Milk fouling in heat exchangers

<br/>The mechanisms of fouling of heat exchangers by milk were studied. Two major fouling mechanisms were indentified during the heat treatment of milk: (i) the formation and the subsequent deposition of activated serum protein molecules as a result of the heat denaturation; (ii) the precipitation of calcium phosphate as a result of the decreased solubility of this salt upon heating. Both foulants are formed in the bulk of the solution and are transported to the surface, where they can be deposited.<p>If the stability of milk is lowered, e.g. by lowering the pH, coagulation of casein micelles can cause extreme fouling. A further cause of fouling is air bubbles, which arise in the milk on heating and stick to the stainless steel wall; they appear to act as nuclei for the formation of protein deposit.<p>Fouling in heat exchangers can be reduced by controlling the formation of activated serum protein molecules and by preventing the precipitation of calcium phosphate. Various ways to achieve this are given.<p>Once formed, milk deposits can readily be removed by alkaline cleaning followed by acid cleaning under the right conditions.