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T
he aim of the food processing industry is to produce safe whole-
some food from specified raw materials. Control of pathogenic
and spoilage microorganisms has traditionally been achieved
by thermal pasteurisation and sterilisation, by chilling and freezing,
by reduction of the water activity in the product and by means of
chemical preservatives.
These processes need to take place in an hygienic environment.
Most often the use of heat together with the application of cleaning
chemicals and sanitisers provides for sanitation of both the process
equipment and its surroundings.
Pasteurisation, sterilisation, sanitisation
The source of heat for pasteurisation, sterilisation and sanitising
operations is usually derived from steam. Steam generated from the
combustion of fossil fuels accounts for over 50% of all the energy
used in the food industry.
A number of innovative pasteurisation, sterilisation and sanitising
processes have been researched over the past few decades. Some
of these have been commercialised. Many of the novel processes
that are employed in the industry have been developed to ensure
less heat damage to the food. This results in products with a fresher,
more natural taste. The energy considerations that were secondary in
the development of the processes are now becoming a consideration.
The energy engineer needs to be aware of the implications of these
novel processes.
The advent of large scale load shedding in South Africa has
brought into focus the vulnerability of the food industry. Power cuts
of even very short duration can result in breaking the integrity of the
process. This may then require recycle or disposal of the product
within the process and the necessity to re-sterilise the equipment. In
cases where indirect steam heating is used there may be burn-on of
sensitive product to the surfaces of the heat exchanger. Cleaning and
sterilisation are then required. Most of the innovative processes are
less prone to the risks of product damage at times of power failures.
Pasteurisation technology
Pasteurisation of beverages may be achieved prior to bottling (so called
flash pasteurisation) or after sealing in the bottle (tunnel pasteurisation).
Novel processes for Food and Beverage
Quality, safety, efficiency
A Murray, consultant
Most of the conventional processes used for the pasteurisation
and sterilisation of food products depend on the application of
heat. Today, there are a number of innovative processes that
cause less damage to the food. Some of these processes make
better use of energy and are less easily affected by interruptions
in power supplies than conventional processes.
Flash pasteurisation typically takes place in a three section plate heat
exchanger, with heating coming first by the use of the regenerative
heat from the exiting product and then from hot water in circulation. In
the third section of the exchanger the outgoing pasteurised product is
cooled. This process requires that filling and capping take place in an
enclosed sanitised area to prevent reinfection. Heating requirements
for pasteurisation vary considerably. A typical flash pasteurisation
process for milk or fruit juice generally requires between 30 and 120 kJ
per kg of product.
Tunnel pasteurisation is a process where the filled beverage
product is pasteurised in the bottle (bottles in this article may also
refer to cans or pouches in certain instances). Bottles on a conveyer
belt move through different temperature zones where heating and
cooling take place.
Filling and capping operations do not require such stringent san-
itising as for flash pasteurisation processes. Tunnel pasteurisation is
safer. While the regeneration in a modern flash pasteuriser exceeds
90%, in a tunnel pasteuriser only 60 or 70% is likely. The energy
requirement could thus be three or four times as much for the tunnel
pasteuriser as for the flash pasteuriser.
Novel pasteurisation and sterilisation processes
Innovative pasteurisation processes may be divided into those where
the micro-organism control is achieved through non thermal process-
es and those where a novel method of heating is used. Four novel
processes are considered:
• Pulsed electric field
• Ultraviolet pasteurisation
• Ultra high pressure processing and
• Induction heating
These are by no means the only innovations in this industry. For
instance, filtration and centrifugation are being used widely for re-
ducing the microbiological load in products where extended shelf
life is required.
Pulsed Electric Field (PEF) technology
In this process, pulses of high voltage (typically 20 - 80 kV/cm) are
applied to foods placed between two electrodes. Usually this is at
temperatures around ambient and for times of less than one second.
PEF technology has found application in the pasteurisation of fruit
juices, particularly in smaller capacity units. Powering smaller capacity
PEF units by PV solar in rural areas has been suggested. The power
requirement is approximately 100kJ per kg making it no more eco-
nomical in terms of energy than conventional pasteurisation. Longer
run times are however possible due to a lack of fouling providing for
some economy.
Heat intensive processes require large amounts of energy – they also
offer many opportunities for improvement. The overall system must be
evaluated and understood in order to optimise the energy usage and
evaluate the real benefit. If done properly, not only will the process
itself not be compromised, it may even be improved in terms of the
quality of the final product.
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ENERGY EFFICIENCY MADE SIMPLE 2015