The term 'Dark Cutting' is used for meat that does not bloom or brighten when it is cut and exposed to air. Beef customers prefer beef cuts to be a bright pinkish colour at retail, they avoid dark coloured meat. Dark cutting beef (DCB) is largely linked with stress and the mobilisation of muscle glycogen—energy store—in the live animal prior to slaughter.

In the time between slaughter and chilling, a chemical reaction known as glycolysis occurs in the muscle tissue. This reaction converts glycogen into lactic acid. This lactic acid causes the meat pH to decline from the neutral value of 7.2 found in the live animal. The amount of pH fall is determined by the quantity of glycogen available in the muscle for conversion to lactic acid.

Desirable eating table beef has an ultimate pH in the range of 5.3 to 5.7. If the quantity of glycogen in the muscle tissue was low, and the pH remains above 5.8, then DCB is a likely outcome.

In addition to the unacceptable appearance, DCB has the following characteristics:

• a high water holding capacity – so the meat loses a lot of moisture during cooking and becomes very dry;
• reduced shelf life – bacteria grow more rapidly due to the higher pH and moisture;
• a sticky texture.

How does low muscle glycogen occur?

• low energy intake by livestock,
• poor livestock handling,
• mixing groups of animals, and
• severe weather conditions during transport.

All these factors have been found to decrease the levels of muscle glycogen in the live animal.
Muscle glycogen, or the energy reserves of the animal, has a large influence on meat colour and pH, see Table 1.

Table 1. Muscle Glycogen Percentage and the Relationship to Meat Colour and Ultimate pH of Meat

Source: Walker,P. (1997) Dark cutting in beef carcasses.

Incidence of dark cutting beef

Industry estimates that the incidence of DCB is 8–10%. There is evidence that processing plants vary in incidence levels from 1–16% and individual slaughter groups are up to 50%.

High risk stock categories include: sick or injured stock, females exhibiting oestrus, entire males, poor temperament stock and young unweaned animals.

Producing the best eating quality

In the interest of consumers of beef, producers should seek to minimise the incidence of dark cutting beef.

Acknowledgments

Michael Beer, NSW Agriculture and Meat Standards Australia Grading Services, Milton Queensland.

Additional information

DAI 245 Dark cutting beef – managing cattle to reduce DCB

DAI 246 Dark cutting beef – the economic loss