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Cork manufacturers' struggles with taint are well documented. The major compound responsible for musty taints associated with cork -- 2,4,6 - Trichloroanisole -- is formed in cork bark by the chemical combination of phenolic compounds and chlorine. The phenolic compounds are present as a result of the breakdown of lignin, which is the hard substance that naturally occurs in tree bark. The chlorine can come either from the environment or from fungi living on or in the bark.
Humans are incredibly sensitive to TCA and its chemical relatives, and we can detect them at very low concentrations. Most people can spot TCA at a concentration of around 5 ng/liter (which is the same as five parts per trillion), although this depends on the wine context: It is easier to spot in tainted whites than heavy reds. This corresponds to the equivalent of a few drops in an Olympic-sized swimming pool. It's likely that the ability to spot TCA is adaptive, because it is indicative of the presence of fungi such as mold in food, which could present a health hazard. (TCA itself is harmless at the levels found in tainted wine.) Some people can detect TCA at concentrations as low as 2 ng/liter, while others don't recognize it at 10 ng/liter.
This makes work very hard for the cork industry. There's no easy way to differentiate a good cork from a bad one, and so winemakers have had to resign themselves either to losing a certain percentage of the wines they seal with cork to taint, or switching to cork alternatives such as screwcaps and synthetic corks.
Many winemakers choose to continue using natural cork. The good news for them is that the cork industry is responding to criticism and doing something about natural cork quality--trying to understand the causes of TCA and also to devise ways of removing it. Some of the solutions are common across many cork companies; others are proprietary. In this article I will try to assess how much progress is being made, and whether the steps that are being taken are likely to result in a significant reduction in the number of tainted bottles, and thus breathe a new lease on life into cork as a wine bottle closure.
There are two rather different, yet complementary, approaches to dealing with TCA. The first is to use quality control measures to try and prevent contaminated cork from being turned into closures. The second is to assume that TCA will be present, and then to remove it by some sort of extractive or washing method--the curative approach. Put both strategies together, and substantial reductions can be obtained, even if neither strategy is 100% effective.
Perhaps the most striking example of the curative approach is that employed by French company Oeneo Bouchage in the production of their DIAM (pronounced dee-ahm) closure. This involves a technology, already used by the perfume and food industries, called critical point carbon dioxide washing. Its use in treating wine was devised by Oeneo (which at that time was called Sabaté) in the late 1990s, in conjunction with the Supercritical Fluids and Membranes laboratory of the CEA (Commissariat à l'Energie Atomique).
Sabaté had experienced terrible taint problems with its Altec technical cork, which was a novel product that combined tiny cork granules with synthetic microspheres to make a durable, functional natural cork-based closure--albeit one where any TCA present in batches of cork was shared equally among all the closures.
Supercritical carbon dioxide is used to remove caffeine from coffee, to extract aromas for perfumes, and, for the non-scientist, it is quite difficult to understand. If you pressurize 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 carbon dioxide, this point is at 31.1°C and 73 bars of pressure.
Sabaté found that this novel technology actually worked and removed all the TCA from the starting material: ground-up fragments of cork. Thus the new generation of Altecs, this time taint-free, was born. These were the first cork-based closures that were completely free from the risk of musty taint. Sabaté changed its name to Oeneo, and the new taint-free Altecs, rechristened DIAM, went into production at a brand new factory in San Vicente De Alcántara, Spain, on the Portuguese border. So far, DIAM closures have been widely adopted, and no incidences of musty taint have been seen in practice.
DIAM represents one extreme in the fight against taint: Take what might well be contaminated material and clean it so thoroughly that all taint is eradicated. The starting material--inexpensive waste off-cuts of cork--looks particularly unpromising, yet the cleaning process works so well that DIAM has proven to be completely taint free. The DIAM range consists of three different closures: DIAM 2, 3 and 5, each with different oxygen transmission properties. This gives winemakers an extra level of control in terms of how their wine will develop post-bottling.
The only problem is that DIAM is quite expensive. It is difficult to give an exact cost, because this depends on who is asking (price can fluctuate depending upon the market, the size of the order, and so on). As a guide, the per-closure price is around double the price of an average screwcap, and then a capsule is needed as well. For this reason, Oeneo also offers another identical-looking product, Reference, which is cleaned by a special steam treatment called Revtech.
In this process, the small granules of cork are washed by steam as they are supended in the air by the steam flow. It's quite effective, but not sufficient to completely eradicate taint. Oeneo says the TCA threshold on this product is lower than 2 ng/l releasable TCA. In practice, this means that customers will only very rarely, if at all, come across a "corked" bottle, although there is some theoretical risk of this occurring.
After a relatively slow start, which was perhaps inevitable after the problems with Altec, DIAM is becoming quite widely adopted. Mytic, the sparkling wine/Champagne cork version of DIAM that is cleaned by the same process, has been particularly successful. After all, even the best sparkling wines are sealed with a natural cork disk/agglomerate combination, so it is not a huge leap to move from these to DIAM, and there are unlikely to be market acceptance issues.
Steam-based treatments have become popular among cork manufacturers, and the success of DIAM has led to a raft of new "microagglomerate" corks. These closures--which have a more sophisticated appearance than traditional agglomerates, with a finer grain from the smaller cork particles used to form them--are a huge TCA risk unless the particles are somehow cleaned, and steam is a relatively inexpensive way of doing this. But if a sophisticated steam method, such as Amorim's ROSA process, can remove around 80% of releasable TCA, then the starting point is highly significant. A combinatorial approach that brings together several preventive steps in the journey from bark to finished closure, combined with a curative method such as steam cleaning, and then finished off with advanced quality control measures such as gas chromotography analysis, will mean that far fewer tainted corks/closures will leave factories.
Tracking the process
"I think it is human nature for people to seek one large 'fix all' component to any potential problem," says David Hanson-Jerrard of Lafitte Cork & Capsule. "However, we believe that, like winemaking, the key to quality is being focused on every aspect of the process. We believe the key to quality cork with low incidence of TCA is knowledge of the cork and testing at all stages of production. This must then be coupled with the appropriate equipment to aid in minimizing the TCA in the corks."
Hanson-Jerrard points out that multiple layers of testing are only useful if they are combined with traceability. "As part of this strategy, we have implemented at our two facilities in Portugal a unique tracking system that allows us to track the final finished cork all the way back through our production to the individual pallet of bark from which it originated."
Scott Laboratories began building what has become a multi-layered cork quality control program in 1977, when it became the first cork supplier in North America to do lab testing. It has added several steps to the process since then. In 1999, Scott was the first to use solid phase micro-extraction (SPME) to detect TCA. Scott prescreens all lots of cork in Portugal with this process. Its corks undergo further rigorous testing at Scott's ISO-certified lab in California, and all lots are subjected to further SPME testing by ETS Laboratories.
Ganau is a quality control innovator from Italy that in 1995 introduced the industry's first non-chemical process, using steam, for cleaning unfinished corks. The company more recently added the Ganau Revolution. This process of purification is applied to the cork planks using super-heated water droplets (up to 120°C) and steam. Fresh, heated water is used for each batch of corks to avoid contamination between batches.
Amorim is the world's largest cork-producing company, and the changes it has implemented in recent years are impressive in their scope. First, the freshly harvested cork oak is laid out to season on concrete rather than bare earth. At the company's cork processing plant in Ponte do Sur there is an enormous area, the size of a few football fields, laid with concrete on which the cork bales are piled in large stacks. Álvaro Coelho & Irmãos (known as ACI in the United States) has a similar facility.
The next stage in cork production is boiling the planks in open pits. In the past this was a potential source of contamination, because repeated batches of bark were boiled in the same water. Amorim now use a system where the boiling water is replaced, and the volatiles are removed (this process is called "convex," for "continuous volatile extraction").
Other companies have changed their boiling systems also. "Five years ago there was a wave of new cork bark-boiling systems, and these were responsible for a tremendous reduction in the levels of TCA," reports Alberto Oliveira of Vinicor USA. "For example, the system Vinocor installed in 2002 is proven to extract at least 98% of all volatiles present in the bark. In 2006 we developed a new protocol that uses a double boiling. This protocol increases the cost of our process, reduces the average visual grade of our corks, but also reduces the quantity of volatiles left in the bark."
The ROSA process is Amorim's proprietal steam cleaning step, and it is now employed for all granules used in production of TwinTop, Neutrocork and Advantec closures. Independent verification shows that it reduces TCA levels in the granules by around 80%. The typical starting point for cork used for making granules is now 2-4 ng/liter TCA, and the facilities producing these granules now have an upper limit for accepting bales of cork of 8-9 ng/liter TCA.
Amorim also developed a separate system, called ROSA Evolution, for treating natural corks. The difficulty has been adapting the system so that TCA is removed but the corks ma intain their physical integrity. Amorim have achieved this by making the treatment step longer and more gentle. Currently, all lots of natural cork that test positive for TCA (more then 2 ng/liter) are treated by ROSA Evolution. "By the end of the year, we hope that most of the cork stopper production will be treated," says Amorim's Carlos De Jesus.
Cork Supply USA has adopted Innocork, a cleaning process for natural corks. It involves a current of steam and ethyl alcohol vapor, which is applied to a vertical drum containing 50,000 corks. The batch process takes about an hour, and it has been implemented for every single lot of natural corks since January 2007. (This is in addition to the company's own version of pressurized steam cleaning, Vapex, which is used for granules for its one-plus-one and microagglomerate corks.)
Finally, there is laboratory analysis. By the time a cork from Cork Supply USA reaches the consumer, it has been tested four times by gas chromatography/mass spectrometry (the company has three of these machines). All cork is tested for haloanisoles and is then tested twice for TCA during production. Finally, when the cork batches arrive in the U.S., they are tested a final time for TCA.
Amorim has two gas chromatography/mass spectrometry machines and five gas chromatography/electron capture device machines, which can process up to 14,000 samples per month looking for TCA down to a detection limit of 0.5 ng/liter. "This plant is one giant TCA preventive measure," de Jesus says. He points out that the company's biggest threat for loss of market share is not screwcaps or synthetic corks, but instead the remaining small cork companies in Portugal that haven't implemented changes in the way they work.
This sentiment is shared by Phillip Durrett, North American sales director for ACI Cork USA. "The Portuguese cork industry in the latter part of the 20th century was a fragmented traditional cottage style industry that distributed its product through brokers in its various markets," Durrett explains. "The bulk of the industry was done by very small firms that boiled and punched the raw product to make wine stoppers. By one count there were over 900 firms producing the product. In the last 20 years of the century, mechanization and centralization began to consolidate the industry into a smaller number of large- and medium-sized firms, which produced cork for export."
Alberto Oliveira of Vinocor USA also points the finger at some of the smaller players, whose products lack traceability. "Just two days ago, one of our California customers called us talking about a cork sales rep who flew from Europe and is currently offering its low-cost corks in the USA," he reports. "This rep is from a small company with very limited resources, with no processing capability in the USA (the corks would have to be processed in Europe months in advance and then shipped), but with low cost."
Oliveira says this is common, and that there are many wineries that will buy from such door-to-door reps on the basis of price. "These reps continue to come in 'selling raids,' because they know there will be someone that will buy from them."
A final method for dealing with taint is to prevent it getting from the cork to the wine by means of a barrier technology. The leading company in this field is ProCork, which has developed a thin, five-layer membrane that is attached firmly to each end of a chamfered natural cork by means of a heat treatment. This represents an effective barrier to TCA transmission and has done well in independent trials conducted by the Australian Wine Research Institute. ProCork is inexpensive, and it can be used with high-grade cork or even cheap agglomerates. It changes the appearance of the end of the cork slightly, but not enough to worry consumers.
Winemakers hope that now that two of the supposed causes of the increased taint rates of the 1980s and 1990s have been removed--namely, a monopoly position for the cork industry (at the time there were no alternatives for winemakers) and increased demand for cork (now eased slightly by the adoption of alternative closures)--there will be a downward trend in taint levels. Couple this with increased quality control and the implementation of curative technologies, and in the very near future we should see taint levels plummeting.
"The industry is moving towards zero TCA taint," claims Carlos Macku of Cork Supply USA. "We are moving to a point where the human senses will not be able to detect TCA. We now no longer talk about TCA tainting wine; instead the conversation is about TCA masking or damping the flavor of wine. At 1-4 ng/liter TCA, you might not detect mustiness, but you could see the aromas being masked. Our objective is to be able to get to a level of less than 1 ng/liter."
Already there are signs this is happening. Results from the faults clinic of the International Wine Challenge--the world's largest blind tasting competition, held in London each year--show a slight decrease in the last few years. In 2007, 3.3% of cork-sealed bottles were deemed tainted. (This is from a sample of some 15,000 bottles of 10,000 different wines from a wide array of different countries.) Given the lag between winemaker closure choice and the opening of the bottle, it will take some time for the most recent changes in closure manufacturing to filter through fully to these results.
What can winemakers do?
Price is clearly an influence in closure choice, particularly for those wines where margins are small. But winemakers need to be asking tough questions of their closure suppliers, especially when they buy corks from agents rather than directly from the closure companies themselves. The traceability all the way from the forest is important, because many large cork companies buy their corks from smaller manufacturers. Without wishing to sound like a cork industry stooge (which I'm not), it seems to me that emergence of alternative closures has had a beneficial impact on the cork industry, and the taint situation is improving. In addition to natural corks that show low taint levels, winemakers now have the option of pretty much taint-free technical corks with consistent performance.
|One measure of TCA's decline
"CQC records for incoming cork shipments continue to improve," says Peter Weber, director of the Cork Quality Council, "but it is difficult to retain the historical perspective that we have displayed in the past. Our minimum reporting level is 1.0 ppt (ppt = ng/liter). For statistical purposes we had agreed to use a plug number of 0.5ppt for any result that was reported as '<1.0ppt.' That seemed an innocuous choice when our average score was 4.0 ppt."
Weber continues, "Our average result for natural corks in Q2 2008 was 0.83ppt. So far we have seen that 85% of all bales are less than 1.0ppt, and 97% are less than 1.5ppt. I am not sure how much lower we can push the number, as we normally see a range of +/- 0.35ppt with our analytical method."
London-based writer Jamie Goode is the publisher of wineanorak.com and specializes in wine science issues. His first book was published in 2005 by Mitchell Beazley. Contact him through Wines & Vines at firstname.lastname@example.org.
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