Stirred yogurt production starts with milk fat and proteins standardization after which milk is homogenized and pasteurized. Heat treatment temperature and time are approximately 90°C for 5 minutes.
After homogenization and pasteurization, milk is let fermenting in ripening tank/s of variable size and equipped with an internal stirring system. Milk temperature at this stage is usually between 35-44°C.
During the fermentation, with inoculated milk completely resting, important physical, chemical, microbiological, organoleptic and nutritional modifications occur completely changing the characteristics of milk. Lactic acid starters use the lactose in milk and transform it into lactic acid.
Milk pH is reduced causing the consequent precipitation of the caseins. Fermentation completed, the mass of the alive lactic acid bacteria is approximately 1% of the total mass of the yogurt. The coagulum formed and the desired acidity reached, yogurt is stirred to obtain a homogeneous and creamy structure.
From the technological point of view the coagulum rupture is a very important phase of production enabling to obtain a product without lumps and whey separation.
The cooling phase is necessary to slow down the metabolic activities of lactic acid bacteria and to start product cooling.