Shrinkage behaviour of skim milk droplets during air drying Original Research Article

Industrial spray drying of milk powder production utilises high solids feed at around 50 wt.% or higher; however there are only a few fundamental studies investigating the droplet drying behaviour. The present work studied the shrinkage behaviour of 50 wt.% skim milk droplet during drying. Temperature effects on both shrinkage kinetics and total diameter reduction were found to be different from low solids milk drying. A high drying temperature at 110 °C led to negligible droplet shrinkage at X range between 1 and 0.3 kg/kg. An increase in temperature resulted in larger particles after drying. The high initial solids could sustain the droplet shape and hinder solute diffusion; as such droplet shrinkage behaviour deviates from the description of ideal shrinkage kinetics. A general correlation of shrinkage coefficient b was established for skim milk with initial solids content of 10–50 wt.%, useful for estimating droplet shrinkage kinetics within this range.