A 2500 year old industry

Jacopo Mazzeo on Portugal’s cork-making tradition

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Cork has been sealing wine for over two millennia. Amphorae containing wine and sealed with cork dating back to the 5th century BCE have been found in Greece. In 1952, French explorer and scientist Jacques-Yves Cousteau recovered from the depths of Italian waters 7000 amphorae that were around 2200 years old. Some were sealed with cork stoppers and still contained wine.

Cork is obtained from the bark of the cork oak tree. The species is found across the entire Mediterranean basin, from Sardinia to Morocco, but Portugal has long established itself as a leader in the manufacturing of cork-derived products. Above all, wine stoppers, which became the industry’s main objective in the 18th century. The flourishing Port wine trade became instrumental to the development of the cork stopper industry. 

“Initially our big customers were the Port wine houses,” says Carlos de Jesus of Amorim, a world leader in the production of cork closures. “Now obviously our market is much bigger, as we sell anywhere to countries like the USA, Spain, and Italy. Meanwhile Portugal represents today only about 7% of our business.”

Although the highest concentration of Portuguese cork forests are found in the south, the Port wine market led the industry to establish in the opposite end of the country, especially in Aveiro, about 50 miles south of Porto. Amorim’s headquarter address itself – Rua dos Corticeiros, meaning Cork Traders’ Street – provides undeniable proof of the town’s significance within the history of Portugal’s cork production. João Rui Ferreira, vice president of the Portuguese Cork Association (APCOR), adds that the north was also Portugal’s most industrialised region, thus better suited to the development of a florid trade.

“That’s where you still find a lot of manufacturing, which certainly played a role in the growth of the cork industry there.”

As the industry grew, cork stoppers established themselves as the go-to choice for wineries across the globe until, in the second half of the past century, the advent of alternative closures threatened its very survival. Synthetic corks were cheaper, while screwcaps, at a time when cork taint was a common problem, offered winemakers a much more reliable option. Over the past decade or two, the cork industry reacted by releasing a number of innovative products – such as stoppers that allow varying degrees of oxygen to get into the wine as it’s stored, or to ensure bottle consistency after long periods of maturation – and by seriously tackling the issue of cork taint, eventually managing to reverse the negative trend.

“When you have a monopoly of the market [as was the case in the past], you aren’t as motivated as when you’re challenged by a multitude of competitors,” explains De Jesus.

“Innovation would have arrived anyway, but it wouldn’t have been as fast as it has been.”

A natural product

Compared to other popular wine closures such as screwcaps or glass stoppers (which require a rubber or plastic seal), cork is an entirely natural product. It’s biodegradable, renewable, and recyclable.

They are made by harvesting the bark of the cork oak tree (not the wood itself), a job that requires a highly specialised workforce as a heavy hand might risk causing serious damage to the tree. Cork harvesters tend to receive a daily compensation that’s significantly higher than the national average, over €100 per day, making it one of the highest paying agricultural jobs in the world. Cork harvesting is a seasonal job, but such a high pay is still critical to the survival of Portugal’s rural communities: it prevents youngsters from migrating to urban areas and depopulating the countryside.

While the pay is high, the cork business isn’t for the impatient. “We have to wait 43 years before a tree starts generating a profit,” says De Jesus. “You have to wait 25 years from planting before you can harvest the first time. But the first time you won’t get quality cork. You need to wait another nine years until you can go back to it, and that’s still not good enough to make quality cork stoppers, so you wait another nine years.”

Once stripped of its bark, a cork oak will take several years to regenerate before its bark can be harvested again. It’s usually another nine years, during which time the tree’s contribution to reducing greenhouse gas emissions increases. According to Amorim, a cork oak stripped of its bark can absorb about five times the CO2 of an unstripped tree.

But cork trees do offer additional environmental advantages: “They’re crucial to the conservation of biodiversity,” says Ferreira, “to protect the forest, and it’s a barrier against desertification, too.” 

A cork stopper for any wine

Cork stoppers come in multiple forms to cater to different needs.

The traditional natural cork stopper is made by punching through a bark strip. Natural cork stoppers are often used for long-lived wines, as they allow a certain amount of oxygen to come in contact with the wine, leading to a slow yet steady maturation. A natural cork will continue to perform its function for years, as long as the quality is sufficient and storage temperature and humidity levels are kept to the required levels.

The byproduct from the manufacture of natural cork closures – granulated cork – is used to produce “agglomerated” cork stoppers, and you may have come across these before. These types of corks are a much cheaper option and are normally found on wines with a short shelf life. 

Not only do natural and agglomerated corks serve diverse functions and come at different price tags, they look different too. Natural corks tend to be fairly uneven and the pattern created by the cork’s grain might still be visible. Agglomerated corks, on the other hand, look a bit like chipboard. What do the corks in your wine look like?



Cork Stoppers FAQ

Are wines closed with cork stoppers any better than those closed with alternatives? 

The short answer is no, they aren’t. Technological advances mean that there are types of cork stoppers and indeed screwcaps or other alternatives to suit pretty much all wine styles and price levels. Some let more oxygen in, others less, meaning that the bottle can age slowly over a longer period of time. 

While no closure is objectively better, wines closed with cork stoppers are perceived as having a higher value, which may lead certain drinkers to feel they taste better after all. A 2017 experiment, held in London, did claim that cork makes wine taste better (for full disclosure, the “Grand Cork Experiment” was organised by APCOR, yet undertaken by an Oxford University team). 

The participants were asked to blind taste and rate wines after experiencing a variety of closures, either by hearing their sound or by simply opening the bottles themselves. The result? Wines associated with a cork were scored higher in all cases… despite all of the wines being identical.

Is your wine corked?

Cork taint is arguably one of the most common wine faults, and no, it doesn’t occur when bits of cork happen to fall into the wine as it’s opened!

It is rather the symptom of the wine being tainted by certain chemical compounds – if you’d like to get technical, these chemicals are TCA (2,4,6-trichloroanisole), and – to a lesser extent – TBA (2,4,6-tribromoanisole).

Cork is the most likely carrier of these compounds, but cork taint might derive from other wooden surfaces too, such as barrels, fixtures, or fittings. This means that a wine may turn out “corked” even if it is sealed with a synthetic closure or a screwcap. Bet you never knew that!

Cork taint presents itself with a musty, dusty smell that can be clearly detected when sniffing the wine. It’s also often perceivable by sniffing the cork itself, which is what sommeliers tend to do whenever they open a bottle.

Unfortunately, corked wine can’t be recovered, and it’s best poured into the drain. The good news is that the incidence of cork taint caused by cork closures has significantly reduced of late. A common occurrence in the past, cork taint is indeed en route to being eradicated, with APCOR claiming it now affects a mere 0.5%-1% of wines sealed with cork.

Is cork used for anything other than wine stoppers?

Cork is used across a wide range of different industries, from design to fashion. According to APCOR data, cork is found in NASA shuttles, in competition kayaks, in tennis and cricket balls, in shoes, and new applications are found on a regular basis.

Wine isn’t the only beverage that favours cork over alternative options either. Olive oil and vinegar bottles may also carry a cork stopper, as well as a range of other alcoholic drinks, from whisky to rum. Some traditional Belgian beers such as Trappist ales and Lambics use cork stoppers too. In fact, Amorim’s De Jesus argues that the growth of the global craft beer movement is translating into a higher demand for cork stoppers destined for the beer industry.


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