Closing the bottle
What is the best way to close a wine bottle? The debate over cork versus screw cap has moved significantly in the last year with a deeper understanding of the issues and a wealth of new ways to stop the bottle such as the Zork have required a more objective look at they way we close the wine.
This page has up to date notes on closures as well as interviews with experts.
- Give me the BIG picture please
- Corked wine - has the worm turned for cork?
- Screw caps and the alternatives.
- What is the best advice
Give me the BIG picture please
Wine has been made and consumed for 8,000 years. It has only been in the last 300 years that cork has been used to close the bottle. Its attributes as a good seal made it the closure of choice - easily removable from a bottle, chemical inertness and long term stability. However as one winemaker once quoted "If they invented wine today they would not use a lump of dead wood to seal it".
Cork is a great seal for wine and the trade and consumers would probably accept the random variability between wines associated with the natural nature of corks if it weren't for the fact that 5% or 1 in 20 bottles are faulty 'corked' also known as (TCA). At worst the wine can smell of damp cardboard, at best the wine loses some of the fruit and does not taste as good as it could. Cork producers did not appear to be worried about this until sales began to decline in 2000 - sales have dropped from 95% of all closures to 90%. This may not seem much when 15 billion natural cork stoppers are being made annually, but with any revolution the start is slow and the industry can see the writing on the wall. The message is clear: improve the product or lose business.
There has been some progress in improving the quality of the cork. For example in Australia, Pro Cork have a cork-based product that looks like natural cork but has a clear thin membrane at each end to stop the wine coming into contact with the cork, thereby minimising the risk of taint. 'Diam' is an agglomerate made by pressing chips of cork together, and is the first cork-based product to be cleaned and effectively TCA free.
The alternatives that have put cork under such pressure have been led by the screw cap or 'Stelvin'. Being 100% TCA free and with easy opening it has made the biggest inroads yet. However, new research has taken the gloss off the screw cap. Its 100% air tight seal results in the wine ageing differently and can also produce sulphur problems.
The synthetic, or plastic, closure has been popular because it is cheapest to manufacture, 100% TCA free and marketing departments love to print anything they like on them. On the downside, they are hard to get in and out of the bottle. They tend to let in large amounts of oxygen so are not suitable for ageing longer than 2 years. Over time they can absorb flavours from the wine known as scalping.
Corked wine- has the worm turned?
Corked wine is the bain of the wine drinker. The wine smells of damp cardboard, and will often lose some or all fruit character. The intensity varies at times only the lack of fruit can be the give away, this usually can only really be told by someone who drinks that wine regularly. Other times the damp cardboard / musty aroma can put off even the most inexperienced drinker.
The aroma is caused by the presence of the chemical 2,4,6 trichloroanisole, (or TCA for short). The exact number of Corked (or TCA tainted) bottles of wine ranges between 5 and 8% as measure in large competitions such as the International Wine Challenge.
The chemicals that cause it (often called precursors) are found in the bark of the tree, and more likely to be close to the ground. Some cork producers discard the bottom 10-12.5cm of the cork oak tree (a member of the Beech family). Drying now also occurs on concrete keeping the cork away from the soil, "concrete is the greatest preventative measure against TCA" according to Carlos de Jesus, of Amorim which has 25% of the global cork market. Cross infection is minimised by removing all wood to store and transport, such as pallets. The cork is then boiled to drive out any TCA. Other improvement has been to stop using chlorine to clean the cork, as TCA likes the presence of Chlorine. Amorim, who now have the equipment to measure TCA (with Gas Chromatography- mass spectrometry) consider that these new measures have improved TCA incident's by 80%.
Diam, another leading cork manufacturer has taken a different approach. Cork granules are cleaned by super critical carbon dioxide. Super critical means that carbon dioxide is held in a state of both a gas and a liquid. In this state it becomes a brilliant solvent cleaning out the TCA from the cork. Diam claim a 98% efficiency which has been backed by the Australian Wine Research Institute. This technology has been around for 20 years and is used to remove caffeine for high quality de-caffeinated coffee.
The work of removing TCA is not always 100%, however if the amount of TCA is reduced then it may exist in undetectable levels in many wines and simply dulls the fruit flavours. Our noses detect TCA at a certain trigger level, which means it can be present we are just not aware of it. But once that trigger level is reached we become acutely aware of the off-smell.
Screw caps and the alternatives.
Screw caps and in particular Stelvin closures (the name for the type commonly used for wine) have been with us since the 1970’s. Initially they where used on very cheap bottles of wine and as such developed a poor reputation. In 2001 The New Zealand Screw cap wine seal initiative consisting of 40 top wineries started to seal wine under screw cap after become frustrated at the poor quality of the corks they were being supplied. Initially only the top wines were sealed under screw cap to help shift the perception of screw caps being cheap, but more recently many different types of wine have been bottled under Stelvin screw cap.
Screw caps are made up of two parts. A metal outer capsule and a disc typically made from a layer of tin sandwiched between PVDC, and white polyethylene. The tin ensures minimal oxygen reaches the wine.
The lack of oxygen means that the wine tends to keep fruit character longer and not oxidise (turn to vinegar) as quickly (for a formal report open ACF combined Media Report). Another interesting point is that under screw cap wines tend to be more reductive. For those who can’t remember doing school chemistry it is the opposite of oxidisation. Too much reductive character in the wine is not the best with flavours such as burnt match, onion, garlic, cabbage, nuttiness, cat’s pee and sweaty aromas can occur. Lower levels of reductive characters are thought by some to produce the mineral character in many top French wine as well as green pepper and black current notes in some wines. So as with oxidisation in wine a small controlled amount can be good, but too much is usually a problem. The rise of the New World fruit driven style of wines was based on not allowing the grapes and wine to contact oxygen, this is known as reductive wine making.
The cork industry has claimed that the lack of oxygen reaching the wine because of the near perfect seal from screw caps causes reductive sulphur like characters. While this does occur, I personally have only noticed this occasionally, and certainly no where near as often as the cork taint. This backed by The International Wine Challenge where in 2005, 5.8% of wines were found to be faulty: 4.09% were corked and 1.71% had other faults - including reduced along with oxidised, volatile or unclean.
What is the best advice?
Plastic corks are the cheapest closure and the lowest quality of all the closures. The main problem is plastic corks let in oxygen, and lots of it. This has a tendency for the wine to turn to vinegar eventually and lose fruitiness quickly.
It is hard to imagine plastic corks letting in oxygen, but they do, mainly down the side between the bottle and the plastic cork. Oxygen seeps down the side, the manufacturers know this and that is why it is so hard to get the cork out let alone back in. A wine that has spent too long in a plastic cork will prematurely age causing the wine to lose fruit aromas. This often takes 1 to 2 years so wines from the current vintage are fine, however if the wine is two to three years old, you should be looking for either a screw cap or a natural cork.
So what is the best to use and when?
Given that cork wines still have a high corked rate, I recommend the screw cap is the closure of choice for modern fruit driven wines that are designed to be drunk young. Ageing wines for a long periods under screw cap is still considered experimental, so it may be better to accept that 5% of wines will be corked and use corks for wines that are to be drunk after 5+ years of ageing.
In reality wines to be aged are normally purchased from specialist wine suppliers not normally on the high street. So if you buy wine at the supermarket or on the high street, then screw cap is probably the best closure for you. If you buy wine for your cellar to lay down for 5-10 years then cork is the safest if somewhat flawed bet. Plastic corks are ok for the current vintage but it can be hard to tell the difference between natural and plastic corks, so go for the screw cap.Tweet