Either for stirred Yoghurt or solidifying yoghurt, milk pretreatment is same, it includes the standardization of fat and dry matter content, heat treatment, and homogenization. the milk is pumped to the milk storage tanks. Herein, assuming that the milk fat is standardized before going into production lines, and the dry matter is standardized in the evaporator. If the dry matter content is adjusted by adding milk powder, the equipments are similar to milk remanufacturing. Any additives, such as stabilizing agent, vitamin can be quantitatively added into the milk before heat treatment.
When the raw milk is cooled to the inoculation temperature after pretreatment temperature, further processing technology should be determined according to the solidification type, mixing type, drinking, frozen or concentrated yogurt. Yogurt organization status and the flavor is important index in determining the quality of yogurt.
Pretreated milk is cooled to the culture temperature, and then continuously pumped to the fermentation tank with the required volume of starter cultures. After the tank is filled full, then start to stir for a few minutes to guarantee the starter evenly dispersed. Fermentation tank is insulated to ensure constant temperature during the whole cultivation. pH meter is installed In order to inspect the tank acidity developing. the typical type of the cultivation is product ion time about 2.5 3 hr, 42-43 ℃ , using the normal production of starter cultures (quantity of 2.5-3%).In order to get the best product, when the pH value achieves the ideal value, bacteria fermentation must be terminated, the temperature of the product should be cooled from 42-43 ℃ to 15-22 ℃ within 30 minutes. At the same time mechanical processing of clot must be softened in order to ensure the viscosity of finished product. Cooling is carried out in a special plate heat exchanger (8), so that the product is not affected by the strong mechanical disturbance. After cooling to 15-22 ℃ , the sour milk is prepared for packaging. Fruit material and spices are added during the conveying process from the buffer tank to the packaging machine, which are added continuously into the yogurt through a variable speed pump and then mixed together. the mixing device is stationary and sanitary, and ensure that fruit material and yogurt mix thoroughly. Fruit material metering pump and yogurt feeding pump is synchronous operated.