Fermented rice sponge cakes are delicious and slightly tart, popular in Asia where they were traditionally fermented before steaming. However, the fermentation process requires skillful planning so I usually let the batter ferment overnight but then the next day I cheat and use baking powder to make it rise. The bacterial culture that is traditionally used is koji, commonly used to ferment miso and many Japanese soy products. I use a mixture of amazake(which contains koji cultures) and kefir as my culture because I find this produces a very active rice flour "sponge". But if you don't have either culture, you can experiment with whatever you have, and even catch some wild yeast if you are adventurous!
Here is the recipe I make every week:
Ingredients:
11/2 cups of rice flour
1 cup of water (or kefir)
some type of probiotic culture
2 mashed bananas
2 tbsp molasses (or any type of sweetener)
1 tbsp coconut oil
1 tsp baking powder
dash salt
oil for greasing
handful of raisins (optional)
1. Combine the first three ingredients and ferment overnight at room temperature. The next morning, it should look spongy when stirred and smell slightly sour.
2. Add the mashed bananas, molasses, coconut oil, baking powder and salt.
3. Grease a glass pan with oil and pour in the batter. Sprinkle with raisins if desired.
4. Steam the batter in a large pot on maximum heat for 20 minutes.
5. Carefully remove glass pan and cool. Serve warm.
*To make the batter rise naturally through fermentation, omit the sweetener, bananas, and baking powder. Anything sweet will turn sour because the mixture will have to sit in the glass pan after the salt and oil is added. Steam for 15 minutes and drizzle the sweetener on top of the sponge cake instead.
*Sponge cakes lose their heavenly soft texture after 2-3 days so do not leave it in the refrigerator for too long! Make sure you warm it up in the microwave before eating.