FOAM TEMPERATURES DURING VAT PASTEURIZATION OF MILK PRODUCTS

Heating rates of foam during vat pasteurization were investigated to determine whether shorter holding times and higher processing temperatures would be feasible from a public health standpoint. A rake of 19 thermocouples, spaced 0.5 inch apart, was installed vertically in a 300-gal vat pasteurizer and the rake was adjusted to measure the temperature of the heated airspace, foam, and liquid product. With 200 gal of ice cream mix (16% milk fat), an 11-inch foam was generated on the liquid surface. The minimum temperature in the ice cream mix foam was below pasteurization temperature for 27 min of the 30-min holding period despite satisfactory temperatures as indicated by the product and airspace thermometers. When a 7-inch foam was generated above 218 gal of chocolate milk, the minimum foam temperature was below pasteurization temperature for the first 14 min of the holding period. Attempts to generate foams on milk were unsuccessful. Because of the slow heating rates of milk-product foams, holding times s...