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Practical Reduction of Orthokinetic Flocculation in Processing of Sterile Milk Concentrates

Dairy Products Laboratory, Eastern Utilization Research and Development Division, U.S.D.A., Washington, D. C.

ABSTRACT

Comparison between sediment deposition rates in milk concentrates sterilized statically and dynamically demonstrated convincingly that orthokinetie flocculation plays as important a part in the coagulation process as does thermal coagulation. Substitution of 2-, 3-, and 4-in. holding tubes for the 5/16-in. Mallory holding-coil furnished conditions for laminar flow and shear gradient variation in processing a large number of concentrates of varying composition. For storage periods up to four months, no measurable amount of sediment was observed in concentrates processed under conditions of reduced velocity gradients, whereas some sediment was usually observed in concentrates processed under conditions of relatively high gradients. A two- to fourfold decrease in sediment deposition was observed in concentrates stored for 8–12 months when conditions favoring low-velocity gradients in the holding period were substituted for those conducive to a high-velocity gradient. Substitution of evaporative cooling for forced convective cooling brought forth further marked decreases in the sediment deposition rate. At the end of 16 months of storage at 70F no sediment was observed in high-fat concentrates (fat to SNF ratio = 1:1.8) sterilized under conditions of reduced gradients.