Effect of hot boning on meat quality

Hot boning of beef and sheep carcases has distinct advantages over cold boning. The warm meat is soft and requires less effort to bone, occupational overuse injuries are less likely to occur, there is potential for improved yield, and expensive chilling of fat and bones is avoided. There are also benefits in terms of certain processing qualities when hot boned meat is used to manufacture meat products. However there are also perceived disadvantages of hot boning; for instance the potential for the meat to be tough, darker in colour, and for some primals to be different in shape. In Australia, hot boning usually means boning carcases that have a deep butt temperature of more than 20°C. It is useful to consider hot boning in two categories—‘true’ hot boning and warm boning.

True Hot Boning

In true hot boning, carcases or sides are not cooled before they are boned. They are boned within 30 to 45 minutes of slaughter. Plants that perform true hot boning generally use plate freezers to cool the hot meat. Even with plate freezers, it can be difficult to reduce rapidly the temperature of large beef primal cuts. Bulk-packed product at average temperatures of 28-30° can normally be cooled in sufficiently rapid time using plate freezers.

Warm Boning

In warm boning, carcases or sides are boned after a period of pre-chilling. Typically, carcases are pre-chilled for 30 minutes to 6 hours. Short pre-chills are used for mutton and longer periods for beef. Warm boning allows for an increase in throughput on the slaughter floor without having to increase chiller space. After warm boning, primals and manufacturing meat can be cooled quickly enough in air blast or plate freezers to avoid excessive microbial growth. Under some blast chilling circumstances the lids may have to be left off the chilled meat cartons in order to cool primal cuts quickly enough.

 Potential improvements in efficiency

The basic concept of hot boning is that slaughtering, boning and packing of the meat is all done within the span of a single working day. An increasing number of plants are hot boning because of the potential for:

  • reduced processing time from slaughter to load out;
  • lower chilling space and other capital cost requirements;
  • reduced energy consumption and other chiller costs;
  • increased boning yield;
  • improved productivity;
  • elimination of hard fat problems; and
  • more rapid product turnover.

Microbiology of hot boned meat

A disadvantage of hot boning is that there is an increased risk that the meat can support the growth of pathogenic bacteria as it cools. In conventional boning, microbial growth on carcases is controlled by a combination of drying and cooling of the carcase surface. When the meat is hot boned and packed, moist meat surfaces may be contaminated and provide an opportunity for microbial growth because they stay moist. The surface temperature of boned meat prepared conventionally in accordance with regulatory requirements is usually less than 15°C for beef and less than 10°C for smallstock. At these temperatures, the growth of pathogenic bacteria is slow and the meat should cool to 7°C within a few hours of boning. At 7°C and below, the growth of pathogenic bacteria is negligible and for this reason, cooling to 7°C or below is regarded as critical for food safety. In the case of true hot boned meat, the boneless meat surfaces could be 20-35°C at the time of packing. At these temperatures, pathogenic bacteria can adapt to their new environment within an hour or two and begin to grow quickly. Therefore, the meat must be cooled quickly to below 7°C after it is boned in order to control the growth of pathogenic bacteria.

The cooling rate is affected by three main factors:

  1. carton size and style;
  2. freezer type;
  3. air temperature and velocity (in blast freezers or chillers).

Because of the potential for growth of pathogenic bacteria, performance criteria are set out by export and domestic regulatory authorities. A trial (see AQIS Notice Meat 00/06) is being conducted in export plants whereby establishments that are hot boning to produce manufacturing meat are required to show that the cooling rates of boneless meat are sufficient to limit the growth of E. coli to prescribed levels.

Some shortening will occur during cooling of hot boned meat. The objective is to minimise shortening. However, providing appropriate attention is paid to the application of electrical inputs and cooling regimes, hot boned meats can be equivalent, or even superior to, conventionally cold boned product in meat quality terms. Some recommendations already exist for electrical inputs that suit different Australian conventional beef side chilling and post boning cooling regimes, and optimise the acceptability of table meats (in terms of both eating quality and shape) and of manufacturing meats (in terms of suitability for end use). However, further research and development is needed in order to better define the electrical inputs for both beef and small stock table and manufacturing meats that are hot boned.