks are being soaked in wine in order to test for taint, four sound corks could reabsorb TCA that had leached into the surrounding wine from a single contaminated cork, reducing the concentration of TCA to a point where it escapes detection. Soaking corks singly rather than in groups of five will therefore be a more sensitive method of screening batches of corks for taint than soaking them in groups of five. Plastic materials such as the lids of glass containers used to store wine samples were also able to absorb chloroanisoles via both direct liquid contact and the vapour phase. Wine cask bladders and polyethylene film were particularly effective in removing TCA from wine.     

The analysis of 2,4,6-trichloroanisole and other chloroanisoles in tainted wines and corks

A new method has been developed for the analysis, by gas chromatography/mass spectrometry, of 2,4,6-trichloroanisole (TCA) and other chloroanisoles in cork-tainted wines, using a polydeuterated form of TCA as an internal standard. In a survey of wines presented at a wine assessment course, 4.8% (i.e. 18 bottles out of 374) were assessed by at least 20% of the participants as being affected by cork taint. TCA was present in each of these 18 wines at a concentration close to, or above the sensory detection threshold. All cases of taint seen by the participants could therefore be attributed, at least in part, to the presence of TCA, and this in turn could be attributed to the cork, since variation in apparent taint between bottles of the same wine was observed in every case. TCA was also found in the corks from the wines. Randomly selected bottles of wines considered to be affected by a high proportion of cork taint, and the corks from those bottles, were also analysed. There was considerable variation in the distribution of TCA and other chloroanisoles between wine and cork. In many cases, chloroanisoles were found only in the cork. TCA in corks was accompanied by varying amounts of 2,4– or 2,6-dichloroanisoles, 2,3,4,6-tetrachloroanisole and pentachloroanisole, indicating more than one origin for chloroanisoles in corks. No chloroanisoles, other than those derived by methylation of products formed by non-enzymatic chlorination of phenol, were detected in any of the samples.     

Effect of wine style on the perception of 2,4,6-trichloroanisole,a compound related to cork taint in wine

2,4,6-Trichloroanisole (TCA) is a fungal metabolite that can contaminate cork stoppers and wines producing a very unpleasant mouldy odour (cork taint). Sensory control is very widely used for the detection of possible TCA presence in corks and wine, but the correct identification of TCA, especially at low concentrations, can be difficult. The aim of this study was to show how wine styles can affect the ability of the same panel to perceive TCA. For this purpose, a panel was selected, according to the panelists’ sensitivity to the TCA stimulus. The triangle test, a sensory difference test, was carried out by the panel with both white and red wines, using samples both free from TCA and spiked with known quantities of this contaminant. The results showed that the panelists identified the difference caused by the added TCA at different significance levels, depending on the wine style, so TCA detection was influenced by wine style for the selected panel.     

Presence of cork-taint responsible compounds in wines and their cork stoppers

 Chloroanisoles [2,4-dichloroanisole, 2,4,6-trichloroanisole (TCA), 2,3,4,6-tetrachloroanisole and pentachloroanisole], chlorophenols [2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol (PCP)] and guaiacol were detected in red and white cork-tainted bottled wines. These compounds were also found in the cork stoppers from those bottles. A significant correlation was found between TCA in wines and TCA in cork stoppers, and between TCA in wine and intensity of cork taint. At low levels of TCA, the presence of guaiacol or PCP were also found to influence in cork taint. Received: 29 November 1999     

Compounds causing cork taint and the factors affecting their transfer from natural cork closures to wine – a review

The compounds causing cork taint and the factors affecting their transmission from cork to wine are discussed. These factors include: the solubilities of the taint compounds in wine, their affinity for the surface and the interior parts of the cork; their location on the surface of and within the closure; the rates at which they can migrate through the cork matrix; the volume of wine in contact with a closure(s); and whether taint transmission is taking place in bottled wine or with corks soaked in wine for screening purposes. 2,4,6‐Trichloroanisole (TCA) has been the primary topic of investigations reported in the general literature and is therefore the main focus of this article.     

Origin and fate of 2,4,6-trichloroanisole in cork bark and wine corks

2,4,6-Trichloroanisole (TCA), which is a major cause of cork taint in bottled wine, is already present in the bark of living cork trees to the extent that it can account for the majority of incidences of cork taint in bottled wine. Other post-harvest sources of TCA are known and may add to the forest-derived TCA in cork. Both the origin of TCA in the bark in the forest, and the means by which additional TCA can accumulate in the corks during manufacture, have been examined. TCA can originate from 2,4,6-trichlorophenol (TCP) produced from naturally-occurring phenol and chlorine from sanitisers and cleaning products, and town water. Also, chlorophenol biocides have accumulated in the environment due to the large quantities used in previous times – TCP has been a minor impurity in pentachlorophenol biocides and a major ingredient in other preparations. There is some evidence that chlorophenols were used in pest management in the forest prior to restrictions on the use of these materials. The factors affecting the uptake and loss of TCA by the bark on the tree and by corks during production, and through to their use in the bottling of wine have been considered in this review.     

Matrix effect during the application of a rapid method using HS-SPME followed by GC–ECD for the analysis of 2,4,6-TCA in wine and cork soaks

An off-flavor in wine known as ‘cork taint’ is of concern in the wine and cork industry. Cork taint imparts a musty flavor to the wine and is primarily due to the presence of 2,4,6-trichloroanisole [2,4,6-TCA] in cork stoppers. During this study, an instrumental method for 2,4,6-TCA analysis was developed and evaluated using headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled with an electron capture detector (GC–ECD). 2,3,6-Trichlorotoluene [2,3,6-TCT] was assayed as the internal standard. The method was developed in synthetic wine and was applied in commercial wine samples, as well as in cork soaks obtained by the extraction of TCA from cork stoppers and cork barks using synthetic wine. The method performance was evaluated through the estimation of its linearity (R² > 0.99), repeatability (RSD value = 5.72%) and sensitivity (recovery > 86%, LOD = 0.177–0.368 ng/L) in different types of samples. Due to the complexity of the samples used, the study has been especially focused on the matrix effects that were identified causing significant bias to the quantitative analysis of 2,4,6-TCA in cork soaks, where there is a lack of previous studies.     

Migration of 2,4,6-trichloroanisole from cork stoppers to wine

The migration of 2,4,6-trichloroanisole (TCA) from cork stoppers to wine is studied under different experimental conditions. Corks that were either naturally contaminated or spiked with a TCA solution were immersed in an ethanol–water mixture (12% v/v) for 6 days or were used as a closure for bottled wines over periods of 1, 4 and 8 months. The TCA content was determined after the stated periods using headspace solid-phase microextraction and gas chromatography electron capture detection. Three different spiking procedures were tested: the injection of a TCA solution into the cork, the immersion of the cork in a TCA in hexane solution, and cutting off a thin slab to inject different quantities of a TCA solution into it before rejoining the two parts. Only the first of these procedures was subsequently used as the immersion technique failed to retain sufficient quantities of TCA and the slab technique retained too much. Corks spiked with 120 ng TCA gave 8% migration after 6 days for corks used in the immersion experiments and less than 1% migration for corked bottles kept for 1 month. When the contact time was 4 and 8 months, migration was 4 and 8% respectively for corks spiked with 1 g TCA. It was concluded that the contact surface, temperature and time all favour TCA migration. Under the same conditions, wine bottled with naturally contaminated cork stoppers showed TCA concentrations which varied depending on the characteristics of every individual cork stopper.     

Search for the contamination source of butyltin compounds in wine: agglomerated cork stoppers

A possible butyltin contamination source in wine was studied in this paper. Agglomerated cork stoppers, which were produced in Portugal, Spain, and Italy, used in wine bottles were examined. The domestic cork products, cork granules, and mucus used for cork products were also analyzed. The levels of mono- and dibutyltin compounds in corks were found in the range from <0.0024 to 3.3 and from <0.0029 to 6.7 microg of Sn/g, respectively. A low level of tributyltin contamination was also found in 2 of 31 tested samples. The presence of butyltin compounds in agglomerated cork stoppers was confirmed by GC-MS. Experimental results indicated that all overseas agglomerated cork stoppers studied contained mono- and/or dibutyltins. Butyltins were not detected in cork granules, mucus, most of the natural cork stoppers, and domestic agglomerated cork products. The concentrations of mono- and dibutyltins increased with the time in a 30-day experiment, showing that butyltin compounds can leach from agglomerated cork to the wine. When the butyltin concentrations in wine samples were compared with their levels in the corresponding agglomerated cork stoppers, a correlation was found. The potential harm of such food contamination was evaluated by the toxic research of butyltin compounds using Daphnia sp. as the experimental model.     

Wine bottle closures: physical characteristics and effect on composition and sensory properties of a Semillon wine 1. Performance up to 20 months post-bottling

A Semillon wine was bottled using 14 different closures: a screw‐cap type, two grades of conventional natural cork, two ‘technical cork’ closures (natural cork with a synthetic component), and 9 closures manufactured from synthetic polymer material. Closure performance was evaluated for physical aspects (e.g. extraction force and energy, change in closure diameter, and ease of closure reinsertion), and for wine composition and sensory properties. Wine under the screw cap closure retained the greatest concentration of sulfur dioxide (SO₂) and ascorbic acid and had the slowest rate of browning. For other closures the trend of SO₂ loss relative to the screw cap closure was apparent from an early stage of testing, and was most evident in the group of synthetic closures, intermediate in the conventional corks, and least evident in the technical cork closures. The loss of SO₂ was in general highly correlated with an increase in wine browning (OD₄₂₀) and the concentration of SO₂ in the wine at six months was a strong predictor of future browning in the wine, particularly after eighteen months. Neither the concentration of dissolved oxygen at bottling (0.6–3.1 mg/L), nor the physical closure measures were predictors of future browning. For several closures upright storage tended to accelerate loss of SO₂ from the wine, but in many cases this effect was marginal. The closures differed widely in regard to physical characteristics, and in general synthetic corks appeared least ‘consumer‐friendly’ in terms of extraction forces, energies, and ease of closure re‐insertion, but there was a trend for natural cork closures to exhibit larger variability in physical characteristics than technical cork and synthetic closures. Sensory analysis indicated large differences in wine flavour properties, with closures which tended to result in the best retention of free SO₂ having wine sensory scores for ‘citrus’ that were generally high whilst scores for the attributes ‘developed’/‘oxidised’ were low. The situation was reversed for wine under closures that performed poorly in the retention of free SO₂. It was found that below a critical level of free SO₂ remaining in the wine, closures exhibited substantially higher ‘oxidised’ aroma. Whilst trichloroanisole‐type (TCA) taint was a noticeable problem for some cork and technical cork closures, any plastic‐type taint appeared not to be a problem with most synthetic closures.     

葡萄酒和软木塞中2,4,6-三氯苯甲醚检测方法的研究进展

本文介绍了葡萄酒和软木塞中2,4,6-三氯苯甲醚（2,4,6-trichloroanisole,TCA）的来源及影响,分析了2,4,6-三氯苯甲醚的检测难点,总结了目前检测2,4,6-三氯苯甲醚方法的总体趋势及现状。按照前处理方法的原理分类,介绍了前处理方法的定义、特点,并概述和讨论了前处理方法在萃取葡萄酒和软木塞中2,4,6-三氯苯甲醚中的应用;根据仪器检测方法的不同特点,总结和讨论了仪器检测方法在分析检测葡萄酒和软木塞中2,4,6-三氯苯甲醚的应用。前处理方法和仪器检测方法相结合,达到了浓缩和检测葡萄酒和软木塞中2,4,6-三氯苯甲醚的目的。     

Transformation ability of fungi isolated from cork and grape to produce 2,4,6-trichloroanisole from 2,4,6-trichlorophenol

The ability of eight fungal strains to transform 2,4,6-trichlorophenol (TCP) to 2,4,6-trichloroanisole (TCA) was studied. These fungi were isolated from cork, belonging to the genera Penicillium, Aspergillus, Trichoderma and Chrysonilia, and from grapes Botrytis cinerea. All, except Chrysonilia, produced TCA when grown directly on cork in the presence of TCP, Aspergillus and Botrytis cinerea being the ones with the highest level of production. It is the first time that Botrytis cinerea, a microorganism often present on grapes and in winery environments, has been shown to transform TCP into TCA. This result can partially explain the wine cork taint before being bottled.     

Determination of Chloroanisoles and Chlorophenols in Cork and Wine by using HS‐SPME and GC‐ECD Detection

Cork taint is an off‐flavor problem in wine, the main reason being the presence of 2,4,6‐trichloroanisole (TCA) in the cork stopper. In addition to the TCA, the presence of other chloroanisole and chlorophenol family compounds (the perception limits of which are very low) can also result in, or contribute to, cork taint problem. In this study, the levels of 2,4‐dichloroanisole (DCA), 2,4,6‐trichloroanisole (TCA), 2,3,4,6‐tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6‐trichlorophenol (TCP), 2,3,4,6‐tetrachlorophenol (TeCP) and penthaclorophenol (PCP) were assayed in cork stoppers (natural, agglomerated and colmate) and in red wine samples from different wineries in Turkey using HS‐SPME and GC‐ECD detection. The performance parameters for all chloroanisole and chlorophenol compounds were as follows: recovery 92.48–102.53%, R 0.992‐0.996. The LOQ values were DCA (8.4 ng/L), TCA (0.8 ng/L), TeCa (0.6 ng/L), PCP (0.8 ng/L), TCP (0.8 ng/L), TeCP (1.2 ng/L), and PCP (1.1 ng/L) respectively. In cork stoppers, the amounts of 2,4,6 TCA ranged between 5.4–130.6 ng/g. The 2,3,4,6 TeCA ranged between 1.12‐8.2 ng/g and the PCA ranged between nd (not detected)‐11.01 ng/g. In the wine samples, 2,4,6 TCA ranged between 1.42–70.2 ng/L. The 2,3,4,6 TeCA ranged between nd‐15.1 ng/L and the PCA ranged from nd‐5.16 ng/L. The results indicated that there was a significant correlation between the TCA in wines and the TCA in cork stoppers.     

Cork-borne bacteria and yeasts as potential producers of off-flavours in wine

Bacteria and yeasts were found to be present within cork lenticels, covered by mucous or fibrous substances. They survived heating, peroxide treatment and contact with the alcohol and sulfur dioxide of wine. 187 bacteria and 36 yeast strains were isolated from cork stoppers of wine bottles and, during various stages of production, from corkwood and new cork stoppers. After culturing, a number of isolates showed the ability to modify the aroma of model systems consisting of dilute or full strength wine and pulverised cork. The aromas produced by isolates of varying cork origin are tabled. A small number of isolates methylated 2,4,6-trichlorophenol, yielding 2,4,6-trichloroanisole, responsible for the typical cork taint. During the boiling of cork slabs, the internal temperature on the inside of a box made from cork slices did not exceed 87°C.     

Transformation ability of fungi isolated from cork and grape to produce 2,4,6-trichloroanisole from 2,4,6-trichlorophenol

The ability of eight fungal strains to transform 2,4,6-trichlorophenol (TCP) to 2,4,6-trichloroanisole (TCA) was studied. These fungi were isolated from cork, belonging to the genera Penicillium, Aspergillus, Trichoderma and Chrysonilia, and from grapes Botrytis cinerea. All, except Chrysonilia, produced TCA when grown directly on cork in the presence of TCP, Aspergillus and Botrytis cinerea being the ones with the highest level of production. It is the first time that Botrytis cinerea, a microorganism often present on grapes and in winery environments, has been shown to transform TCP into TCA. This result can partially explain the wine cork taint before being bottled.     

The location of 2,4,6-trichloroanisole in a batch of contaminated wine corks

Straight wine corks, from a batch with a high proportion of contamination with 2,4,6-trichloroanisole (TCA), were dissected into various sections and the TCA content of these fractions was determined. TCA was found to be concentrated in the outside portion of the cork, and also in the older bark. There was no significant difference in TCA content between the lenticel and non-lenticel cork fractions, between the light and dark portions of the growth rings, nor between the ends and centre parts of the corks. The concentration of TCA in the outer part of the corks indicates that the biomethylation step in the formation of TCA in these corks followed the punching stage of production.     

The effectiveness of electron beam irradiation to reduce or eliminate mould in cork stoppers

The objective of this research project was to reduce or eliminate moulds known to cause TCA using electron beam (e‐beam) irradiation. Four types of cork were inoculated with Paecilomyces viridis, Penicillium glabrum, Penicillium chrysogenum, Mucor racemosus, Trichoderma viride, Aspergillus oryzae and Cladosporium oxysporum. Cork samples were treated with 5, 10 or 15 kilograys (kGy) of e‐beam irradiation, respectively. Sensory evaluation revealed that irradiation had little or no effect on the overall quality of wine with irradiated corks stored for 56 months. Cork samples viewed under a scanning electron microscope (SEM) showed some structural changes compared to control corks. The results suggest that e‐beam irradiation can significantly reduce or eliminate the moulds known to cause TCA in cork.     

葡萄酒及软木塞中TCA的检测分析方法研究现状及应用前景

软木塞污染已经成为葡萄酒行业最为严重的问题之一,而导致软木塞和葡萄酒污染的最主要物质之一就是TCA。本文主要介绍葡萄酒和软木塞中TCA 的检测方法和萃取浓缩方法,同时也对TCA 检测的应用前景和发展趋势进行了展望。     

Evaluation of the performances of synthetic and cork stoppers up to 24 months post-bottling

In recent years, as a consequence of higher market prices for cork and of the qualitative problems created by natural stoppers, the demand for alternative seals has increased remarkably . Since 1990, numerous manufacturers of plastic materials have begun production of synthetic stoppers for the closure of wine bottles. The application of the first experimental products was highly unsatisfactory and showed the need to carry out more research into the characterisation of the materials employed and their interaction with the "matrix wine". The object of this study was to estimate the mechanical characteristics of a particular kind of synthetic stopper and to compare the physico-chemical profiles of different Italian wines bottled with corks, or with synthetic stoppers made of expanded polyethylene, during the wine conservation phase. Analytical and statistical data produced give assurance that for these wine types, the employment of the synthetic stopper helps to increase the shelf-life of wines ready to consume within 1–2 years after bottling.