Evaporation In The Food Industry

The term evaporation used in the food industry is referred to the procedure of heating liquid to its boiling point to remove water as excess vapour. This happens due to the increase in temperature and/or pressure. Based on general knowledge, water boils at 100°C but actually begins to evaporate at 0°C. The amount of evaporation depends on the amount of water that needs to evaporate and on temperature. The latent heat of condensation is used to raise the temperature of the liquid food to boiling point, and to evaporate the water. The vapour is then removed from the surface of the boiling liquid. It is essential to work at low temperatures because food products are heat sensitive. This is done by boiling the liquid portion under vacuum. Evaporation

Evaporation is then used to pre-concentrate the food products – prior to drying, freezing and sterilisation- by reducing the water content almost completely to increase the solid content of the food. This process acts as a preservation technique according to P.G. Smith (2010) by a reducing the water activity and also changes the colour of food (Anon, 2013). The aim of this to increase microbiological stability and shelf-life and also to reduce costs and save energy concerning transport and storage which is achieved by reducing the product bulk volume. This is of great convenience for the consumer or the

It was developed commercially through the use of vertical tube heated from the outside with steam. The liquid on the inside of the tube was brought to a boil with the vapour generated with the formation of a core in centre of the tube. More vapours are formed as the fluid moves up the tube resulting in a higher central core velocity forcing the remaining liquid to the tube wall. Falling-film evaporators have the feed being introduced into the top of the tube moving – under gravity rather than against it – downward on the inside of the vertical tubes as a thin film. The design of such an operation is very complicated as the distribution of the liquid film flowing downward in the tube is more difficult to obtain than an upward-slow system such as the rising film evaporator (Goff, 2013). To accomplish this, its makes use of specially designed spray nozzles. It allows a greater number of effects than the rising film evaporator and can handle more viscous liquids and gives rise to shorter product contact time (Helman, 2003). This evaporator type is best suited for highly heat sensitive products such as orange juice and for steam utilisation in beet and cane sugar factories and