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Steam Infusion Heater For Ultra High-Temperature Pasteurization

Division of Microbiology, Food and Drug Administration, Department of Health, Education, and Welfare, Cincinnati, Ohio 45226

ABSTRACT

The steam infusion heater as aligned for flavor standardization cannot be used for ultra high temperature pasteurization because of a potential variable holding time. To eliminate this variable holding time, the product flow control valve was placed upstream from the infuser, and the timing pump was inserted at the discharge of the infuser. Temperatures at the holding inlet were essentially constant (±0.5 C) for cream at 1,140 liters per hour, a temperature increase by steam infusion of 22 C, and a holding temperature of 88 C. Other tests on water, milk, and cream verified that temperature control in the holding tube would be satisfactory for this process. Residence times, however, can be reduced by product displacement in the holding tube from noncondensable gases. Residence time measurements at 110 C for water were 5% lower with an infuser pressure of 0.2 atm above the product saturation vapor pressure than with an infuser pressure of 0.6 atm above the product saturation vapor pressure. An infuser pressure at least 0.6 atm above the saturation vapor pressure will be sufficient to prevent significant reduction in residence times from noncondensable gases. Accordingly, the infusion equipment as realigned will give the temperature control and constant residence times from noncondensable gases. Accordingly, the infusion equipment as realigned will give the temperature control and constant residence times in the holding tube, which will fulfill the public health requirements for pasteurization.