Syneresis

Abstract

Publisher Summary After gelation of the milk during the manufacture of acid- or rennet-curd cheeses, the coagulum is subjected to various treatments with the objective of expressing whey. Rennet- or acid-induced milk gels are quite stable if left undisturbed but if they are subjected to external pressure or are cut and broken, the paracasein matrix rearranges and contracts, owing to various protein-protein interactions, expressing the aqueous phase of the gel known as whey. This process is essentially a continuation of the gel assembly process and is known as syneresis. Control of syneresis is essential as it allows the cheese maker to control the moisture content of the cheese; moisture level, in turn, has many effects on cheese quality, texture, and flavor. In general, the higher the moisture content of the cheese, the faster it will ripen and the less stable it will be. Syneresis is promoted by cutting or breaking the curd, acidification through starter action, heating (cooking) and stirring the curds-whey mixture, and pressing and salting the curds. The composition of the milk also affects syneresis; decreasing the fat content decreases the rate of syneresis and increasing the casein content of milk may increase the rate of syneresis. Methods used experimentally to measure syneresis include measuring the shrinkage of curd, determining the amount of whey expelled (either directly or by following the dilution of an added tracer dye), and determination of the dry matter level or the density of the curd. However, all these methods have certain inherent drawbacks and experimental conditions must be standardized carefully to obtain reproducible results.