Fresh foods such as meat, sausage, fish, and cheese are usually vacuum packaged at a pressure of around five millibars.
At this pressure, the oxygen content in the remaining residual air is so minimal that the activity of various microorganisms is prevented.
Industrial vacuum equipment supplier Busch sales and marketing representative Lesley Hammond explains that this method significantly increases the shelf life of the packaged products.
She warns, however, that such low pressures also cause water to start evaporating at low temperatures.
“While water at normal atmospheric pressure only evaporates or begins to boil at a temperature above 100 ºC and at a pressure of 30 millibar it starts to evaporate at room temperature. At a pressure of 8 millibar, water evaporates already at a temperature of 4 ºC – even in cooled rooms.”
She explains that this is why fresh foods always generate water vapour during the packaging process, and this water needs to be extracted by the vacuum pump together with the air from the packaging chamber.
If the vacuum pump rarely or never reaches the operating temperature owing to very short run-times, the water vapour condenses almost completely inside the pump, warns Hammond.
This leads to an accumulation of water in the interior and in the oil of the vacuum pump. This causes the oil to lose its lubricating and sealing function, which can have a negative effect on the performance and service life of the vacuum pump.
She adds that to ensure the reliable and trouble-free operation of chamber agingmachines, there are a number of recommendations to follow.
Firstly, Hammond explains that the operator should allow the vacuum pump to warm up before packaging by running the packaging machine five to ten times without any product and packaging bag, while making sure the chamber is dry for this.
Secondly, the user should ensure that the vacuum pump in a chamber machine is serviced regularly and that the service program is followed regularly to ensure the pump performs at optimal performance.
This program ensures that condensed water vapour that has mixed with the oil is removed from the vacuum pump. This program should be started at least once a week. Depending on the packaging machine, it takes between 10 and 20 minutes. The vacuum pump is brought to operating temperature so that the water in the vacuum pump evaporates again and is discharged.
“The service intervals depend on the operating conditions, the number of packaging cycles, and the type of goods to be packaged. A reliable indicator of when an oil change needs to be performed is the visual condition of the oil.”
In addition, she says, it is important to note that when changing oil, the exhaust filter in the oil separator should always be replaced as well. For vacuum pumps with a pumping speed of 25 cm/h or more, the oil filter also needs to be changed. The sealing rings on the service openings should also be replaced in order to prevent leaks.
For convenience, Busch offers service kits for all R5 vacuum pumps, which contain all the necessary parts, adds Hammond. Busch Vacuum Solutions offers a global maintenance service so that this work can also be carried out by a service technician directly at the customer's premises. Different types of service contracts are available.
In addition, using suitable vacuum pump oils and checking the oil level and oil quality weekly is another way of ensuring efficiency.
A visual inspection should be carried out once a week to check that the oil quantity and quality are correct. This can be done quickly and easily through the oil sight glass. The oil in the vacuum pump should be colourless to yellowish and clear.
She explains that if the level falls below the minimum mark on the oil sight glass, oil must be topped up. If the oil is milky and cloudy, this is a sign that water has mixed with the oil and formed an emulsion.
The service program then needs to be run. If this has no effect on the visual condition of the oil, an oil change needs to be performed. Darkening of the oil is a sign that some substances, for example spices, have been deposited in the oil or that it has aged too much. An oil change also needs to be performed if this is the case.
“The quality of the oil in vacuum pumps and the correct quantity play an important role in the packaging process and in protecting the pump. It is therefore essential to choose the correct oil to ensure the vacuum pump and thus the packaging machine function properly.”
Hammond explains that Busch Vacuum Solutions has developed special oils for vacuum pumps in packaging machines.
The VSA vacuum pump oil is suitable for packaging very moist products, since it has been designed for the extraction of air with a high-water vapour level. For less moist food, the VSL vacuum pump oil can also be used. Both oils are food-grade synthetic oils with H1 approval and have a service life of up to four times longer than mineral oils.
Busch also offers suitable oils for packaging with oxygen as a modified atmosphere.
She concludes that observing these instructions will help to ensure trouble-free operation and a long service life for the vacuum pump, as well as optimum packaging results.