Portugal is the world’s largest producer of cork with 7,000 sq. kilometres under cultivation and 30 million corks made a day
Imagine having to wait 25 years to harvest your first crop.
That’s what growers in southern Portugal do when harvesting cork.
Cork has many uses from sealing champagne bottles to garment-making to use in the aerospace industry.
In the 1700s, Dom Perignon, a wine-making monk, revived the use of cork as a tasteless odorless seal for port. Back then, stoppers were cut by hand, and a man could make about three stoppers per minute. Today, Portugal is the world’s largest producer of cork with 7,000 sq. kilometres under cultivation turning out 30 million corks a day.
Cork trees are members of the oak family and green cork oak trees are the only tree from which the bark can be stripped off and the tree will regenerate and produce more cork. However, producers must wait nine years for the next harvest.
Mature trees are stripped in summer every nine to 10 years to reveal a raw red undercoat.
Portugal produces almost 50 percent of the world’s cork, while neighbouring Spain produces 30 percent.
Despite the trend for screw tops on wine bottles, the cork industry is growing.
That’s what we learned when we recently visited the Novacortica cork factory at Sao Bras de Alportel in southern Portugal.
This family company traces its origin in the cork industry back to 1935.
It takes a long time to establish a cork farm, so farms are often passed on from one generation to the next.
Cork trees grow throughout the area and are protected by the government. All trees are marked with a date number indicating when they were last harvested. Cork trees grow large, allowing sheep and cattle to graze under them.
Harvesting is carried out from May to September when the sun’s heat expands the bark so it detaches easily from the trunk.
The tree is able to breath and produces one new layer of cork bark each year like annual rings. In the cool weather of fall, the bark glues itself back to the trunk. Trees can be 300 years old with up to 20 harvests.
Virgin cork, which is the first harvest at 25 years, is very rough and is used for cork stoppers. With the second harvest, at 34 years, the bark gets a bit smoother and the best cork at 43 years has very smooth bark.
At Novacortica, the two main products are small cork disks, which are later glued to the bottom of champagne stoppers, and cork granules for use in the textile and manufacturing industry.
At the cork factory, the first stage in the production line boils raw cork bark planks for one hour to sterilize them and allow the planks to absorb water.
Different products are made from the outside, middle or inner part of the bark. The thickness depends on the growing seasons. In nine years, the cork is usually thin, and in 12 years the cork bark will be thicker.
At the next stage of processing, the cork is sliced into the three thickness components. The planks are separated into quality categories based on their thickness, porosity and appearance and cut into three strips.
A machine then punches out cork discs about 26 by six millimetres in size. Discs are Novacortica’s most important product. All the unused bark from the disc operation is ground into different textures for different products and sold to other manufacturers. The granules are graded by density and used to make compressed champagne and wine stoppers, building insulation, gaskets, flooring, clothing, upholstery fabric, soles for shoes, high fashion handbags and other products.
The best material for high quality stoppers or discs comes from the outer edge of the cork bark. High quality stoppers sell for $1.55 to $4.65 each and are used for long-term storage of five- to 30-year-old high quality wine and champagne.
The granules are glued together using food grade adhesives and compressed into unbreathable cork stoppers that keep the gas in the champagne bottles. For high quality champagne stoppers, two discs are glued to the bottom of champagne cork as a breathable surface, which prevents any possible tainting of the champagne from the compressed, non-breathable cork.
A separate machine polishes the outside of each cork.
Granules from the outer part of the bark are oxidized and bendable and are compressed for flooring.
The middle part of the cork bark is very smooth and is ground, glued and compressed into big blocks and sliced paper thin. These strips are used in the textile industry. They are glued to textiles and the material can be coloured and used to make clothing, high fashion purses, ladies handbags, furniture fabric and even water proof umbrellas. The umbrella’s cork and nylon skin lets light through and a wax coating makes it water proof.
The inner part of the bark is very porous and flexible. It is ground into granules that are compressed and used for making the soles of shoes and hot pad coasters.
Fine grind is used to make stoppers for one-year wines because corks made from this material don’t breathe.
Problems with a fungus in the cork, which can taint the wine, along with environmental sustainability concerns that followed largely unsubstantiated rumours of wholesale cutting down of cork trees, started a move toward the use of screw tops and cheaper synthetic stoppers in the wine-making industry. However, high-quality wine and champagne producers still prefer to use natural cork in many cases.
At Novacortica, visual inspection and colour scanning technology sort the discs into different quality grades to prevent potential tainting problems caused by corks.
As well, rumours of unsustainable harvesting have been calmed and recycling is becoming an important story within the industry because many countries are able to regrind corks into reusable granules for other materials.