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Taint
necessarily solved I’ll begin with the big news. Sabaté, the world’s second largest cork manufacturer may have found a cure for cork taint. Their new supercritical carbon dioxide (CO2) extraction process, named ‘Diamant’ (‘Diamond’, in English), was recently unveiled to a group of 18 journalists—16 French, one Italian, and me—at a press conference held at the high-security research laboratories of the Commissariat ŕ l'Energie Atomique (French Atomic Energy Commission, CEA), near Montelimar in Provence. By this technique Sabaté have been successful in removing as much as 97% of 2,4,6-trichloroanisole (TCA), a compound that causes musty taint in wines at even fantastically low concentrations. But although this looks to be a highly significant breakthrough, Sabaté aren’t making too much noise about it just yet. This is because they’ve got to wait two years for a new factory to be built before the Diamond process can be operated on an industrial scale. In the meantime, they’ve got closures to sell and customers to keep loyal to existing products. Amorim, the world’s largest cork manufacturer have also got a new industrial process, called ‘ROSA’. Because of the patent situation, precise details of this technique, which relies on steam treatment, are still confidential. Unlike Sabaté’s Diamond process, ROSA doesn’t take out virtually all the TCA. Instead, Amorim hope that the 60–80% reduction they say this process achieves will be enough to reduce TCA to levels where the incidence of taint is commercially acceptable. Of course, we have all heard previous claims for TCA-eliminating techniques which have come to nothing, so a degree of caution—if not scepticism—is entirely appropriate here. And with such significant commercial interests at stake, there is need for recourse to solid independent data to back-up any claims made by the closure manufacturers. With this in mind, my goal in this article is to compare the two processes and assess whether there is a realistic prospect of a cure for cork taint on the horizon. I’ll also discuss what sorts of further studies are needed to verify the claims made by Sabaté and Amorim about the effectiveness of their taint-beating processes. But is it time to
forget about corks? The same study indicates that screw caps provide a good, taint-free seal, but one that is considerably better than that of natural corks. While this sounds like a good thing, where wines sealed with screw caps have been compared side by side with the same wines sealed with corks, the consistent verdict has been that those sealed with screw caps taste fresher. That is, they are different. Of course, with some new world wine styles fresher and frutier may be better, it isn’t necessarily the case with old world classics. Putting it another way, we like the way that wines currently age when they are sealed with a natural cork that isn’t tainted. No one wants to wait 50 years for their newly purchased first growths to come round, especially if the purchaser is in their middle age; they certainly don’t want them age into something quite different. Get rid of the taint problem, and suddenly the market for alternative closures has shrunk dramatically. However, because cork is a natural product it is variable, so fine wines sealed with natural corks will evolve at slightly different rates. Despite this variability, it is likely that taint-free natural corks would be the closure of choice for most winemakers, if they were to be produced. Sabaté’s Diamond process
Supercritical CO2 is a slightly difficult concept to explain in simple terms, but I’ll have a go. If you pressurise a gas, at a certain point it becomes a liquid. If you then juggle the parameters of pressure and temperature, at a specific combination of these – known as the critical point – the interface between the two disappears, and you then have the penetration power of a gas and the extraction power of a liquid. For CO2 this point is at 31.1 °C and 73 bars of pressure – a conveniently low temperature, even though the pressure is on the high side (73 times atmospheric pressure). Other advantages of using CO2 are that it is cheap and environmentally friendly. The technique is already used to remove caffeine from coffee and by the perfume industry to extract fragrances. Aracil says that, ‘the Diamond process shows an efficiency rate around 97% for TCA extraction’. Initially, the Diamond process was used to treat the cork flour that is the basis for Sabaté’s Altec closure—it is later blended with polymer microspheres and stuck together with a binding agent. Wines sealed with prototype Diamond-treated Altecs showed no detectable TCA, both by sensory and chemical analysis, in a rigorous independently conducted panel study carried out in the UK last year. So it looks like Diamond works. ‘For obvious reasons, Sabaté rejects any idea of offering a “zero TCA” guarantee,’ says Aracil, ‘first of all because TCA can come from other sources than cork, and also because 0% doesn’t exist from a scientific point of view’. But he says that the maximum residual level of TCA is ‘between the quantification and detection limits of the analytical method, that is between 0.2 and 0.5 ppt.’ Since then, and significantly, the Diamond process has been extended to treating sheets of raw cork bark, which can then be used to produce what are effectively taint-free natural corks. ‘We had to face some difficulties with deformation in the early stages of our trials,’ reveals Aracil, ‘but we’ve since been able to optimise the parameters to get satisfactory results with cork planks.’ Tests show that the cleaning process doesn’t alter the mechanical properties of the cork significantly [note added later: but it does alter them a bit - a key question will be whether this reduces the life expectancy of the closure at all, potentially making it unsuited for use on wines intended for long term ageing.] The current production capacity of treated corks at the CEA facility is small, at around 100 000 per year – sufficient only to supply test corks to customers. Sabaté have decided to implement the Diamond process on an industrial scale, but first they have to build a new factory. This will be in Estremadura, in Spain, where they already have a facility, and the first commercial release of Diamond process closures will be Spring 2005—almost two years away. The overall investment in project is in the region of 15 million euros. Initially, two product lines are envisaged: a range of Altec-like technological corks, and high-grade natural corks targeted at ultra premium producers. If it all works out, then they’ll extend the industrial site to increase capacity. Amorim’s ROSA process I spoke to Antonio de Barros, Amorim’s Executive Vice President, about what Amorim are doing to tackle cork taint. ‘We became aware of the problem in 1978’, he recalls, ‘and we’ve been trying to fight it ever since.’ He admits that in the past the industry tended to ignore cork taint. ‘The problem has become more apparent as wine has become more sophisticated and subtle: winemaking has changed a lot. Over the last 10 years we have been doing whatever is necessary to try to control the problem.’ De Barros notes that one of the key steps for Amorim has been to renew the R&D department, bringing in Professor Miguel Cabral, ‘with a total focus on TCA control and removal’. Miguel Cabral told me of the three different approaches Amorim are taking to address the taint problem. ‘The first is a new boiling system that has been in place for a few years’, he says. ‘It’s completely different in several ways. The most significant difference is that the cork planks are extracted with boiling water plank by plank: in the previous system the planks were close together so extraction was not so easy.’ Linked to this boiling system, Amorim have devised a process known as Convex (for ‘continuous volatile extraction’), by which all the volatiles present in the water during the boiling process are cleansed at the same time. Second, Amorim have introduced chemical analysis for TCA in to their quality control, involving gas chromatography–mass spectrometry/solid phase microextraction (CG–MS/SPME). Amorim has five different machines. ‘We can do 400 analyses of cork soaks in 24 h’, reveals Cabral, ‘and the current threshold is 5 ng/l (1 ng/l = 1 ppt) TCA for a soak of 50 corks.’ According to Cabral, half the volatiles from the soak would be expected to get into wine after 14 months, so this threshold would correspond to a wine with a TCA level of 2.5 ng/l. How many batches of corks fail to meet this threshold? ‘An enormous amount of batches are clean,’ says Cabral, ‘then some have 20–30% of bales with above threshold levels.’ Thirdly, and most importantly, Amorim have also developed a curative strategy. ‘We have tried a few different approaches’, reports Cabral, ‘but the best is ROSA’. ROSA, which stands for ‘rate of optimal steam application’, is a special method of steam cleaning, but because of the patent situation that is all that Cabral was prepared to tell me. He claims that it significantly reduces the TCA in cork granules, with a reduction of 80–85%. ‘We’ve asked two institutes to validate this independently’, he reveals, ‘the Campden and Chorleywood Food Research Association (who found an 80% reduction) and Geisenheim (who showed a 75% reduction)’. Amorim already have two ROSA machines in place, with three more expected by the end of the year. ‘All our granules will be done eventually, and by July 80% of granules will be ROSA treated’, says Cabral. The ROSA technique can also be used for disks and corks. ‘The reduction in TCA has been very good but there has been high deformation: we had to change from a continuous to a batch system’, says Cabral. At the moment Amorim are doing tests at an industrial scale. ‘We have not yet achieved the same results but we are not far off, with a 60–70% reduction in TCA’, he told me. ‘There is no problem with the mechanical performance of the treated corks’. This raises a critical question. What effect will a 60–70% TCA reduction in cork sheets have on the incidence of cork taint? Without proper data, this is almost impossible to answer. It could be that this is enough to bring the level of TCA in the 5% or so of corks that are currently tainted down to below threshold levels, effectively eliminating taint, or alternatively 30–40% of the current TCA level in those corks might still be enough to taint the wine. What next? What are badly needed are good independent data on the taint rates associated with closures that have been through these treatments. Sabaté have set the standard here with their independently run, rigorously scientific panel test of wines sealed with a range of Altecs, including prototypes that have been through the Diamond process. This showed convincingly that wines sealed with the Diamond-treated Altecs are effectively TCA free. They need to repeat some of this work for Diamond-treated natural corks, and Amorim should really do a similar, transparent and independently verified testing of ROSA-treated closures to demonstrate the efficacy of this process in a real world situation, with bottled wines. I find these developments, and particularly the Diamond process, very exciting. But I’m not going to get too carried away until I see treated, virtually taint-free corks rolling off production lines in numbers sufficient to bottle significant quantities of wine. There’s always the danger that the added cost – both to the manufacturer and the producer – of eliminating TCA from cork will prove to be a barrier to the large-scale application of these techniques, even if they are proven to be effective. In some major markets, such as France and Italy, consumer acceptance of screw caps and synthetics is poor, and this, coupled with the low profile of cork taint in these countries, might mean that wine producers are unwilling to pay a premium for closures displaying significantly lower levels of taint. But I wouldn’t want this rather depressing thought to take too much of the gloss of what are some very promising and highly significant developments. And I’m looking forward to seeing some rigorous scientific trials of treated corks in the near future. One further thought relates to the potential mechanical properties of the corks treated by these sorts of techniques. It's likely that the internal structure and thus mechanical properties of the closures will have been altered to some degree. Could this raise question marks about their long-term stability? If so, then we're a bit stuck: only long-term ageing trials will prove their suitability for fine wines intended for long ageing. It's a similar problem to that faced by screwcaps. I'd be interested to see good data on the performance of these treated corks compared with non-treated controls, just to put my mind at rest on this issue.
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For the trade and the consumer alike, what matters is the number of
bottles that are ruined by cork taint. From this perspective, any
measure that results in a reduction in this number is to be welcomed,
whether it is the replacement of natural corks with screw caps or
synthetic corks, or the application of TCA reduction techniques for
production of natural corks. But because of the apparent unsuitability
of screw caps and synthetics for fine wines destined for ageing, the
prospect of taint-free natural corks is an exciting one. If Sabaté
manage to produce commercial quantities of effectively taint-free
natural corks—as it seems they may—then it would be hard to imagine
a fine wine producer who could afford not to use these closures.
Likewise, if Amorim’s ROSA process produces corks that show a
sufficiently low rate of taint—say, less than 1%—this will probably
be enough to satisfy many producers.