Effect of precipitation temperature and pH on the mechanical strength of batch precipitated acid casein curd

Abstract

SUMMARYThe precipitation stage in acid casein manufacture controls the initial strength of the casein curd, which is an important factor in determining fines losses during processing. A plate extrusion method was used to determine the mechanical strength of casein curd, precipitated batchwise at temperatures from 25 to 53 °C over a pH range of 3·9 to 5·1. Curd strength was determined either immediately after acidulation or after cooling for 2 h at 25 °C. Curd was stronger immediately after acidulation than after cooling and increased in strength as precipitation temperature and pH were increased. Curd precipitated at high temperature and high pH was mechanically strong, had a large particle size, and had high total solids and Ca contents. The relationship between these curd properties is discussed, and it is concluded that Ca retention at high precipitation temperature and pH is largely responsible for the characteristic curd properties under these precipitation conditions.