After seasoning, corkwood is boiled to remove organic solids lodged in the lenticels or pores and to bring it to the correct moisture content for processing (13-14 per cent relative humidity). This maximises the cork's thickness, compressibility and elasticity during processing.

At Amorim's plants at Ponte de Sôr and Coruche, cork planks are boiled in closed steel tanks fitted with a special device known as CONVEX^® that continuously traps and removes volatile organics such as trichloroanisole (TCA) from the washwater.

The boiling system, introduced in 2000, departs from traditional methods in several important respects. Cork planks are boiled in smaller, 2-tonne batches. Improved water circulation and more even temperature distribution boosts the extraction of contaminants.

The new process is dynamic. Washwater is pumped through the tank and passed through a filter to remove suspended solids. The entire volume of water in the tank is filtered every 20 minutes. Only non-chlorinated, filtered water is used and it is regularly tested to ensure the absence of chemicals such as organochlorines.

The filtered washwater passes through the CONVEX^® (continuous volatile extraction) process. Volatile compounds in the water, such as TCA, are quickly and efficiently removed from the water, which then returns to the boiling tank.

Tests have shown that this sophisticated boiling process significantly reduces the presence of contaminants such as TCA and results in very clean corkwood for processing.

The correct moisture content is needed to maximise the cork's compressibility and elasticity during processing. Traditionally this was done by boiling the corkwood a second time and then allowing it to dry to the correct humidity. Implementation of the new boiler process has now eliminated the second boiling stage.

Once boiled, the planks are stacked and allowed to dry and stabilise in a sterile and well-ventilated areas. During the stabilisation period, the planks become flatter and reach their optimum humidity for processing (13-14 per cent) after about three days.

Because of the lower humidity content of the cork after boiling (20 per cent compared with 40 per cent under the old process), the cork planks need only be left to stabilise for three days (instead of three weeks), considerably reducing the risk of mould growth.

After stabilisation, each plank's border is prepared and its edges trimmed before an initial manual grading. The planks are sorted into quality categories based on their thickness, porosity and appearance.

Planks that contain faults are eliminated and granulated for use in other non-wine stopper cork products.

Only the best quality planks are chosen for whole corks and technical stoppers.

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