Oak, a natural product from the cork oak tree is harvested after every nine years. Cork oak trees reach maturity at the age of 20 years when harvesting is done for the first time. This initial harvest is usually of poor quality, density and volume. The process is repeated after nine years, but after every harvest, a mark is put on the tree to indicate the next time it will be ready for harvest.

This is to avoid harvesting before time. Most of the cork oak trees are found in Spain and Portugal with the later accounting for half of the world’s cork production. The production of cork can go on for 150 years.

The cork, which serves as a natural insulation for the trees has many uses. It is light, does not get affected by water or insects and is a great insulation material when harvested. The insulation is made possible because of the air and space that is found between the cells. It also insulates the trees against fires. This is especially important in the hot Mediterranean regions where bushfires are a common occurrence. The most common use is the manufacture of cork, which is used as bottle stoppers. Here is the process on how to make cork.

1. The Harvest of Cork

It all begins with locating the trees that are ready for harvest. When harvested before time, the cork will not have achieved the right density and thickness. The harvesting process is careful not to mess with the actual tree, that is, not cutting the live tree.

Portions of the desired size are achieved by making horizontal cuts at the base of the branches or the tree trunk then cutting vertically to free the parts from the tree. A special hatchet is used for this work.

After harvesting, the pieces are left in an open area to cure. This process can take one to six months with chemical reactions taking place because of the exposure to sunshine, rain, and air.

By the end of the process, the cork will have lost close to 20% of its overall moisture and flattened for easier manipulation. Storing them on concrete rather than on the bare floor is recommended because it avoids contamination.

2. How to Clean the Slabs

The next process involves immersing the planks into hot water to remove dirt and soften them further. The water is treated with a fungicide that helps remove tannin and other water-soluble components from the cork.

They can be left submerged in the boiling water for up to 75 minutes. Boiling them in clean water avoids contamination. This process further flattens the piles making it easier to work on them.

Once they are removed from the water, the outer layer of the planks is scrubbed to remove the low-quality cork, flatten it more and remove any remaining dirt and particles. After that, the pieces are piled in a dark room for a few weeks under controlled humidity to allow them to cure further.

The next process of how to make cork involves sorting them depending on their quality and then cutting into rectangular shapes of uniform sizes. The low-quality stacks will later be crushed to make agglomerated cork.

3. The Manufacture of Cork Bottle Stoppers

The high-quality stacks are piled together and placed in a steam room for up to 20 minutes to allow them to soften. Each slab is taken through a machine that drills metal cylinders into pieces to cut the predetermined size of the cork tubes. The size will depend on the required shape and size of the stoppers.

Mostly, bottlers will determine the required size and shape. It is also possible to get other cork stopper shapes. This is achieved by passing the slabs through a machine with a specific knife angle that cuts them into particular shapes and sizes. A lot of care and precision is required to produce the right sizes and shapes and reduce wastage.

Once all the stacks have been cut into the desired shapes and sizes, the stoppers are put into a solution that cleans then sterilizes and treats them. Bleaching also takes place during this stage.

After that, the corks are dried then marked appropriately. A sealing agent such as paraffin can be applied on the corks. A further hand selection takes place where high-quality corks are separated from the low-quality ones. They are later stacked together in sacks where the air is removed and replaced with sulfur dioxide that ensures the corks remain sterile.

The process of making cork bottle stoppers also produces a lot of waste. The waste materials are grounded to produce agglomerated cork.

4. Agglomerated Cork Production

The waste cork is cut into smaller pieces then washed and dried before it goes through grinding machines. The process is to ensure the particles get small in size. More washing and drying is required after the grounding. After that, the particles are checked to ensure they are all of the same size.

The grounded cork is heaped into a mold then covered securely. A steam of 600° F is used to heat it up. The process makes the particles stick together. Baking can also produce the same effect.

The block of agglomerated cork is then coated with an adhesive. This binds the particles even more. Later on, the blocks are heated to allow the adhesive to work through the mold. They are then exposed to the air to let them cool and cure. The blocks can now be cut into the desired shapes and sizes depending on their use.

Agglomerated cork can be used to manufacture sheets for different uses. It can be used to make roofing sheets, insulating material for helmets and soundproof systems, shoe insoles and dartboards. Cork is also used to polish diamonds. Because of its versatility, flexibility and resilience, it can regain its original shape and size when pressed, it is a popular component in the manufacturing industry. It is also a great flooring material because it is not slippery.

The use of cork spans many years. It has been found in Egyptian tombs meaning that the product was still in use thousands of years ago. Even then, it was used to make bottle stoppers as well as fishing floats and sandals. The material was also used to provide an insulated roof. This kept off the cold and heat, stabilizing the temperatures in the house. Also, it was an excellent carpet.

Back then, people harvested cork from wild trees, but when its reputation grew, many people embarked on planting the trees and learning how to make cork. This has continued over the ages. Today, production of cork products is easier and there is less wastage as the manufacturing process has become more sophisticated.

Also see:

Where Does Cork Come From?
What Are Cork Cells?
Is Cork a Type of Wood?
What Tree Does Cork come From?
Are Cork Trees Endangered?
What Country is the Leading Producer of Cork?
How is Cork Harvested?