Energy Efficiency Made Simple Vol IV 2015

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.

Novel processes for Food and Beverage Quality, safety, efficiency A Murray, consultant

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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). 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.

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ENERGY EFFICIENCY MADE SIMPLE 2015