Alternative Wine Closures

TCA (2,4,6-trichloroanisole) is the main compound responsible for cork taint: one of the most odour-intense compounds known, with a distinct musty, mouldy aroma. One study put the aroma threshold of TCA in a Pinot Noir wine at 1.4 ng/L, and some tasters at the AWRI can detect TCA in wines at less than 1 ng/L. In AWRI sensory evaluation, TCA at a concentration as low as 1 ng/L suppressed the ratings for overall aroma intensity and for positive fruit-derived characters of a Semillon wine. New Zealand winemaker Kim Crawford put the effect this way to Wine Spectator in 2001: in the majority of cases, the wine is not actually 'corked' but 'just dull and flat and stripped of flavor.' TCA generally forms when moulds growing on cork come into contact with trichlorophenol, a chlorophenol biocide used by industry as a general disinfectant, and convert it to TCA. Cork is not the only source: TCA can also be formed in oak, so a wine can have a TCA taint without any contact with cork. A related compound, 2,4,6-tribromoanisole (TBA), has a similar musty, mouldy aroma and has been detected in barrels, plastics including synthetic closures, natural corks, wood structures including walls, floors and ceilings, and the atmosphere of wineries.

• Prescott et al. (2005) put the consumer detection threshold for TCA at 2.1 ng/L and the consumer rejection threshold at 3.1 ng/L.
• TCA can be formed in oak, so a wine can carry TCA taint without any contact with cork.
• Natural corks can show high levels of variability in their oxygen permeability, depending on the grade of cork used.
• A closure study run from 2001 to 2003 by Washington's Hogue Cellars found that wines under natural cork had unacceptably high levels of cork taint and aged inconsistently, depending on the seal maintained by the individual corks.

In 1964 the then-director of Australia's Yalumba winery approached the French company Le Bouchage Mechanique about creating a screwcap sealing system, but the first Stelvin cap was trialed by a Swiss wine in 1972. In 1973 a group of Australian wineries including Yalumba, Penfolds and Tahbilk started commercially releasing wines under the twist-off. The closure was stigmatized as a seal for lower-quality wines and was mostly phased out in the 1980s; even Yalumba abandoned it until 2000. In 2000, 14 Riesling producers from South Australia's Clare Valley, under the leadership of Andrew Hardy, then winemaker at Knappstein's and president of the Clare Valley winemakers association, banded together to battle cork taint by putting screw caps on some percentage of their latest Rieslings. Jeffrey Grosset put 80 percent of his Riesling under screw cap that year. In New Zealand, beginning with the 2001 vintage, more than 25 estates planned to move from corks to screw caps, and the group formed to promote them, the New Zealand Closure Initiative, had 27 members by August 2001. A screw cap's oxygen performance depends on its liner. Saranex and tin/saran are the two key liner materials, with saranex typically giving marginally higher OTR values than tin/saran, and screw caps overall sit at very low to low OTR with a high degree of consistency. As of March 2019, screw caps sealed about 90% of all bottled wine in Australia.

• Yalumba approached Le Bouchage Mechanique about a screwcap sealing system in 1964, and the first Stelvin cap was trialed by a Swiss wine in 1972.
• The 2000 Clare Valley move included Grosset, Mount Horrocks, BRL Hardy's Leasingham, Mitchell and Taylors.
• Saranex and tin/saran are the two key screw cap liner materials; saranex liners typically have marginally higher OTR values.
• Wine Spectator credits screw caps with ensuring consistent quality and eliminating the possible cork contamination of TCA.

Technical or agglomerated corks sit at low to moderate OTR, with lower variability than natural cork stoppers. Oeneo's Diam process uses supercritical carbon dioxide, also used for decaffeinating coffee, as an efficient solvent, being halfway between liquid and gas. Some 95 per cent of a Diam cork is processed cork; the rest is acrylate and polyurethane. Diam uses finely milled, suberin-rich cork flooded with supercritical carbon dioxide, which sluices out chemical impurities including TCA, just one among around 125 chemical products extracted by the solvent; the cleaned cork is then mixed with acrylate microparticles and a binder. As of 2014, Diam corks came in three levels of permeability, and Diam had recently launched a top-of-the-range Diam 30, guaranteed to perform faultlessly for 30 years. In Chablis, Fèvre and Benoît Droin had both adopted Diam corks for all of their production, and both claimed no more corked bottles or premox problems; Hugel in Alsace, and Jadot and Bouchard Père et Fils for their white wines, also used Diam. The original research and patent for Diam corks belonged to Sabaté, and in 2003 the Sabaté name disappeared as the company became known as Oeneo.

• Technical/agglomerated corks have lower variability than natural cork stoppers, with low to moderate OTRs.
• Diam's cleaning step uses supercritical carbon dioxide, a solvent also used for decaffeinating coffee.
• As of 2014, Diam offered three permeability levels and a Diam 30 guaranteed to perform faultlessly for 30 years.
• By 2014, Fèvre and Benoît Droin in Chablis had adopted Diam for all of their production, with Jadot and Bouchard Père et Fils using it for their white wines.

Synthetic closures typically fall within the moderate to high OTR range, with significant variability among the products available. Moderate OTR values can lead to the development of cooked and stewed fruit characters, and high OTR values can lead to significant oxidised characters developing over a relatively short shelf life. In its own closure study, begun in 2001 and completed in 2003, Washington's Hogue Cellars found that bottles sealed with synthetic stoppers tended to oxidize after about two years. Hogue's Fruit Forward wines, bottled with a synthetic stopper called Supreme Corq since the 1999 vintage, were to move to screw caps as of the 2004 vintage. Kumeu River winemaker Michael Brajkovich told Wine Spectator in 2001 that he once tried a type of synthetic plastic stopper and found it worse than corks, leading to oxidation in as little as six months. Robert Joseph suggested in Decanter that one attraction of synthetics is that, for the casual corkscrew user, they may pass for natural cork.

• Synthetic closures typically have moderate to high OTR values, with significant variability among products.
• Hogue Cellars' 2001 to 2003 study found that bottles under synthetic stoppers tended to oxidize after about two years.
• Synthetic closures are among the plastics in which TBA, a compound with a musty, mouldy aroma similar to TCA, has been detected.
• Michael Brajkovich of Kumeu River saw oxidation in as little as six months under a synthetic plastic stopper he tried.

Glass closures are among the most common commercially available closures used in the global wine industry. By February 2004 a division of aluminum company Alcoa had invented a resealable glass stopper called Vino-Lok. The closure requires a specially designed wine bottle: an aluminum cover on top is removed to reveal the glass plug, which is pulled out by hand and can be put back in. Thomas Strieder, business development manager of Alcoa's closure division in Germany, called it real glass with a liner the same as screw caps, and added of the screw cap: "The screw cap is perfect from a quality point of view, but it has an image problem." Among the first wineries to try Vino-Lok was Weingut P.J. Valckenberg in Germany, which manually stoppered 2,800 bottles of its Riesling Spätlese Trocken Rheinhessen Wormser Liebfrauenstift-Kirchenstück 2003.

• Vino-Lok, a resealable glass stopper, had been invented by a division of Alcoa by February 2004.
• The closure requires a specially designed bottle; an aluminum cover is removed to reveal the glass plug.
• Alcoa's Thomas Strieder called the stopper real glass, with a liner the same as screw caps.
• Weingut P.J. Valckenberg was among the first wineries to try Vino-Lok, on 2,800 bottles of a 2003 Riesling.

Oxygen transmission rate (OTR) is a measure of the volume of oxygen that diffuses through a barrier over a given period of time, and for bottled wine the barrier for oxygen permeation is the closure. Oxygen drives many of the important sensory changes which occur in wine as it ages, and it indirectly results in the degradation of the key antioxidant sulfur dioxide. AWRI closure trials have shown that closure OTR can have a significant impact on the shelf-life of a wine: very low OTR values can lead to reductive attributes if appropriate precursors are present, low OTR values can lead to retention of fresh fruit characters, moderate OTR values can lead to cooked and stewed fruit characters, and high OTR values can lead to significant oxidised characters over a relatively short shelf life. Suppliers of technical/agglomerated, synthetic and screw cap closures have all developed closures with defined OTR values that can be tailored for differing wine styles and methods of winemaking. Fine wineries long shunned screw caps because of their association with inexpensive jug wines, and many people felt red wine needed porous cork to let in small amounts of oxygen. Jeffrey Grosset believed that wines do mature under screw caps, in a different and perhaps slower way, and research done by the AWRI in 1986 found that oxygen was not required for a wine to mature. Grosset's U.S. distributor, John Larchet, was less certain, telling Wine Spectator there was a stronger marriage to cork in the United States than elsewhere.

• AWRI closure trials: very low OTR can lead to reductive attributes; low OTR retains fresh fruit; moderate OTR brings cooked and stewed fruit; high OTR brings oxidised characters.
• The Mocon Ox-tran method and chemiluminescence are the most widely used methods for measuring OTR.
• Fine wineries long shunned screw caps because of their association with inexpensive jug wines.
• Diam commercial director Pascal Popelier told Decanter's Andrew Jefford: "Diam is not better than screw cap."

Primary sources: https://www.awri.com.au/wp-content/uploads/2019/03/oxygen-transmission-rate.pdf, https://www.awri.com.au/industry_support/winemaking_resources/sensory_assessment/recognition-of-wine-faults-and-taints/wine_faults/. Secondary sources: https://www.winespectator.com/articles/where-did-screwcaps-for-wine-come-from-53184, https://www.winespectator.com/articles/riesling-producers-in-australia-opt-for-screw-caps-20730, https://www.winespectator.com/articles/talking-about-a-revolution-new-zealand-winemakers-ditch-corkscrews-for-screw-caps-20999, https://www.winespectator.com/articles/new-glass-wine-stopper-hopes-to-oust-cork-21902, https://www.winespectator.com/articles/hogue-cellars-releases-results-of-wine-closure-study-switches-to-screw-caps-22059, https://www.decanter.com/wine-news/opinion/jefford-on-monday/jefford-on-monday-debating-diam-8087/, https://www.decanter.com/features/which-cork-is-best-246798/. Last verified 2026-10-05