On the basis of the experimental data provided by Harvey & Walker (1960) and Peterson, Johnson & Price (1949) various mixtures of methyl ketones (mixture K1) and fatty acids (mixture FA) were made up in proportions corresponding approximately to those found in a mature Cheddar cheese (9–10 months old). Only those carbonyl compounds which showed a significant increase in concentration as the cheese matured were included since it was assumed, for these experiments, that these ketones were the key flavour-producing compounds. It was visualized that there might be differences in the uptake of the various ketones by the curd so three additional ketone mixtures (K2, K3, K4), in which the balance of the various constituents had been altered, were also prepared.