Non-agglomerated milk is usually referred to as ordinary milk powder. The most common ones are skim milk and whole milk powders.

The applied drying process may be either one-stage drying, see Fig. 113 or two-stage drying, see Fig. 114.


 


Prior to the evaporation the milk is clarified in a separator to remove dirt etc., and if skim milk powder is produced the fat is also removed.

In the evaporator the milk is pasteurized at 70-100ºC depending on the powder specification to be complied with (see page 43). The milk is then condensed to 48 50% solids depending on the milk quality and the drying system used.

The spray dryer is operated at temperatures of 180-200ºC for whole milk powder and 180-230ºC for skim milk powder.

In one-stage drying the spray dryer is operated in such a way that the powder has reached the final moisture content when leaving the drying chamber. In the two-stage drying process the primary drying is carried out to about 2-10% above the final moisture content. The excess moisture is evaporated in a static fluid bed and/or a Vibro-Fluidizer, and the cooling is done in either a pneumatic cooling system, or in a Vibro-Fluidizer.

Both rotary atomizer and nozzles may be used for atomizing the concentrate. If nozzles are used, it is necessary to heat the concentrate to 60-70ºC immediately before the atomization in order to lower the viscosity. Today most new dryers operate with heated concentrate, also if they are operated with rotary atomizers, as it, besides the pasteurizing effect, brings along 3-5% extra evaporation capacity.

Typical drying conditions are shown below:

		ONE-STAGE				TWO-STAGE
		Nozzles		Wheel		Nozzles		Wheel
		Skim	Whole	Skim	Whole	Skim	Whole	Skim	Whole
Drying temp.	ºC	180	180	200	180	210	200	210	200
Solids cont.	%	45	42	48	48	47	47	48	48

The powder can be characterized by:

Consisting of single particles
High bulk density
Dusty if it is skim milk powder
Non-instant