Food engineering, or food process engineering, is the application of the principles of science to the efficient commercial production of safe wholesome food from defined raw materials. Physics is the scientific basis of food process engineering but thermo-bacteriology and predictive microbiology are also relevant.
Aspects of chemical and agricultural engineering are common to food engineering as are also aspects of food science. Food process engineering was originally an offshoot of chemical (process) engineering. Many of the unit operations encountered in chemical engineering are also applicable to food. Food processing includes, for instance, fluid and solids handling, heat transfer, filtration, evaporation, leaching, distillation and drying. The approach to mathematical modelling that both chemical and food engineers employ is the same. The principles of chemical engineering kinetics are now being applied in predicting the growth or destruction of microorganisms in food.
Thus, the similarities between chemical and food engineering far outweigh the differences. Food processing does however have some special features:
Today, while many universities overseas provide degrees in food engineering, formal training in food engineering locally is limited to part courses at a couple of our Southern African universities.
Two international associations promote the link between food and engineering principles. The International Association of Engineering and Food only exists to organise a Congress, the International Congress of Engineering and Food (ICEF), every three to four years. This congress is attended not only by food process engineers but also by engineers from other disciplines, food scientists, mictobiologists and chemists. The eleventh such congress will be held in Athens in May 2011. Separate from this, the International Society of Food Engineering (ISFE), a subgroup of IUFoST, provides a network for those involved in the engineering side of our industry.
Over the last two decades advances in food engineering have been driven by two forces – market requirements for innovative foods and minimal heat treatments; Market requirements for hygienic design and food safety. Rather less emphasis has been placed on such important topics as sustainability and food security. To meet these demands of the marketplace in regard to innovation the engineer has been moving away for the traditional unit operations approach and drawing on increased knowledge of the physical properties of food products. He has also been adapting advances in other sciences notably materials science and computer technologies.
At the same time there has been a focus on hygienic design. In particular risk analysis and verification have become a part of the design of machinery for use in the food area. Hardware such as double seat valves have been developed to allow for safer processing.
Mathematical Models
A classic example of the study of food properties is the mathematical modeling of the frying of potato chips and the cooking of hamburgers. Prof Paul Singh’s examination of the microstructure of french fries revealed that there is a boundary between the crust consisting of potato solids, oil and water vapour and the core which consists of water and potato solids. Singh used a moving boundary model to predict the cooking times under varying conditions. The relevance of the study of chips and hamburgers was indicated by the statistic that hamburgers were at the time of the research the third best selling restaurant item in the US and french fries were the second best.
Diffusion in foods is also important in the development of active packaging and edible films. Active packaging and films interact with food. For example, by way of a gas or vapour emission they may act as an oxygen scavenger or prolong shelf life in some other way. Research in this field involves the construction of the packaging material or film, the prediction, using mass transfer principles of the resultant effect, and the validation of that prediction. Where an oxygen scavenger or a mould inhibitor is released, its rate of diffusion in the product is important. Moisture transfer in composite foods has been experimentally and mathematically investigated. For instance the use of moisture barriers between layers in products such as sponge cakes result in better shelf life. Similarly better knowledge of rheology has led to advances in many food products notably chocolate.
Other Sciences
Advances in other branches of science have led to the advances in novel thermal and non thermal processing methods during the past two decades. The food industry has borrowed from the mineral processing industry in regards to the use of high pressures. Similar cylinders to those originally designed for the manufacture of artificial diamonds are used for the pasteurisation of a variety of meat, seafood and guacamole products. High pressure processing was envisaged more than a century ago but was not possible commercially until cylinders could be built to withstand pressures of more than 6000 atmospheres.
Advances in control technology have made the development of the ohmic heating process possible. This process relies on accurate feed-forward control. However, the intense research into these non-themal processes has not yielded the commercial boom that was expected in the early nineties. Part of the reason is that the non thermal processes have almost without exception proved to be useful for pasteurisation but not suitable for sterilisation processes. The two leading novel technologies have been pulsed electric fields and high pressure processing. There are very few pulsed electric field plants world wide . High pressure processing has been more successful but the technology is expensive and has found most of its use for niche high value products such as abalone and lobster.
Novel thermal processes have also produced less commercial benefit than was imagined. Neither the Ohmic (electro-heating) nor the very promising induction heating process have found wide commercial application.
The future
In the future engineers working in the food industry are going to be concerned with finding ways to process more efficiently. Centrifuges that require less power are already being advertised. More efficient CIP will be possible using more advanced measurement and control. There will be an increased focus on membrane processes. Osmotic evaporation is one process that holds potential. Heat pump applications may become viable again. Another trend will be increased emphasis on nano technology.
Andrew Murray is a consulting food process engineer. He is particularly concerned with hygienic design and energy efficiency in the food industry. He is a committee member of the International Society of Food Engineering and a member of SABS TC 242 tasked with Energy Management Standards.
