As it can be seen from Fig. 132, the majority of the lactose is crystallized after 3-4 hours. A continuous semi-crystallization process has therefore been developed. The resulting powder exhibits good physical properties.

Fig. 132  Lactose crystallization as a function of time

The whey is precondensed to 50-52% solids, after which it is flash-cooled to 30ºC. The concentrate is pumped to an ordinary single-walled tank equipped with an agitator. The volume of the tank corresponds to 2-3 hours production. The concentrate is seeded as described above in order to start the crystallization.

When the tank is full the product is discharged at the same speed as new product is pumped in. The semi-crystallized concentrate is pumped to flash cooler No. 2 where it is cooled to 15ºC and pumped to a new tank with a volume corresponding to 2-3 hours in order to finish the crystallization. Because of the heat created by the crystallization, the temperature will increase by 2-3ºC. When the tank is full the spray drying is started. See Fig. 133.

Fig. 133 Evaporator, two flash coolers with crystillization tanks,
and a compact dryer for continous production of semi-crystallized whey powder