Curd syneresis

Typically, five steps, or groups of steps, are involved in the conversion of milk to cheese curd coagulation, acidification, syneresis (expulsion of whey), moulding/shaping and salting. These steps, which partly overlap, enable the cheesemaker to control the composition of cheese, which, in turn, has a major influence on cheese ripening and quality. 

Gel strength (curd tension). The gel network continues to develop for a considerable period after visible coagulation (Figure 10.8). The strength of the gel formed, which is very important from the viewpoints of syneresis (and hence moisture control) and cheese yield, is affected by several factors - the principal ones are summarized in Figure 10.9. 

Syneresis. Renneted milk gels are quite stable if undisturbed but synerese (contract), following first-order kinetics, when cut or broken. By controlling the extent of syneresis, the cheesemaker can control the moisture content of cheese curd and hence the rate and extent of ripening and the stability of the cheese - the higher the moisture content, the faster the cheese will ripen... 

Good analytical methods for monitoring syneresis are lacking. Principles that have been exploited include dilution of an added marker, e.g. a dye, which must not adsorb on to or diffuse into the curd particles, measurement of the electrical conductivity or moisture content of the curd or by measuring the volume of whey released (probably the most commonly used method although only one-point values are obtained). 

Milk-clotting is a complex process, involving a primary enzymic phase in which K-casein is altered and loses its ability to stabilize the remainder of the caseinate complex, a secondary non-enzymic phase in which aggregation of the altered caseinate takes place, a third step where the aggregate of casein micelles forms a firm gel structure and a possibly separate fourth step where the curd structure tightens and syneresis occurs (McMahon and Brown 1984B). 

The casein micelles become surrounded by whey proteins and cannot interact with one another, thus reducing whey syneresis. This results in a soft curd that retains more moisture. The yield of cheese is increased due to the incorporation of whey proteins and the higher moisture content. Overheated milk requires longer rennet coagulation times. If milk is heated for 30 min at 75° C, it will not clot at all (Ustu-nol and Brown 1985). 

Lawrence, A. J. 1959. Syneresis of rennet curd. Part II. Effect of stirring and of the volume of whey. Aust. J. Dairy Technol. 14, 169-172. 

Walstra, P., van Dijk, J. M. and Geurts, T. J. 1985. The syneresis of curd. 1. General considerations and literature review. Neth. Milk Dairy J. 39, 209-246. 

The primary (enzymatic) phase of renneting overlaps somewhat with the secondary phase of aggregation. The gel subsequently undergoes syneresis to produce curds and whey while a slow but more general proteolysis of the caseins begins, which eventually contributes substantially to the distinctive flavor and texture of cheese. The enzymatic coagulation of milk and formation of the curd has been reviewed by Dalgleish (1987). Here, attention will be confined to parts of the subject that most clearly relate to the structure and stability of bovine casein micelles. 

Reduction of milk allergenicity is possible by a cross-linked reaction of milk proteins with microbial transglutaminase (m-TG) (Wroblewska et al. 2008). Diary products thus obtained possessed better functional properties with weaker syneresis and stronger curd. Also, the organoleptic properties of yoghurt prepared with m-TG make a favorable impression on potential allergic consumers. 

The physical impedance to syneresis by the fat globules, which, in effect, act as stoppers in the pores of the para-casein matrix and thereby reduce the loss of starter cells in the whey exuding from the curd the retained starter cells aggregate around the fat globules... 

Consider the making of curd (green cheese) from milk. The milk is made to gel by the addition of rennet. Then whey has to be removed by syneresis. What measures can you think of to enhance the rate of syneresis ... 

Emmons, D. B., Price, W. V., and Swanson, A. M. (1959). Tests to measure syneresis and firmness of Cottage cheese coagulum, and their application in the curd-making process, J. Dairy Sci. 42, 866-869. 

M. J. Mateo, D.J. O Callaghan, C.D. Everard, M. Castillo, F.A. Payne, C.P. O Donnell, Evaluation of on-line optical sensing techniques for monitoring curd moisture content and solids in whey during syneresis. Food Res. Int. 43(1), 177-182 (2010). doi 10.1016/j.foodres.2009.09.023... 

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