Recently stripped corks trees in the Alentejo in southern Portugal

Everything You Could Ever Want To Know About Cork Trees

As you travel through Portugal, particularly the Alentejo and Algarve regions, you will see gnarly, reddish and rather sculptural oak trees sporting large numbers in white paint on their trunks.

These are the Quercus Suber, an evergreen Oak tree, dropping acorns and growing a thick bark that is commonly known as a cork tree - and they have a fascinating history!

Table of Contents

Where does Cork come From?

Cork comes from the bark of the cork oak tree, which is primarily found in Mediterranean countries such as Spain, Portugal, and Italy.

The bark is harvested every 9-12 years, and the process does not harm the tree. It is a renewable resource and also biodegradable.

Cork trees in the Alentejo, Portugal

It is the primary source of cork for wine bottle stoppers and a multitude of other uses, such as cork flooring and for the cores of cricket balls. 

Portugal produces about half the world output of commercial cork, and its exports over recent years have accounted for around 70 percent of world trade.

A cork tree, stripped, just after harvest

About The Cork Tree

Cork Oak is native to southwest Europe and northwest Africa where it is well suited to this climate: An abundant and evenly distributed rainfall, short summer dry periods tempered by atmospheric humidity, very mild winters, clear skies and plenty of sunshine, very permeable, moist and deep siliceous soils.

A fascinating and important tree, Cork Oak forests - Montado - support diverse ecosystems and for this reason are a protected species, with their harvesting process being heavily legislated and regulated in Portugal.

The species, which covers approximately 8 percent of the total area of Portugal and constitutes 28 percent of its forests , grows best in the central and southern parts of the country where the largest stands supplying the greatest percentage of high-grade cork are to be found.

A truck full of cork bark

A Brief History of Cork

Cork has been part of human history for thousands of years. The earliest written records come from the ancient Egyptians, Greeks, and Romans, who prized cork oak bark for its versatility.

The Romans in particular used cork to seal wine amphorae, fashion sandals, and even create roofing materials thanks to its natural insulation.

Centuries later, during the Moorish period, cork oaks continued to shape the Iberian landscape. The Moors valued cork as a natural insulator, using it in construction to keep houses cool in summer and warm in winter.

Curving road lined with cork oak trees, some with bark stripped, under a blue sky with wispy clouds.

They also expanded the management of cork forests, helping establish the montado system - a unique balance of agriculture, grazing, and forestry that still defines much of southern Portugal.

By the 18th century, cork production had become an economic cornerstone, with Portugal emerging as the world’s leading supplier. Exports boomed, especially after glass bottles became standard for wine, and cork stoppers were in high demand.

Towns across the Alentejo and Algarve thrived on the trade, and families passed down harvesting techniques much the same way they are practiced today.

That legacy continues: Portugal now produces over half the world’s cork, with traditions rooted deeply in history but adapted for modern sustainability.

Cycling through the cork oak landscapes of the Alentejo or visiting factories in the Algarve, you’re tracing a living heritage that links ancient Rome, Moorish innovation, and today’s global wine culture.

How is Cork Harvested?

Every year from Mid May to Mid August , well-trained seasonal harvesters stage their harvest of the Cork Oak in Portugal.

Once a tree is about 25 years old it can be harvested for its ‘virgin cork’ and then every 9 years after the cork ‘bark’ is harvested, and the year is marked on the tree with the last number of that year (ie. A tree harvested this summer will be painted with a 9).

Portuguese law prohibits stripping the trees more than once every nine years in order to protect the species. 38 year old bark (roughly the third harvest) is when the bark becomes of high enough quality to produce wine stoppers.

The harvest of the height of the tree is determined by the diameter, if the tree is 1 metre in diameter, you can harvest three metres of the height of the tree. 

A Cork Oak lives for about 150 - 200 years on average meaning that it will be harvested about 15 times over its lifecycle. 

A cork farmer driving a tractor loaded with cork bark during the harvest

How is Cork Processed?

After harvest, trucks carry the cork to plants to be stabilized and prepared for cork stopper and other production processes. First, the slabs of bark are pressed under concrete slabs for 6 months, the cork is then sterilized using a big boiler.

Next, the cork is classified into quality grades for different uses, with experienced cork workers visually assessing the quality of the bark. Wine cork stoppers are made in the north of Portugal and then exported all over Europe.

The residual cork wood can be used for flooring and building materials (see other uses below) but also a new market in cork-based eco-fashion has become a trend in recent years.

Why Are Numbers Painted on Cork Trees?

If you ride through the cork oak forests of the Alentejo or Algarve, you’ll notice something curious: many trees have large white numbers painted on their trunks. Far from graffiti, these numbers are part of the careful system used to manage cork harvesting.

Each number represents the last year the tree was stripped of its bark. Since cork can only be harvested about once every nine years, the painted numbers help farmers know when each tree will be ready again.

For example, if you see a tree marked with “7,” that means it was last harvested in 2017 - and the bark won’t be touched again until 2026.

This practice not only keeps the industry organized but also highlights the sustainable rhythm of cork production. Unlike most forestry, cork harvesting doesn’t harm the tree; instead, it allows the oak to regenerate new bark, continuing a cycle that can last for centuries.

Some cork oaks in Portugal have been harvested more than 20 times in their lifetimes, each round leaving behind another painted reminder of their living history.

About the Cork Industry

The European cork industry produces 300,000 tonnes of cork a year, with a value of €1.5 billion and employing 30,000 people.

Wine corks represent only 15% of cork usage by weight but 66% of revenues.

Of the producing countries, Portugal, plays an important part in the industrial utilization of cork, and so rightly occupies the foremost position.

The cork industry in Portugal has around 500 factories, which employ about 20,000 workers, equipped with the latest machinery and utilizing the latest technological advances, enabling the industry to meet the demand for any product.

This industry produces stoppers, discs, different types of floats, shoe soles, printing paper, cigarette tips, bath mats, table mats, hat bands, fishing rod handles, different kinds of packing.

Cork wool is produced for cushions and mattresses and granulated cork employed chiefly as insulating material in ship-building, as a protective packing for fruit and eggs, and as tubing for plastic substances.

Top Cork Itineraries in Portugal

If cork trees are Portugal’s quiet giants, the best way to meet them is not from a moing vehicle window, but from the seat of a bicycle. Riding through the Alentejo or the Algarve, you’ll find yourself surrounded by the twisting trunks and silvery leaves of native cork oaks - part of the unique montado landscape that has shaped life here for centuries.

Alentejo: Cork Trees and Castles
In the Alentejo, cork forests spread across rolling hills, side by side with olive groves and vineyards. Cycling here, you’ll pass through whitewashed villages where Moorish architectural touches are still easy to spot - from fortress walls to narrow cobbled lanes.

The Alentejo Bike Tour lets you experience this blend of nature and history first-hand, pedaling past ancient cork oaks, pausing at medieval castles, and enjoying the slow rhythms of a landscape that has changed little since Moorish times.

A man pretending to bite into a slice of cork

Algarve: From Forest to Factory
Further south, the Algarve adds another layer to the cork story. Here, cycling routes take you through inland hills rich with cork oak forests before reaching São Brás de Alportel, home to one of Portugal’s traditional cork factories.

On our Algarve Bike Tour, you’ll step inside to see how bark from those very trees is transformed into stoppers, flooring, and even fashion. Along the way, the ride also passes through towns like Silves, once a Moorish capital, where history and craftsmanship meet in vivid color.

From cycling under the shade of centuries-old cork trees in the Alentejo or tracing the journey from forest to finished product in the Algarve, these itineraries really bring Portugal’s cork heritage to life - slowly, sustainably, and always with a touch of adventure.

The Biggest Cork Tree

Near the Portuguese town of Águas de Moura the Sobreiro Monumental (Monumental Cork Oak) is located, a tree of 234 years old, 16 metres (52 ft) tall and with a trunk that requires at least five people to embrace it.

It has been considered a National Monument since 1988, and the Guinness Book of Records states it as the largest and oldest in the world.

Share this article with a cork lover, or come and cycle through the Alentejo or the sunny Algarve in southern Portugal to see these spectacular trees and their native forests for yourself!

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