It's a reasonable question. Why not, for example, just use a spray dryer to make the powder from the liquid milk? The question is answered by simple arithmetic.


It is much less expensive to evaporate water in an evaporator than a spray dryer. The evaporator is used, therefore, to evaporate as much of the water from the milk as possible yet still leave a pumpable feed, of the correct viscosity, to be atomised into the ideal droplet form in the spray dryer.

Consider this:

Say we start with 1000kg of liquid whole milk which has 125kg of dry solids (12.5%). The spray dryer needs a feed at approximately 50% dry solids. To achieve this the evaporator must remove 750kg of water (leaving 250kg of feed at 50%). The remaining water, up to 125kg, can then be removed in the dryer. This means that the evaporator has removed over 85% of the water (750kg out of 875kg) leaving the dryer to remove as much of the remainder as is required.

The figures are even more impressive for skimmed milk @ 9% dry solids (90% of water removed by evaporator) or whey @ 6% dry solids (96% water removed by the evaporator).

That's why you need an evaporator. To find out why you need a good evaporator, click on Choosing The Right Dairy Technology