Natural Corkstopper production

ACI’s corkstopper production process description

Producing a corkstopper was, for a long time, a task based on a family handcraft tradition.
The enclosed industrial tradition that existed in Portugal and the low professional training in this area led to the successiveness of errors when handling this material, errors that were passed on for generations.

ACI, a company that analyzed all corkstopper production steps from the cork oak to the bottle, identified all the critical control points of the process where TCA formation could occur (TCA-CCP).

After having achieved this identification, the R&D task force developed both innovative systems that would be capable of extracting possible undesirable compounds and preventive procedures to avoid its formation.

Now, a brief description of the production process:

1)Cork Harvest

After the cork harvest, the corkwood planks are placed randomly on the ground, while they wait to be collected.
It is important that the planks are placed with the belly (the part in contact with the trunk of the tree) facing up so that the sap dries faster, making the plank drier on the side where more moisture is present. This way, we minimize the microbiological development and the appearance of greenwood.
Other very important step is taking the corkwood planks out of the forest soil onto an appropriate “parking” spot.

2) Seasoning

This step has the main goal of oxidizing the products “brought” from the tree, making them chemically more inert.
Here, the corkwood planks are stored in piles with low height, randomly distributed so that the ventilation between piles is facilitated, also allowing a space of about 6 meters between piles.
This distribution allows paths for water drainage in order to avoid microbiological growth, one of the most common causes of the appearance of off-flavours.
The pavement used in this storage area is cement, with a slope sufficient to assure the drainage of the pluvial waters.

3)Cutting the wedges

The wedges are the bottom part of the corkwood plank, the part that was in contact with the soil.
After the seasoning period and before boiling, the wedges are cut.
Due to the higher intensity of microbiological activity in this part of the corkwood plank, the probability of TCA formation is very high.
Hence, the need for its physical elimination. In order to do that, mobile cutting systems go from pile to pile to separate this undesired part of the corkwood.
This cork material, after separation, is ground and the resulting granules are used in other applications, such as decorative products.

4)Boiling

The boiling of the corkwood is the operation within the production process where there is a bigger opportunity of releasing volatile compounds and where TCA existence can be screened batch by batch.
For many years, this operation was not given the necessary importance in what corkwood cleaning is concerned.
The boiling operation was performed with the single purpose of making the corkwood more flexible so that it would be easier to work with.

ACI, being aware of the importance of the operation, developed a boiling system that, besides allowing a high release of volatile compounds, was able to establish a relationship between the TCA contents in the condensed steam released from the controlled opening of the boiling system and the releasable TCA contents in the corkstoppers that will be produced from each cork batch.
This way you can control, batch by batch, the corkwood that will be used in the production of corkstoppers.

The batches that are considered “risky” will be visually re-inspected and go through re-boilings until the TCA values on the condensed steam are within the previously established parameters. This is the most important control point of the whole process. The system also determines if the TCA contamination is superficial or in the core of the corkwood tissue. When the contamination is deep in the core of the corkwood, the batch will be visually re-evaluated to check for the existence of wedges and will remain untouched for at least 3 days before it is again submitted to the boiling process.
The resting period has as main goal allowing the TCA to migrate to the surface of the corkwood planks so that it can be more easily extracted by the boiling system.
ACI’s boiling system consists of an autoclave with controlled opening, allowing temperature levels of about 100^o C. With this temperature and with the existing movement between the corkwood planks within the autoclave bed, the volatile compounds have a higher possibility of leaving the corkwood.
Concerning the control analysis, this is performed directly via SPME, only depending on the running time of the GC.
On the following day, the analysis results of each batch are evaluated, selecting the ones that go straight to corkstopper production. The corkwood planks selected through this process are put aside for 5 days in order to stabilize both moisture and size.

5) Corkwood Sorting

After the 5-day resting period, the planks are sorted both by grade and size. During this operation, planks that show problem such as yellow stain are set aside. The stain appears on the bark of the corkwood, being easily identified by its visual aspect. Its appearance is due to a specific type of fungus that can generate TCA. These planks will then be used to the production of other cork products, such as decorative materials.

8) DrasRed

Prior to the mechanical finishing of the corkstoppers, these are submitted to odor removal process using steam, baptized DrasRed (stands for “drastic reduction”)
As said, this system uses dry steam as main extraction agent.
Taking in consideration the dynamics of this system, a “Venturi” effect is generated in the porosity of the corkstopper, allowing an effective extraction of eventual contaminants in its interior.
Studies were conducted on the addition of solvents to this system in order to evaluate possible benefits of its inclusion. The reached conclusion was that the increase in the effect did not justify the increased environmental pollution they generated.
With the data available nowadays, the TCA decrease that occurs with this process is sufficiently effective to face the contamination degree that exists in our production process.

11) Washing

The washing of the corkstoppers is other production operation where there is an opportunity to diminish a possible TCA contamination.
The usage of high oxidative solutions together with the mechanical dynamics of the washing system generates a decrease of about 25% of the releasable TCA content.

12) Drying

The drying process is another step where there is an opportunity to decrease any TCA contents left.
Bearing in mind that TCA is volatile and that the drying uses enforced hot air, conditions are together to cause release of volatile compounds.
Maintaining moisture in corkstoppers bellow 8% is one of the requirements to avoid microbiological growth.

15) Packaging

The package has as purpose the maintenance of the corkstopper in perfect conditions until its usage.
As so, a sealed polyethylene bag is used, in which interior SO₂ gas replaces the air. This gas is used in order to achieve a very low possibility of germ contamination inside the bag.
To correctly store this package, the storage area should maintain adequate temperature condition (15^o to 20^o C) with moisture levels of 50% to 70% so that the corkstoppers are kept in perfect usage conditions.