Just One Glass
If you are enjoying the peace and quiet of time alone and only want a single glass of wine, don't decant the whole bottle.
Simply pour a glass, leaving the remainder in the original bottle. Quickly replace the cork (hint: turn it upside down and it will push back into the mouth) to help preserve the free sulfites within the bottle. There are many reusable replacement corks available that are a great convenience if you rarely drink the entire bottle.
By quickly replacing the cork, the shelf life will be extended, but how long the life will be depends upon the wine varietal, the temperature at which it is stored, and the amount of sulfites that were left in the wine. Refrigerated wine will remain fresher for longer periods.
Swirling the wine in the glass will introduce oxygen and release the free sulfites, imitating the Decanting process. Enjoy!