Tag Archives: cork

Screwcaps and ageing

Screwcap closures have had some bad press, but in my opinion, any wine destined to be drunk within a year of production should be sold in a screwcap bottle.

Ch.Margaux is carrying out trials with screwcaps

Ch.Margaux is carrying out trials with screwcaps

What is good about screwcap bottles

  • The closure does not contaminate the wine. The wine may still be corked because of contamination during wine production, but at least the screwcap won’t have caused it.
  • Every bottle will be the same as the next. There are some caveats, and you should refer to a previous blog for further details. Every natural cork is different, whereas every screwcap closure is identical.

What is bad about screwcap bottles

  • Removing a screwcap just doesn’t have the same theatre as removing a cork. Sadly, I can’t think of any solution to this problem.
  • Production of ‘reductive’ chemicals in the wine because air is excluded. These are sulphur compounds which may be produced in the bottle because of the absence of air. These compounds disappear quickly after a bottle is opened, but can be excluded by modifying the winemaking process.
  • A little bit of oxygen appears to be necessary for a wine to age gracefully. Original screwcaps allowed almost no air to reach the wine.
  • Screwcaps were associated with cheap wine, so producers of quality wine tended to shy away.

New developments

  • The seal in a screwcap is provided by padding at the top. Different materials are being used for this padding, which allow different amounts of oxygen to pass through. This means that they can potentially be used for ageing fine wine.
  • The obvious thing is to try long term tests, and some tests were initiated in the 1980s in Australia. However, the prestigious Château Margaux in Bordeaux has started their own long term trials. Endorsement by one of the great old names in the wine business would make all the difference in the acceptance of screwcaps. Time will tell.

Conclusion
By choosing the correct seal, there will be screwcap closure for every wine, but it may take a while to prove the point.

Bottle variation

Bottles of the same wine may taste very different, and variations increase as a wine gets older. In fact one bottle of a mature wine may be wonderful, and the next over-the-hill. Why?

different bottle sizes

different bottle sizes

The blend
Virtually all wine is a blend from different barrels or vats. If the mixing vat is not big enough to take all the wine, then one batch may well differ from the next. So, there may be a difference before the wine is even bottled.

Bottling
A particular wine may be bottled in batches rather than all at the same time. The fill levels, added sulphur dioxide, entrained oxygen, and gas injected above the wine may all vary at each bottling session.

The closure
Historically this was always natural cork. It is a fine closure, but every cork is different and will allow differing amounts of air to diffuse through. This causes bottles to mature at different rates. One big advantage of screwcaps is that each closure is the same.

Transport and storage
This is a major issue, and can completely destroy a wine.

  • Temperature – is covered in more detail by another post. If the temperature gets too high, the wine will be damaged, perhaps fatally. Cases of wine stored at different temperatures will mature at different rates.
  • ‘Lightstrike’ – damage by over-exposure to UV light.

Bottle size
The larger the bottle, the more slowly and gracefully a wine matures. This may just be because the gap between the cork and the wine is the same for a half bottle, a bottle or a magnum. Any air in that gap will be spread more thinly in a magnum than a half bottle, meaning that it will be oxidised more slowly.

Age of the wine
The older a wine, the more time there is for all these influences to take effect, and the higher the chance of one bottle being very different to the next.

Putting the fizz into sparkling wine

Sparkling wines are more popular than ever, as they are lively and refreshing. How are they made, and what produces the bubbles?

Champagne cork and muzzle

Champagne cork and muzzle

Where do the bubbles come from?
Sparkling wines have carbon dioxide dissolved under pressure . When the bottle is opened, the pressure is released and the gas starts to evaporate. Bubbles form on irregularities on the glass, or material suspended in the wine.

What if there are no bubbles?
The main reason for bubble-free sparkling wine is dirty glasses. There is nowhere for the bubbles to nucleate.

What is the gas pressure within a bottle?
Champagne usually has a pressure of around 6 bar – 6 x atmospheric pressure – at room temperature. Which is why you get a mess if you open a warm bottle. The pressure decreases rapidly as the wine is chilled, which is one very good reason for serving cold Champagne. Other sparkling wines have a similar, or lower pressure.

Where does the carbon dioxide come from?
When sugar ferments in the presence of yeast, it produces alcohol and carbon dioxide. The more sugar you have, the more alcohol and carbon dioxide is produced.

  • In most sparkling wine production, grapes are fermented to a still wine. Sugar and yeast are added, and the second fermentation produces carbon dioxide for the sparkle.
  • In some rare cases there is just one fermentation, and the carbon dioxide retained, rather than allowed to evaporate.
  • The cheapest way of introducing the gas is to inject it into still wine, but this produces a coarse result.
Stopper to keep the fizz in a bottle

Stopper to keep the fizz in a bottle

Producing bubbles using a second fermentation
Starting with a still wine, there are three main methods for producing the bubbles:-

  • The method used in Champagne, now generally known as the ‘traditional method’. Wine is put into a bottle, along with sugar, yeast and nutrients. This second fermentation produces carbon dioxide. The debris is removed, and the wine sold in the same bottle.
  • The transfer method, in which secondary fermentation is in a bottle, but the wine is then transferred to a vat, where the debris is filtered out. The wine is sold in a different bottle.
  • The Charmat or Tank Method, where the second fermentation is carried out in tanks. The wine is then filtered and bottled under pressure.

The quality factor
Quality sparkling wines undergo a number of processes and maturation to give the same depth and complexity as a fine still wine, but they also have the prickle of bursting bubbles on the tongue.

Screwcaps versus cork for wine bottles

branded natural cork

natural cork

Natural cork provides a very good seal for a wine bottle, but a screwcap is potentially better still. There are pros and cons for each of them.

Sealing liquids

  • Cork has a unique cellular structure which allows it to be compressed, and then spring back to its original shape. This provides a very good seal to prevent wine from seeping out. It can still seep out if the bottle is overfilled, the cork damaged, or because of poor storage.
  • Screwcaps prevent any wine from seeping out.

    screwcap

    screwcap

Sealing gases

  • Cork. Oxygen can slowly diffuse through the cork into the wine. Some corks are more porous than others, and some have defects; this allows more rapid diffusion of oxygen into the wine, and more rapid ageing.
  • Screwcaps. The original screwcaps allowed almost no oxygen into the wine, and this may cause unpleasant odours to develop. Different seals are now available which allow controlled amounts of oxygen into the bottle.

Contamination

  • Corks can be contaminated with TCA, a very small amount of which makes the wine undrinkable. Refer to this earlier post for details. This is cork’s biggest disadvantage.
  • Screwcaps do not contaminate the wine.

Storage

  • Cork. Bottles have to be stored with the wine in contact with the cork. If not, the cork dries out, and becomes a less effective seal. Rapid temperature fluctuations can cause a cork to move within the bottle neck, which can also cause sealing problems.
  • Bottles sealed with screwcaps do not suffer from these problems.

Long-term ageing

  • Cork has been used as a wine closure for centuries, and there is plenty of evidence that a good wine, with a good cork, stored in a good cellar, ages gracefully.
  • Screwcaps have been around for decades, and there is evidence that some wines age well. However, plenty more trials will be needed over many years, before everyone is convinced.

Conclusion

The scientist in me says that a screwcap with the right seal, is the perfect closure. No bottles will be contaminated, and every bottle in a batch will mature the same way. My heart however, would rather see a cork pulled from a fine bottle of wine, rather than someone crack open a screwcap.

What is meant by a corked bottle of wine?

selection of natural corks

Bleached and unbleached natural corks

A ‘corked’ wine has a mouldy taste and smell. This is caused by chemicals leached from the cork, and is nothing to do with bits of cork floating in the wine.

Where does natural cork come from?

Natural cork is made from the bark of the Quercus suber oak tree, and Portugal is by far the largest producer. The bark is stripped from the tree, and this particular species is able to regrow its bark. Individual corks are then punched out from the bark. Various treatments are carried out along the way.

Origin of cork taint

The main culprit is a chemical called TCA, 2,4,6-trichloroanisole to be precise, although other similar compounds are also responsible. There are several possible sources of these compounds, and they involve fungi, microbes and chlorine treatments, either of the cork oaks, or the punched corks themselves.

How bad is the problem?

There was a time when the percentage of ‘corked’ bottles was estimated at between 2 and 6%. I would say that the incidence has decreased, but the problem has not been eradicated.

What are the cork producers doing about it?

There are two general approaches:-

  • Change the sterilising treatment – in the past hypochlorite bleaches were used to kill off microbes in the cork. Now they use peroxides, or microwave treatments to remove unwanted life in the corks.
  • Use of high tech analytical equipment, such as mass spectrometers and gas chromatographs. These can detect extremely low levels of contamination.

What are winemakers doing about it?

Apart from changing away from natural cork, the best a winemaker can do is to buy top quality corks. Samples from a batch can be tested by immersing them in wine, to see if there is any contamination.

Threshold levels of taste and smell

The threshold level is the minimum concentration at which a person can detect a smell or taste. TCA can be detected at incredibly low levels of a few parts per trillion (yes, a million-millionth). There are two interesting observations:-

  • Some people are far more sensitive to cork taint than others – they have a much lower threshold level. So that one person thinks a wine is just fine, and another that it is undrinkable.
  • The threshold level increases rapidly as the alcohol content increases. Which is why cork taint is very rare with bottles of spirit.

Can cork taint be completely removed by changing to screwcaps or plastic corks?

The answer is no, but the incidence will be much lower. TCA can contaminate other wooden objects in a winery, particularly oak barrels. So some contamination is always possible.