Once the bottle is open

in

Slipping a small silver spoon into the neck of the bottle to conserve the wine longer is a myth.

Champagne can be kept for a few days, rarely more than two, using an adapted cork stopper. This will limit the amount of gas escaping but will only have a very limited anti-oxidation effect.
Make sure you choose the right bottle shape for the number of people to be served:
A half bottle for an aperitif for 2 people
A regular bottle for 3 to 4 people
A magnum if there are more than 6 of you.

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