CORK
The next time you pull a cork out of a wine bottle, stop and think of all the corks you have pulled over the years and how wonderful it is to open a great bottle of wine. Recently I had an opportunity to visit with one of the world’s largest producer of cork products in Portugal, Amorim. The visit highlighted the first steps of the manufacturing process of the cork tree bark – and gave some insights into the cork industries steps to reduce that bane of wine drinkers, Cork Taint!
In Portugal alone there are more than 670,000 hectares (Approximately 2,600 square miles) of cork forests, which produce more than half the world’s cork. The area under cork forest is growing by 4 per cent a year. Management of the cork forests in Portugal – from cultivation to harvesting – is strictly controlled. The trees cannot be cut down without permission and the bark can only be stripped once every nine years. Cork is a truly sustainable resource. The cork oak tree has a life span of around 170 – 200 years during which time it will be stripped around 15 – 18 times.
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Today’s forest is relatively young – the average cork oak is 72 – 75 years – ensuring sufficient cork to supply the world’s winemakers for the next 100 years. A cork tree has to be at least 25 years old before the first harvest and it is not until the third harvest that the bark can be used for the production of wine corks. Bark from the first two harvests (Virgin and Secondary) is used for other cork products (flooring, shoes, insulation etc).
The harvest takes place between June and September because at this time of the year the tree is growing. This means that the bark can be easily removed from the trunk and a new outer skin grows quickly to protect the inner bark. Stripping the outer bark is a very delicate operation carried out by skilled workers using special axes. Once stripped, the tree is marked with the year of harvest and you see these numbers on trees as you drive along.
After harvest the bark is seasoned for six months in the open air, stacked on stainless steel pallets above the ground. It is boiled in water at 100 degrees Celsius for 90 minutes to remove contaminants. The planks are then left to stabilize for two to three weeks. The bark is sorted into quality categories before being boiled and dried again. Only the best quality bark is chosen for natural cork stoppers and discs for sparkling wine.
The overall cork processing system has changed significantly over the last 10 years. In the late 1990’s, cork taint was a major issue. In order to address this issue, Amorim and other major cork producers have taken huge strides to improve the manufacturing process. This starts at the tree by not utilizing the portion of the bark in contact with the dirt; air drying the bark on concrete sloped areas; boiling the material (and filtering the water continuously to eliminate contamination); the use of stainless steel pallets rather than wood; and the continuous testing to safeguard each step of the process to eliminate contamination. While cork taint will always be a problem it is clear the cork industry is working towards major improvements.
The corks undergo exhaustive quality control and testing at each stage of processing. While at the Amorim facility, I visited there testing laboratories where testing of each lot was performed throughout the manufacturing process. In addition to taste and sensory analysis, the battery of tests covers humidity and microbiological content, capillarity, recovery, sealing ability and performance over time.
Once the bark has been thoroughly cleaned, it is inspected and sorted – some to become cork stoppers for wine and spirits and some as other manufactured goods. During our tour, we followed the manufacturing of disks used as part of the champagne cork process. These disks go through a variety of steps, punching sorting, resorting, branding before becoming quality disks for the end of the champagne cork.
Those portions of the tree that are destined for wine stoppers are individually inspected and graded according to the overall quality of the material. This is all done by hand using knives, keen eyes and lots of experience. Once the sorting process has been completed they are shipped to another plant where they are punched and further sorted and cleaned. Once they are ‘corks stoppers’ they are shipped around the world.
