Data on the early studies on the curd character of milk are found in Utah Agricultural Experiment Station Bulletin 207 and, therefore, are not included here. The key to research in this field came to light with the development of the "Hill Test," the results of which were first published in 1923. This test furnished a means of quantitatively measuring the difference in curd character of various milks.
The term "soft-curd" milk originated with R. L. Hill to describe milk which on coagulation with pepsin or rennin forms a curd that is soft and clabbery in consistency, differing widely from the tough rubber-like curd obtained from most samples of cows' milk. In the earlier writings the term "soft-curded" milk was used, but since this sometimes gives the impression that the milk referred to as soft-curded has been coagulated, the term has been changed to "soft-curd" milk. It is by means of the Hill Test that the softness of the curd in milk can be determined.
Hill, R. L., "Bulletin No. 227 - Soft-Curd Milk" (1931). UAES Bulletins. Paper 193.