part 5 of the series: Natural Cork versus Alu Screw Cap
Screw cap closures consist of an aluminium cap with threads which fit the neck finish of a bottle and a liner of plastic (often PVDC), cork, rubber, or other soft material as wad to make a seal with the mouth of the bottle. While they can form a very tight seal, there is debate as to the extent of reduction and is one factor that limited the use of plastics and screw caps in the past. Reduction which results from too little oxygen being present during winemaking and aging, increases the presence of unfavourable sulphur based components that cause an odour of rotten eggs. Certain varietals and winemaking styles are more susceptible to reduction and closures that allow minimal oxygen ingress such as screw caps are suspected of increasing the potential for this undesirable condition to occur. But about this later in the last chapter of this series: “Understanding how different closures perform.”
The metal screw cap, then baptized the Stelvin cap, was developed in the late 1960s by the French company La Bouchage Mecanique, later acquired by Pea-Pechiney, which became part of Alcan, then Rio Tinto Alcan and recently bought by Amcor. It was preceded as a closure by a Stelcap/cork combination (closed with cork, with a Stelcap on top). The Stelcap was also a long-skirted screw cap, but with a different inner lining (paper over cork, instead of tin covered by PVDC in a Stelvin).
The distinguishing features of wine screw caps, in particular Stelvin brand ones, are a long outside skirt, for aesthetics, to resemble the traditional wine capsule (“foil”) and the use of the plastic PVDC (polyvinylidene chloride) as a neutral liner on the inside wadding.
Aluminium screw caps, commonly called Stelvin, although it is a trademark, must be used with specifically developed standardized neck finishes: i.e. BVS finish BVP-GME 30.13 and BVS finish US-GPI 1680-03.
Wine connaisseurs intending to lay down bottles of Bordeaux and other exclusive cabernets for (sometimes) many years, are wondering whether they can trust these ‘modernized’ closures to protect their precious wine.
A definitive answer isn’t there yet and might be years away. Plastic cork has been in use for some 15 years, and screw caps for only a few decades. And to make it more complicated they are generally only used on bottles of inexpensive table wine – not for wines worthy of maturing, leaving the wine collector with the ‘fairy-tale or not’ of the screw cap related problems of (oxygen) reduction (rotten egg smells) associated with screw cap liners and the possible downside of the copper fining used to avoid the smells.
In 1997 before any serious winemaker thought of screw caps, as there was the infamous assumption that wine wouldn’t age with screw caps, Californian PlumpJack Winery embarked on a bold experiment. It decided to bottle half of its reserve cabernet with natural cork and half with screw caps.
Ten years later, PlumpJack hosted a “vertical tasting” of its reserve cabernet, comparing the cork-enclosed bottles to the screw cap versions for each vintage since 1997. According to the company, there was no appreciable difference between the two, although the company acknowledges that it’s possible that after another decade, the screw cap bottles might not show as well. Until then, PlumpJack remains committed to screw caps for some of its age-worthy reds.
And at the other side of the aisle we have a New Zealand wine that became the bestselling Sauvignon Blanc in the US – with the use of a selected natural cork stopper given as a key factor in the wine’s sales success. The brand was packaged specifically for the US consumer by sealing the wine under cork, a move that meant bucking the screw cap trend so endemic in New Zealand.
Consumer surveys show that the aluminium screw cap is well recognised for superior quality but not fully accepted for its appearance. To imitate the appearance of the bottle closed with a cork, Guala Closures of Italy introduced the Wak closure as answer to the famous shape of the wine capsule.
The ‘cheap appearance’ of the thread is not visible from the outside but is inserted into a long aluminium shell (first screwed on the bottle neck finish and then tucked under a standard BVS neck ring).
It’s always the British coming up with the ultimate: A UK wine merchant has launched two new wine ranges packaged in an inventive plastic bottle that has proven to keep wine fresh for at least two years, and also is claimed to be environmentally friendly. Even more amazing: according to the company, the bottle looks just like glass, yet it is safe, won’t break, and has a plastic screw cap, making it quick and easy to serve then reseal.
When do we go too far. Wine like bottled water?
The last chapter of the series will describe the performance of the different closures for wine bottles. A comparative analyses.
to be continued