The post-mortem pH of cod and haddock muscle and its seasonal variation.

The post-mortem pH of cod muscle, which strongly influences its attributes as a food, is subject to seasonal variation. For most of the year the average of a batch lies above about 6.7, but for a short time in the summer it suddenly drops to low values, rising again just as suddenly. It is now thought that heavy feeding immediately after starvation causes this sharp fall. Fillets from fish frozen at such a time gape and have a tough texture after cooking. The low-pH period is fairly short, so cod are in fact suitable for freezing for all of the year outside certain summer months. The phenomenon has been observed in cod from a wide range of fishing grounds. Haddock show no such seasonal variation, but their post-mortem pH is lower on average than that of cod.