Cork it tight to prevent the leftover wine from getting oxidised and flat, advises Reva K. Singh in her Wine Clinic column. But if you put a regular cork back in an open bottle of bubbly, the pressure from the carbonation inside will cause the cork to pop out. Use a Champagne stopper instead.
Keeping sparkling wine chilled also helps retain the bubbles. Since carbon dioxide is more soluble in cold liquids than in warm, making sure the leftover Champagne or sparkling wine is well chilled will keep your wine fresher with more bubbles than might otherwise be the case.
Placing a metal spoon in the neck of the bottle is another way to keep the air in the bottle cooler. The bottle with the spoon gets a “cold plug” on top of the wine unlike the bottle without the spoon. The weight of this colder denser air means that less gas can escape so the bubbles are preserved.
However, no matter what method you use, your bubbly will become flat once it’s left open for more than a day or two.