In the dairy industry, problematic milk fouling deposits are found
to form on heat transfer surfaces during thermal treatment of milk.
Milk fouling deposits formed under normal pasteurisation conditions
generally contain 50e60% protein, 30e40% mineral and 4e8%
fat. Such fouling deposits decrease heat transfer efficiency and exert
adverse effect on product quality and safety (Bansal and Chen, 2006;
Fryer et al., 2006). Cleaning operations are crucial in the dairy and
food industries to obtain microbiologically safe products. Industrial
cleaning for dairy processes are of great importance for ensuring
hygienic production conditions. The build up of a deposit layer increases
pressure drop (due to the increase in surface roughness and
the decrease in cross-sectional area of the flow channels) and reduces
heat transfer efficiency. Increased costs are therefore incurred
to operate the plant. Fouling can also compromise product quality,
by cross contamination or microbial growth on the deposit. It is
necessary to stop production to clean the process plant; in the food
industry this must often be done daily. Removal of milk fouling
deposits by effective cleaning-in-place (CIP) procedures is therefore
essential. This is most commonly achieved by circulation of 0.5e1.5%
NaOH solution or formulated caustic detergent solution at high
temperatures (70e80 C) (Bylund, 1995) under increased turbulence
and flow velocity (Fig. 1) (Jeurnink et al., 1996).