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Understanding technical corks: how high-quality, inexpensive one-plus-ones and agglomerates evolved.

Technical corks are proving to be increasingly important wine bottle closures, but compared with synthetics, screwcaps and natural cork, they get relatively little coverage, to the point that many people in the trade aren't even familiar with the term "technical cork." It refers to a natural cork-based closure made by combining discs or granules of natural cork to produce an inexpensive closure solution. They now represent around half the business of Amorim, which is by some distance the world's largest cork company. This article will take a closer look at this category of closures and assess their merits compared with other closure solutions.

Champagne corks

The story begins in Champagne, France, birthplace of the original technical corks. Although people commonly think of sparkling wine corks as being mushroom shaped because of the way they appear when removed from the bottle, before they're inserted they consist of a cylinder roughly twice the diameter of the bottle bore, with a distinctive deep chamfer (the technical expression for the smoothing off of the rim) at the top. The problem with producing such a large-diameter cylinder entirely from natural cork is that most cork bark is not thick enough to make them. As a result, Champagne corks are made largely of agglomerate cork--the only natural cork elements are the two or three discs that are in contact with the wine.

Normally, natural cork is punched tangentially to the face of the bark, which has first been cut into strips of suitable width. But with thinner pieces of bark, it is possible to cut sheets of high-quality cork a few millimeters thick in a plane parallel to the flattened cork bark planks, and then punch discs from these. By gluing these discs onto the end of an agglomerate cork component, Champagne corks can be made affordably, with just the high-quality cork in contact with the wine.

The agglomerate component of Champagne corks is made by bonding together small cork fragments--typically 5mm to 8mm in diameter--using food-grade glue that includes polyurethane. The production process is based on extrusion, producing long tubes or rods of agglomerate that are then cut to the appropriate length. Agglomerates are extremely cheap because they are made from pieces of bark that otherwise would not be suitable for cork production as well as the material that is left after corks have been punched out of planks. In its various forms, agglomerated cork is the basis of most technical corks on the market today.

The Twin Top and its competitors

The most significant technical cork is the Twin Top developed by Amorim (whose products are sold in the United States by two wholly owned subsidiaries, Amorim Cork America and Portocork) in the mid-1990s. It's a closure that adapts the technology used for Champagne cork production. "Champagne corks are not only an important product for cork companies," says Carlos de Jesus of Amorim, "but also led to the development of the Twin Top."

Cork companies realized that Champagne corks were performing well, de Jesus says, with low levels of taint and consistent physical performance. "We asked ourselves how we could transfer this technology to still wine closures and get good results."

The Twin Top has an agglomerate core sandwiched between two discs of good-quality natural cork. The advantage of having natural cork at both ends of the closure is dual: first, no orientation machine is needed before the cork is applied on the bottling line, and second, the consumer sees nice-looking natural cork (not agglomerate) when they remove the capsule. Launched just 15 years ago, the Twin Top is now the best-selling technical stopper in the world, with sales of 650 million units per year. They are usually employed for large-volume, price-sensitive wines for which the cost of good, natural cork would be prohibitive.

Other cork companies now produce their own versions of the Twin Top, which is also known generically as the "one-plus-one" (although, technically, this should really be two-plus-one or one-plus-two.) Cork manufacturer MA Silva's version is called Silktop, while Cork Supply USA offers the Vapex 1+1.

The reasons behind the success of this closure are several. First, because the bulk of the closure is agglomerate, the one-plus-one is a pretty consistent closure with predictable levels of oxygen transmission. Second, because only relatively small discs of natural cork are needed, it's possible to source very high-quality cork at a low cost to produce these discs, which will be the only part of the closure in direct contact with the wine. Some companies such as MA Silva offer a range of one-plus-ones graded by the visual quality of these end discs. This leads to perhaps the main reason one-plus-ones have been popular: cost. They're considerably cheaper than whole natural corks and compete favorably with synthetics and screwcaps--in many cases, undercutting them. "The main advantage of using a technical cork is price," says Adolfo Hernandez of MA Silva. "A natural cork can cost anywhere from 20 cents to over $2 each, but technical corks range from 6 cents to maybe 10 cents per stopper."

Microagglomerates: the next generation

While the one-plus-one is the most popular technical cork, it is rapidly being caught up to by a new generation of closures known as microagglomerates. While the agglomerate portion of the one-plus-one is made up of relatively large particles of cork, microagglomerates are made up of much smaller granules that lend an altogether more attractive, uniform look. Because the agglomerate portion of the microagglos (as they are commonly-referred to) is much more attractive, it is not sandwiched between cork discs.

The first microagglomerate was the Altec, which was revolutionary at the time but turned out to be fatally flawed. Introduced in 1995 by French cork company Sabate, Altec was made of finely ground cork flour glued together with synthetic microspheres to produce a cork-based closure that looked classy and had uniform properties. The synthetic microspheres were needed to provide a degree of elasticity to the Altec: Without them, the closures would have been too rigid, because of the very small size of the cork granules employed.

The market, dissatisfied at the time with the quality of cheap natural cork and not convinced by the first generation of synthetic corks, endorsed Altec to the tune of buying 2 billion units during the following years. (Remember, this is before the screwcap revolution, which began in Australia in 2000.) But grumbling about the organoleptic impact of Altec soon started. Some people complained of a glue taint while, in fact, the problems were caused by a consistent low level of 2,4,6-trichloroanisole (TCA, now commonly known as cork taint.) Using small granules of cork during the manufacturing process had spread out the TCA naturally present in the cork, so instead of having a few contaminated closures in a batch, every closure was contaminated to a low degree. Unfortunately for Sabate, this low level of TCA was above the detection threshold for some tasters. It was a major disaster, and by 2002 sales plummeted.

Sabate, to its credit, responded well. Sabate looked at ways of removing any contamination from cork, and with the help of the French atomic energy commission it came across a process that actually worked. It involved the use of carbon dioxide in a state known as its critical point. At a particular combination of pressure and temperature, the liquid/gas interface disappears, and you then have a substance that can penetrate like a gas and can clean like a liquid. For carbon dioxide, the critical point is not too hard to achieve: It's 31.1 [degrees] C and 73 bars of pressure--a conveniently low temperature, even if the pressure is on the high side. This technique has been used to remove caffeine from coffee and by the perfume industry to extract fragrances.

After trials, the new version of Altec, called Diam, was released commercially in 2005, and after restructuring Sabate changed its name to Oeneo-Bouchage. The Diam range has expanded and currently consists of Diam versions 2, 3 and 5 (in ascending order of cost and impermeability to oxygen) as well as the Mytik sparkling wine closure. Oeneo has improved the look of the closure by adding a grain effect, to make it look more like natural cork, as well as features such as end printing. Diam's great benefit is that it is taint free, according to the company, because of the effectiveness of the production process. However, because of the added cost of the supercritical carbon dioxide treatment, Diam costs a little more than some other technical corks on the market.

Following the initial market success of Altec, other cork producers began work on microagglomerates and now most offer them as part of their portfolios. For leading cork manufacturer Amorim, their microagglo, Neutrocork, has been experiencing rapid growth in sales. "It is now the fastest growing technical stopper," reports Amorim's de Jesus. He says that sales have grown over the past four years at 20% per year, with a current figure of 410 million units. For the microagglo category as a whole, corresponding growth has been 12%. "It's a workhorse in getting wines back to cork from plastic closures," says de Jesus. "It can undercut the synthetic corks by as much as 50%, depending on the market and the quantity." MA Silva's microagglomerate is Pearl, while Cork Supply offers the Vapex microextra.

Defeating taint

One of the issues facing manufacturers of any natural cork-based closure is the issue of taint. The presence of TCA in cork oak bark is a significant problem, and for natural cork the reported taint rates in the late 1990s and early 2000s were extremely high. Reports from Australia at the time suggested that as many as one in 10 wines were affected by cork-related taint issues. As there was no alternative to natural cork until the advent of synthetic corks in the late 1990s (and from 2000 onwards the widespread adoption of screwcaps, particularly in New Zealand and Australia), the pressure on the cork producers to do something about taint issues wasn't all that strong. But since the loss of significant market share to alternative closures, the cork industry has invested a lot of money in searching for remedies.

There are two ways of addressing taint. The first is by curative measures, attempting to remove TCA from products during the production process. The second is by improved quality-control steps. Both approaches have been adopted by cork companies in their attempts increase the reliability of technical corks, and especially so since the disaster of Altec. Because of the averaging process of using many small granules, it is imperative that agglomerates and microagglomerates are made from cork that has been cleaned in some way.

Amorim was the first to use steam-based methods for cleaning cork granules. Their technology, called ROSA, involves suspending the granules in steam under pressure, which removes a good portion of any TCA present. It's not as effective as using critical-point carbon dioxide, but it is much cheaper and takes out around 70%-80% of TCA. "Steam works," says de Jesus. "It's natural, it's inexpensive, and it's not highly invasive." Unsurprisingly, other companies are now using variations of ROSA for their products as well. "Our SARA process is similar to the Amorim ROSA process," says MA Silva's Hernandez, "and gives an 80% reduction in TCA." Cork Supply's steam-cleaning process is named Vapex. De Jesus points out that techniques such as ROSA are much more effective when they are coupled with preventive processes that seek to reduce any TCA present in cork in the first place. After all, an 80% reduction in TCA is only effective if this brings the total level down below the perception threshold; 20% of a large initial TCA level is still a huge problem.

The leading cork companies have made significant improvements in the way they deal with cork bark during the production process. One is that most cork is now stored on concrete, not bare earth, while it is waiting to be processed. Another is the boiling stage: It's important that the water used to boil the planks, necessary to clean and soften them, is kept clean and properly filtered so that the risk of cross-contamination is reduced. Then care needs to be taken with the conditions these boiled planks experience before the cork is cut or punched. There has also been investment in gas chromatography equipment so that TCA, which causes contamination at incredibly low concentrations;, can be detected in quality-control steps. A big problem for natural cork is the many small players who still operate using older processing practices. For technical corks this is less of an issue, because these require larger scale operations that can only be carried out by bigger players that are much more likely to be implementing effective preventive and quality-control measures.

While cork companies don't give guarantees about TCA levels, they do talk about their own data on releasable TCA levels. Cork Supply says that the releasable TCA level for the Vapex microextra cork is consistently <0.9ng/L (nanograms per liter, which is the same as parts per trillion, ppt), with an average of 0.5 ng/L. Amorim says that average releasable TCA for Twintop is 0.52 ng/L and for Neutrocork it is 0.55 ng/L. These figures arc close to the detection limits of current technology and are well below the perception thresholds in humans.

Basic agglomerates

Taking a step back, there is still a place for basic agglomerate corks at the very bottom end of the wine market. These are effectively one-plus-ones without the cork discs at either end--simply the agglomerate portion, with large granules. "There's still a market for agglomerates," says de Jesus, "but it is not something we expect to see grow." Amorim recently introduced a slightly more up-market agglomerate product called Advantec, which has a coating that hides the less appealing look of agglomerate cork. This is also made by granules that have been cleaned by ROSA. "In 2010 every product Amorim sold saw growth," says de Jesus, "but big growth isn't in the low end of the market."

Concluding comments

Technical corks are an important segment of the closures market, and they look set to experience continued growth, especially in markets where in-neck closures are considered to be important for consumer acceptance. They have also come at the right time, as the cork industry has had to fight back against the growth in alternative closures, most significantly synthetic corks and screwcaps.

"R&D for technical stoppers has helped maintain the 70% market share for natural cork," says de Jesus. "Without the technical stoppers we couldn't keep delivering to the wine industry during the growth that the industry has experienced. Technical stoppers allow us to use a lot more of the raw material, which has been fundamental to keep up with demand, while at the same time delivering the quality and TCA control wineries need."

"Technical stoppers allow us to use a lot more raw material."

-- Carlos de Jesus, Amorim


* Wineries have been adopting natural cork-based, agglomerated closures because they offer increasingly better quality for a low price.

* The article details various types of technical corks and discusses recent breakthroughs in TCA control.

* Micro-agglomerates are the most upscale option, offering cork-like appearance and prices competitive with synthetic closures.

London-based writer Jamie Goode is the publisher of and specializes in wine science issues. His first book was published in 2005 by Mitchell Beazley. Contact him through Wines & Vines at
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Title Annotation:CLOSURES
Comment:Understanding technical corks: how high-quality, inexpensive one-plus-ones and agglomerates evolved.(CLOSURES)
Author:Goode, Jamie
Publication:Wines & Vines
Geographic Code:1USA
Date:Aug 1, 2011
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