It’s triggered when the filamentous fungi, which naturally reside in cork’s small air spaces, become exposed to the chlorophenol compounds contained in manmade biocides (i.e., pesticides, fungicides et al). The filamentous fungal reaction is nothing other than a natural form of fungal self-defence, as the fungus seeks to neutralize the presence of the chlorophenols.

The fact that TCA, and the analogous taint known as TBA (2,4,6-tribromoanisole), are not naturally occurring in nature is a hugely significant consideration. It means the existence of cork taint is not due to the presence of natural filamentous fungi but rather to the contamination of cork tree bark and wood by synthetic chlorophenols such as TCP (2,4,6-trichlorophenol).

Cutting the long-sad-story short, once contaminated with TCA or TBA, a good wine’s fate is abruptly sealed. Destiny is swift to call it by its heartbreaking new name: unpalatable waste.

Of course, in the years since this distasteful discovery, notwithstanding the vast improvements made in cork forest management and cork production, the issues associated with cork taint remain. You see, it has been found that chlorophenol residues are extremely slow to degrade in nature. Seven decades have already passed with little evidence to foster much hope. Adding to the conundrum, one must also consider the lengthy 9-year period that lapses between individual cork tree harvests. However it might one day play out, for now one is left with little choice but to view the annual financial losses due to such cork-related flaws as none other than an incurable constant.

Cork industry commentators suggest the annual level of flawed waste is now down to 1-2% of production.
(Source: Tom Jarvis, Wine Searcher 2019)

According to other independent sources, it may well be between 2-5%.
(Source: Jamie Goode, Flawless 2018).

Much remains to be learned about the level of unreported consumer experience.

In the interest of maintaining clarity, let it be noted that natural cork is not alone when it comes to the issue of tainting. Both TCA & TBA have been uncovered in wine cellars, among contaminated hardwood surfaces, including woods that are used in barrel construction and/or other wooden storage and shelving systems.

Of course, regardless of the source of the taint, it’s with the cork stopper in hand that the wine consumer will encounter the aroma of musty disappointment. And once encountered, there’s no surprise when consumer reasoning begins to critically question bottling practices and especially cork stopper selection.

Reasonable consumers wonder why?
Like, when faced with the choice of bottling wines with a predictably flawed material or deciding to change to an untainted alternative, why do so many industry players appear so emotionally invested in trying to make natural cork stoppers fit-for-purpose?
Is it really a matter of maintaining tradition?
Or, might it simply be the blind acceptance of an economically wasteful “habit”?

In the early 1960’s, out of necessity, the screw cap was envisioned as a taint-free wine bottle closure. Subjected to countless trials and international studies, by the late 1990’s, its suitability as an alternative wine bottle closure was successfully proven. Many in the global winemaking community have since heeded the good news.

According to current supplier data, aluminium screw caps now account for 37% of the annual global order of +30 billion wine bottle closures. While 54% of winemakers continue to choose natural cork, usage has apparently declined by -7% since 2015. In the same period the demand for screw caps has actively grown by +9%. (Sources: Amcor Stelvin & Guala Closures Group 2023 / Euromonitor 2021).

It’s worth noting that in tandem with the upward turn in screw cap usage, other technical closures like DIAM and Ardeaseal are also gaining a foothold.

[Quick back-track: If we accept the indication that cork taint results in annual losses of 1-2%, then what does 1-2% of 54% of circa 30 billion closures actually look like? Well, it would be 162-324 million bottles of wasted wine per year. Hardly a trivial number. Indeed, one imagines such levels of waste would be untenable in any other industry. So why is it that the wine world and wine consumers are still prepared to accept it? To sustain tradition? Really?].

To understand the modern dynamics, we must first return to the screw cap’s place and time of origin. Curiously it was designed and developed in tradition-rich Europe. To be precise, it was conceived in the R&D department of Le Bouchage Mécanique, Chalon-sur-Saône in Burgundy, France. As history recalls, the prototype was first registered in 1959 (Source: Amcor Stelvin).

A key stimulus for the research and development came from Switzerland where winemakers urgently sought an alternative closure. In those years cork taint was plaguing Swiss Chasselas wine production. While no-one could be sure of the precise cause, the cork stoppers were deemed ‘obvious culprits’. A speedy solution was needed and the first working screw caps were made available for trial in 1964. By the early 1970’s the initial trials had been successfully completed. Chasselas, and its Swiss custodians, no doubt celebrated.

Yet, despite the early positivity, further European interest in the screw cap was surprisingly unforthcoming. Instead, it was to come from the southern hemisphere where inquisitive Australians began trials of their own in 1973. Continuing throughout the 1970’s, even when high profile winemakers like Yalumba and Pewsey Vale began bottling and promoting the new cap’s credentials, sadly Australian market research revealed significant consumer apathy (Source: Damien Wilson, Case Study 2010).

Undeterred by the prevailing consumer sentiment, winemaker interest in the screw cap remained strong. Technically the trials had proved successful. What’s more, consumer awareness and future acceptance had been primed to grow. And as history so often teaches us, it was only a matter of time before the sentiment would change.

And it did. With dependable quality cork supplies becoming increasingly difficult to source in the 1980’s and 1990’s, wineries in Australia, and by now also in New Zealand, were quick to switch to the proven alternative.

With both Stelvin screw caps and the specially threaded BVS bottles (Bague Verre Stelvin) readily available, the enlightened few soon charted the path to screw cap acceptance.

Today in the Austral-Asia trading area, the twist-off experience has reached an impressive +77% market acceptance. In terms of the Australian market alone, 87.9% of all wines produced in 2018 were sealed with screw caps. Looking specifically at Australian white wines and you’ll find screw cap usage has grown to 97.3%.
(Source: James Halliday Wine Companion 2018).

Well, as previously alluded to, the global spread of screw cap acceptance is entirely non-uniform. The +77% acceptance in the Australasia market exists in marked contrast to the screw cap’s place of origin. Europe-wide acceptance stands at a listless 34%. While in Italy, home of Gli Svitati, it’s floundering at 20%.
(Source: Amcor Stelvin & Guala Closures Group 2023)

In 2023 it’s hard to find a convincing explanation for Italy’s enduring resistance. Without open discussion, those trying to reason ‘why’ are left to speculate. And so ‘speculate’ one must.

Superficially speaking, there appears to be a heavy measure of misinformation about the screw cap’s technical capability. Most likely born from a lack of first-hand experience. Sadly, ill-informed hearsay tends to sustain traditional intransigence.

Furthermore, insubstantial comments which suggest the idea that “aluminium screw caps lack the emotional sensitivity of natural cork” or that “screw caps are unsuitable for high-value products”, are as misguided as they are unworthy.

To discredit alternative materials with such throwaway remarks is quite disingenuous. One would expect a more gracious and self-assured stance from those who espouse traditional values. After all, rather than being closed-minded, the advocates of screw caps are open to discussing and sharing their wealth of direct experience and scientific data.

It should probably go without saying, but let it be said anyway; the visible use of aluminium screw caps among many high-end producers of premium spirits, distillates, and perfumes, not to mention many of the great wines of the southern hemisphere, quickly dispels the misleading myth surrounding high-value products and screw caps. A move toward an assured quality alternative is precisely because high-end products need high-quality closure assurances.

By adopting such a highly visible stance Gli Svitati recognized the immediate need to demonstrate their quality intentions. And duly they did, as they put both their wine and screw cap sensibilities to the 100+ attentive audience test. In what was a novel tasting format, each winery presented a sample pair of wines, sealed years previous, using both traditional cork and aluminium screw cap.

1. Prà, “Soave Classico” 2010 – (this was the first vintage using screw cap)
2. Walter Massa, Barbera “Monleale” 2016
3. Pojer e Sandri, “Sauvignon” 2007 – (the first vintage using screw cap)
4. Jermann, “Vintage Tunina” 2013
5. Franz Haas, Pinot Nero “Schweizer” 2015

In brief, the performance of all five screw-capped wines was outstanding; the freshness, colour vibrancy, fruit, and aromatics of each wine was found to be splendidly framed and displayed.

Sadly, the same could not be said of the wines sealed with cork. While three-out-of-the-five performed exceptionally, regrettably two wines served were oxidized to a point beyond drinkable.

[Special Note: The tasting experience I had was shared by those guests seated nearest to me. The real-time bottle opening and service was intended to mirror how a consumer would encounter these wines immediately upon opening, defects if they occurred were included. The wineries were endeavoring to create a unique shared experience and I believe they succeeded. With more than 100 attendees, other tasting tables no doubt had differing experiences. I was more than satisfied with the authenticity and sincerity of this unique sampling.]

While obviously the two faulty wines were a disappointment for the two producers on hand, nevertheless it was this inconvenient truth that aided the twisting debate. In a semi-scientific way, I daresay a peaceful conclusion was reached; for the Italian and European markets to dispel the screw cap taboo, winemakers and consumers must expand the wine closure conversation to now contextualize the meaning of ‘traditional quality’ in terms of the closure’s ‘structural variability’.

Of course no-one is saying that screw capped wines are defect-free. Faults including TCA & TCB taints, together with reductive off-notes, have been detected in wines sealed with screw caps.

However, when cork or wood associated taints are found in screw-capped wines, it can be stated, they are not caused by the cap. Discovery of such a defect immediately points to a winemaking related issue, most likely associated with cellar practices and/or a cellar equipment contamination (i.e., one that has manifested itself in the wine during the pre-bottling phase).

Unlike cork or wood taint, the presence of reductive off-notes and flavours have been commonly associated with the use of screw caps. This flaw tends to stem from extended periods of reductive bottle ageing (i.e., which is bottle ageing in the absence of any oxygen transmission through the cap).

During the early years of screw cap use, when the original SaranTin liner was the most regularly employed liner seal, it functioned as a complete oxygen barrier (i.e., with an OTR close to 0.0mg O₂/year). In the absense of any gaseous exchange through the cap, wines sealed with the original SaranTin liner could present with off-flavours and aromas associated with development of volatile sulphur compounds (VSC’s). In Australia, Riesling and Sauvignon Blanc were two of the white wines most often affected.

Though ageing under SaranTin can and occasionally does contribute to this flaw, it is now accepted that it might not always be solely due to the use of the screw cap. It is also understood that similar reductive off-notes may already have developed in pre-bottled wines. Once bottled and sealed the issue would be exacerbated by subsequent reductive bottle ageing. Discovery of such a fault will always require a more detailed investigation.

In light of the pioneering downsides, to negate the issue of VSC’s developing post-bottling, winemakers have since adapted and can now use other liners like Saranex, with OTR’s of circa 1.0 – 1.5mg O₂/year.

Indeed, as mentioned earlier, a new liner seal is available in which an active ‘scavenger’ layer has been incorporated, which is designed specifically to bind with and deactivate the presence of VSC’s in the bottle.

Known as the ALKOvin liner, it is produced by Meyer Seals in Germany and has been on the market since 2017. Offering a similar OTR to SaranTin, over the past 4-5 years, it has been successfully put to the test by the AWRI and independent winemakers in Australia and New Zealand. (Source: Meyer Seals 2021-2023).

As reductive faults are often cited as being the screw caps Achilles heel, it is only fitting to add one final footnote from Professor Mattivi’s data. It regards a 10-year-long independent survey carried out by the International Wine Challenge (IWC) from 2007 to 2017, during which time +118,000 wines were submitted to the IWC for competitive tasting.

As part of their in-house review, the IWC judging panels recorded the percentage incidence of reductive faults in each of these wines and remarkably, wait for it, they discovered the incidence rate to be the same for each and every closure type, including screw caps.

While everyone would probably have expected the screw caps to be the worst performing closure, this result is an important turn-up for the books. Even if such a survey might contain the occasional false positive, this discovery points to an ‘interesting reality’ where reductive faults (i.e., the presence of VSC’s) should be as much of a concern for the winemaking process, as they are when it comes to choosing the bottle closure. Indeed, it could even be suggested these findings have far greater general implications for winemaking than they do for closure selection.