Background
There are two types of muscle shortening which result in tough meat. These can be monitored by measuring pH/temperature changes with time
Cold shortening
This is more likely in conventional operations where electrical stimulation is not used.
Avoidance of cold shortening can normally be achieved by ensuring that no muscle temperature falls below 10oC in the first 10 hours post slaughter. Measuring the pH/temperature relationship, however, is recommended to validate the process.
Hot shortening
There is a risk of hot shortening where electrical stimulation is applied.
pH / temperature measurement programme
It is recommended that a programme of measurement be adopted to ensure that neither cold nor hot shortening is induced.
To completely avoid cold shortening the pH should be below 6 before muscle temperatures reach 18oC or less.
To avoid severe cold shortening the pH should be below 6 before muscle temperatures reach 8oC or less. In this case additional post slaughter practices to improve meat quality are recommended (eg extended ageing or hip suspension)
To avoid hot shortening the pH should remain greater than 6 until the temperature has reached 35oC or less.
Initial benchmark and annual review
Initial benchmarking should be undertaken to establish the appropriate daily monitoring:
