A bottle of wine needs a closure to prevent rapid oxidation and facilitate transport.
The three main practical systems currently employed worldwide are closures (stelvins), synthetic corks and “real” corks. They work in different ways and deliver different outcomes.
A stelvin screw top closure creates a perfect seal. It is the modern day solution to ensuring no air is allowed to enter a bottle, offering also a very practical simple method of opening. A capsule closure typically consists of an aluminium screw cap with internal barrier seal which prevents air ingress. No corkscrew requied!
Synthetic or plastic corks also create an effective oxygen barrier between the wine and outside world. They are useful for wineries with cork insert bottling plants that want a risk free low cost solution to sealing a bottle. They do require a corkscrew to open and are sometimes hard to remove.
Real corks range enormously in price and quality. The purpose of a real cork is that, over time, it will pass a tiny quantity of air which helps the wine mature. The main downside with a cork is the risk of a “bad cork” giving the wine a so called “corked” undrinkable taste. Newer technical corks remove the adverse taints and also provide a very easy closure to remove with that characteristic “pop” but do not break into pieces.
Some wines, particularly less expensive white and red wines, do not benefit from a cork and gentle ageing process and hence a cheaper closure is practical. For high quality red and dessert style white wines, a good quality cork or technical cork combined with steady ongoing ageing in bottle is critical and cork is still the closure of choice in these cases.