Cheese syneresis

The strength of the rennet-induced gel is also adversely affected by heat treatment of the milk, again presumably because the whey protein-coated micelles are unable to participate properly in the gel network. Gels from severely heat-treated milk have poor syneresis properties, resulting in high-moisture cheese which does not ripen properly. Syneresis is undesirable in fermented milks, e.g. yoghurt, the milk for which is severely heat-treated (e.g. 90°C x 10 min) to reduce the risk of 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... 

Gels prepared from heated milk synerese poorly (assuming that the milk does coagulate). Such reduced syneresis properties are desirable for fermented milk products, e.g. yoghurt (milk for which is severly heated, e.g. 90°C x 10 min) but are undesirable for cheese. 

Promotes syneresis and hence influences cheese composition. 

Salting promotes syneresis and hence reduces the moisture content of cheese about 2 kg of water are lost for each kilogram of salt absorbed. 

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). 

Combined or single effects of heating and acid production by the starter bacteria increase whey syneresis and establish moisture levels for a given variety of cheese. Almost 96% of the moisture lost in Cheddar cheese during cooking occurs in the first 30 min (Lawrence 1959). A comprehensive review of syneresis has been written by Walstra et al. (1985). 

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. 

The enmeshed fat globules occupy the spaces between the protein strands and may be considered to impede physically the aggregation of the para-casein matrix, to a degree dependent on their volume fraction and size distribution. Consequently, a higher fat level leads to slower syneresis during manufacture (Dejmek and Walstra, 2004), and an increase in the level of MNFS in the cheese (Tunick et al., 1995 Poudaval and Mistry, 1999 Fenelon and Guinee, 1999) the increase in MNFS has a major impact on cheese yield and quality, as discussed in Sections 11.4, 11.6-11.9. 

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 ... 

Carudan. [Grindsted Prods.] Locust bean gum controls syneresis, inqnoves texture in processed cheese. 

Cutting of the gel into cubes, as in Cottage cheese, initiates syneresis which is enhanced by cooking and stirring, as in the manufacture of rennet-... 

---