Fat powders are popularly made by the technique of spray drying (Blenford, 1987).
The fat is first made into an O/W emulsion with an aqueous solution of carrier powder
(e.g. milk power, starch, dextrin). The emulsion is then supplied to the spray tower
atomiser by a high-pressure homogeniser to ensure the feed is homogeneous. The fine
spray of emulsion droplets is projected into a hot air stream to evaporate the moisture.
The moist air and fine particles are collected in a cyclone, and the dry fat powder is
collected at the base of the drying chamber.
The design of spray driers has advanced significantly from the single-stage spraydrying
system, in which the drier discharge tended to be at a relatively high temperature,
to the double-stage and triple-stage systems, which reduce the energy consumption
so that the product can be produced at lower temperatures. Thus more temperaturesensitive
and high-fat products could be handled. Figure 2.11 shows the layout for a
simple single-stage system.
As with powdered fats, the design of the atomiser is critical to the success of
the plant. The geometry of the spray chambers is also very important, where the air
flow can be counter or concurrent, and it is important that the spray must not strike
the tower wall until dehydrated, otherwise it will stick and burn onto the wall and
ultimately interrupt the air stream. The volume of air, its velocity and temperature
must be controlled to be consistent with the heat sensitivity of the product.