Short answer
Pasteurized milk receives a specified heat treatment to reduce microbes. Ultra-pasteurized milk receives a higher-temperature treatment that extends its refrigerated shelf life. An ‘ultra-pasteurized’ label alone does not mean the carton can sit at room temperature; shelf-stable milk also depends on an appropriate commercial-sterility process and aseptic packaging. 1 2
Ultra-pasteurized milk is a subtype of pasteurized milk, using a higher temperature process for extended refrigerated shelf life.
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At a glance
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| Question | pasteurized milk | ultra-pasteurized milk |
|---|---|---|
| Typical heat process | Lower temperature, longer time | Higher temperature, shorter time |
| Shelf life (unopened, refrigerated) | Shorter | Longer |
What each thing is
Pasteurized milk. Pasteurized milk in the US is fluid milk heated to a regulated temperature and time combination to reduce microbial content, then kept refrigerated to maintain safety and quality. 1
Ultra-pasteurized milk. Ultra-pasteurized milk is fluid milk thermally processed at or above 280°F for at least 2 seconds, resulting in extended refrigerated shelf life compared to standard pasteurized milk. 1
Key differences
The main distinction is the thermal process: pasteurized milk is heated to a lower temperature for a longer time, while ultra-pasteurized milk is processed at a much higher temperature for a brief period, resulting in longer refrigerated shelf life. 1
How to tell them apart
US milk labels will state ‘pasteurized’ or ‘ultra-pasteurized.’ However, both types are typically found in the refrigerated section unless the product is also aseptically packaged, which is a separate labeling and packaging process. 1 2
Where they overlap
Both pasteurized and ultra-pasteurized milks are heat-treated to reduce microbial content and are generally sold refrigerated in the US. Both must be kept cold unless specifically labeled and packaged as shelf-stable. 1 2
Edge cases
Ultra-pasteurized milk can be packaged aseptically to become shelf-stable, but not all ultra-pasteurized milk uses aseptic packaging. Some ultra-pasteurized products still require refrigeration and are not shelf-stable. 2
Why the distinction exists
The higher temperature used in ultra-pasteurization destroys more microbes, extending shelf life under refrigeration. Aseptic packaging, when used, creates a sterile environment allowing some ultra-pasteurized milk to be stored unrefrigerated until opened. 1 2
Common misconceptions
A common misconception is that every ultra-pasteurized carton is shelf-stable. The US ultra-pasteurized definition addresses heat treatment and longer refrigerated life. Room-temperature storage depends on additional processing and protective packaging, so shoppers should follow the storage directions on the specific carton. 2
Examples
At a US grocery store, you might find pasteurized milk in the refrigerated dairy case and ultra-pasteurized milk nearby, also refrigerated. On a shelf, boxed milk labeled ‘ultra-pasteurized’ and ‘aseptic packaging’ can be stored at room temperature until opened. 1 2
Sources
Sources checked October 3, 2026.
- US Food and Drug Administration — 21 CFR 131.3: General provisions. Definitions of pasteurized and ultra-pasteurized.
- USDA Food Safety and Inspection Service — Shelf-stable food safety. Aseptic packaging versus refrigerated milk.