1. With a view to a chemical study of the ripening of cheese made from raw and from pasteurised milk, two sets of three loaf Cheddar cheese were made from clean milk and from market milk respectively, so that in each set there was one cheese made from raw milk, one from milk flash-pasteurised at 165° F., and one from milk flash-pasteurised at 185° F.

2. Analyses of the whey drawn from each cheese showed a tendency, especially with market milk of lower hygienic quality, for pasteurisation to cause more of the soluble milk proteins to be incorporated in the cheese.

3. When acidity developed rapidly in the whey after cutting, the resulting cheese was depleted of a proportion of its mineral constituents.

4. The cheese made from pasteurised milk developed a bitter flavour, which was very pronounced in those made from the milk heated to the higher temperature.

5. The chemical analyses showed that in both sets, pasteurisation reduced the quantity of ultimate decomposition products which were formed during the process of ripening.

The experiments recorded here were carried out at the National Institute for Research in Dairying, Shinfield, Reading. The author desires to express his appreciation of the facilities which have been placed at his disposal and of the interest that has been taken in the work by various members of the staff, in particular by Miss D. V. Dearden (who was responsible for the making of the cheese), Capt. J. Golding, and Dr R. Stenhouse Williams. Acknowledgment is also due to Prof. Wm Riddet, Dairy Research Institute, New Zealand, who suggested the desirability of an investigation of this nature.