Rennet and Cheesemaking

Abstract

The action of rennet on milk leads to the formation of a coagulum or gel. This structuring of the milk protein is the first step in the production of cheese curds and in cheesemaking. To understand the action of rennet and the subsequent sequence of events leading to curd formation, it is necessary first to describe the composition and physico-chemical properties of the milk caseins. The principal casein proteins (a s1-, (3-and K-casein) are described, current theories on casein micelle structure are considered, and the action of rennet on casein micelles is explained. The gelformation involves two stages. Thefirst is enzymic and the second an association and aggregation of the enzymically altered casein micelles. The influence of temperature, pH and salt concentration are considered. Rennet, the commercial enzyme preparation made by a saline extraction of calf abomasum, contains several gastric and tissue enzymes. The principal milk-clotting enzyme in the preparation is Chymosin (EC 3.4.4.3); its characteristics and properties are discussed. Other milk coagulating enzymes and rennet substitutes are considered, including some aspects of identification. The overall contribution of rennet to cheesemaking is assessed, particularly its involvement in the ripening process, and new and potential developments in the rennetting process are discussed.