Cork stoppers are as natural as ever, but they are now increasingly high-tech !

Par J. Peyceré
Le 14/06/2022
Glass bottle closures using natural cork still remain definitively modern and highly technical. Admittedly, in the last 20 years, screw finishes have expanded their reach: first of all, in the New World (the United States, then Australia, South America and South Africa) and even in Europe, initially in the north before conquering markets including the very traditional French market, going so far as to attack the wine for ageing sector. Admittedly, in the last 20 years, the bag-in-box has also established itself in large retailers. To a certain extent, ‘plastic’ closures have also attempted to take market share away from cork. This is not to mention the elegant glass closure developed in recent years. None of this prevents the cork/glass pairing from offering a robust and flexible solution that is particularly suited to wines, beyond any considerations related to tradition and aesthetics.
Cetie Guide No.1 describes the corking of still wines and revision work on this guide has just begun in the ad hoc working group, to take the various developments in this field into account.
We continue to call them ‘still wines’, which is not a legal denomination but which is generally defined as wines having a level of carbonation below 1.2 grams per litre of liquid. By way of comparison, the range of carbonation levels of refreshing carbonated beverages and beers is in the order of 4 to 10 grams per litre, or even 12 to13 grams per litre for ‘quality sparkling wines produced in specific regions’ (QSWPSR) such as Champagne. A still wine always contains a little carbon dioxide which, depending on the palate, becomes perceptible between 0.5 grams and 1 gram per litre, although the consumer will still not associate it with a ‘semi-sparkling’ wine. This effect generates a sensation of freshness that is increasingly sought after by winemakers, particularly in some rosé wines.
In addition to developments in the wines themselves, bottling techniques have advanced, with closure in controlled atmospheres seeing strong growth. These techniques aim to limit the presence of oxygen in the headspace between the liquid and the closure, to eliminate the effects of wine oxidation. They consist in partially replacing the air in contact with the wine either with nitrogen or carbon dioxide or with a fairly high vacuum in this area. Implementing these techniques is complex to varying degrees and requires equipment that is perfectly adjusted in order to be effective. Although these various techniques have the same aim of protecting the wine, they have different effects on the physical behaviour of this headspace:
  • added carbon dioxide tends to dissolve into the wine and to reduce the effects of temperature on pressure increases in the bottle,
  • whereas nitrogen is insoluble, it will tend to amplify the pressure increase in the event of rising temperatures.
These considerations may be taken into account when selecting a closure length from among the main standards, with the usual lengths being 38, 44, 49 and 53 mm, and when selecting the bottle model and its filling level (the liquid level at which the bottle is considered to offer its nominal capacity).
Cork stoppers in particular appear to be the same as 15 years ago when the previous version of Cetie Guide No.1 was published. Firstly, however, agricultural practices for growing and harvesting cork have changed and secondly, treatments and cork stopper inspection systems have evolved, allowing what used to be an unpredictable risk?—the notorious cork taint?—to be almost completely eliminated. In addition, major standardisation work has been undertaken to thoroughly revise the ISO 633 international standard, simply titled Cork — Vocabulary, the latest version of which was published in 2019 in a bilingual French/English version. Regarding complex corks, development has continued to move forward, offering all possible functions with every desired dosage, from agglomerated and microagglomerated cork stoppers to every variation and combination of these agglutinations, with natural cork discs. These different kinds of corks are less elastic than pure cork. For the same bottle neck, they, therefore, require a smaller diameter than for pure cork stoppers. This also means that they are a little more sensitive to variations in neck diameter from one bottle to another.
Furthermore, the cork sector has also worked on end-of-life for cork stoppers, which are now all recyclable, with collection systems that are increasingly visible and available, particularly in France. Although the corks that are collected are not turned back into corks, they can, for example, be transformed into insulating material, which reduces the use of raw material.
Lastly, the glass bottles that are intended to accommodate these cork stoppers still have a plate finish with a bore diameter of 18.5 millimetres. This finish, initially defined in Cetie data sheet GME50.01 was adopted by a French standard and then by European standard EN 12726 in 2000. However, this standard included a slight geometrical modification intended to harmonise the diameters of overcaps. It, therefore, entailed a change in the diameter of bottle finishes, which could not be implemented immediately, and was finalised through to the mid-2010s by different glass manufacturers. Bottles have therefore only really been standardised since relatively recently.
To complete the picture, mention should also be made of the overcap, also called the overseal as it proves the integrity of the bottle?—this is the tamper-evident feature and is also where the seal is affixed confirming payment of excise duties in certain countries, such as France and Austria. Here the main development has been the abolition of the requirement for this label since 2018 in France. Since then, bottles can do without an overcap. This visual revolution reveals the side of the cork!
In addition, with all of the developments in first bottling and closure/overcapping machines, there is more than enough reason to thoroughly revise the Bottling Guide dedicated to final corking of wine bottles!

J. Peyceré, Cetie Secretary General, for french Magazine Liquides & Conditionnement N°418


Chaired by Jean-Marie ARACIL (FFL (Fédération Française du Liège)

The main objective of this group is to revise GUIDE N°1 to take into account the evolution in this field since the last publication (2007).
The guide focuses on the EN12726 finish closure and will address the overall functions of the natural cork closure and its limitations,
  • the functions of each component;
  • the specifications of each of the elements in relation to each other;
  • the appropriate installation conditions to fulfil the overall functions within the defined limits;
  • the end of life of corks and closure elements.
Developments in the supply of stoppers and materials will also lead to a review and possible revision of the Cetie data sheet EC3.01 - Good practices for the use of synthetic stoppers, which also dates from 2007.
The most specific aspects of this revision could be dealt with in a sub-group to maintain the dynamics of the work on Guide N°1 

Scope of the guide

This guideline applies to the capping of still wines with a cork mouth finish as per CETIE data sheet GME 50.01 which has been used as a base for the European standard EN 12726.
If the application is done on another finish, the user must carry out sealing tests to ensure that this application is technically acceptable.
The term “still wines” does not exist in the legislation. Still wines are defined as having a level of carbonation below 1.2 grams per litre of liquid, and for which the over-pressure due to carbon dioxide is below one bar in sealed containers when kept at a temperature of 20°C.
For wines with a level of carbonation above 1.2 grams per litre of liquid (but below 2 000 mg), suitable stoppers must be used (diameter above 24 mm for natural cork, to be defined for other types of stoppers). Downloads are currently available from 2008 (the revised version is under drafting stage)

       GUIDE N°1 (EN)
       GUIDE N°1 (FR)
       GUIDE N°1 (SP) (1992)
Created 01/01/1992
Status Published document
Edition First edition
Published on 01/01/2008

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