What is the correct position for storing champagne or sparkling wines-- vertically or horizontally?
Answer From Expert Roger Bohmrich MW
You will find some knowledgeable wine people who say that Champagne does not have to be laid down because the internal pressure acts to "seal" the cork in the neck of the bottle. There may be some validity to this, but it is the riskier option. Why run that risk, particularly with an expensive bottle? I would argue that it is always better to keep liquid in contact with the cork. This is the most secure way to store all wines with such closures, still or sparkling, and is certainly best for long-term cellaring.
If you are simply keeping a few bottles of sparkling wine in the refrigerator for a dinner or party, no harm will be done if the bottles are upright for a few days.