Final answer:
Some milk can stay fresh without refrigeration due to UHT pasteurization which sterilizes it by heating to 138 °C, followed by sealing it in airtight containers, allowing it to be preserved for up to 90 days.
Step-by-step explanation:
The reason some types of milk can stay fresh and safe without being refrigerated is due to a process called UHT pasteurization. This method involves heating the milk at ultra-high temperatures (around 138 °C) for a very short period, typically 2 or more seconds. By doing so, it effectively sterilizes the milk, killing any harmful microorganisms present. After pasteurization, the milk is then sealed in airtight containers, which prevents new bacteria from contaminating it. As a result, this milk can be stored for extended periods, often up to 90 days without refrigeration, as long as the packaging remains unopened.
Contrast this to raw or unpasteurized milk, which contains microorganisms that can lead to spoilage or even foodborne illnesses if consumed. Therefore, such milk requires refrigeration to slow down the growth of these microbes. The refrigeration reduces the energy of the molecules, thereby lowering the rate of reactions that lead to spoilage. When milk is kept at room temperature, the higher energy of the molecules increases the rate of spoilage reactions, making it unsafe to consume after a short period.