Instant whole milk powder (IWMP) is designed to rapidly dissolve in water, which depends
on the particle size distribution (PSD) and agglomeration. The warm and delicate milk powder exiting
the dryer is transported via either pneumatic conveying or bucket elevators to packing. The gentleness
of this powder transport process is important for IWMP, as it can break down the agglomerates,
generating excess fines, which leads to poor dissolution properties. This work looked at the
breakdown of milk powder at two different, geographically separate, industrial IWMP plants, using the
Malvern Mastersizer, a laboratory laser diffraction instrument, and sieving, to evaluate the importance
of breakdown on the final product properties given different conveying methods. It was found that the
method of measurement affected the results, with sieves showing a larger powder size reduction
during transport as compared with the Mastersizer. PSDs with a larger average size at the start of
powder transport showed more breakdown, with a greater decrease in the average particle size.
However, the larger decrease was not enough to compensate for the initially larger average particle
size, and powder that started out with larger agglomerates at the fluidised beds still had a larger
average particle size at packing. The Mastersizer appeared to break the large agglomerates during
measurement, especially with powder that had not been through the entire transport line, thus
masking the extent of the size reduction, however this could only occur to weaker agglomerates. Thus
in order to produce IWMP with the desired functionalities, the focus should be on improving
agglomeration as oppose to reducing transport breakdown to achieve the desired particle size
distribution.
