The significance of powder breakdown during conveying within industrial milk powder plants

•Two industrial milk drying plants produced powder of different functional quality.•It was expected that this was due to different particle breakdown during transport.•The change in particle size between the two industrial plants was comparable.•Powders with a larger particle size initially had a larger particle size after conveying.•Focus should be on making the correct particle size pre-transport, not on conveyor optimisation.

Instant whole milk powder is designed to rapidly dissolve in water, which depends on the particle size distribution (PSD). The fragile powder exiting the dryer is conveyed for packing which breaks down the particles, worsening the dissolution properties. This work investigated the effect of conveying on the final functional properties using two industrial plants with differing transport systems; a pneumatic system and bucket elevator. It was expected that the plant with the bucket elevator consistently produced powder with superior dissolution due to lower breakdown during transport. This was evaluated using the change in PSD. It was found that the plant with the bucket elevator had at least as large a change in the median particle size as the plant with the pneumatic transport system, contrary to the expectation. However, the plant with the bucket elevator had an initially larger particle size, and so the percentage of fine particles that negatively impact dissolution, remained low post transport. When quantified using the change in bulk density, having an initially low bulk density compensated for large increases in bulk density during conveying and powder with lower bulk density pre-transport showed better wettability post transport. Thus in order to produce powder with the desired functionalities the focus should be on improving the initial agglomeration and generating larger particles and lower bulk density pre-transport, as opposed to optimising the powder transport.

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