rava idli batter can be preserved for the next day when it is stored in a refrigerator. but remember to keep the batter for the next day before adding eno to it. once eno is added, it cannot be preserved. so take a proportion of rava batter in a bowl, preserve it in the refrigerator, add eno to the remaining batter, and steam idlis. the batter stays good for a day when kept in the refrigerator. as curd is added to the batter, do not preserve it for more than 2 days as they may turn sour and you might get sour idlis.