During a routine inspection of Cheddar cheese manufactured at a commercial factory in New Zealand, some lots of 6-month-old cheese were found to have developed a pinkish colouration on the surface of the 20 kg blocks of cheese. Colouration did not always occur uniformly on all six faces of the rectangular cheese block, or even on a single face of the block. Furthermore, not all blocks from within the same day's manufacture were equally affected. When an affected block was removed from its bag and cut across, colouration was sometimes found to penetrate approximately 1–2 cm down into the cheese. In those blocks where a plug of cheese had been removed previously, a pinkish zone surrounded the plug-hole cavity.

The pinkish colouration was observed to fade slowly (over about 12–24 h) when the cheese surface was exposed to air.

Annatto, known to cause pink discolouration in “coloured” Cheddar cheese (Govindarajan & Morris, 1973) and in processed cheese made using coloured Cheddar, was not used in the manufacture of the present cheeses and could therefore be excluded as a cause of the colouration.

The flavour profiles of all affected cheeses were considered by experienced industry cheese graders to be easily within the normal range of flavour profile expected for a cheese of this type i.e. there was no evidence of any off-flavour development.

The present short communication describes the microbiological and chemical investigations carried out to determine the origin and nature of the pinkish colouration in Cheddar cheese.