Wine and cork have been allies for a long time, sharing a journey that spans millennia. Cork displays an exceptional combination of properties that have earned it a reputation as one of the most advanced materials on Earth.
Natural cork is elastic, lightweight, impermeable to liquids and gases, fire and heat resistant. It is an excellent thermal and acoustic insulator, as well as hypoallergenic, and can withstand high levels of friction while retaining a texture that is soft to the touch.
For thousands of years, natural cork has been associated with the storage and preservation of prized foods and drinks. The ancient Egyptians, Greeks, and Romans mentioned cork as their preferred material for producing stoppers with which to seal their wines and olive oils.
According to historical accounts, in the 17th century the French monk Dom Pierre Pérignon was working on improving the process of making champagne. In order to preserve the bubbles, he turned to a plant whose bark had been widely used for centuries: the cork oak.
Despite the effectiveness of the cork, the second in-bottle fermentation generated bubbles of carbon dioxide gas, thereby building up pressure and causing many champagne bottles to explode in the winery.
The solution to this problem was found in the 19th century with the introduction of the muselet – the French word for “muzzle” – a small wire cage that keeps the champagne cork firmly in place.
Since then, and for the past 400 years, cork has been the chosen closure for wine bottles, fomenting a cork industry valued at 4 billion dollars and producing cork stoppers for 20 billion bottles per year.
The popularity of the material increased its cultivation throughout the western Mediterranean where groves of cork oaks cover an estimated 2.2 million hectares. Figures show that 49.6% of global production is concentrated in Portugal, followed by 30.5% in Spain, 5.8% in Morocco, 4.9% in Algeria, 3.5% in Tunisia, 3.1% in Italy, and 2.6% in France.
In Portugal, the cork oak forests are known as montado, whereas in Spain they are referred to as dehesas. The word derives from defesa, Latin for “defence”, indicating that these were seen as protected forests, primarily used for livestock grazing.
Nowadays, cork oak forests are multifunctional agricultural systems that provide economic benefits to the rural areas where they are cultivated, as well as having a great ecological value, because these woodlands help combat desertification, soil erosion, and biodiversity loss, as well as aiding carbon capture and storage.
Every year, cork oak trees absorb up to 14 million tonnes of CO2, and its capacity to store carbon is passed across cork-derived products.
In fact, the process of harvesting cork actually aids carbon capture: trees which have been stripped of their cork bark absorb between 3 to 5 times more CO2 than those that have not.
From a soil conservation standpoint, cork oaks encourage rainwater to filter into the ground and prevent erosion. As a result, they regulate the water cycle and significantly reduce the risk of drought.
Finally, cork oaks are slow combustion trees. Considering the widespread incidence of forest fires in places like Portugal and Spain, largely propagated by the adverse climate conditions of hot dry summers, cork oak forests act as a natural fire retardant.
The cork we use in the wine industry originates from the bark of the cork oak (Quercus suber L.). Anatomically speaking, cork is a tissue called phellem, part of the periderm in the bark system of trees. It is a protective tissue that separates the living cells of the plant from the outside environment (Pereira, H., 2007).
In the cellular structure of cork, we find its greatest secret: a closed-cell foam, each cell filled with a mixture of gases similar to air, and a percentage of suberin deposited into the walls of said cells.
Suberin is a polymer found in the lignified cell walls of plants, comprised of fatty acids that offer a barrier to dehydration.
The high gas content is responsible for the light weight of cork, whereas the alveolar structure of the cells, akin to small interconnected cushions of air, contributes to the material’s elasticity. Given all of these structural characteristics, cork is known as “nature’s foam” in the industry.
The chemical composition of cork, which informs its quality, depends on multiple factors, including geographic provenance, climate and soil conditions, genetic origin, tree size and age, and growing conditions (Silva, et. al., 2005).
Generally speaking, the average chemical composition of virgin cork consists of 45% suberin, 27% lignin, 12% polysaccharides, 6% tannins, and 5% ceroids.
Both the structural and chemical properties make cork an unparalleled material for a great many industrial applications.
In the exhibition entitled planet cork in Porto’s WOW cultural district, we can find countless examples.
In the transportation sector, Siemens recognized how the advantages of cork could benefit the design of the world’s lightest underground rail: Inspiro. Given that cork is extremely lightweight, it can reduce energy consumption and lower the cost of building modern transportation systems.
Cork is used to produce artificial grass for football stadiums in Belgium, the Netherlands, Germany, and Canada. This 100% Portuguese project, a pioneer in the world of sports, is FIFA certified.
At this time, cork is also used in the production of surfboards, padel tennis rackets, and skateboards.
The possibilities are so far-reaching that even NASA chose cork to protect the heat shields of its spacecrafts, integrating the material into their thermal protection systems. When Neil Armstrong walked on the moon, cork was along for the ride.
Without a doubt, cork is an unrivalled material, not only in providing applications in countless sectors, but also in offering solutions to mitigate runaway climate change.
In order to keep reaping these wide-ranging benefits, the wine sector must recycle the significant amount of cork waste it generates, working with cork collection systems that companies like Amorim introduced in Portugal with their Green Cork programme. Similar initiatives were quickly adopted in other countries like the US and Canada (ReCork), France (EcoBouchon), Italy (Etico), the UK, South Africa, and Australia.
After all, the useful life of a cork lasts far beyond a bottle!
Marta Juega, PhD
1. Helena Pereira, ed., Cork: Biology, Production, and Uses, Amsterdam/Oxford, Elsevier Science, 2007.
2. S.P. Silva, M.A. Sabino, E.M. Fernandes, “Cork: Properties, Capabilities, and Applications”, International Materials Review, vol. 50, no. 6, 2005, pp. 345–365