In ripening and mature Cheddar cheese, 2 distinct types of birefringent microscopic crystalline inclusions are found. One of these is an irregularly shaped large aggregate of needle-like crystals (LAC). The histochemical demonstration of Ca in the LAC together with their total absence from cheese made with δ-gluconic acid lactone (GAL) instead of starter bacteria suggests that they are composed of Ca lactate.

The other type of inclusion is a smaller aggregate of crystals (SAC). They are more numerous than the LAC and are concentrated in areas which probably correspond to the lines of curd particle fusion. The SAC appear in cheese immediately after pressing and increase in number until the cheese is about 1 month old. They can be detected in unsalted, milled curd after 1 d and are present in large numbers in cheese made with GAL. These observations together with histochemical evidence that they may contain phosphate groups suggest that the SAC are probably composed of Ca phosphate. Their location in spaces between the fat and casein phases of the cheese indicates that they crystallize from pockets of residual whey. Each SAC is composed of a large number of very long (maximum length 4·5 μm), thin (maximum diam. 25 nm) crystals each of which is covered by a thin layer of electron-dense material tentatively identified as casein.