The effects of ageing and the importance of temperature

Despite the differences between muscles, overall ageing increases meat tenderness. Ageing can also have a marked effect on colour and shelf life. Meat is usually aged by storing it at chill temperatures, either on the bone or in vacuum packed primals, to effect tenderisation. The toughness of meat decreases, quickly at first and then more slowly, due to naturally occurring enzymes in the meat resulting in protein breakdown and a weakening of the muscle structure.

The rate of muscle cooling within the carcase post-mortem is not uniform, even within the same muscle: the centre of a muscle can take a lot longer to cool than the outside edge of a muscle, and the position of a muscle within the body will also determine how quickly and to what degree chilling will take place.

Rapid or blast chilling – as low as -30ºC for 30 to 90 minutes – can reduce evaporative weight loss and improve some aspects of carcase quality. However it can also lead to a phenomenon called cold shortening and, unless chilling follows electrical stimulation or pelvic suspension, a reduction in meat tenderness will probably occur.

Shortening and its effect on meat tenderness

As well as managing the animal prior to and during slaughter, the plant staff must be diligent with meat post-slaughter

Muscle will attempt to shorten if it goes into rigor mortis below about 10ºC (called cold shortening) or above 20ºC (called hot shortening).

a. Cold shortening

This phenomenon occurs when the muscles are cooled too rapidly after slaughter, while still in a pre-rigor mortis condition. This causes the contractile elements of the muscle fibres to shorten, which results in a very appreciable reduction in the tenderness of meat.

b. Hot shortening

Hot shortening generally produces a lesser shortening and reduction in meat tenderness in comparison to cold shortening.

Electrical stimulation (ES)

The application of an electric current to the carcase following slaughter lowers pH more quickly. The effect is to hasten the onset of rigor mortis in the carcase. Electrical stimulation not only prevents cold shortening but can cause an early tenderisation post mortem, so it can be used to reduce the ageing period – while still producing tender meat.

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