The screw top may be the greatest thing that's happened to wine since the grape
Restaurant owner and writer for the Arizona Republic
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When Australian and New Zealand winemakers first decided to use screwcaps, they did so partly based on the extensive information that was available, but also as a result of the practical experience that fellow winemakers openly shared with them. Many winemakers had been conducting internal experiments for several years, therefore, samples with reasonable bottle age were available for tasting.
In addition to this, a series of trials had been undertaken by both the University of Burgundy (1960s) and the Australian Wine Research Institute (1970s) and consecutive tastings proved that screwcaps were indeed a viable alternative to natural cork.
As a result, winemakers in both Australia and New Zealand decided that it was time to take the leap of faith that was necessary to get the ball rolling. As Michael Brajkovich MW, Chairman of the ISI points out,
“At Kumeu River we were considering doing a proportion in screwcap and still having cork available for customers who wanted it. But then my brother Paul asked me if I was confident that the screwcap was significantly better. I said yes, and based on extensive tastings of aged Rieslings from Australia, I had no doubt that our wines would benefit over the long term as well. As a result, he decided to put everything under screwcap, and communicate with our customers that we are doing it because we knew that the wines would be better - and that has certainly proven to be the case.”
Brajkovich hits on a key point here – the decision to use screwcaps is one for the winemaker, not the marketeer. Winemakers who use screwcaps do so because it allows them to bottle their wines in optimum conditions, knowing that the airtight seal will guarantee that their wines arrive on the consumer’s tables in pristine condition.
As Tyson Stelzer points out in his winemaking manual, Taming the Screw, the advantages of using screwcaps to seal wine bottles are numerous and may be summarised as follows:
No cork taint
everyone you ask will give you a different answer, but the general consensus from the trade is that between 5-15% of wine is adversely affected by 2,4,6 trichloroanisole. This can occur simply when chlorine is used to wash the cork bark or, more worryingly, it can be due to a contamination of the trees themselves due to the use of organic pesticides which contain chlorine and in this case, affect several harvests.
No more sporadic oxidation
The ideal closure should provide an air tight seal to the wine bottle. A good quality cork is a perfect closure, however, as with all natural products, quality variations mean that “random oxidation” has become the second biggest problem linked to natural corks.
“Driven” closures - whether they are natural or synthetic – need good elasticity in order to fill the gaps and irregularities within the bottle neck. In addition to this, natural corks also contain pits, cracks or insect holes and these create a weakness within the seal that can lead to leakage and oxidation.
Traditionalist criticise screwcaps saying that they are not romantic, however, this industrially-produced closure has the advantage of being more consistent identical, therefore making bottle variation a thing of the past.
Screwcaps also seal from around the outside of the bottle, therefore imperfections within the bottle neck are immaterial and the pressure (approx. 160kg) exerted on the head of the screwcap during bottling ensures that it is totally airtight.
Screwcaps avoid flavour modification, including scalping
Cork is a natural product, therefore, it is inevitable that it will impart some level of taste on the wine to a lesser or greater degree.
As John Belsham of Foxes Island and also current NZSCI president says, “We ran a very simple trial of putting corks into glasses of acidified water. There was a varying degree of colour and flavour taint in all glasses – all except one - the glass containing no cork.”
Screwcaps are totally neutral and therefore do not modify the wine in any way, allowing it to retain the original characteristics and age uniformly.
AWRI research has discovered that the TDN flavour molecule - which gives a kerosene type flavour to white wines - is totally absorbed by plastic closures and partially absorbed by natural cork. This is known as flavour scalping and according to the AWRI, there is no evidence of flavour absorption from screwcaps and this therefore explains why they are so well suited to delicate, aromatic wines such as Rieslings.
Both red and white wines can age under screwcap
Contrary to popular belief (and perhaps a little bit of propaganda), both red and white wines can actually age under screwcaps and over 40 years of experiments back up this claim.
Following the AWRI/ACI closures trial in the 1970s, Dr Bryce Rankine stated that,
“… the range of wines examined retained their quality with a stelvin closure significantly better than with a cork”.
Subsequent trials have proven that screwcaps retain fruit, diminish the incidence of oxidised characteristics and bottle variation better than any other closure currently available on the market.
Before deciding to bottle their Chablis Grand Crus under screwcaps, Michel Laroche undertook similar comparative experiments, using 11 different types of closure over a 5 year period. His findings confirm the AWRI results and the percentage of his wines sealed under screwcap has significantly increased since he introduced them with the 2002 vintage.
Among some of the oldest red wines under screwcaps is a 1966 Mercurey which, when tasted 38 years later, showed remarkable freshness and structure and samples from Australian wineries confirm these results.
Perhaps one of the greatest areas of debate is the importance of oxygen in winemaking and bottle ageing. Revered oenologists, such as Ribereau-Gayon and Peynaud, have long claimed that oxygen ingress is not a condition for wine ageing. in the bottle, or for the development of bottle bouquet.
“Reactions that take place in bottled wine do not require oxygen”
“… it is the opposite of oxidation, a process of reduction or asphyxia, by which wine develops in the bottle.”
The reactions that produce what we know as bottle bouquet are reductive, and occur at low redox potentials in the relative absence of oxygen. The rate of oxygen ingress through a screwcap with a tin liner is very small, and appears to be comparable to that of a very good natural cork or technical cork. It is also very consistent, thereby minimising bottle variation.
A reliable long-term seal
Many people, wrongly, associate screwcaps with wines that will be drunk young, therefore associating them with cheaper wines.
Over the past 30 years, screwcap manufacturers have researched the question of the best available liner at great length. In stark comparison to the liners used in the 1960s (at the time of the first trials) and also in the early 1970s, liners are now made of an intricate layering of food grade polymer (in contact with the wine), tin and a final all-important layer of expanded polyethylene which maintains the pressure and ensures that the screwcaps maintain an airtight seal.
Currently, some screwcap manufacturers guarantee their closures for 10 years (compared to 3 years for most synthetic corks). The oldest bottled samples available are now over 30 years old and are still holding up well - so the real answer is that we don’t know how long screwcaps can seal bottles, as we quite simply haven’t got that far yet !
Screwcaps have also taken the complication out of cellaring and storing wines as one no longer has to worry about humidity or bottle orientation.
Traditionally, bottles were stored horizontally in order to retain liquid contact with the cork, which forms an important part of the cork sealing mechanism, thereby preventing excessive oxygen ingress and oxidation. Screwcaps, however, can be stored either vertically, horizontally or even upside down.
Screwcaps are also far more resistant to temperature change than traditional corks. Liquid is incompressible, therefore, in the past, cork-sealed bottles had to be protected against dramatic temperature changes that would cause the wine to expand and add pressure to the cork, in some cases causing leakage.
As Michael Brajkovich explains,
“When we first started using screwcaps in 2001 we did a very rudimentary test in a hot water bath, using a cork-sealed and a screwcap-sealed bottle. As we gradually heated the bottles, it wasn’t until about 40 degrees that the cork started to show signs of weeping. The headspace had been filled and the liquid was moving out past the cork under hydraulic pressure. By this stage the screwcap had started to clearly bulge, but it did not show any actual leakage until just over 50 degrees. That was good enough for us.
Of course one should never subject wine to such extremes, not even to 30 degrees, but it’s heartening to know that - in our experience at least - screwcaps can perform to high temperatures".
Whilst it is unlikely that anyone will expose their wines to such temperatures, this is extremely useful in order to avoid that your wine suffers from the vagaries of transport and storage.
Contrary to popular belief, screwcaps can and are recycled as aluminium is one of the most cost effective base materials saving up to 95% of the energy needed to produce new aluminium. Screwcap manufacturers are constantly exploring new methods to improving the recycling aspects, including machinery that removes the skirt from bottles.
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