For the Rewena starter: Boil 3 medium slices of potato with 1 cup water until soft. Cool to lukewarm and mix in 2 cups flour and 1 teaspoon sugar to form a paste. Cover and stand in a warm place until the mixture has fermented.
5 cups plain flour
1 teaspoon salt
1 teaspoon baking soda
Preheat the oven to 230°C.
Sift flour and salt into a bowl and make a well in the centre. Fill with the Rewena starter and sprinkle baking soda over the top. Combine and knead mixture for about 10 minutes, adding a little water if the mixture is too firm.
Shape into loaves or place the mixture into greased loaf tins. Bake for 45-50 minutes.