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In this study, the effects of heat treatment of milk on the rheological properties and microstructure of acid milk gels formed by the hydrolysis of glucono-δ-lactone were investigated. Gels were formed from reconstituted skim milk, with or without added whey protein concentrate (WPC), which had been heated at temperatures in the range 75–90°C for 15 or 30min. The rheological properties of these gels were determined using dynamic low-amplitude oscillation in the Bohlin rheometer. The large deformation and fracture properties were studied using a low, constant shear rate method with gels formed in the rheometer. Microstructure was determined using confocal scanning laser microscopy and permeability measurements. Heating milk above 80°C resulted in an increase in the pH of gelation, a reduction in the gelation time and a marked increase in the storage modulus compare to unheated milk. Addition of WPC to …