1. A method for preparing rennet reference standards by freeze-drying is described.

2. A substrate has also been developed using ordinary spray dried separated milk powder which will give reproducible results under specified conditions. These include:

(i) A constant temperature (37° C.) for the duration of the test.

(ii) The exclusion of added calcium ions until actual testing begins.

(iii) The equilibration of the milk at 37° C. for 2 hr. before use.

3. The construction and use of an automatic apparatus for recording rennet coagulation time is also described.

4. The instrument error of a single observation is about 1·0%.

5. With liquid rennet extracts, the total experimental error, based on one sample of three replicates, is 2% or less: with two samples, it is 1% or less.

6. With freeze-dried rennet preparations, the experimental error with two ampoules, sampled thrice with three replicates per sample, was ±2·.0%. With three ampoules it was ±1% or less.

An extraction method is described for determining the volatile fatty acids in cheese. The method, dependent upon Soxhlet extraction and micro-distillation, is speedy with regard to actual manual operation and gives results in accordance with those obtained by lengthier established methods.