Some Experimental Results

Most of the rheological methods described earlier have been used at one time or another for the study of cheese. Problems associated with penetrometers and tests on the surface have already been indicated. The most satisfactory tests are made on samples cut out specifically from the cheese mass. In this case the sample can be inspected to insure that there are at least no major cracks or other in-homogeneities in it and the dimensions can be precisely determined. The force-compression test using small prepared samples has been widely used for routine measurements. However, in spite of its widespread use, there has been no consensus of opinion on the most suitable operating conditions. Sample size and shape, rate of compression, and even temperature have all varied. A most interesting feature is that, notwithstanding these differences and the number of cheeses which have been examined, the forcecompression curves show a remarkably common pattern. This underlines its general usefulness.

There are several important considerations to be taken into account when deciding on the operating conditions. In the first place, the sample should be large enough to be representative of the whole (72); the more heterogeneous the cheese, the larger the sample. On the other hand, it should not be so large that it may contain hidden cracks or irregularities. These two requirements are almost mutually exclusive. As a compromise most workers have taken samples with linear dimensions of 10 to 25 mm. The preferred shape has usually been a cylinder. It is easier to prepare a rectangular sample with precise dimensions but the symmetry of the cylindrical shape helps to minimize the development of irregular cracks during compression (63). A wide range of compression rates has been used: from 2 mm/min up to 100 mm/min (3.33 x 10~5 to 1.66 x 10"3 m/s). The faster rates tend to obscure the true behavior at the onset of compression unless a recorder of very short response time is available. The strain rate at any instant depends on both the rate of compression and the height of the sample at that instant.

Table 1 summarizes the principal measurements that have been reported on hard cheeses using the forcecompression test. In order to produce this table and make the results from different workers comparable, the original curves from the references cited have been transformed

Table 1. Principal Measurements of Hard Cheeses Using the Force-Compression Test
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