Screwcaps for wine
... why we use them at Featherstone Estate Winery
A screw closure is a mechanical device which is screwed on and off of a "finish" on a container. Either continuous threads or lugs are used. It must be engineered to be cost-effective, to provide an effective seal (and barrier), to be compatible with the contents, to be easily opened by the consumer, often to be reclosable, and to comply with product, package, and environmental laws and regulations.
Its use as an alternative wine closure is gaining increasing support as an alternative to cork for sealing wine bottles. A screw cap is a metal cap that screws onto threads on the neck of a bottle, generally with a metal skirt down the neck to resemble the traditional wine capsule. A layer of plastic (often PVDC ), cork, rubber, or other soft material is used as wad to make a seal with the mouth of the bottle.
The screwcap on a wine bottle isn't the same as those used for other food and drink: it has been specially developed for protecting fine wine over an extended aging period in the bottle. Specifically, the part in contact with the wine, is designed to stay stable and flavour neutral for decades.
Benefits and concerns
In brief, compared to cork: screw caps prevent the wine faults of oxidation and of cork taint, and are easier to open. The chief cause of cork taint is the presence of 2,4,6-trichloroanisole (TCA) in the cork, which taints the wine. Corked wine containing TCA has a characteristic odor, variously described as resembling a moldy newspaper, wet dog, damp cloth, or damp basement. In almost all cases of corked wine the wine's native aromas are reduced significantly.
The production of TCA in wine is complex, but most results when naturally-occurring airborne fungi are presented with chlorophenol compounds. Chlorophenols taken up by cork trees are an industrial pollutant found in many pesticides and wood preservatives, which may mean that the incidence of cork taint has risen in modern times.
All the serious research comes up with the same figure: 5% of wine closed in cork suffers from cork taint. Lower levels of cork taint are the most unpleasant in that they spoil the personality of the wine subtly, 
but it takes an expert to identify it as corked: most people just don’t think the wine is very nice. Badly corked wine is easy to spot, but somewhat rarer.
If 5% of our wine were damaged this way that would be 200 cases of Featherstone wine ruined every year (just imagine being given 200 cases of our wine then being told to pour it all down the drain!). In addition to cork taint are the problems associated with leaking corks and random oxidation. Traditionally associated in the US with extremely inexpensive jug wines or even "skid row" wines, the screwcap is making a comeback. Screwcaps have a much lower failure rate than cork, and in theory will allow a wine to reach the customer in perfect condition, with a minimum of bottle variation.
Cork, of course, has a centuries-old tradition behind it and some argue that the slow ingress of oxygen plays a vital role in aging a wine, while others argue that this amount is almost zero in a sound cork and that any admitted oxygen is harmful. Various studies are underway, although one data point is that producers in Champagne have aged their wines under crown cap (the cap that is on beer bottles) for quite some time with no apparent outcry. This is a debate that will take quite a while to settle.
Stelvin screw caps
The most known brand of wine screw caps is Stelvin, a brand of Rio Tinto Alcan. The brand is so common that it is genericized in common use, with many in the wine trade referring to screw caps as "Stelvin closures", regardless of brand.
History
The Stelvin was developed in the late 1960s and early 1970s, and commercialized in the 1970s. It was developed by French company La Bouchage Mecanique, thence acquired by Pea-Pechiney, which became part of Alcan, now Rio Tinto Alcan. It was developed at the 1964 behest of Peter Wall, Production Director of the Australian Yalumba winery, working with other companies. It was preceded as a closure by a Stelcap/cork combination (closed with cork, with a Stelcap on top): the Stelcap was also a long-skirted screw cap, but with a different inner lining (paper over cork, instead of tin covered by PVDC in a Stelvin).
It was originally trialled in 1970/71 with the Swiss wine Chasselas, which was particularly affected by cork taint, and first used commercially in 1972 for the Swiss winery Hammel. It was adopted commercially in Australia in late 1976/early 1977. For noble wines, wines from the 1971/72 vintage (such as Haut-Brion ) were sealed with Stelvin, then tasted in 1978, and found similar to cork-closed wines.
Adoption
Screw caps met with customer resistance in Australia and New Zealand, and were phased out in the early 1980s, only to be reintroduced gradually in the 1990s. They were widely adopted in the 1980s by Swiss winemakers, and have shown increasingly wide adoption in the succeeding years.
In New Zealand, adoption went from 1% in 2001 to 70% in 2004. Domaine Laroche in Chablis, France has been bottling their Chablis, Premier crus and Grand Crus on Screwcap since 2001 vintage. Other notable producers that have switched to screwcaps are R.H. Phillips in 2004, Hogue Cellars in 2004... and Featherstone Estate Winery in 2007.
Source: Wikipedia and VQA Ontario
