The debate regarding screwcap closures has been along divided lines for quite sometime now, with the pro-screwcap group focusing on the fresh, untainted nature of the wine. Those opposed to screwcap point to its failure and unreliability, but is this a fair analysis of the screwcap?
South Africa has a healthy track record when it comes to metal closures and MCG Industries based in Paarden Eiland, Cape Town is seen as the market leader. MCG Industries was originally owned by MCG UK, who acquired the company in 1957. In those years MCG were seen as pioneers in terms of screw-cap closures. In 1979 the company became aligned by way of a Technical agreement with Alcan ( then LBM ), well respected and known for the Stelvin closure. MCG retained this connection with Alcan until 1999 and during this time manufactured a range of Stel ( Deep Drawn Pilfer Proof ) closures for wine and spirits , one such closure which seems to have stood the test of time , has been on Capenheimer since the mid-eighties . MCG became completely SA owned in 2000 and their attendance of the 2001 Synthetic Cork Symposium was a catalyst for SA export of screw-caps. It was at this symposium that valuable contacts were established and later built upon for export of SA produced screwcaps to Australia. The Australians were more than satisfied with the quality and performance of the SA product, referred to as SAVin and still today top Australian producers continue to import from MCG. Since 2001 Australia has been actively involved as the main testing ground for screwcap closures. Interestingly enough New Zealand is perceived to be the forerunner, after establishing ‘The Screwcap Initiative’ in 2001. So where does this leave South Africa? Ironically, we have been the last of these three countries to embrace the closure.
So what is it about screwcap closures that we should know in terms of performance? The single most quality that screw-cap brings is consistency. Cork shortages and possible neglect of forests has led to an increase in TCA, thus rendering the product less reliable. On the point of reliability, screw-caps may also disappoint if the application thereof is not done to exacting standards. This requires further explanation: there is a choice in terms of the type of liner that is used. The liner consists of a backing section of extruded foam of a specific density which has excellent recovery properties .It is to this backing material that a choice of membranes is bonded which will give the liner specific barrier properties to oxygen ingress . The density of the liner is important especially during application and it is this combination of backing foam with bonded membrane that creates the barrier and seals off the wine from oxygen ingress. When applying the closure to a bottle it is vital that the closure conforms as intended and fits like a glove. The cap must align itself to the bottle and the rollers of the capping head that shape the final position of the closure must be at the correct setting to ensure that a thread is created which will keep the closure in position much like a clamping device. Two types of liner give customers an element of control over the desired permeability of the seal. The Saranex liner is made from layers of polyethylene, PVDC (polyvinylidene chloride) and expanded polyethylene, whereas the Saran Tin liner has a layer of tin sandwiched between PVDC, white kraft and expanded polyethylene. This tin layer means that it is much less permeable than the Saranex liner and less oxygen is allowed to enter the bottle. The Saran Tin liner tends to be used for wines stored for longer periods of up to 10 years or more , with the Saranex intended for storage of between two and five years. Thus, there is a liner for a specific style of wine. White wines tend to retain their freshness and most importantly, require lower levels of SO2, whilst red wines made in a light to medium New World style tend to retain fruitiness and colour longer than if bottled under cork.
How do we explain unwanted smells in our fresh, recently bottled white wine, when we have taken the necessary care at bottling? The cause of this unpleasant smell is due to the presence of certain sulphur-containing molecules, sulphides that may have been created during the fermentation process and have undergone further transformation through combination with other molecules, thus becoming either oxidized or reduced at various stages of the maturation process. During racking, wine is aerated and the smelly compounds tend to disappear, but this does not mean that they have been removed altogether. The airtight feature of the screwcap means that free sulphur dioxide is trapped for longer than with a cork closure and thus makes the wine more reductive. Over a period of time the smelly compounds are oxidised and the smell disappears. It is clear that the choice of liner used will either encourage oxygen ingress or block it completely. Some wines rely on slow oxygen ingress to develop and soften the wine over a period of time. The decision to use SAVin or cork should thus rest on the style, quality and age-ability of the wine under discussion.