Suck it up - vacuum packing fresh meat

Vacuum or inert gas packaging is today the most common method of packaging fresh meat, sausages and cold meats and convenience products in a non-perishable, hygienic way with suitable portion sizes that is attractive to the consumer. Vacuum packaging has existed for more than 45 years and the actual operating principle of the machines used in 1963 is still in use today. The vacuum pump remains at the heart of every packaging machine. The quality of the vacuum pump largely defines the quality of the packaging machine and, therefore, the quality of the packaging.

The correct choice and optimum design of a vacuum pump is, to a large extent, the decisive factor in the quality of the packaging, and consequently in the shelf life and quality retention of the packaged product. The correct choice of vacuum pump also influences the operating safety and economic viability of the packaging machine. In order to achieve the best possible results in vacuum packaging, it is necessary to consider the entire meat processing sequence. This is the only way to incorporate all parameters from the process chain that can influence the physical packaging procedure.

After slaughter, several biological processes take place in the meat. First, the meat becomes tough and dry, which can indirectly be traced back to the formation of lactic acid in the muscle fibres. Later in the process, protein-metabolising enzymes loosen the meat tissue. This permits the meat to absorb moisture once again and to become juicy and tender. However, if this process lasts for too long, too much protein is metabolised. This leads to the production of ammonia and the meat becomes inedible. Meat maturing and spoilage are therefore processes that blend into each other.

Vacuum packaging removes oxygen from the meat, reducing the activity of bacteria that require oxygen and thereby achieving a significant increase in shelf life. The removal of oxygen slows down the meat maturing process considerably and maintains the quality of the meat over a long time period.

Physical packaging processes

Vacuum packing fresh meat.

Pumping air out of the packaging machine chamber reduces the pressure and residual oxygen content. During this evacuation, a pressure reduction occurs simultaneously inside the piece of meat and on its surface. This reduction in pressure allows gas inclusions from within the meat to expand and escape. If the meat has a high moisture content, the water on its surface may evaporate if the vapour pressure is too low, which will lead to a rapid increase in the gas mixture within the chamber.

Due to this increase in gas mixture, the pressure within the chamber now only decreases at a slower rate as the vacuum pump must evacuate the additional water vapour that has been created.

This water content which has been vaporised during the evacuation, along with the temperature of the meat itself, has a considerable influence on the pressure that can be reached within the packaging machine chamber.

On ‘Skin Packaging’ machines, aerating the packaging chamber presses the bag onto the surface of the meat and compresses the residual atmosphere within the bag.

Depending on the product composition (gas inclusions and moisture content), the pressure inside the packaging bag may once again rise following the vacuum packaging process, since the residual gas can leak out of the meat.

The pressure, at which the best packaging results can be achieved, therefore, depends on the composition of the meat.

Water vapour tolerance

Water vapour tolerance is an important feature of a vacuum pump. This must be defined according to use. The following parameters influence the water vapour tolerance of a vacuum pump:

• The pressure range within which the vacuum pump operates
• The prevailing ambient and product temperatures
• The mode of operation of the vacuum pump
• The installation position of the vacuum pump within the packaging machine

Pressure range

The pressure range within the packaging machine depends on the performance of both the vacuum pump and the packaging machine itself. Best-in-class, modern rotary vane vacuum pumps can achieve a final pressure of 0.1 hPa.

A number of factors define the pump-down time of the machine, such as the chamber size, net volumes, vacuum cycle and vacuum port of the packaging machine, along with the suction capacity of the vacuum pump.

The triple-point (or three-phase point) of water is the point at which the three phases of water (vapour, liquid and ice) occur simultaneously, typically at approximately 6 hPa. In some cases, the rate at which the water triple-point is reached during the vacuum packaging cycle is dependent on the factors as identified above.

Water vapour curve.

Temperatures

The ambient temperature is set at a maximum of +12°C and the product temperature at a maximum of +7°C under the Meat Hygiene Regulations. These values vary in practice. Both temperatures have a direct influence on the operating temperature of the vacuum pump.

Installation and operation

The way in which the vacuum pump is installed (installation space, ventilation, etc) and the mode of operation of the packaging machine (cyclic operation, intermittent operation) also have a considerable influence on the operating temperature of the vacuum pump.

As a rule of thumb it can be said that: the higher the operating temperature of the vacuum pump, the higher its water vapour tolerance.

Optimum packaging

In order to be able to achieve the best possible packaging results, the interaction of the individual influences must be taken into account in the vacuum pump design. A complete overview of meat processing and cooperation between vacuum pump manufacturers, packaging machine manufacturers and operators are the most important preconditions for achieving the best quality.

Thanks to a dedicated range of products developed specially for vacuum packaging and long experience built up over several decades, Busch has particular competence in this industry. After all, Busch developed the first vacuum pump to be used specially for this purpose back in 1963