According to a report by the Food and Agriculture Organisation of the United Nations, at least one-third of food is lost or wasted between harvest and household. In North-America and Europe, this means more than 100 kg of food lost per capita – summing up to 1.3 billion tons annually worldwide! A reduction to this huge mass of food produced in vain would contribute greatly to reducing the greenhouse effect.
How can vacuum technology help to reduce food waste and improve packaging?
1. Packaging under vacuum helps to keep the food longer
Because vacuum food packing removes the air from the package before sealing it, the longevity or ‘shelf life’ of food can be improved significantly. For example, at pressures near 1 mbar, almost all oxygen is removed. This drastically reduces the growth of bacteria and fungi, as they need oxygen to grow, and enables food to last much longer. Using vacuum packing, the lifetime of packed beef is between 2-4 weeks, while for pork or sausages it’s up to 10 days.
In vacuum food packaging, evacuation (the process by which air is extracted from a container) is generally done by single-stage rotary vane pumps or dry screw pumps. The advantage of dry screw pumps in this application are their long maintenance intervals and therefore higher uptime of packaging machines.
Also, quality assurance is an important issue for the food industry. The leak tightness of a package must be ensured to preserve quality (and therefore shelf-life), as well as prevent bacteria or spores entering.
In order to keep bacteria and spores out, the leak tightness has to be < 10−5 Pa·m3/s.
2. Vacuum cooling helps to keep fruit and vegetables fresh
Vegetables, salads and flowers can be cooled very efficiently by vacuum – and directly after harvesting, if required. Rapid vacuum cooling means that entire food containers can be evacuated to pressures of > 6 mbar. Below 23 mbar, the food starts to chill. Using vacuum food packaging technology, an entire container can be cooled and ready for shipment in less than 30 minutes.
This rapid cooling is achieved thanks to the phase diagram of water. At 20C, the water vapour pressure is 23 mbar. When its reduced to 8 mbar, the water in the fruit or lettuce has to reduce its temperature to 5C. The loss of water content in contrast is negligible, and the products stay fresh. Evacuation to pressures below the triple point of water (6 mbar) has to be avoided as the food would freeze and the cell structure could be damaged.
Vacuum technology rapidly cools food products from their centre, providing much longer storage life by immediately slowing the growth of bacteria. This method requires very little energy and investment, and can even be done in remote areas where no fresh water is present.
Typically, the vacuum pumps used are either mid-size, single-stage rotary vane pumps with pumping speeds up to 300 m³/h (often with roots pumps on top) or dry screw pumps due to their high water vapour tolerance.
Central vacuum system for a refrigeration plant. Source: Leybold GmbH
3. Vacuum drying helps to preserve fresh fish and meat
Fresh food products rapidly deteriorate unless some way can be found to preserve them. Since ancient times, food like fish or sausage has been dried under the sun and in fresh air. This is because bacteria need water to grow.
There are 2 different processes to dry food with the support of vacuum:
Vacuum Microwave Drying ('VMD') and Freeze Drying ( 'FD', 'Lyophilisation')
Phase diagram of water
In VMD, the products are heated by microwave to 35-60C while the vacuum pump keeps the pressure around 10 mbar. The water content then evaporates. In FD, the products are cooled to -20-40C and the water sublimates at pressures below 0,1 and -1 mbar from the solid phase.
This process is also used for freeze drying coffee, pharmaceutical products and conserving historic books in libraries.
The vacuum pumps used are either single-stage (VMD) or double-stage (FD) rotary vane pumps, combined with water condensers and open gas ballast or dry screw pumps. Dry pumps have an advantage in that they can handle the water vapour from the drying process, so the condenser is unnecessary.
These few examples show the diversity of vacuum applications in food processing and how vacuum technologies help to reduce waste and contribute to our environment.
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