Is milk preserved longer by placing an opened, but re-capped, milk carton/jug in a second sealed layer, all inside a fridge?
I’ve worked at two cafés that, after opening a milk carton or jug, put it inside a second sealed layer — such as a big airtight bag, or food container — before putting all this in the refrigerator. But any evidence that this extra step makes the milk last longer?
The owners of these two cafés are different people. But both argue that once the cap is unscrewed — even after you recap the carton/jug and put it back into the refrigerator — the carton/jug is no longer airtight, and fully sealable. After opening, even in a fridge, air can always enter the carton/jug, accelerating spoilage. Both owners always store an opened milk carton/jug in the refrigerator with their caps on, inside an additional airtight bag or container in an attempt to extend shelf life.
Source for top pic. Bottom pic.
Top Answer/Comment:
Sounds like a holdover from older paper/cardboard cartons or TetraPaks without a screw-top, that would be "slightly open" once pried or cut open, even if re-folded. A practice becomes ingrained, the reasons for doing it become obsolete, but actually thinking about it and changing the practice, rather than continuing to follow the outdated practice is not the path chosen by quite a large part of humanity, actually.
Not difficult to demonstrate that the average plastic screw-top is, in fact, airtight at reasonable pressures.
Could even be fun - get an empty carton, some sodium bicarbonate, and some vinegar. Put in the carton and screw the cap on tight. Do that somewhere the resulting minor explosion and mess won't be a problem once the pressure gets unreasonable.
Unfortunately, even that probably won't affect the beliefs of the managers who want workers to follow the outdated practice based on things not-now-true.
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