Question: how to test the difference between plain flour and self raising flour?
Answer: Add about 1/2 teaspoon of each flour to separate glass ramekins or bowls. Then, stir in 1/2 teaspoon white distilled vinegar into each of the flours and watch. The flour that bubbles and foams – just a little – is the self-rising flour. The one that does not is your all-purpose flour.