It has been shown that the acidity developed in a vat of milk at the “running” stage has a very important influence on the quality of the resultant cheese. A high acidity causes increased mineral losses in the whey and a corresponding lowering of the mineral content of the cheese, while it also has a detrimental effect on the body of the cheese. The acidity at “running” also controls to a great extent the acidity of the cheese produced. Even where the acidities at the late stages of the process are kept the same, vats of cheese made at a high “running” acidity show more acid characteristics than cheese made at low “running” acidity.

The quantity of lactose incorporated in the cheese is also of importance in determining the acidity of the cheese. An increase in the lactose content, either by raising the lactose concentration of the cheese milk or by the addition of lactose to the curd, produces a more acid type of cheese at maturity, although some unfermented lactose is still present in the cheese at 4 months after manufacture.

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.

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.

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.