How cork is harvested: the bark regrows and the tree is left standing

Cork is harvested from the cork oak, Quercus suber [3]. Amorim describes the harvest as taking place "without any tree being felled" [1]. Amorim also says the cork oak is the only tree whose bark regenerates [1].

The tree is stripped, left to regrow its bark, and stripped again. For how cork behaves once it is a board, see cork and pin boards: material and behaviour.

A cork oak is not stripped young. Amorim says it takes each tree 25 years before it can be stripped for the first time [1]. Another Amorim page describes the same age together with a trunk diameter of 70 centimetres [3]. The same page says the trunk is measured about 1.3 metres above the ground [3].

The first bark is called virgin cork. Amorim says it does not have the desired quality [2]. The first cork to reach "the ideal conditions for the production of natural cork stoppers" is the third stripping, about 43 years after planting [2].

After the first harvest, the tree is left to regrow its bark. Two Amorim pages describe harvesting every nine years [1][2], and another Amorim page describes later strippings with an interval of at least nine years [3].

Amorim says a cork oak lasts about 200 years on average and may be stripped around 17 times in that life [1]. The table below sets out the cycle in one place.

Work happens between May and August [1][2]. Amorim says this is the tree's most active period of growth [1][3].

One Amorim page adds that the bark is easier to remove then [3].

One Amorim page says the stripping is done by specialised professionals who use a single tool, the axe, and that it is carried out manually [3]. Another describes a vertical incision, then a horizontal one [2].

After each stripping, Amorim describes an "original process of self-regeneration of the bark" [3]. The bark grows back completely and acquires a smoother texture [2].

Each tree is also tracked: a number from 0 to 9 is painted on the trunk to show the harvest year [2].

Every published figure here describes one producer's own practice, so treat it as background on the material, not as a description of any particular board or supplier. The guides do not say how timing varies between producers or regions. If a cork claim matters to your order, ask the supplier for its own written description of where its cork comes from and how it is processed.

Amorim's page on the process describes harvested planks being stacked outdoors for a minimum of six months, boiled for one hour in stainless steel tanks, and graded by appearance, thickness and porosity [2]. Other producers' processes may differ, and the guides do not cover how boards are made.

For a buyer, the practical point is that the bark, not the tree, is the raw material, and that each stripping is separated from the next by years of regrowth. Because cork is graded by appearance, thickness and porosity [2], ask a supplier to confirm in writing which cork type a board uses, for example natural bark sheet or agglomerated cork; see agglomerated cork vs cork bark sheet in pin boards. If you are choosing between surfaces, read pin, cork, magnetic or glass board: which to choose, and for larger orders see the boards buying guide for offices and schools.

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1. Cork, Amorim Cork (amorimca.com). amorimca.com
2. Raw Material and Industrial Process: From bark to bottle, Amorim Cork. amorimcork.com
3. About the oak tree, Amorim Cork Solutions. amorimcorksolutions.com