The screw cap revival owes much to the wineries of the Clare Valley in Australia, who, as a group, bottled their vintage 2000 Rieslings under screw cap. However, it is in New Zealand that screw caps have really found their home. In less than four years, the screw cap has become the standard closure for bottled New Zealand wines.

The New Zealand Screwcap Wine Seal Initiative, formed in May 2001, has 51 wine company members. However, many more of New Zealand's 500 wine producers are using screw caps for some or all of their production.

One of New Zealand's biggest contract bottlers, the Marlborough Bottling Company, reports that over 80 percent of its output last year was under screw cap. In one month, October 2004, Marlborough's screw cap rate topped 93 percent. Other contract bottlers around the country report similar rates.

Villa Maria, New Zealand's third largest producer, with an annual crush of over 8,000 tons, has committed to 100 percent screw cap, for both domestic and export markets. Some wineries have adopted caps for lesser-priced wines and retained natural corks for premium or super premium wines. Te Mata Estate, for instance, uses screw caps for the entry level Woodthorpe range and high-grade natural corks for its flagship Coleraine, one of the country's most prestigious red wines.

In the past year, the numbers have been boosted even further with New Zealand's largest wine company, Allied Domecq Wines New Zealand, employing screw caps for standard production lines, not just for airline bottles. Formerly Montana Wines, producers of the Brancott and Stoneleigh brands, Allied Domecq now bottles a third of all its brands under caps. The company's overall screw cap percentage is higher than this, however, as caps seal some of its highest volume lines, such as the Montana Classics range.

A few high profile producers, notably Dry River and Stonecroft, have stuck with natural cork for their total production. Nevertheless, pundits claim that around 70 percent of all bottled New Zealand wine is now under screw cap.

The issue has received regular attention from the mass media. Screw caps have captured the attention of the New Zealand public, from high-involvement wine aficionados to everyday drinkers who often buy what is on special at their local supermarket. And, increasingly, these people are choosing screw-capped wines.

Despite this remarkable performance, screw caps have a long way to go. There are issues relating to consumer acceptance, allegations that they are causing reductive or sulphidic wines, and questions about their performance, especially for long-term aging. Technical standards are still evolving. International success is not yet guaranteed.

Excessive Sulphides: Fact or Fiction?Critics argue that screw caps are acceptable for short-term drinking but that corks are superior for wines intended for lengthy bottle maturation.

A Wellington-based American wine writer, Paul White, has publicized what he sees as excessive sulphide levels in wines sealed under screw cap. "The Screwcap Initiative over-promised perfection without having perfected the process and set themselves up for criticism whective potential is there, but is the character reductiveness or flintiness? Or is it something derived from the winemaking, the oak or the lees aging?"

Some of the information is contradictory.

For instance, the chief judges' report at the recent Air New Zealand Wine Awards expressed concerns that "too many wines were showing sulphides that were under screw cap." Yet of the 16 wines that won trophies in that competition, including the champion and runner up, all but one was under screw cap. And the exception? A bottle-fermented sparkling wine.

My own regular tastings have not revealed anything like the problems alleged by Paul White and his panel of "professionally qualified" judges. And, in a couple of instances, the tastings have been remarkably similar in subject matter.

However, as Australian author Tyson Stelzer noted, "Many people remain unconvinced. And a perceived problem is still a problem." Research is starting to provide some answers.

Peter Godden, industry services winemaker-manager at the Australian Wine Research Institute (AWRI), presented ongoing data from the institute's "Wine Bottle Closure Trial" at the first International Screwcap Symposium, hosted by the New Zealand Screwcap Wine Seal Initiative in Marlborough last November. This trial commenced in 1999, with the first results published in June 2001. It was this paper that first raised the alarm regarding "reduced" aromas in screw-capped wines.

Godden also spoke of other work that the AWRI has been conducting, including a commercial closure trial funded by manufacturers, which commenced in 2002. Initial results from this trial, first published in August 2004, do suggest that screw caps have a slightly higher occurrence of reduced aromas or "struck flint" character as the AWRI refers to sulphide aromatics.

The AWRI now has an overriding project called "Wine and Oxygen," led by Dr. Elizabeth Waters. In one experiment conducted by Waters' team, a reference wine was bottled under cork, under screw cap and in glass ampoules sealed with airtight stoppers. The ampoules showed a much higher incidence of "struck flint" or "rubber" characters than the screw cap version, which was in turn higher than the standard cork version.

Godden is particularly concerned that the AWRI's own information is being used incorrectly. "There may be problems," he said, "but we need to deal with them in an open and objective way. The closures do not cause reductive characters to form. Indeed, there have always been reductive wines; it is basically a winemaking issue."

In contrast to the above examples, Godden mentioned a recent AWRI Advanced Wine Assessment course. The AWRI runs these courses for the Australian wine industry, and students are asked to rate wines for certain characters. At the September 2004 course, attendees rated a higher proportion of reductive wines under natural cork than under screw cap.

Godden would also like to dispel one myth: "Oxygen does get into screw caps. Not much, but it does." The rate of permeability is low but remarkably consistent as AWRI data shows (see Table below).

Some technical corks, made from cork crumbs held together with glue, also maintain a consistent rate of oxygen ingress. Altec, one of the best-known brands, performed well in this regard.

Natural corks, on the other hand, display a wide range of oxygen permeability. Nevertheless, the very best corks are more initial dip, however, the SO₂ decline evened out to a constant rate (Charts 1 and 2).

A similar pattern was found with screw-capped wines, albeit that average DO levels were initially much lower and hence sulphur levels started out from a higher base. Overall, screw caps resulted in higher levels of total and free SO₂ retention, though the long-term rate of SO₂ decline was about the same as natural corks.

Brajkovich surmises that natural corks provide an initial hit of oxygen at bottling, thanks either to the "pistoning" effect of the cork entering the bottle neck or because the compression of the corker jaws squeezes air out of the cork into the bottle headspace. This explains why wines sealed with natural corks generally show higher levels of dissolved oxygen (and lower sulphur dioxide) than screw-capped wines from an earlier stage. However, once that initial bottle shock period is overcome, in the long term, good corks provide as good a seal as screw caps and have similar rates of permeability.

A recent paper published by the Australian Closure Fund supports these conclusions. Clare Valley producer Jeffrey Grosset established the Australian Closure Fund to sponsor research into wine closures. The fund's first project was based on in-house trials conducted by Southcorp research winemaker Allen Hart, with support from the AWRI. The wines in the trial were Seppelts Great Western Sparkling Shiraz, which had been stored on lees for some years under crown seals, and Penfolds Bin 389. Bin 389, a red table wine, was sealed under ROTE screw cap, natural cork and two types of synthetic corks. The Bin 389 was aged in bottles for up to six and a half years and evaluated at regular intervals (Charts 3 and 4).

Hart's analyses of dissolved oxygen and sulphur levels in various Bin 389 samples provide uncannily similar results to the Screwcap Initiative trials. The figures show extreme variability between bottles sealed with cork, with some bottles showing high levels of additional oxygen and others relatively little. Hart suggests that this variability is the ultimate cause of "random oxidation." However, the oxygen permeability of screw caps was very consistent from sample to sample.

The principal conclusion of Hart's paper, which backs up research first published by French academic Jean Ribereau-Gayon in 1931, is that oxygen is not a vital component for the aging and development of bottled wine.

Randall Grahm, who has been a major supporter of screw caps at Bonny Doon Vineyards in Santa Cruz, California, believes that claims of reduction problems are total rubbish. "Reduction always is and always was a winemaking issue."

He points out that certain Italian wines, such as Dolcetto, are highly reductive when bottled under cork. "It is the winemaker's job to determine that the wine's reductive potential has been sufficiently diminished before bottling," said Grahm. "This is easily done by doing a test bottling some time in advance of the actual bottling. We have observed no problems so far, but that is not to say there might not come a wine that will surprise us. But my sense is that for any competent winemaker this is no biggie."

Grahm also dismisses claims that wines age better under corks than with screw caps. “and bottling as it relates to screw caps. The book was published with the backing of both the New Zealand Screw Cap Initiative and the Australian Wine Closure Fund. A major concern is that substandard wines, including poorly made, reductive wines, may give screw caps a bad name.

"It is not enough for the screw cap to be superior," said Stelzer. "It must also be perceived as being superior by the average consumer. Consumers must be convinced that screw caps give them a tangible advantage over corks."

He harks back to 1984 when screw caps were last launched on a widespread basis in Australia. The wines that were bottled under screw cap back then were low-priced white wines and wines served in economy class on airlines, helping to create an image of a cheap closure.

"There is no statement that we can make that speaks louder than the message sent by committing our best wines to screw cap first," said Stelzer. "And it makes so much sense. If there is any wine that is deserving of a closure that maintains fruit definition, surely it is the wine that is made from the very best fruit. If there is any bottle that demands an airtight seal, surely it is the bottle destined for a long life in the cellar. And if there is any sector of the market that understands the advantages of screw caps, is it not the same sector that is prepared to pay a little more to purchase a premium wine?"

The Marketing DilemmaOne who is concerned about wines aged on lees, in a reductive environment, is New Zealand Chardonnay specialist John Hancock, winemaker and part owner of Trinity Hill. At this stage, his premium wines, including his Gimblett Chardonnay, are still under cork.

Hancock would like to dispel any rumors that he has moved away from screw caps. "I don't have concerns about screw caps; however, we just don't know at this stage. Our wines are slow evolving, and we don't want to make a rapid decision. We are flexible."

Hancock points out that 50 percent of Trinity Hill's production is under screw cap, including all their aromatic white wines. "We are certainly not against using screw caps, but they could be another impediment for people not to buy those top-end wines from us."

John Thorogood, from UK wine merchants Lay & Wheeler, agrees with Stelzer that producers should put their best, rather than the least expensive, wines under screw cap. He labels the wine bottled under caps in the 1970s as "pretty dire." "We need a positive quality statement," he said.

In short time screw caps have come from nowhere in the UK to be commercially significant. And, as Thorogood observes, three or four years is a very, very short time in the wine industry.

Lay & Wheeler's own records put the figures for corked wines at around six percent, with wines that are "cork affected" much higher still.

Lay & Wheeler have conducted consumer surveys, in both the off-trade and the on-trade, on various aspects of wine consumption. In their most recent survey, several questions about screw caps were posed.

When asked whether they would consider purchasing a white wine under screw cap, 81 percent of respondents said that they would whereas only 65 percent would consider a red under screw cap. In a restaurant situation, 70 percent might buy a white under screw cap while only 60 percent might go for a screw-capped red. However, if a sommelier discussed the issue of screw caps with them, less than 10 percent said "No."

"We need to create more information for retailers and consumers," said Thorogood. "And we have a responsibility to the consumers that our wines get to them in the b have to work with revised memories for wines in such closures. Laroche has researched the closure field for several years after toting up the numbers on wines that were corked or had other problems and becoming dissatisfied with corkage losses of approximately 5 percent. He has been asked to discuss his tests and complaints by officials of major Portuguese cork-producing associations.

His feelings about such losses proved out at the tasting. Of the 56 bottles opened by sommelier Andre Compeyre of Restaurant Alain Ducasse, one was tainted and a second was discarded as questionable.

In addition to Laroche, Bordeaux's Andre Lurton is bottling three of his Bordeaux Blanc whites from the 2003 vintage in screw caps. The wines are Château Couhins-Lurton (Cru classé de Graves), Château La Louvière (Pessac-Léognan) and Château Bonnet (Entre-Deux-Mers). wbm

—Mort Hochstein

Franz feels that it is possible to push the screw cap message too hard in the United States and that there is still the need to educate. The small population of wine drinkers makes for an easy target. However, having an alternative closure introduces "more complexity." And Franz believes that screw caps will be challenged by both synthetic closures and "higher end bag-in-the-box wines."

"Universal acceptance at the retail level is not yet a fact, and there has also been reluctance from restaurants to stock screw-capped wines," said Franz. "However, once Americans are convinced that caps are acceptable for any wine, then they are going to demand that all wine be under screw caps."

Chuck Hayward from The Jug Shop in San Francisco believes that one of the problems in America is that the wine media did not support the move to screw caps as strongly as they did in other countries.

He is marginally more optimistic about the screw cap's prospects in the U.S. and notes that the technology has gone through three distinct phases: the novelty phase, the resistance phase and is just now entering the acceptance phase.

"The biggest resistance to screw caps came from the restaurant side of the industry. At the more formal, white tablecloth restaurants, sommeliers were concerned about the appearance of screw cap bottles on the table as well as opening the wine in accordance with accepted procedures from the Court of Master Sommeliers. So it was left to the retail segment of the market to introduce the new closure to the public."

Chuck Hayward also believes that consumer acceptance is riding high in the U.S. "It is at the trade level where the need for education is most critical. That is because the trade is listening closely to the success stories as well as the problems that are arising with screw caps. We can expect to hear much conflicting and confusing information over the next few years."

Hayward is especially critical of larger American wineries holding back, with a wait-and-see attitude. "Unfortunately, our country lacks a screw cap consortium to educate the trade and the press about the need for new closures. There is a danger in America that screw caps will be marginalized as 'something crazy Kiwi and Aussie wineries invented.' Larger American wineries can wait for the furor of bad points due to cork taint, as well as debates regardinrs at bottling, can also have a huge influence on how wine develops in bottle. "Understanding how to manipulate all of these bottling variables to optimize how wine flavor and aroma develops is the future, and it is extremely exciting.

"In this context, closures will be considered as part of the winemaking process, as the changes in a wine that can be induced by the closure are profound, and in many cases of far greater magnitude than many vineyard or winemaking variables. One thing that flows from this acceptance is that one will need closures that are manufactured to ever-tighter specifications in order to predict and reproduce performance," said Godden.

Godden notes that there are already screw cap liners with different levels of air permeability on the market. He predicts an even greater array of "designer closures." "There is likely to be an ever-increasing number of widely accepted alternatives. TCA-free technical corks will certainly be a major part of the closure mix for a long time. Into the future, TCA will not be the cork industry's biggest challenge."

Nevertheless, there is a growing body of evidence that bottled wine does not need oxygen in order to age properly. And as screw caps are used on an ever-increasing range of wine styles and varieties, knowledge is being accumulated on how to prepare wine for bottling and how to carry out bottling successfully.

If there are ongoing problems with sulphides or reductive characters, solutions may be at hand, with emerging technologies such as micro-oxygenation and lees fining. Or perhaps, as Alastair Maling MW has suggested, winemakers need to go back to basics and handle their fruit, their ferments and their maturing wine properly to begin with. wbm