Wine closures are an interesting subject, and one of great importance. Their function is to protect wine from oxidation, during its storage. Everyone dismisses them until asked directly the question, “To cork or not to cork?” From the initial question this becomes a very tense issue for some and a new challenge to be answered to others. It usually comes out to what the consumer wants out of the wine, and how they approach it. The decision usually falls to one side or the other depending on the following variables: corkage/TCA taint (“TCA” is explained below), oxidation, and aesthetic appearance.
So many people are hesitant to speak on this subject, for lack of wanting to make a firm opinion, or worried that there isn’t enough significant “data” to support their conclusions. “Lies, lies, and damn statistics!” coined by Mark Twain, meaning data will tell you what you want to get out of it as all variables are what you input. So people can be quite sensitive about closures, when they talk about them at all! There are so many factors involved in the closure’s debate outside of the actual product; there’s the lobby’s for the cork and alternative closure industries, PR people on both sides, and the wineries looking to their consumer base.
So here are all the options for wine closures with more to come, no doubt, in the future.
The Challengers to cork
Synthetic corks are made from plastic compounds designed to look and “pop” like natural cork, but without the risk of TCA contamination. Disadvantages of some wine synthetic corks include a risk of harmful air entering a bottle after only 18 months, as well as the difficulty in extracting them from the bottle and using the plastic cork to reseal the wine.
Screw caps or “Stelvin Caps” are closures made only from aluminium material that threads onto the bottleneck. They are now the predominant closure used by Australian and New Zealand wineries. Screw caps form a tighter seal and can keep out oxygen for a longer time than cork. These benefits aid in maintaining the wine’s overall quality and aging potential. Extensive quality tests show convincing results: apart from protecting against cork taint, screwcaps are also beneficial in the aging of wine, particularly preserving the aromatic freshness. Another advantage of screw caps and other cork alternatives is wine does not have to be stored laying down as with cork which must be kept moist so as not to dry out and shrink.
Vino-Seal, or Vino-Lok, is a plastic/glass closure released by Alcoa. Since its introduction into the European market in 2003, many wineries have utilized Vino-Seal. Using a glass stopper with an inert o-ring, the Vino-Seal creates a hermetic seal that prevents oxidation and TCA contamination. A disadvantage with the Vino-Seal is the relatively high cost of each plug and cost of manual bottling due to the lack of compatible bottling equipment outside of Europe.
Invented and developed in Adelaide, SA, the Zork is an alternative wine closure that seals like a screw cap and pops like a cork. The Zork closure consists of three parts; an outer cap providing a tamper evident clamp that locks onto the European band of a standard cork mouth bottle, an inner metal foil which provides an oxygen barrier similar to a screw cap, and an inner plunger which creates the ‘pop’ on extraction similar to cork and reseals after use. An excellent alternative but it is relatively expensive.
The traditional crowned bottle cap has been used in the sparkling wine industry as a closure during the bottle fermentation process. Normally the cap is replaced with a cork before shipping, though recently some producers are releasing wines using the crown cap as their closure. The crown caps provide a tight seal without risking cork-taint. Although easier to open, crown caps eliminate part of the ceremony and mystique of opening a sparkling wine with a pop!
Cork the current contender
Natural cork closures are used for about 80% of the 20 billion bottles of wine produced each year. After a decline in use as wine-stoppers due to the increase in the use of cheaper synthetic alternatives, cork wine-stoppers are making a comeback today, particularly in the USA. Wine consumers still like the ritual of extracting a cork.
Cork is a suitable material for use as a bottle stopper. Because of the natural elasticity and impermeable structure of cork, it is easily compressed upon insertion into a bottle and will expand to form a tight seal. The interior diameter of the neck of glass bottles tends to be inconsistent, making this ability to seal through variable contraction and expansion an important attribute. However unavoidable natural flaws, channels, and cracks in the bark make the cork itself highly inconsistent. In a 2005 closure study 45% of corks showed gas leakage during pressure testing both from the sides of the cork as well as through the cork body itself. Trichloroanisole (TCA) is one of the primary causes of cork taint in wine and is caused by natural wood moulds reacting with chlorine bleach used to clean the cork (giving the wine a mouldy wet carpet smell and makes it dull and lifeless). Estimates of spoilage range from 5 to 15% and can be very high with low grade corks.
And the winner is?
Since the mid-1990s, a number of wine brands, particularly in the new world outside Europe, have switched to alternative wine closures such as synthetic plastic stoppers, screwcaps or other closures. Screwcaps are often seen as a cheap alternative destined only for the low grade wines however in Australia and NZ many premium wines are now using this seal. These alternatives to real cork have their own properties, some advantageous and others controversial. For example, while screwtops are generally considered to offer a TCA free seal they reduce the oxygen transfer rate to almost zero, which can lead to reductive qualities in the wine, however this is generally more about the winemaking and not the closure itself. Also, under pressure in recent years major cork producers have developed methods that remove most TCA from natural wine corks (down to 2% spoilage from good quality cork).
However it has always stunned me how an industry could allow such a high spoilage rate with its product (corked wine) and consumers accept it. It is doubtful any other industry other than wine would be able to withstand such a failure rate. It must be something about the romance of wine and the aesthetic quality of pulling a cork that blinkers our rational thinking.
Whilst natural cork stoppers (like oak barrels) are important because they allow oxygen to very gradually interact with wine for proper aging, and are best suited for quality bold red wines purchased with the intent to age, my view is that most wines are not made for long aging and alternative closures, such as screwcaps, offer a 100% effective closure at least expense. It will be interesting to compare aged wines over time using both cork and alternative closures.