The Wonders of Cork

Before you slip into your favorite Birkenstock sandals in preparation for your next adventure, consider for a moment the history, science and each pair. Karl Birkenstock invented his contoured cork footbed sandals back in 1964. However, cork footbed sandals go much further back in time. Pliney The Elder, the encyclopedist for the Roman Empire, glowingly described the wonders of cork as a footbed for sandals. One could argue that the Roman legions might not have been able to walk to the ends of the Empire without cork footbed sandals.

Cork is an amazing material. By volume, cork is 90% air, trapped inside a honeycomb grid of 14-sided tiny cells. Cells are so tiny that a cubic centimeter of cork has 40 million cells. When Robert Hooke examined thinly sliced cork under a newly invented microscope in 1660, he discovered cork was porous. The perforations reminded Hooke of monk’s cells where they slept and prayed. Hence the name cell. This structure gives cork remarkable craftsmanship built into qualities. Cork is super light, a fabulous insulator, flame resistant, non-allergenic and rot-resistant.

Portugal is the leading producer of cork. Cork forests, called montados, are a hap-hazard mixture of pine and cork oak trees. They thrive in a Mediterranean climate with well-drained sandy soil. The montados are important ecosystems that provide habitat for hundreds of animal and plant species, not to mention that over 100,000 people economically depend on the cork forest directly and indirectly. Similar to the Amazon rainforest the montados absorb millions of tons of carbon dioxide.

Cork wine stoppers represent 70% of the economic value of cork but only represent 25% by volume. The remaining material is used for a variety of products, including Birkenstock sandals. Nothing is wasted. Cork can be harvested without hurting the tree. Harvests take place every nine years. The quality of the cork improves with age. It takes 43 years before cork bark is good enough to make wine stoppers. Productive cork trees can live for more than 200 years. The Portuguese have a saying, “If you want to make a business for your grandchildren, plant cork trees.”

Bark strippers are called tiradors. They work in pairs. They are always men. The profession is a highly skilled one that is passed from one generation to the next. The cork harvest takes place in the dry summer months when the bark does not grip as tightly to the trunk. One tirador clambers up the tree with a sharp fan-shaped ax. His partner starts at the base with his ax. They make a series of horizontal and vertical cuts. They need to be most careful to not cut through the phellogen, the layer of living cells which allow the cork’s regrowth. Big slabs can then be pried from the tree. When stripped of its outer bark the remaining living layer of bark is a bright yellow, which will turn to a red color in a couple of days. The red naked trunk is painted with a number designating the year so they know when that tree can be harvested next. These slabs are frequently hauled away by mules due to the inaccessible terrain. Cork bark slabs are then stacked and dried for 6 months. Slabs are then boiled to be ready for cork stoppers production. One tree produces 3,000 to 5,000 wine stoppers per harvest.

So now you know. Your Birkenstock sandals not only support your feet but an entire natural ecosystem, a way of life for hundreds of thousands of people, and help reduce carbon dioxide emissions for all of us. Birkenstock sandals can make you feel good in a variety of ways.