Footprint

It was exciting to see teams of four men vigorously harvesting cork last week in the Alentejo region of Portugal, just south of Lisbon. In temperatures of 32C (apparently temperate for the time of year) they swarmed over a tree, stripping the cork from the entire trunk in about quarter of an hour – typically they will do 25 trees in a day.

A tree is harvested in 15 minutes once every nine years.

Although it looks brutal, the trees recover, being fit for reharvesting every nine years, and typically living 200 years. Growing on sandy soil, the cork oaks provide acorns to feed pigs that produce the delicious local pork, as well as preventing desertification, and acting as a habitat for 24 species of reptiles and amphibians, 160 species of birds, and 37 species of mammals.

I had not realised the synergy between the production of wine corks, of decorative products such as flooring, and of the ‘black cork’ that is used for thermal and acoustic insulation. The best pieces of cork are used for natural cork stoppers, with the waste from this process and from inferior pieces used to make granules that then find a variety of uses. They can be bound to make floor and wall tiles, as well as decorative products and cheaper corks.

Black cork is produced in a different way. The white granules cannot be used, as they come from material that has already been boiled, releasing its resins. So the source material for black cork is from branches, pruned in the autumn and then stripped as part of a local cottage industry, and milled into granules.

I visited cork producer Amorim Isolamentos’s factory, where, after milling, the granules are formed into blocks in an autoclave. The heat makes the granules expand and darken, and they release their resin which binds them together. Carlos Manuel, general manager of Amorim Isolamentos, boasts that the only products the factory uses are cork, water and packaging. More than 90 per cent of the energy for heating comes from biomass, consisting of cork dust from manufacturing.

Alumasc Exterior Building Products, which used cork from Amorim on flat-roof refurbishments in the 1980s, is starting to use it now as part of its external walling system. The main attraction is its environmental credentials compared to other insulation materials.

Filed under: Sustainable products