What is Pasteurization (HTST)?
High temperature, short time (HTST) pasteurization heats milk or another liquid product in continuous flow to a set temperature, holds it in a holding tube for a minimum time, then cools it rapidly.
Where HTST is used
HTST is the standard continuous process for fluid milk, cream, flavored milk, ice cream mix and many juices. In the United States, Grade A plants operate it under the Pasteurized Milk Ordinance as adopted by state regulators, with a recording chart and a flow diversion device that sends under-temperature product back for reprocessing.
The legal time and temperature
FDA's definition of pasteurized in 21 CFR 131.3 sets the HTST point at 161 degrees Fahrenheit (about 72 degrees Celsius) held for at least 15 seconds. The same table allows 145 degrees Fahrenheit for 30 minutes for batch pasteurization, and shorter holds at higher temperatures, down to 0.01 second at 212 degrees Fahrenheit. Products with 10 percent or more fat, or with added sweeteners, must be heated 5 degrees Fahrenheit higher.
Inside the plate heat exchanger, the regeneration section warms incoming cold milk with outgoing pasteurized milk, so the heating and cooling sections only make up the difference. Fouled plates and leaking gaskets cut regeneration, and the boiler and chiller both pick up the shortfall.
What Aqueduct tracks around a pasteurizer
Aqueduct does not replace the legal recording chart. It meters the utilities around the unit: hot water or steam into the heating section, chilled water or glycol into the cooling section, and product flow, so heat and cooling per liter can be trended run by run. A slow rise in both at steady flow is the usual sign that regeneration is slipping and the plates are due for inspection.