How does ultrahigh-temperature pasteurization differ from regular milk pasteurization?

Ultrahigh-temperature (UHT) pasteurization differs from regular milk pasteurization—most commonly the high-temperature short-time (HTST) method—primarily in the intensity of heat applied and the resulting shelf stability of the product.

• Temperature and Duration: Regular HTST pasteurization heats milk to approximately 72 °C (161 °F) for 15 seconds. In contrast, UHT pasteurization uses much higher temperatures of 138–150 °C (280–302 °F) for only one or two seconds.1234
• Storage and Shelf Life: Regular pasteurized milk is not sterile, contains small numbers of harmless bacteria, and must be kept refrigerated, typically lasting about two weeks. UHT milk, when processed and placed into sterile, hermetically sealed containers (such as laminated boxes or metal cans), is shelf-stable and can be stored without refrigeration for six to nine months.1243
• Flavor: Because of the extreme heat involved, UHT-treated products may not taste as fresh as those processed with conventional, lower-temperature methods.1

Once opened, both UHT and conventionally pasteurized products have similar spoilage timelines and should be refrigerated.3