Wine Bottle Closures – Natural Cork versus Alu Screw Cap (part 2)

Cork is harvested for commercial use primarily from the cork oak (Quercus suber) that is endemic to the western Mediterranean countries. Once the trees are about 25 years old the cork is stripped from the trunks every nine years. The trees live for about 200 years. Cork is composed of suberin, a hydrophobic substance, and due to its impermeability, buoyancy, and elasticity, it is most commonly used for wine stoppers.

The cork industry is generally regarded as environmentally friendly. The sustainability of production and the easy recycling of cork products and by-products are two of its most distinctive aspects. Cork oak forests also prevent desertification and are the home of various endangered species. Cork forests throughout Spain, Portugal and Italy have achieved the Forest Stewardship Council (FSC) certification, which recognizes that these forests and operations are managed to international social and environmental standards.

There are two types: the whole cork stopper and the technical cork stopper. For the whole cork the best quality bark is punched by skilled workers, who can punch 20,000 corks in a day. Hand punching results in a more consistent quality, because a skilled worker can choose the best sections in the cork strip. Much of the corkwood left over from punching is sent for granulation and use in making technical corks.
Technical corks are manufactured corks, usually combining a body of agglomerated natural cork granules and fine natural cork discs that come in contact with the wine.

Although cork is one of the oldest stoppers for wine bottles, it has been under pressure of, and in many cases replaced by synthetic cork (plastic) stoppers or aluminium screw caps, due to the fact that natural cork might taint the wine. Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine. Though modern studies have shown that other factors can also be responsible for taint, the cork stopper is normally considered to be responsible, and a wine found to be tainted on opening is said to be “corked”. Cork taint can affect wines irrespective of price and quality level.

The chief cause of cork taint is the presence of 2,4,6-trichloroanisole (TCA) in the wine, which in many cases has been transferred from the cork, but which also can be transferred through the cork rather than from it. The production of TCA in cork or its transfer by other means into wine is complex, but most results from naturally-occurring airborne fungi presented with chlorophenol compounds, which they then convert into chloroanisole. Chlorophenols taken up by cork trees are an industrial pollutant found in many pesticides and wood preservatives, which indicates that it is a problem of modern times.

But times move on and the cork industry hasn’t been nescient. A number of independent analyses provide scientific evidence of improvement in performance and particularly the drop in the incidence of 2,4,6 trichloroanisole (TCA) contamination, underscoring the progress that has been made by the cork industry in recent years. The problems associated with TCA contamination are now a rarity and has fallen to less than 1 ppt. However random oxidation remains a problem.

Corticeira Amorim, the world’s largest cork producer refined its practices in the control of TCA, as all cork planks now undergo a technically refined boiling process to deliver cleaned planks with the right humidity for punching, in the shortest possible time (now three days rather than three weeks previously). Any batches too dry for the production process are then given a second boiling. However, recent experiments have proved that vaporisation by steam, rather than boiling, for a second time not only dramatically halves the levels of TCA pre-cursors in any suspect lots, but also reduces the amount of water used in the process.
Research is also underway to develop machines that use humidity rather than steam to remove volatile TCA over a longer treatment cycle, which would eliminate any colour variations that could be formed through the original process.

Amorim offers a range of products from the top grade hand-punched whole corks to its best-selling Twin Top that has whole cork discs at either end of a fine composite shank. The company might not be threatened by the alternative closure market, but it launched the Acquamark closure in response to the heightened competition. The Acquamark, touted as providing a natural cork stopper at a competitive price, is a whole cork stopper. The lenticels, or minute spaces are filled with cork particles and sealed with a water-based coating, from which it takes its name, ensuring total particle retention while the stopper is in the bottle.

But Corticeira Amorim is not the only one with innovations in natural cork stoppers.
to be continued

2 responses to “Wine Bottle Closures – Natural Cork versus Alu Screw Cap (part 2)

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