How they get corks into bottles
The traditional method was to insert a dry slightly-smaller-than-the-neck-of-the-bottle
cork and let the
wine soak into the cork, causing it to expand. Because some wine would often leak around the cork and go mouldy,
bottle top wrappings were added to conceal the unsightly
mould. Contrary to popular belief, this does not spoil the wine - it just doesn't look too nice.
Today most companies use a corking machine which creates a
vacuum inside the bottle causing the dry cork to be pulled in. Typically the wine should be between 18ºC and 22ºC otherwise the wine will expand/contract when its temperature changes - causing the cork to be pulled in or pushed out. Again the cork is left to absorb some of the wine which causes it to swell slightly.