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Cork Myths and Curiosities

Did you know that a single cork stopper can show a balance of up to -562g of CO2?

And that cork was used in Ancient Egypt and can be used to produce energy? Did you know that scientific research consistently proves that consumers associate cork with high-quality wines?

Find out everything you’ve always wanted to know about cork.

Scientific trials such as the AWRI’s comparative closure trial have concluded that there is no such thing as a perfect closure.

"No one closure tested in this study could be considered entirely suitable by all criteria assessed, for the long term storage of wine."
Awri Media Release, "First Results of the Awri Wine Bottle Closure trial published 12 July 2001

Corks, especially Twin Top, performed at or near the top on all key parameters, without the presence of sulphide-like odours or premature oxidation. Even after 63 months, Twin Top continues to perform well.

According to the former director of the AWRI, Professor Peter Hoj, all closures can be improved:

“All could perform better: cork producers needing to go further in reducing taint; screwcap producers having ‘a long way to go’ to improve liners and gas exchange, and also in preventing damage to caps when knocked; and synthetics are still considered to ‘scalp’ flavour from wine”
Prof. Peter Hoj, quoted in "Australia pulls out the stoppers", Chris Snow, Herald Sun, 11 September 2004, P94

No closure is perfect, as the AWRI comparative closure trial concluded, and it would be irresponsible of any supplier to claim perfection for their product.

Cork has been doing a remarkably good job for centuries. In fact, as we learn more about post-bottling wine chemistry, we can only marvel at the unique contribution cork makes to wine preservation and development.

As we understand it better we are able to further improve its performance.

The incidence and intensity of TCA continues to fall and the latest research shows that cork is remarkable consistent in terms of oxygen ingress.

That does not mean that cork producers can relax. Amorim will remain ever vigilant against TCA. Our R&D effort will help us better understand and control oxygen ingress through corks and we will work with winemakers to minimise the risk of ‘random oxidation’ associated with bottling line operations.

While the problem curve for cork is coming down, the problem curve for screwcaps is going up.

Screwcap producers and wine researchers are a long way from knowing how to avoid the sulphide-like odours (SLOs).

More and more questions are being raised about the effect of the screwcap on wine development.

While there may have been some occurrences of SLOs in wines sealed with corks, several studies by the AWRI have confirmed these are not nearly so frequent as they are in wines sealed with screwcaps.

Feedback from winemakers suggests that screwcaps make even greater demands on bottling line management than cork closures. They are vulnerable to bottle finish variability, capping faults and bottling line faults, all problems that screwcap proponents acknowledge.

Such problems have existed on bottling lines for years and apply equally to cork closures. It is unrealistic to hope they will be overcome simply with a change of closure.

“Mr Eggins [chief winemaker, Taylors Wines] said screwcap seals could break during storage, which led to wine going off through oxidation. If a stack of wine was stored on an uneven floor, pressure from bottles above could break the seals on bottles below”
Adam Eggins, Chief Winemaker of Taylors Wines (Who use screwcaps exclusively) quoted by Geoff Strong in the Melbourne Age

Post-bottling wine chemistry is a very complex issue and the closure is only one of a number of factors affecting wine development (others include the chemical composition of the individual wine, headspace volume and gas composition, free SO2, bottling conditions, etc).

Research is improving our understanding but wine researchers don’t yet know enough about how all the factors affect wine development to predict let alone control what will happen in the bottle.

Experts such as Dr Alan Limmer believe that the likelihood of reduced characters forming after bottling varies from wine to wine, vintage to vintage, placing severe demands on the winemaker wanting to control them.

Meanwhile, cork has been proven over centuries

It is a mistake to equate the best quality corks with screwcaps, which have a much stronger tendency to impart reduced characters to wine and restrict wine development.

While screwcaps may be suitable for some wines intended for quick drinking, very little is yet known about the impact of screwcaps on more complex wines intended for long-term cellaring.

Current thinking suggests that wines will develop more slowly under screwcap and may develop into different wines. They may never develop the characters winemakers and consumers appreciate in cork-sealed wines.

In those markets with greatest experience of screwcap, there is growing recognition that the issue of cork vs screwcap is far less clear-cut than screwcap advocates claim.

No. Research and practical experience have shown all closures are subject to some degree of variability. In fact, they show that when properly handled cork performs remarkably consistently.

The high degree of consistency claimed for screwcaps depends to a large extent on eliminating all other sources of variation, including bottle finish variability, capping faults and bottling line faults, all problems that screwcap proponents acknowledge.

These same factors affect the performance of cork, although feedback from winemakers suggests that screwcaps make even greater demands on bottling line management than cork closures.

Amorim staff can advise on correct bottling line procedures to help avoid random oxidation (see Focus, ‘Choosing and Handling Cork’).

Cork is not the only source of TCA contamination of wine, so changing closures will not eliminate the risk of TCA taint. There are also other taints that have nothing to do with cork, such as TBA (triboromoanisole) and brettanomycaes, and using screwcaps will not protect against these.

“That venerable and venerated doyen of wine, Len Evans AO and OBE has been selecting those Qantas wines for 42 years and chairman of the panel for 37. At a recent tasting some of his fellow judges rejected some of the wines because of the dreaded and oft mentioned ‘cork taint’. Trouble was that the ‘tainted’ wines were under screwcap!”
Sydney Daily Telegraph, 11 March 2006

Winemakers and researchers are still learning about the interactions between the wine and the closure, including the ability of the closure to absorb certain flavour compounds from wine.

At this stage it appears that synthetic closures have the greatest tendency to scalp flavours, whereas screwcaps scalp little if any flavour. Cork appears to lie somewhere in between.

It may be that in some cases the ability to modify flavour has a beneficial effect, for example in modifying high concentrations of TDN, which imparts a kerosene-like flavour to Riesling.

Some researchers also claim that cork has the ability to remove sulphide compounds from wine, but this is unproven.

Winemakers have begun to use screwcaps, especially on fresh aromatic and quick drinking wines, but most also use cork.

As well as concern about suphide like odours, many winemakers have expressed caution about their suitability for wines with greater complexity.

They have concern that screwcaps will slow down bottle ageing, creating ‘Peter Pan’ wines, ‘frozen in time’, which never develop the same character as they do under cork.

Some winemakers have returned to cork, disappointed with the effect on wine quality.

We are confident that with further experience winemakers will recognise the value a cork closure can add to their wine.

It would be surprising if good winemakers chose to completely ignore new products available in the market. However, as Penfolds Chief Winemaker Peter Gago has said, screwcaps must prove they can perform well over decades and still allow the wine to develop the characters wine-lovers value.

Winemakers should do due diligence and when they do we are confident they will recognise the value cork can add to their wines, a value that has been proven over centuries.

Not at all. The overwhelming majority of consumers in all markets prefer cork to screwcaps (and synthetic closures).

Even where consumers accept alternatives, they still prefer cork. In US four out of ten markets and in the UK three out of ten consumers say they dislike buying a wine sealed with a screwcap.

Research consistently shows that consumers value cork as a natural and environmentally friendly closure. They appreciate its traditional association with wine and that fact that it allows the wine to develop interesting and complex characters over time.

Some customers may value the convenience of screwcaps, but most still prefer cork. Amorim is investigating the potential to develop a technical cork that can match the convenience of screwcaps while retaining all the benefits of natural cork.

Market research has consistently shown that consumers prefer cork. They value it as a natural and environmentally friendly closure. They appreciate its traditional association with wine and the fact that it allows the wine to develop interesting and complex characters over time.

Even in Australia were screwcaps are more common consumers still overwhelming associate cork with wine for special occasions and associate screwcaps with cheaper wines.

Winemakers should take care before risking that special association with cork and the rituals of wine that set wine apart from other beverages.

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