An apparatus for the objective determination of the heat coagulation time of milk powder solutions is described. In the apparatus a chromium plated iron piston is moved by means of a ring magnet, driven by a control mechanism, through a heated cylinder containing a small sample of milk. When the milk coagulates, the increased impedance between the inner wall of the cylinder and the metal piston overcomes the magnetic strength of the ring magnet and the magnetic coil moves away from the piston core, resulting in a momentary change in coil current, which after amplification is used to stop a digital clock. The method was tested with 10 and 20 % milk powder solutions at various pH values, at temperatures of 120 and 140 °C. The results are comparable with those obtained using a traditional method involving visual determination of coagulation (Davies & White, 1966).

Three microbial rennets, Noury rennet (Mucor pusillus, Lindt), Rennilase (M. miehei) and Suparen (Endothia parasitica), were assessed as calf rennet substitutes for Feta cheesemaking, in comparison with calf rennet. Cheeses prepared were all of good quality with similar organoleptic properties. Yield (referred to 55% moisture), moisture content, NaCl and protein content did not differ significantly. Different rates of proteolysis were observed in the cheeses, the highest of which was exhibited by calf rennet followed by Rennilase, Noury rennet and Suparen preparations. These calf rennet substitutes are well suited for Feta cheese manufacture.

Commercial and pure chicken pepsin preparations were compared with rennet as cheesemaking coagulants. From the milk clotting and caseinolytic activities and enzymic stabilities, predictions were made of the relative activities of the chicken pepsins and rennet during cheese ripening. By this means mixtures of chicken and pig pepsins for cheesemaking trials were formulated. These and mixtures of chicken pepsins with rennet were approximately additive in coagulating activity provided they were used immediately. The amounts of chicken pepsins used in laboratory scale Cheddar cheesemaking trials were minimized by acidification and calcification of the milk. The nature of the coagulant did not affect the cheesemaking conditions, yields or cheese composition. Cheeses made with chicken pepsins alone showed faster proteolysis, more intense flavour, off-flavours and bitterness and were softer than those made with rennet. Cheeses made with chicken pepsin/rennet mixtures were intermediate and those made with chicken pepsin/pig pepsin mixtures were similar to those made with rennet. It was concluded that neither of the chicken pepsin preparations was suitable for Cheddar cheesemaking and that the predictive tests had led to correct assessments.