Figure 17. Variation of firmness with saturation of glycerides.

Figure 18. Relation between elastic recovery and moisture content.

proportion of solid fat. In these particular experiments the cheese produced in December appeared to be anomalous. However, even including the December result, the relation was statistically significant: excluding it, it was highly so and this regression has been drawn on the figure.

The water serves two functions, one purely physical, in that it is a low viscosity liquid, the other in its action as a carrier for the substances dissolved in it which may undergo chemical reactions with the fat or casein. It has already been stated that the water occupies the space not taken up by the casein matrix and the fat. Provided that there is a sufficient quantity, it takes up all of that space. Only near the outer surface, for instance, in the rind, is there likely to be any deficiency. In the case of Swiss-type cheeses, which contain eyes filled with gas, the main body of the cheese is still replete with water. The rheological consequence of this arrangement is that the water acts as a low-viscosity lubricant between the surfaces of the fat and the casein. The greater the space between these, which is another way of saying the higher the water content of the cheese, the easier the flow of water within these spaces. Hence there should be less restraint on the movement of the casein mesh around the enclosed fat. This freer movement should manifest itself as a lesser resistance to the deformation of the whole cheese and as a greater recovery after deformation.

Taking the latter point first, a study was made of the elastic recovery of samples of some ten varieties of cheese after they had been compressed (29), but only up to a point at which no visible damage to the structure had occurred (Fig. 18). The cheese with the lowest water content, Par-migiano, showed the least recovery, while a Mozzarella with over 50% water showed the most. From the figure it is seen that while there was considerable scatter about the regression line, as was to be expected with cheeses of different origins, a general trend was well established.

The lubrication effect can be more clearly demonstrated with a single variety and within a single cheese. In a freshly made cheese the water is distributed more or less evenly throughout the whole mass. During the maturation period of those cheeses which are allowed to ripen in air, water evaporates from the surface and is only slowly replaced by more water migrating from the interior. A moisture gradient is set up within the cheese. Measurements made on Emmentaler cheese (62) (Fig. 19) showed a very close relation between the water content of successive layers and the firmness as determined by a penetrometer. Similar results have been obtained with Edam cheese (66). In that series of experiments a close relation was observed between the water content of the cheeses and the firmness, although they were made in two batches at different temperatures (Fig. 20).

In its other role as carrier of active ingredients the presence of water is principally seen in the effect on the

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