Yoghurt, yogurt, youghurt, or yoghourt (see spelling below), is a dairy product produced by bacterial fermentation of milk. Fermentation of the milk sugar (lactose) produces lactic acid, which acts on milk protein to give yoghurt its texture and its characteristic tang. Soy yoghurt, a non-dairy yoghurt alternative, is made from soy milk. It is nutritionally rich in protein, calcium, riboflavin, vitamin B6 and vitamin B12.