Closures for wine bottles come in many forms but which are the best? Screwcaps have proven a contentious issue amongst many wine enthusiasts but do they serve a purpose?

The Cork Oak

The bark of cork oak is a unique material in that it has microscopic suckers that grip the bottle neck making it ideal for sealing glass bottles.

It’s impervious to liquids, does not react with wine, and does not rot. However, cork can be affected by weevils and fungi which leads to a wine being corked or having a tainted aroma or flavour.

The cork oak grows in the western Mediterranian and Portugal. Its bark is stripped every 12 years but only the fourth, fifth, and sixth strippings produce the highest quality cork. These trees have a lifetime of 150 to 200 years.

Preparing the cork


After stripping the bark in large planks they are left out in the open air to dry for two winters and one summer before being used. As the bark dries it loses its sap and its tissues are tightened.


Once drying is complete the planks are boiled for up to 60 minutes during which time the cork will expand by around 20% and acquire elasticity. The boiling process also serves to sterilise the planks. After boiling the planks are left to dry for 2 or 3 weeks before being cut.

Producing the cork closure


The planks are cut into strips matching the length of the required cork (around 24mm being the most common size). These strips are then put through a punch to form the individual corks.


Each cork is sanded to obtain a regular and smooth surface before being washed to remove any dust.


Often a manual process, each cork will be checked to ensure that it’s suitable for use.

Other closures

Some wine bottles are closed with screwcaps or synthetic corks made from plastic foam. These closures are often used for wines that are intended to be concerned quickly within about 3 years.

Whether these closures are suitable for wines that are laid down in a cellar for long periods only time will tell.

Cork sizes

There are several sizes of cork, the most common being around 24mm for most standard wine bottles to Champagne corks that are around 31mm. Did you know that it is compulsory to label Champagne corks with information such as the vintage, place of bottling, and the name of the producer or wine?

Long corks

Long corks are generally used to seal high-quality wines that age over decades and it is common practice for winemakers to recork their wines every 25 years.

Short corks

Shorter corks are used for wine that has a shorter lifespan.

Agglomerated corks

These are corks made of many combined pieces of cork and are most commonly used for Champagne corks.

Synthetic corks

Made from plastic foam are used for wine that needs to be kept for a short amount of time.


A contentious issue! Whilst not approved of by everyone screwcaps do have their benefits. Screwcaps remove the risk of the flavours of the wine being spoilt by natural cork and premature oxidisation. In Switzerland and New Zealand, the use of screwcaps is very common.