Cork

Cork is a vital ingredient in wine, although it’s one that’s come under increased scrutiny and question in recent years due to the repeated occurrence of TCA in wines. Despite all the controversy that surrounds cork, it’s hard to imagine not hearing that resounding pop when opening a bottle of wine. The cork industry in Portugal is determined to make all associations with cork as positive as that sound, so they invited me to the country to discover what exactly they’re up to these days.

what is cork?

A cork tree is a type of oak grown in Mediterranean countries. Portugal accounts for 50% of cork production, the rest from Spain, France, Italy, Tunisia, Algeria, and Morocco. It’s a tree that requires a great deal of patience to harvest, as it takes 43 years between planting the tree and being able to use it for quality cork production. The first harvest takes place after 25 years; a second nine years later; and then the third after another 9 years will be the first to be actually used. After that, a tree can be harvested up to twenty times, giving it a lifespan of over 200 years. As was repeatedly emphasised to me, the cork industry is an extremely sustainable one.

sample taken from a cork tree in 2018

cork harvest

Unlike with other trees, cork trees are not cut down to be harvested. Instead, the outer bark is removed, leaving the rest of the tree to continue growing. The bark replaces that which has been harvested, until nine years later it is ready to be harvested again.

The harvest takes place from the end of May through the summer months, when the bark is at its growing peak. A team of experienced harvesters cut the bark with an axe, careful not to damage the tree. Harvesting, as with the cork industry as a whole, is extremely regulated. Only a third of the tree can be harvested, and a cork tree can never be cut down without permission from the authorities.

cork tree harvested in 2017

cork issues

After harvest, the cork bark is laid out for 6-9 months to dry it. This is where problems can begin. Up until the 1990s, the cork industry had no competitors; then came along screw caps with their clean, reliable aromas. Cork had been taking its position for granted and lax practices had afflicted the industry. The bark was exposed to rain and laid on wet, humid soil, allowing mould to develop.

This may seem an obvious cleanliness issue, but it went beyond that. A naturally-occurring chemical compound called TCP feeds on mould to produce another compound called TCA. This is completely harmless, but it latches on to corks which transfer it to a wine to produce nasty, wet cardboard aromas - such a wine is described as “corked.”

freshly washed cork

In the 1990s, it was estimated that 10% of wines were corked and the industry’s reputation was - seemingly at least - irreparably damaged. Screw caps and plastic corks were the new norm, and cork was the past.

cork fightback

These issues, however, snapped the cork industry out of its complacency and it has undertaken huge efforts to make cork as free from TCA as it is possible to be.

The bark is now dried on concrete or cement floors, covered in corrugated iron to drain any rainwater away. After the drying is complete, the edges of the barks are cut to ensure that any mould is removed. The barks are then put in a bath of boiling water for 58 minutes, in part to flatten them but also to thoroughly cleanse. As the abbreviation TCA suggests, chlorine is a key component in the development of the compound, so the water used is chlorine free and constantly cleaned.

corks being tested for any TCA taint; any guilty samples are placed on the blue trays

TCA cures

These are preventative measures, but cork producers now also attack any TCA that has survived. One producer I visited, Cork Supply, employs sensitive tasters to smell hundreds of thousands of corks to reject any affected with TCA; another, Amorim, has developed expensive, highly-advanced machines to sort through millions of corks. They both offer a high-end range of cork that guarantees no TCA.

types of cork

Natural cork is used for the highest quality and most expensive wines, cut directly from the bark. On opening a wine, these can be recognised as there will be no break from top to bottom. These are the corks that the industry is putting its primary, costly efforts into guaranteeing no TCA, as opening any expensive bottle of wine affected will do continued permanent damage to the industry’s reputation. Although production of natural cork is lower than other types, it accounts for 60% of value.

Agglomerated cork has two discs of natural cork at either end, with granulated cork in between. This middle part comes from corks not deemed high enough quality on their own, but perfectly acceptable. The agglomerated cork replicates the qualities of natural cork, without adding ageing potential to the wine.

There is also the champagne cork, which is much thicker to withstand the pressure of the CO2 in the bottle. These always have two discs at one end. Champagne producers were the first to understand the romance of opening a bottle of wine, and put a lot of pressure on cork producers to ensure consistent quality. Thus, even though sparkling wine is more susceptible to TCA, incidences are much lower than still wine. This indicates that the concerted efforts of the cork industry to reduce the unwelcome appearance of TCA are likely to bear fruit.

And then there is the plastic “cork,” a cheap, short-term alternative. Sales are rightly dwindling, but can still account for up to 2 billion of all bottlings.

rivals to cork

There are 18 billion bottles of wine bottled each year, of which 12 billion have a cork. That’s a 70% share, but the cork industry has been extremely worried about screw caps - a type of closure that I found cork producers nervously dismissive about.

The perceived advantage of natural cork is that it allows a wine to very slowly receive oxygen and thereby become more complex in the bottle. This is something cork producers are still scientifically researching, though I think they’ve yet to come up with any hard evidence other than sensory perception.

Natural cork does allow a lot of oxygen into the wine upon immediate bottling - perhaps the cause of bottle shock - but after that oxygenation is very gradual. In contrast, a screw cap either allows no oxygen into the wine at all - intended for a wine that requires no ageing - or, for the higher quality wines, it allows the same amount year in year out.

Whether one of these rates of oxygenation is superior to the other is, I think, down to personal opinion. I have tasted older wines bottled under screw cap which have retained their fresh, fruity appeal while demonstrating developed complex aromas. Those under cork are likely to feel more mature and developed - perhaps, one might argue, more naturally.

are the cork producers’ efforts working?

The cork industry claim that 1.2% of all wines bottled under cork are tainted by TCA. That’s a figure difficult to prove, as identification of TCA is very much dependent on the awareness of the taster and their willingness or ability to report it. Certainly, incidences of TCA are much, much lower than they were fifteen years ago, and the industry has to be praised for that. I hope that positive progression continues, but it’s simply impossible to eradicate TCA completely. And, as a quick snapshot, over a seven day period before and after my trip to Portugal I tasted five corked wines. I taste a lot more than most people, but that’s nearly three times the 1.2% rate cited. A lot of work to be done, but at least the cork industry is undertaking it.