Types of wine closures

Wine bottles stacked in shelves

Bark in a bottle

Over the years, a variety of measures have been taken to protect wine from oxidation, during its storage. In ancient times, a layer of olive oil was poured over wine being stored in amphorae. As recently as the mid-17th century, oil-soaked rags were still stuffed in the necks of more conventionally shaped bottles. The natural elasticity and impermeability of cork, made it an ideal stopper for wine bottles and it quickly became the preferred closure.

Cork comes from the bark of quercus suber (Cork Oak) with 52% of world production coming from Portugal, and 32% from Spain. Wine corks can be made of a single piece of cork, or made of granular particles called 'technical corks'. 80% of the 20 billion bottles of wine produced each year use natural cork closures. However there are problems - studies have revealed that 45% of corks showed gas leakage during pressure testing. This causes uneven rates of oxidation (and potential ageing) of wine.

Of equal concern is the problem of 'cork taint', caused by the presence of the chemical trichloroanisole (TCA). TCA dulls a wine's fruit characters, and can gives it unpleasant mouldy/musty aromas. It is estimated that up to10% of wines have cork taint. For this reason - particularly in Australia and New Zealand - alternative wine closures are becoming increasingly popular.

Screw caps

Screw caps (or 'Stelvin') are the most popular alternative. Makers of aromatic dry white wines, which more readily reveal the unattractive 'charms' of TCA, were the first to seriously investigate alternatives to cork. In 2002, after trials over a number of years, all producers of Clare Valley Riesling, put their wines under screw cap. The success of this venture (and the accompanying education campaign), emboldened others to follow suit. In 2003 Marlborough Sauvignon Blanc producers, did the same. So quickly has the Australasian wine consumer embraced this form of closure, that more than 80% of white wines, and the majority of red wines, now use screw cap.

Naturally screw caps have their detractors. Being a perfect seal, screw caps stop oxidation and therefore slow the natural ageing process. This can also cause reduction which suppresses a wine's aromas, and may accentuate unpleasant aromas of sulphides used to protect the wine during the bottling process.

Crown caps

Crown caps are used by the sparkling wine industry (including Champagne), during the secondary fermentation process, and only replaced by cork closures during disgorgement, prior to shipping. Crowned bottle caps provide a tight seal, without the risk of cork taint. Unfortunately they can't provide the characteristic opening 'pop' associated with opening a sparkling wine - and have not met with the same acceptance, that screw caps have.

Other types of closures

Designed to look and 'pop' like a natural corks, synthetic corks made of plastic or other polyester, have not generally lived up to expectations - often being an imperfect seal, imparting slight chemical flavours to the wine, and not being recyclable or biodegradable.

Vino-seal or vino-lok employs a glass stopper with a hermetic seal that prevents oxidation and TCA contamination, looks to be a most promising, but comparatively expensive alternative.

Zork is a South Australian invention that seals like a screw cap and pops like a cork, consisting of an outer cap that locks onto a standard cork bottle; an inner metal foil that prevents oxidation; and an inner plunger which creates the 'pop' on extraction and reseals after use. Like the vino-seal, its main drawback is its relative expense, compared to other closures.

Naturally the cork industry is happy to debunk the effectiveness, or faults associated with these alternative closures, but while corks continued to be affected by uneven oxidation, and TCA contamination, other closures are likely to capture an increasing market share.

Wine bottle being uncorked

Closure examples

Cork

Picture of a cork

Screw caps

Picture of a screw cork

Crown caps

Picture of a crown cap

Vino-Lok

picture of a Vino-Lok