Wine Bottle Closures - Metal Screw Cap Closures Versus Cork

Topics Covered

Background

Reasons for the Shift from Cork to Metal Closures

Why are Problems with Cork on the Increase?

Is Synthetic Cork an Alternative?

Screw Cap Closures

Support for Screw Seals

Origins of the Screw Cap

The Stelvin Capsule

Types of Liners

Usage of the Different Types of Liners

Market Trends for Stelvin Capsules

Wine Bottles

Effects of Screw Cap Seals on Bottle Manufacturers

Screws Cap Seals Versus Cork Seals

Wine Connoisseurs

The Vineyards View

Summary

Background

To cork or to cap? It’s a big question for wine producers that has been rapidly fermenting among oenophiles and growers from the hallowed cellars of Bordeaux, up the slopes of sunny California and over to the relative upstarts in New Zealand’s blossoming wine industry.

Reasons for the Shift from Cork to Metal Closures

The reason for this shift from cork to metal is that an increased amount of wine is being contaminated by cork taint, leaving the wine tasting musty and dull. The culprit for this unpleasant phenomenon, which can spoil up to one in 10 bottles, is trichloroanisole (TCA), a compound formed when chlorine used for bleaching reacts with mould already growing in the cork. Humans are incredibly sensitive to the compound and can detect it even at weak dilutions of six parts per trillion. TCA can flourish in several areas of a bottling facility, such as drains and barrels, but corks pose the biggest problem.

Why are Problems with Cork on the Increase?

The problem of tainted corks is thought to be on the up because cork manufacturers are finding it increasingly hard to find supplies of good quality cork to meet demand - more wine than ever is being sold in bottles, rather than in bulk form.

Is Synthetic Cork an Alternative?

Of course, another alternative is the synthetic ‘cork’, which is already in widespread use - but some wine tasters complain of ‘plastic taint’, and many consumers find them difficult to remove.

Screw Cap Closures

Support for Screw Seals

One of the champions of the screw cap cause is a collection of New Zealand wineries who formed the New Zealand Screwcap Wine Seal Initiative in 2001. Now numbering more than 40 producers, the group's aim is to ensure the quality of their wine in response to escalating cork tainting problems. They had an almost immediate impact with the proportion of New Zealand wine using screw caps shooting up from zero in May 2001 to 14.4% by December 2002.

Origins of the Screw Cap

The New Zealand group has worked closely with Pechiney Capsules, whose Stelvin model has one of the largest shares in the wine screw capsule market. Originally developed in the 1970s, Stelvins were used to bottle cheap wines, but failed to take off. The seal was updated successfully for today’s market, and French-based Pechiney is expected to present a new seal innovation to the design in the next few months.

The Stelvin Capsule

The Stelvin capsule is made up of a screw cap, a long printable skirt and a liner specifically designed for contact with wine. The glass bottle used with the cap has a Stelvin Neck Finish with a screw thread beginning at 2.8mm below the neck top, and the closure is re-drawn to avoid leakage.

Types of Liners

Two types of liner give customers an element of control over the desired permeability of the seal. The Saranex liner is made from layers of polyethylene, PVDC (polyvinylidene chloride) and expanded polyethylene, whereas the Saran film etain has a layer of tin sandwiched between PVDC, white kraft and expanded polyethylene. This tin layer means that it is much less permeable than the Saranex liner and less oxygen is allowed to enter the bottle. Pechiney’s customers tend to use the Saran film etain liner for wines stored for longer periods of up to 10 years, with the Saranex intended for storage of between two and five years.

Usage of the Different Types of Liners

Different regions have their own liner preferences. ‘Australians always prefer the Saran film etain liner for both their red and white wines. But in France, both liners are used interchangeably for red and white wines,’ says Caroline Lenglin from Pechiney.

Market Trends for Stelvin Capsules

Stelvin sales have doubled in the past two years, predominantly in New Zealand and Australia, but also in the French wine growing areas of Bordeaux, Alsace and Bourgogne. ‘If we consider current estimates that more than 5% of wine sealed with a cork is tainted, we could see the market for screw cap wines capture 10% of the market share in five years time,’ says Lenglin.

Wine Bottles

The UK glass industry would remain largely unaffected by a move to screw caps in wine bottles since most bottles are imported from France.

Effects of Screw Cap Seals on Bottle Manufacturers

Looking further afield from a production perspective, an enormous number of screw top bottles are already produced for spirits and fortified wines, so a change to bottling wine with screw caps should not pose any problems, and in fact may be easier, according to Peter Grayhurst from British Glass. ‘Bore control needs a much tighter tolerance for cork or synthetic closures, so screw tops may be slightly easier to manufacture, but otherwise there is not much difference between the two processes,’ he says. ‘I don't think there will be a move to screw finishes that quickly - but you never know!’

Screws Cap Seals Versus Cork Seals

Wine Connoisseurs

So what do connoisseurs in the wine industry think about screw caps? John Corbett Milward from the UK’s Wines and Spirits Association is pragmatic about the issue. ‘There is no official view - let the market decide how people close their bottles,’ he says. ‘My belief is that people haven’t attempted to keep wines for a long time with a screw cap, but as far as use is concerned, some people like them and some don’t. We have no particular concern over the use of the materials.’

Pierre Mansour from the Wine Society, the world’s oldest co-operative wine club, agrees with Milward saying, ‘We don't care how a wine is closed, as long as what’s in the bottle is good.’ The Wine Society started closing one of their own label 2002 New Zealand Sauvignon Blanc with screw caps and have ‘no qualms’. ‘I’m very happy with the quality and there is zero tainting,’ adds Mansour.

The Vineyards View

There is however one common point on which the wine industry agrees - it is up to the producer to decide how to close their wine. The conservative French wineries will have an important vote as they mature their wines in cellars for long periods, but at the moment they are not bowled over by the idea of breaking with tradition and throwing away the corkscrew - despite the benefits of reduced TCA.

Slow oxygenation is needed to age some types of wines and screw cap producers argue that wine is aged by oxygen in the wine itself and a tiny amount of residual air held between the cap and wine. But many producers remain resolute in their belief that oxygen is able to gradually seep through cork and into the bottle, and that this is the only way wine can mature. Some Bordeaux producers lay their wines for between five and 50 years - so it would be a long wait to see if screw caps were successful.

Summary

A few French experts have stuck their necks out to sing the praises of the screw cap - but they are in the minority. Maybe when French wineries start bottling their premium Bordeaux wines with screw caps, we will know that they have achieved acceptance. In the meantime, it seems change is likely to move at the pace of a maturing fine wine - all in good time.

 

Source: Materials World, Vol. 12, No. 3, pp. 37-38, March 2004.

 

For more information on this source please visit The Institute of Materials, Minerals and Mining.

 

Date Added: Jun 23, 2004 | Updated: Jun 11, 2013
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