On Cork
Tuesday, June 1st, 2010Lately I’ve been having a love affair with cork. Cork is sustainably harvested, rapidly renewable, recyclable, compostable, natural, durable, and easy-care, and its harvest is the keystone in both the conservation of a unique ecosystem and the continuation of a traditional rural cultural heritage. It does need to be transported from Europe to reach us, but I feel that this negative is outweighed by its many positive qualities.
Cork is actually the bark of the cork oak tree (Quercus suber). Each year, cork oak grow a thick layer of bark cells (or phellem) that accumulate as annual rings, instead of being shed. The outer layer of waxy cork bark can reach a thickness of 6 inches (15 cm) or more. Its role is to protect the tree from wildfire damage: cork oaks evolved in dry, fire-prone Mediterranean ecosystems, and their thick outer bark can char while still insulating the sensitive inner stem tissues from heat, so that any damaged branches in the crown can resprout quickly from stem buds.
On a microscopic level, cork is a honeycomb-like network of 14-sided air-filled cells, with about 200 million cells per cubic inch. This structure makes cork both an excellent acoustic barrier and (as noted above) thermal insulator, so that cork floors are comfortable in both hot and cold weather. The spongey cellular structure also gives elasticity that also makes floors comfortable underfoot and bulletin boards resistant to permanent marks.
Pretty pastoral, isn't it? A cork forest in Portugal's Alentejo region, via wineanorak.com
The cork oak forests are a model example of a sustainably managed landscape, extending across Portugal, Spain, France, Algeria, Morocco, Italy, and Tunisia. While the geographic distribution is broad, 50-70% of commercial cork production is in Portugal, with the forests mostly privately owned by farmers. Cork oak woodland ecosystems support both high plant diversity (among the highest in Europe at 60-100 species per 0.1 hectare [PDF]) and high animal diversity. They contribute to the survival of several endangered species, including the Iberian lynx, the Iberian Imperial eagle, and the Barbary deer (or Atlas deer). In addition, Europe’s entire White Crane population and millions of other northern European birds winter in the cork oak forests of Spain and Portugal, and the cork oak forests on both sides of the Strait of Gibraltar are crucial for other migratory birds. North African cork oak woodlands provide habitat for the endangered Barbary macaque. Cork oak forests are also crucially important to soil conservation, moisture retention, and fire prevention in the regions where they grow, and cork oak plantations are credited with preventing desertification in arid southern Portugal by reducing erosion of the sandy soils. New book Cork Oak Woodlands on the Edge from Island Press looks like it’s a must-read for those engaged in study and restoration of these habitats.
No trees are cut down to harvest cork (that would actually be illegal in Portugal!). It takes 20-25 years for the tree to mature; once mature, the bark is carefully stripped by hand, in late spring to early summer, by skilled workers using small specialized axes and taking care not to damage the underlying vascular cambium, every 9-12 years (The frequency of harvest is also legislated in some countries). The trees themselves regrow their bark and can live for about 300 years (some sources say as long as 500 years). There’s a marvelous photo-tour of the entire cork production process at wineanorak.com and a detailed description at the website of the Portuguese Cork Association APCOR – I highly recommend that you take a look.
The Whistler Tree, via corkqc.com
The oldest known cork tree still being harvested, called the Whistler Tree for its colony of birds, was planted in Portugal in 1789.
The cork harvest also represents a rich cultural heritage of techniques and ways of life, which have existed for more than 3000 years in the Mediterranean region. (In fact, cork stoppers have been found in Egyptian tombs, and cork was also used by the ancient Romans and Greeks as roofing and insulation.). A 16th-century French Benedictine monk named Dom Pierre Pérignon (you might have heard of him) is considered responsible for the widespread use of cork stoppers to preserve wine in bottles in the 17th through 20th centuries. Today, cork stopper production is a keystone of the western Mediterranean rural economy. Cork is also used to make flooring, insulation, fishing buoys and floats, fly-fishing rod handles, shoe soles, badminton birdies, aircraft parts and the nose of the Space Shuttle – but demand for wine stoppers has until recently created the profit that drives this traditional rural economy. Cork oak habitats are also used as grazing land, and allow local people to make a living through the collection of herbs, wild berries, mushrooms, firewood, and sweet acorns, and the production of honey and charcoal.
So where do these rumours of cork being an endangered species, or there being a worldwide cork shortage, come from? Nobody is sure, but they roughly coincided with the introduction of inexpensive alternative stoppers made of plastic for the winemaking industry. They’re marketed as a measure used to prevent so-called “cork taint” or contamination of the wine with 2,4,6-trichloroanisole (TCA) which gives a mouldy flavour. This really is not necessary, since TCA taint is often not caused by the stopper. Halogenated phenols, the precursors to TCA, are widespread because of their use as pesticides, herbicides, and sanitation agents – and research has shown they’re often present in wine even before it is bottled. Furthermore, cork stopper manufacturers have developed a new technique of boiling and drying the cork that considerably reduces any spoilage caused by bacteria. Also, alternative stoppers can cause their own unique wine taint called ’sulphidisation’.
Without demand for cork stoppers, flooring, and other products, the cork oak woodland ecosystem, peoples’ livelihoods, and a traditional rural Mediterranean way of life could disappear as forests are sold as real estate, and abandoned or cleared. In order to address these issues, in 2006, the World Wildlife Fund started a huge campaign to conserve cork oak landscapes, including Forest Stewardship Council (FSC) certification of sustainably-managed forests, restoration of damaged forests, local job creation, and lobbying for change in government policies. Their campaign to educate European winemakers has been fairly successful. Local groups are also advocating for direct conservation by the creation of national parks in these areas.
But the best way for North Americans to help protect the cork oak forest is to use products made from sustainably harvested cork from the Mediterranean. Here’s an overview of cork products for interiors:
Cork flooring is a secondary product of the cork wine-stopper manufacturing process: yup, 100% post-industrial recycled content. Typically, after punching stoppers out of the best-quality bark, the remainder is granulated, then heat and high pressure is applied to the ground cork granules so that the natural waxes in the cork bind them together. (Some manufacturers also add a binding agent at this point, so be sure to check.) This process is used to make cork underlay, planks, tiles or sheets that are suitable for flooring or wall applications (depending on their thickness), in a variety of patterns, and can be installed unfinished or prefinished. The specs for cork plank flooring typically include a lifespan of 50+ years (compare with 20 years if you’re lucky for vinyl flooring), slight offgassing of natural oils, natural antimicrobial & mildew resistance, and costs on par with hardwood flooring. Some cork floors also recover well from large amounts of pressure (so they’re OK for kitchens & laundry rooms with heavy appliances).
I recently became aware of cork countertops, and I’m very excited about them. Suberra have the only version currently available in North America, and they say that their compressed cork slabs are urea-formaldehyde free and resistant to water, stains, and 350 degree F heat. Wow! It’s been reviewed by This Old House and mentioned in ICFF roundups at Treehugger and Apartment Therapy.
Compressed cork has also been used by Jasper Morrison and Daniel Michalik to create some seriously sexy pieces of modern furniture. What a way to bring texture into a room!
Jelinek Cork are selling cork penny-tile mosaics made from post-consumer recycled wine corks: so cool! Jelinek also have cork acoustic tiles that can be installed on walls or ceilings, and cork fabric. Cork fabric is actually cork veneer laminated onto an upholstery-grade dimensionally-stable polyester backing (cotton backings don’t seem to be available in the North American market). It wears like cow leather, which makes it suitable for accessories or furniture, and it can be cleaned with soapy water either by hand or machine (90 degree F).
I think we’re going to be seeing a lot more cork coming into our homes as the current generation of designers realize its’ unique physical properties are also uniquely sustainable!
