From wooden stopper to high-tech product – bottle stoppers

For the longest time in the 20th century, corks were considered to be the only true closure for a wine bottle. Nobody probably ever questioned that. However, with increasing consumption, the natural product revealed its weaknesses. “Cork taint“ made alternative stoppers seem attractive – although not really acceptable at first. Today, a lot has changed in both sectors.

The stopper of a wine bottle actually does not have to be able to do much. It should be impermeable, hygienic, tasteless, long-lasting and naturally removable. A minimum amount of air permeability is a welcome added benefit. Nevertheless, the subject of wine closures goes far beyond the simple material properties.

For a long time corks were unchallenged as the best solution. Due to its elasticity the natural material can be compressed in order to then press watertight against the walls in the neck of the container. In ancient times, Greeks, Assyrians and Egyptians took advantage of this for their amphorae.

Later – apparently for cost reasons – a switch was made to wooden & clay stoppers, which were wrapped with hemp and dipped in oil. This was rather meagre and less pressure-resistant in terms of hygienic standard. This came back to roost when sparkling wines came into fashion in the 17^th century. That is why Benedictine monk Pierre Pérignon switched back to corks again for his new development champagne. The international trade relations at the end of the 19^th century were so interwoven that cork closures gained acceptance on a broad front.

The small cylinder from the bark of the Mediterranean cork oak proved to be very advantageous because of its fine air permeability. Oxidation gives wines a nutty aroma, as is desirable with sherry, for example. In contrast, young white wines lose their fresh fruity taste. Aromas of rotten eggs and burned rubber emerge under anaerobic conditions. A bit of aeration prevents that. As is also the case with the oxidation of phenols in red wine, this enhances the mouthfeel. A good cork allows precisely this dose, namely about one milligram a year. Moreover, sulphur is reduced through the cumulative effect.

Corks are obtained from the bark of the Mediterranean cork oak (Quercus suber). The bulk of world production comes from Portugal, where Quercus suber plantations in the Alentejo region characterise entire landscapes. As the global demand for wine skyrocketed in the 1980s, more and more of the hastily punched closures developed the infamous “cork taint”.

The industry reacted hesitantly at first. Musty corks were discounted as a natural phenomenon. In reality, cork taints are man-made. The unwieldy name of the aromatic hydrocarbon that is the primary cause of cork taint is “2,4,6-trichloranisole”, and it is therefore merely called “TCA” for short. The halogenated anisole is formed when microorganisms decompose cork or wood and chlorine compounds come into play in this connection.

Unfortunately, this was not at all uncommon. Many vintners used chlorinated wood preservatives in their cellars, occasionally even special cleaning agents for barrels. Mould fungi repel chlorophenols by chemically converting them. The foul-smelling anisoles – which are present in practically any organic material, even cellulose filters for wine filtration, and also attach to plastics – remain in this connection.

Even the slightest amounts in the air can contaminate the wine when it is pumped over: 0.5 nanogram – one two-billionth of a gram – is regarded as the threshold value. In the worst case, entire cellars are contaminated with load-bearing pieces of wood, which must then be exchanged. A small business can hardly afford that.

Other vintners were quite amazed when their wines corked with plastic corks. The stoppers had been put in a contaminated storeroom. Even the quantity which the seal of a screw cap absorbs can be enough. And it can even affect wines which have been produced under consideration of all risks. During one overseas transport the contents of a container spoiled because its wooden bottom had been treated with a chlorinated cleaning agent. Even the cork bark on a tree often contains traces of chlorine that has comprehensively spread in the environment. Then the reputation was ruined around the turn of the millennium.

The hour of alternative closures struck. Plastics also have elastic properties and presented themselves as an alternative. But plastic stoppers hardly allowed any air through. The handling often became a nuisance. The plastic cylinders ruined many a corkscrew. For a long time, conservative groups of drinkers were shy of models in pink or neon yellow. As if that was not enough, the stoppers became brittle and leaked after a few years.

The alternative providers ramped up their research departments and entered into worldwide partnerships with universities specialising in viniculture. In particular, the variance in the oxidation of natural cork offered a point of attack. For it had allowed countless vintage wines to age early. Nomacorc countered with controlled air flow rate. Upon request there is less air at first, then more in the maturity phase. Viventions, the company that is part of the closure conglomerate, today offers plastic stoppers with varying oxidation rates, including computer-aided advice for vintners with regard to their individual requirements. With special analytical devices such as “NomaSense oxo-luminescence technology”, an attempt is even being made to strengthen specific individual aromas such as berries, chocolate or spices and avoid ageing tones.

Closures made of renewable resources such sugar cane, produced with renewable energies and recyclable, are taking more ground away from corks. The optically enhanced closures are said to last up to 25 years.

Screw caps have also been tested billions of times, from the milk carton to cola bottle. Australian vintners have been using them since the seventies and swear by their durability. Yet they also twisted off the air in the wine. Today screw caps are on the market with oxidation rates similar to corks – except more accurately selectable.

Glass cones with a silicone lip seal according to the same principle. The Vinolok seems worthwhile and is primarily used for wines in the higher price segment, to this day with a clear market share.

The manufacturer of a granulated cork is called Diam. For this purpose, finely ground cork particles are treated in a bath consisting of hot, compressed, supercritical carbon dioxide, and thus liberated from TCA and about 125 other chemical compounds, and then “satin-finished” with silicone and/or paraffin. Adieu cork taint!

Diam is permeable to air in various levels over the entire surface of the material, not only on the edge. Top vintners such as Fèvre (Chablis), Hugel (Alsace), and not least oenologist Michel Rolland use Diam. The company is so convinced that is gives a guarantee of 30 years. Yet the closure is seen as controversial. Individual vintners and dealers complained about notes of glue or bitterness, while others refer to blind tasting sessions in which Diam screw caps were superior.

The latest trend is called Helix. It is also a granulated product that looks something like a champagne cork, only with an external thread with a strong pitch. According to company statements, Helix can be unscrewed by hand without any problems. The disadvantage is that the bottles require a corresponding internal thread, although only minor modifications are said to arise in bottling plants. According to the manufacturer Amorim, Helix is a “game changer” that the industry has been seeking for years. Five million euros in developmental costs and three patents are said to be behind the stopper.

In the meantime, scientific studies have established that TCA does not smell much at all, but rather suppresses part of the sense of smell. That has only helped the manufacturers involved to a limited extent so far. The discovery that 2,4,6-tribomoanisole (TBA) – which is closely related to TCA and also used in many wood preservatives, and can also readily cause cork taint via screw cap – caused further confusion.

The production of natural cork had to become more secure in this field of tension. The peeled bark was no longer dried on the forest floor after harvesting. It was cleaned with high water pressure, naturally without chlorine, and then with microwaves.

Trained “super noses” fished out the remaining error specimens during the quality control by Amorim. In cooperation with several viniculture schools the market leader ultimately developed a so-called gas chromatograph that measures the TCA content of a cork and can automatically sort it out if required. Cheaper and better than the sniffers! After an investment of ten million euros, Amorim guarantees TCA content below the perception threshold of 0.5 nanogram per litre. This is equivalent to a drop in 800 Olympic-size swimming pools. It is an impressive comparison, however, one could smell out five drops again. Californian competitor Cork Supply draws even with a similar product.

After the second half of the 20^th century, many medium-sized enterprises suffered from too much competition and not enough capital. They would have needed it in order to react to the TCA problems with research and development. Only the major companies were able to get that under control in the end. In the first decade of the 21^st century, over sixty companies in Portugal closed or were bought out. The inventor of Diam is also no longer there. The company Sabaté, at one time number 2 among cork manufacturers, ended up with barrel maker Seguin Moreau in a roundabout way.

An oligopolistic market that is divided into varying systems remains. Four out of the ten billion corks that are produced in a year come from Amorim, which as a result leads the field with an annual turnover of 900 million euros.

A screw cap is on up to one-fourth of all bottlenecks. Yet the market seems to be relatively saturated. Plastic corks are somewhat lower. But approximately two-thirds of the 18 billion wine bottles produced every year are still sealed with a cork product. The share is slightly increasing, which also has to do with the success of prosecco, which is mainly corked.

The market is stabilising after the severe upheavals. In the meantime, advantages and disadvantages of various systems are not only known, but also dwindled. So a thing or two is a question of purpose or also merely style, which is what manufacturers keep an eye on if at all possible.

In matters of environmental compatibility, plastic corks initially look bad, but in the meantime are also made of sugar cane instead of petroleum. The C0₂ imprint of cork is nevertheless considered better in comparison to aluminium production. The “Friends of the Earth Germany” (BUND) calculates that the Portuguese cork forests alone accumulate five million tonnes of carbon dioxide. Cork oaks are about 40 years old during the first harvest. Harvesting is conducted in nine-year cycles. Animals such as migratory birds and lynxes appreciate the peace and quiet. The BUND warns against the threat to the cultural landscape.

Even if the consumer hardly perceives it, stoppers are a cost factor. An aluminium screw cap costs four to five cents, whereas a granulated cork costs ten cents. A natural cork costs about 40 cents to one euro. Another twelve to 14 cents are added on top of that for a gas chromatograph. The prices are not yet established with Helix. The expensive developmental costs must first of all be recouped.

There have never been any consistent figures with regard to cork taints. Estimates range between one and twenty per cent, but what is common to all studies is that TCA problems are clearly on the decline. With twelve billion corks per year and an assumed bottle price of only three euros, even an error rate of one per cent means a loss of about 350 million euros.

As expected, inexpensive wines get cheaper stoppers. The best corks are plugged in premium bottles, even if a Châteaux such as Margaux has played with screw caps on the second wine. Establishments such as Laroche and Lurton returned to corks after similar attempts.

Which closure has which image, is a tricky question. Marketers readily identify national preferences. In Australia and New Zealand with their extremely fresh & fruity white wines, screw caps tend towards 100 per cent, if one first excludes Penfolds and Cloudy Bay’s corked up pinot noir “Te Wahi”. To some extent vintners even have decades of experience with premium wines.

However, the demand for cork is increasing in several key export markets. This includes England, whose habits exporters are keeping a watchful eye on. The degree of acceptance of screw caps is traditionally high. But as of late, corks are in demand again, primarily among more expensive wines.

Germany – as in many questions regarding the subject – is rather conservative. An expensive wine with screw cap still ensures insecure reluctance in wide circles. The polarised discussion which is held for this reason is particularly characteristic for the country. In contrast, Italy is as usual dynamic. Many vintners have tried alternatives. Most people continue to rely on corks in the matter of bella figura.

In Europe, screw caps celebrated early successes in Austria. After the diethylene glycol wine scandal in the mid-1980s, there were signs of radical change there. Screw caps are the rule on many white wines. As is to be expected, this is vice versa in Portugal.

Traditionalists readily sneer at the USA as the world’s largest wine market with the age-old statistic that only every fourth household there even has a corkscrew at all, and they roll their eyes at garishly coloured plastic stoppers. But corks are also gaining ground here. In China, packaging and purchase price are considered an essential price for the value. Nomacorc maintains its own production facility here. But cork is regarded as the gold standard.

Barack Obama may have also noticed this. When he served his counterpart Xi Jinping a Viognier with screw cap at a dinner in the White House in 2015, the Chinese press reacted quite irritated.

Matthias Stelzig