A critical review of milk fouling in heat exchangers

Fouling of heat exchangers is a problem in the dairy industry and costs billions of dollars every year. It has been studied extensively by researchers around the world, and a large number of studies are reported in the literature. This review focuses on the mechanisms of milk fouling, investigating the role of protein denaturation and aggregation as well as mass transfer. We also endeavor to review the effect of a number of factors which have been classified into 5 categories: (1) milk quality, (2) operating conditions, (3) type and characteristics of heat exchangers, (4) presence of microorganisms, and (5) transfer of location where fouling takes place. Different aspects have been discussed with the view of possible industrial applications and future direction for research. It may not be possible to alter the properties of milk since they are dependent on the source, collection schedule, season, and many other factors. Lowering the surface temperature and increasing the flow velocity tend to reduce fouling. Reducing the heat transfer surface roughness and wettability is likely to lower the tendency of the proteins to adsorb onto the surface. The use of newer technologies like microwave heating and ohmic heating is gaining momentum because these result in lower fouling; however, further research is required to realize their full potential. The presence of microorganisms creates problem. The situation gets worse when the microorganisms get released into the process stream. The location where fouling takes place is of paramount importance because controlling fouling within the heat exchanger may yield little benefit in case fouling starts taking place elsewhere in the plant.