By Cristal Guiet on June 7th, 2023

The production of natural cork is a very time-consuming and labor-intensive process and therefore more costly to a winery.

Natural corks have been used since the 17th century, and are often associated with fine wines.

There is a certain air of prestige and a sense of tradition that is associated with the popping sound that a cork makes when it is pulled out of a bottle.

The ritual includes inhaling the lovely aromas that the cork has absorbed during the time it spent in the bottle stimulating the olfactory senses.

Sadly, this also could be a moment of disappointment when instead of fresh wine aromas, your nose is accosted by the horrible moldy odor of the dreaded “cork taint”.

The threat of cork taint has led many winemakers to consider choosing alternative forms of bottle closure such as synthetic corks or screw caps. Not only is the wine kept fresh and drinkable, but these alternative closures are also much cheaper to manufacture thus reducing the operating costs of a winery.

There is an ongoing debate as to whether one form of closure is better than the other.

In the following article, we will investigate the origins of these three different closures and examine the benefits and disadvantages of each one.

Natural Corks

Natural corksPhoto by Elisha Terada

Cork stoppers were first discovered in ancient Egyptian tombs. Though glass bottles were only created in the 14th century, other storage vessels were already being sealed with some form of cork.

It was only in the 17th century that there was widespread use of corks as they were very convenient for sealing glass bottles. This increased demand for cork resulted in oak cork forests being planted and cultivated specifically to supply closures.

Wine corks are made from cork oak trees that grow in the Mediterranean region of Europe.

Corks are made from an environmentally friendly material that is completely biodegradable (they take around 3-10 years to decompose completely) and are easily recycled without any toxic residues.

How is a natural cork made?

Cork is harvested from cork oak trees and Portugal is the leading producer of natural cork supplying 50% of the world's cork of which the majority is wine stoppers.

A tree must be at least 25 years old before the bark is thick enough to be harvested for the first time. Thereafter, the harvest takes place every nine years.

It is only at the time of the third harvest that the cork is deemed good enough for the production of wine corks.

The trees can live up to three hundred years, so the owners can expect at least twenty harvests that are suitable for producing wine closures.

Once the bark has been cut off of the tree it is boiled for one hour to make it flatter, the boiling also helps to kill any bacteria or insects that may have infested the cork while it was growing.

The cork sheets are then pressed flat to ease the production process. The cork is carefully examined for any evidence of remaining fungus or bacteria.

The cork is then separated into the cork that can be used for wine stoppers. The remaining cork is used to make other cork-based products.

France is one of the biggest buyers of high-quality wine corks, the Italians tend to buy ones of lesser quality, however, the Italians are beginning to move towards using screw caps and synthetic closures.

Synthetic corks

Synthetic corks
Courtesy: Wikipedia

Synthetic corks are made in the same shape as natural corks. They can be made from many different materials including glass.

For many years they have been used to replace natural cork for bottles of wine that are made for immediate consumption.

They are made from synthetic resin, taking on the shape that is desired before they are dried and then cured.

Screw Caps (Stelvin)

Screw caps have gained popularity over the past twenty years and are seen as being a reliable form of closure and around thirty percent of all wine bottles on the market are sealed screw caps.

Screw caps (aka Stelvin) are often associated with large production wineries that produce wine en masse. There is a further misconception that associates a screw cap with inferior-quality of wine. This is just not true.

The first screw cap was patented on August 10, 1889, by Dan Rylands in Barnsley UK for as a closure for whiskey bottles.

Unfortunately, the quality of the first screw caps was deplorable and they were not often used. It was only in the 1950s that a screwcap was invented for sealing wine bottles by Le Bouchon Mécanique in Burgundy.

In 1964, further improvements to the design were implemented at the request of Peter Wall the owner of Yalumba, a winery in Australia.

Peter wanted a closure that would prevent “cork taint” in his wines. The new screw caps were built with several exterior layers of aluminium alloy and a soft expandible disk line that created a seal.

Several years of innovation of the screw cap followed, however, it was only in 2000 that a group of Australian winemakers in the Clare Valley led by Jeffrey Grosset decided to use screw caps on their premium wines.

Screw caps soon gained widespread acceptance and in 2001, a group of winemakers in New Zealand tired of the ongoing struggle of “cork taint” engaged in a three-year study regarding the viability of using screw caps to seal their wines.

It was concluded that the Stelvin cap was the best way to bottle and seal their wines in optimum conditions at the same time ensuring that the consumer received the wine in perfect condition.

There have been further advances in the design of screw caps and they are even designed to mimic a natural cork, allowing a miniscule amount of oxygen into the wine which is necessary during the aging process.

This innovation means that wines that are sealed under screw caps can now plausibly age for a limited amount of time.

StelvinPhoto by

Different types of wine closures

Wine corks come in many shapes and forms and are made from wood, plastic, metal, and glass.

Types of wine corksCourtesy: advanced

Champagne corks are more complex to create and are made from three different pieces of cork, two disks of cork on the top which are connected to the longer cork at the base, which are all glued together and polished (however rest assured that none of the glue touches the Champagne).

They are more elastic than traditional natural corks and are designed to expand into a mushroom shape when they come into contact with the CO2 and the 6-8 bars of pressure that are present in sparkling wines.

Natural corks are the traditional form of closure used for around 70% of all wine bottles. As a general rule, all fine wines are sealed with natural cork.

During the aging process, complex and subtle flavors develop in the wine that comes from the wine’s contact with the cork.

Colmated corks are the same as natural corks, the lenticels (tiny pores that are seen in natural cork) are compressed by using powdered oak and a strong industry-grade binding agent. They are more reliable than natural corks.

Grainy (Agglomerate) corks are made from a combination of small particles of wood fibers and leftover granules from natural corks. The two components are pressed together to form the cork.

These low-cost corks are only suitable for sealing wine for a maximum of two years. These corks are so tight that they do not allow oxygen to enter and spoil the wine.

Technical corks have an agglomerate cork body and a disk attached to either one or both ends. The cork is less permeable than a natural cork.

Still, it is resilient which means a better resistance to alcohol and oxygen but also maintains its form despite any pressure that is produced by the liquid in the bottle.

Capped corks are a combination of plastic and natural cork with a plastic top and a cork shaft.

These corks are often used to seal beverages that are meant to be drunk in one sitting such as beverages that have a high percentage of alcohol.

Zork - invented by the Australians, Zork closures are a combination of a screw top and a plunger that eliminates the danger of cork taint and oxidation.

Helix corks - are made of agglomerate cork and have the same design as a capped cork but screw into the interior of a bottle creating the seal.

Tasting corks - A capped cork that is used to seal bottles of wine during a wine tasting and resemble a capped cork.

Vino-lok/Vinoseal - A capped cork that is made of glass and has an O-ring to create a seal between the closure and the bottle.

Crown Caps - though commonly used for beers, crown caps are sometimes used to seal sparkling wines.

Is one closure design better than the other?

This is one debate that often becomes more confusing before it makes any sense.

Below we have listed the advantages and disadvantages of the three main closure types.

Closure Type



Natural Cork

- Allows for a very small amount of air to interact with the wine (which comes from the cork itself - a cork is made up of 80% air which is compressed into it when the cork is made).

- This oxygen is necessary for most of the natural reactions of the 100+ chemical compounds that occur during the aging process, including the polyphenols that help the wine to gain and maintain its color.

- Most of the air is released into the wine during the first year spent in the bottle.

- Expands and contracts naturally ensuring that the seal between the wine and the air is always snug.

- Allows for environmental consistency which is essential for wines to age properly.

- Farming cork provides over 10,000 jobs every year.

- Cork is a renewable resource and is completely biodegradable.

- The cork trees trap large amounts of carbon dioxide which helps to lessen pollution.

    - Cork Taint (TCA which is caused by the fungus L’Armillaria Mellea which is a parasite that is found in the cork oak) - However, manufacturers of natural corks are working tirelessly to reduce the occurrence of cork taint by using a more thorough and careful screening and production processes to ensure that wood is free of any defects such at TCA.

    - About 3% of all bottles of wine in the world that are sealed using natural corks have TCA according to the Cork Quality Council.

    Synthetic Corks

    - The risk of cork taint is minimized.

    - Lighter than natural corks.

    - Cheap to manufacture.

    - Are not very durable so have a short lifespan.

    - Do not allow the wine to come into contact with air so not suitable for ageing wines.

    - Are rigid in shape and therefore do not expand and contract in the neck of the bottle which can lead to the unwelcome intrusion of external oxygen, potentially rendering the wine undrinkable due to oxidation.

    Stelvin (Screw Cap)

    - Elimination of TCA Allows enough oxygen to enter the wine thus making it possible to age wines for a decent time period.

    - Easy to open and also reseal opened bottles of wine and keeps the opened wine fresher for a longer period of time.

    - It can be stored upright thus maximizing storage space.

    - On very rare occasions can be pierced with sharp objects which creates a microscopic hole in the seal which causes the wine to become oxidized. - In rare cases, bacteria can be trapped in the bottle.

    Is the type of closure that your bottle of wine is sealed with important?

    The answer is very dependent on what type of wine you are buying. We have learned that the screw cap has undergone massive innovations and therefore is a very good alternative to natural cork.

    If you are buying a young wine that is destined for immediate or short-term consumption then a synthetic or agglomerate cork is a perfectly suitable form of closure.

    Screw caps are a guarantee of no cork taint, and are a perfect closure for immediate and short-term consumption but are also suitable for aging wines that already have good structure, body, and tannins at the time of bottling.

    If you are purchasing wines for long-term aging, a natural cork is still the best option as it is perfectly designed for long-term ageing. It is clearly obvious if a bottle has a Stelvin closure.

    However if you are unsure of what type of cork has been used to seal your bottle, your local wine professional will be able to assist you.


    Author: Cristal Guiet

    Cristal has more than twenty three years of experience in the wine industry. In addition to creating wine lists in Michelin three-star restaurants, working with prestigious London wine merchants, and starting her own wine tourism company in France, Cristal has been writing about wine for over fifteen years. She holds the Advanced degree from Wine and Spirits Education Trust (WSET), and resides in London.

    Difference between Natural corks, Synthetic corks, and Screwcaps

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