Dosa batter can typically last for about 12-24 hours without refrigeration, depending on the ambient temperature and humidity. After this time, it's likely to become overly fermented and sour.
Dosa batter is a fermented mixture of rice and lentils. The fermentation process is driven by microorganisms that thrive in warm environments. Without refrigeration, these microorganisms multiply rapidly, accelerating the fermentation. The ideal temperature for fermentation is around 80-90°F (27-32°C). At room temperature, which is usually around 70-75°F (21-24°C), the batter will ferment more slowly than at higher temperatures, but still significantly faster than in a refrigerator.
The fermentation process produces lactic acid, which gives dosa batter its characteristic sour taste. While a slight sourness is desirable, excessive fermentation will result in an overly sour and unpleasant taste. The batter may also become too thin and watery, making it difficult to spread on the griddle.
Several factors influence how long dosa batter can last without refrigeration:
To extend the shelf life of dosa batter, it's best to refrigerate it as soon as it has fermented to the desired consistency. Refrigeration slows down the fermentation process significantly.
If you need to store dosa batter for an extended period, freeze it in small portions. Thaw it in the refrigerator overnight before use. This will help preserve the flavor and texture of the batter.