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Diffusion and mass transfer are ubiquitous operations in food processing. The application of electric fields can influence the mass transfer properties of foods. A small scale processing unit was used in the development of a method that would allow real-time measurement of diffusion of dyes into gel samples (at a range of temperatures and electric field strengths). The depth of penetration and localisation of infused material can be visualised and measured using image analysis methods.

Ohmic heating is a process in which electric current is passed through a food; the material heats as a result of its electrical resistance. The process has been studied intensively over the last 25 years as a result of commercial processes being developed by EA Technology and APV in the UK. The aim of this chapter is to outline and review the work on the modelling of ohmic heating and experimental work that has been conducted. Models have been written to describe the heating of simple solid-liquid mixtures, and it has been shown (both experimentally and by modelling) that solids can heat faster than liquids. This makes the process very attractive for heating solid-liquid mixtures quickly. Modelling the flow and heating of two-phase mixtures is very difficult, but some approximate models have been written to simulate the process, and these have been validated by experiments using methods such as temperature mapping with MRI. As well as sterilisation and pasteurisation processes, ohmic heating has been shown to be effective in processes such as thawing and in enhancing mass transfer between solids and liquids.

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