A method of producing microparticles by spray drying comprises the steps of providing a spray-drying feedstock solution comprising water, a volatile divalent metal salt, weak acid, 5-15% dairy or vegetable protein (w/v) and 1-20% active agent (w/v). The feedstock solution is adjusted to have a pH at which the volatile divalent metal salt is substantially insoluble. The feedstock solution is then spray-dried at an elevated temperature to provide atomised droplets, whereby the volatile divalent metal salt disassociates at the elevated temperature to release divalent metal ions which crosslink and aggregate the protein in the atomised droplets to produce microparticles having a crosslinked aggregated protein matrix and active agent dispersed throughout the matrix.
