Natural cork is the traditional wine closure that allows a small amount of air to pass through for wine maturation. However, corks can be tainted by a mould called TCA (trichloroanisole), which imparts a stale smell like wet cardboard into the wine, and causes the wine to lose its aroma. If the cork is only slightly tainted, most consumers will not notice the smell but the wine will still be affected, usually resulting in mute aromas and short length. A lot of consumers then blame the wine, believing it is badly made. While there is no official statistics on the percentage of cork-tainted wine, various researches showed that it ranges from 1% to 7%.
Plastic (or synthetic) cork was then developed to remedy the issue. While plastic cork seals properly, it loses elasticity over time (about 12 months) therefore it is not ideal for wine that is intended for long ageing. It is also tighter therefore more difficult to pull out.
Screw cap, also called Stelvin cap, was a project initiated in early 70s by Australia wineries again to protect the wine against cork taint. In the early days, screw capped wine could taste like burnt matches because the absolute lack of airflow into the wine led to reduction. However, exactly because of the lack of air, wine tasted fresher and fruitier for a longer period.
With technological improvements and better hygiene, the problems of cork taint and reduction are now greatly under control. Cork manufacturers apply 100% quality check to their top quality corks for taint before shipping while screw cap manufacturers can control the amount of air going through the cap, so customers can decide the airflow they would like in the wine based on the ageing potential.
Therefore, the choice of closures is really up to the wineries. We can find all kind of closures at all price levels. Some wineries use a mix of closures depending on their export markets. Generally speaking, New World producers tend to use more screw caps. UK consumers prefer screw caps for convenience and saving of opened bottles. There are also more white and rosé wines under screw caps to preserve the fruitiness. Plastic cork, by comparison, is less common compared to natural cork and screw cap but some consumers like the sound of ‘pop’ when pulling out the cork which a screw cap cannot satisfy. In addition, plastic cork comes in different colours offering more flexibility in terms of marketing.
The latest closure is a combination of plastic and glass called Vino-Seal, but it is expensive and requires a different bottling line therefore it is not common.
Only cork closure and crown cap (uncommon) are used for sparkling wine as it can withstand the pressure inside the bottle therefore sparkling wine can can be affected by cork taint as well.