What is an appropriate action when storing leftover wine?

Sealing leftover wine tightly and refrigerating it is the appropriate action because this method helps preserve the wine's taste and quality for a longer period. Exposure to air can lead to oxidation, which adversely affects the flavors and aromas of the wine. By sealing the bottle, you minimize the amount of air that comes into contact with the wine, thereby slowing down the oxidation process. Refrigeration further helps maintain a stable temperature and slows chemical reactions, allowing the wine to remain enjoyable for several days after opening.

Other methods, such as leaving the wine open at room temperature, would accelerate spoilage due to increased exposure to oxygen and warmth. Adding sugar to the bottle is unnecessary and can alter the flavor profile in an undesirable way. Pouring wine into a smaller container might seem viable to reduce air exposure, but if the smaller container is not sealed well, it can still lead to rapid oxidation. Therefore, sealing and refrigerating are the best practices for preserving leftover wine.