If you can't finish a bottle of wine but don't want to toss out the remaining amount, Redditor Axel927 suggests a cheaper alternative to wine stoppers or other tools: just pour the leftover wine into a smaller container.

The reason has to do with wine oxidizing due to exposure to O2 in the air. This starts a chain reaction in the wine, forming hydrogen peroxide followed by acetaldehyde, which affects the taste. This process can start almost as soon as the wine is uncorked (or once the cork starts to fail).

The best method is to store it in a mason or canning jar, and make sure the seal is airtight before stashing it somewhere that is 70 degrees F or cooler. As long as the wine takes up most of the container volume, then there will be less room for air.