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Smell and appearance can reveal obvious spoilage, but they cannot detect every microorganism capable of causing foodborne illness.
Some harmful bacteria don't necessarily produce a noticeable bad smell, taste, or visible change.
That's why proper refrigeration, handling, and storage time matter rather than relying entirely on a “sniff test.”
This principle applies to many foods, not only milk.
Your nose is useful for detecting spoilage—but it isn't a food-safety laboratory.
© USDA