Syneresis

Our discussion now moves from the very slow movement of separating emulsions to the faster flow of syneresis, an earlier process in cheesemaking. Syneresis, the expulsion of whey from shrinking cheese curd, begins immediately after disturbance of the curd by cutting. Control and understanding of conditions affecting rates of syneresis would aid in the reproducible manufacture of quality cheese. Until recently, all methods for measuring syneresis involved mechanical disturbance of the curd (Berridge and Scurlock, 1970; Geurts, 1978; Marshall, 1982; Green, 1987), accelerating whey expulsion and leading to varying results (Walstra et al., 1985). Differences in T2 relaxation rates between entrapped and expelled whey allow the non-invasive estimation of volume of expelled whey and shrinkage of curd (Ozilgen and Kauten, 1993). Free whey has a much slower relaxation rate than does whey within the curd; an echo time of 300 milliseconds allows the signal from sequestered whey to relax significantly, while leaving the signal from expelled whey relatively intense (Figure 6). Characterisation of whey expulsion may not require complete 2-dimensional images if syneresis occurs at the same rate throughout the curd volume. Projections, one-dimensional representations of intensity along one spatial axis, display the quantities of curd and whey accurately, and require orders of magnitude less time (1 second) for acquisition. Thermocouples monitoring temperature at several locations in the curd do not significantly degrade the data. This system permits non-invasive observation of syneresis under varied conditions of temperature, calcium chloride concentration, pH and grade of milk. Addition of chemical shift imaging techniques

Figure 6. T2-weighted images of cheese curd before (left) and after cutting demonstrate syneresis, the expulsion of whey from shrinking curd. An echo time, or pause before acquisition (Figure 2) decreases the signal contribution from the faster relaxing curd associated whey, and enhances the relative intensity of slower relaxing expelled whey. Addition of cuprous sulfate to the circulating water surrounding the incubation chamber greatly increases the relaxation rate of the water, rendering it invisible.

Figure 6. T2-weighted images of cheese curd before (left) and after cutting demonstrate syneresis, the expulsion of whey from shrinking curd. An echo time, or pause before acquisition (Figure 2) decreases the signal contribution from the faster relaxing curd associated whey, and enhances the relative intensity of slower relaxing expelled whey. Addition of cuprous sulfate to the circulating water surrounding the incubation chamber greatly increases the relaxation rate of the water, rendering it invisible.

(see Emulsion section) can also illustrate relative quantities of fat contained in curd and whey during syneresis.

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