Influence of Drying Methods on Density and Porosity of Milk Powder Granules

Abstract

Using He as the displacing gas, there was rapid penetration of conventional spray-dried, spray-dried foam and vacuum-dried foam particles; all whole milk powders had true densities averaging 1.30 g/cm3. The measured true density of a commercial instantaneous skimmilk powder was 1.48 g/cm3. With H2, N, decalin or Hg as a displacing medium, there was a wide variation in the porosity of particles produced by different drying technics. Conventional spray-dried material contained small amounts of occluded gas exchanged only with great difficulty, if at all. Spray-dried foam particles contain relatively large volumes of gas which can undergo exchange slowly and completely. The small quantities of trapped gas in vacuum foam-dried particles can undergo rapid and complete exchange.