Yes, appam batter can be stored in the refrigerator after fermenting. This will slow down the fermentation process and keep the batter usable for several days.
Once your appam batter has fermented to the desired consistency (usually indicated by a slight sour smell and a bubbly appearance), you can transfer it to an airtight container. The cold temperature of the refrigerator significantly slows down the activity of the yeast and bacteria responsible for fermentation. This prevents the batter from over-fermenting, which can lead to a sour or unpleasant taste. Properly stored, fermented appam batter can typically last for 2-3 days in the refrigerator. Before using the refrigerated batter, allow it to sit at room temperature for about 30 minutes to an hour to slightly reactivate the fermentation process. This will help ensure the appams are light and fluffy. Give the batter a gentle stir before using.
To prevent the batter from becoming too sour during refrigeration, consider adding a pinch of baking soda just before making the appams. This will help neutralize any excess acidity and improve the texture of the appams.