In this example, partial homogenization is used, so only the cream is treated. The reason for choosing this system is that it can manage with a smaller homogenizer (12) and thus consume less power, while still maintaining a good homogenization effect.
The working principle of the system, also described in Chapter 6.3, will be: After passage of the standardization device, the flow of cream is divided into two streams. One, with the adequate hourly volume to give the market milk the required final fat content, is routed to the homogenizer and the other, the surplus cream, is passed to the cream treatment plant. As the fat content of the cream to be homogenized should be a maximum of 18 %, the ordinary cream of, say 40 %, must be "diluted" with skim milk prior to homogenization. The capacity of the homogenizer is carefully calculated and fixed at a certain flow rate.
In a partial homogenization arrangement, the homogenizer is also connected with the skim milk line so that it always has enough product for proper operation. In that way, the relatively low flow of cream is compensated with skim milk up to the rated capacity. Following homogenization, the 18 % cream is eventually mixed in-line with the surplus volume of skim milk to achieve 3 % before pasteurization. The milk, now with standardized fat content, is pumped to the heating section of the milk heat exchanger where it is pasteurized. The necessary holding time is provided by a separate holding tube (14). The pasteurization temperature is recorded continuously.
A booster pump (13) increases the pressure of the product to a level at which the pasteurized product cannot be contaminated by untreated milk or by the cooling medium if a leak should occur in the plate heat exchanger.
If the pasteurization temperature should drop, this is sensed by a temperature transmitter. A signal activates the flow diversion valve (15) and the milk flows back to the balance tank. See also Chapter 7.
After pasteurization, the milk continues to a cooling section in the heat exchanger, where it is regeneratively cooled by the incoming untreated milk, and then to the cooling section where it is cooled with ice water. The cold milk is then pumped to buffer tanks and then to the filling machines.