Concentration of acid whey followed by spray drying is severely obstructed due to presence of lactic acid (LA) and calcium (Ca). These compounds first prevent lactose crystallisation and consequently cause stickiness during spray drying and caking upon storage of the powders. The present study examined the effects of the presence of LA, Ca and their mixtures on the physio-chemical and thermal properties of spray dried lactose powders. Spray drying of pure lactose achieved a yield of similar to 81%, which was significantly reduced in the presence of high concentrations of LA (1% w/w) or Ca (0.12% w/w) yielding only similar to 52%. Powder particles increased in size giving a D[4,3] of 956 gm, with SEM images confirming the presence of linked strands instead of well separated spherical powder particles as observed for pure lactose. The yield of crystalline lactose increased with subsequent decrease in Ca concentration (similar to 81%) resulting in well separated spherical powder particles. FTIR analysis suggested that water molecules in the hydration layer of lactose and the structural changes of the lactose molecules at the molecular level appeared to play major roles governing the thermal anomeric characteristics of the spray dried lactose powders in the presence of both LA and Ca. Formation of calcium lactate, which apparently restricted the diffusion of lactose molecules, partly played a role in changing the anomeric properties of the spray dried lactose powders, once the appropriate stoichiometry was reached. Manipulating lactose-water interactions via mutarotation between a and 13 anomeric forms of lactose in acid whey may improve the crystallisation behaviour of lactose and thereby address some of the processability issues. (C) 2016 Elsevier Ltd. All rights reserved.