It has been shown by experiments in milk that the enzymes of commercial rennet in conjunction with the lactic acid bacteria occurring in Cheddar cheese can bring about protein breakdown similar in extent to that found in the ripe cheese as far as the non-protein nitrogen is concerned. The amino nitrogen produced is, however, much less than in cheese. This may be ascribed to the higher pH of cheese as compared with that of the milk cultures, since acidity adversely affects the peptidases present. Attention is drawn to the differences between the conditions.

Rheology is denned as the science of the deformation of matter. It includes the study of all deformations, recoverable (elastic) and non-recoverable (plastic). In this paper cheese is primarily considered although the fundamental principles apply to all materials.

The elastic and plastic properties of cheese exercise a great influence in the ripening processes and the incidence of faults. Although much progress has been made in the bacteriological and chemical investigations of cheese ripening, little fundamental work on the nature of and the factors controlling the physical properties of curd and cheese has been carried out.

The experiments described above have shown that on the whole there is a close relationship between titratable acidity and lactic acid concentration in wheys obtained under various conditions of cheese-making. Variations in the rate of acid development or in the lactose content of the cheese milk have no significant effect on the relationship. Variations in the mineral content of the curd brought about by differences in the composition of the milk or by different acidities up to the running stage do have a certain effect. In curd with a lower mineral content there is a less complete neutralization of lactic acid and the wheys show a higher titratable acidity for the same lactate content. The differences, however, are small and affect only the wheys coming off late in the cheese-making process.

A number of chemical substances that might be expected, or have been claimed, to affect the rate of chemical ripening have been incorporated in cheese at “salting”. The effect in most cases has been insignificant. It would appear that cheese is a remarkably stable system, the chief factors in the rate of chemical ripening being the concentration of rennet, salt and free water. The importance of the interrelationship between the last two factors has been discussed.