Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization sterilizes food by heating it above 135 °C (275 °F) – the temperature required to kill spores in milk – for 1 to 2 seconds.
Ultra-high-temperature processing - Wikipedia, the free ...
https://en.wikipedia.org/wiki/Ultra-high-temperature_processingWikipedia
Interesting that it can be done inside the paper cartons. or perhaps added after.... thanks for the info!