Bark to Bottle: The Journey of a Wine Cork

The wine cork is either overlooked or completely overthought about in a wine drinking experience.  Many people are, validly, consumed with fear that the cork may be tainted so most do not stop for a moment to consider the wonder that is a wine cork.  These days there are many different closure alternatives to natural wine cork but, since cork is the traditional method of closure, it is worth diving into the details.  The use of wine corks can be traced back to ancient times when early civilizations in Greece and Rome discovered that the bark of the cork oak tree (Quercus suber) provided an effective seal for wine containers.


Let’s start with a few of the most surprising facts about a wine cork that can probably delight even the biggest of wine nerds.  Wine corks are made through a fascinating process that begins with harvesting cork bark from cork oak trees.  These cork trees need 25 years before they are ready for their maiden harvest.  This first harvest is termed ‘virgin’ cork and is generally not very good quality.  The bark will need to regrow for a further 9 years before it can be harvested again.  On average, it will take 43 years (the third harvest of the tree) after the tree was planted for the cork bark to reach the level of quality required for producing natural corks.  Just like oak barrels, when it comes to truly comprehending the time it takes to produce something as simple as a cork, it really is a marvel!

Cork trees in Comporta Village, Portugal. Portugal exports around 65 percent of the world’s cork and is also a major importer of cork, which it uses for processing and subsequent export. There are at least 40 million cork stoppers produced daily in Portugal.


Incredibly, the cork oak is the only species of tree that can regenerate bark after each harvest – ringbarking almost any other tree would kill the tree.  The bark grows back completely, acquiring a smoother texture after each harvest.  Cork harvesting is typically done by skilled workers known as “extractors”.  They carefully remove the outer layer of the bark from the tree using specialised tools, ensuring not to damage the tree’s living ‘tissue’ underneath.


This process is labour-intensive and requires expertise to preserve the trees and allow them to regenerate for future harvests.  The process from bark to bottle is a lengthy one – it continues as follows:

  1. The harvested cork will be brought to a yard, labelled, and assigned a batch number to ensure traceability right down to the specific location of each cork forest. The cork will be stacked and ‘rested’ in this yard for several months to stabilise, developing a more even moisture content.
  2. Once rested, the planks will be sorted based on quality. The thicker, best quality planks will go on to make natural cork stoppers and the thinner planks go towards making technical stoppers or other cork products.
  3. Next, the cork planks will be subjected to a boiling process. This acts as a treatment to remove any organic compounds or impurities that may be present.  It also ensures they are at the required moisture level for pressing.
  4. After boiling, once the cork planks are at optimal moisture for pressing, they will be trimmed, prepared, assessed and sorted into categories. The sorting is based on key characteristics such as appearance, thickness, and porosity.  Only the best quality planks are selected for producing cork stoppers.  Those with defects are sent to be ground into small pieces and will be turned into other cork products, such as composite corks which are made from tiny pieces of natural cork that have been pressed into shape.
  5. The selected planks, used for top-of-the-range natural cork stoppers are cut into strips and punched with a machine, or by hand depending on the facility, to extract the cylindrical stoppers. The new ‘corks’ are then photographed by computers, and classified based on visual quality.  Many of them are rejected at this step and then ground to make other cork products.
  6. The corks go through intense sampling called gas chromatography analysis, a high-tech process that can detect undesirable characteristics, like… you guessed it- TCA or cork taint! Cork producer, Amorim has a specially patented process called ROSA Evolution.  This process puts the corks through further evaluation and then uses steam treatment to eliminate any trace of TCA.  If the minimum percentage of TCA is detected, it is immediately returned to the source.
  7. Near the end of the process, natural stoppers are polished to obtain a smooth finish. They are then washed and dried.  All these processes aim to minimize the risk of microbial contamination.  From here they will be ready for the finishing touches such as producer branding, packaging, and finally shipping out to become part of the finished product – a bottle of wine!


As one can see, from start to finish, making a cork is an incredibly laborious process. Given the many years of time, expertise and effort that go into the process, it is somewhat of a shame that corks just get thrown out without a second thought, or worse, blamed for any other fault, subpar wine, poorly aged wine, or different personal preference of the consumer.



This blog was edited and posted by Digital Squeak.