The process of converting milk into yoghurt involves the bacterial fermentation of cow milk. The milk sugar or lactose is transformed into lactic acid, which then has the effect on the milk's protein of giving it a more consistent texture and taste. The bacteria is administered in controlled conditions and temperatures, with the level of acidity regulated in order to prevent extra bacteria, which is killed off. Heat treatments also increase the protein level of the milk. The live action culture that remains as yoghurt is believed to nutritionally positive, while pasteurized yoghurt, subject to higher levels of bacterial regulation, has a longer expiry time. Flavours and different consistencies can be added to the yoghurt during its production in order to produce different effects. Types such as frozen and drinking yoghurt are subject to increased 'breaking' or reduction in consistencies, while frozen yoghurt is also blended with solid ice cream to produce its particular quality.
