How can I check if my flour is self-raising or plain? If I have some unlabelled flour in the cupboard, is there a way I can determine if it is self-raising flour or plain flour, before cooking with it and just checking if the cake rises? :)
Put your flour in water.  It should be slightly fizzy due to the presence of baking powder if it is active self raising flour.  If it is plain it should react like normal flour.