Whenever I empty a carton of a drink such as milk or orange juice, I replace the cap on the container and leave it aside ready to throw out. Invariably, when I return the carton seems to be under some pressure as the sides are bulging and stiff. Why does this occur? This does not seem to happen with cartons that have held carbonated drinks.
I was interested to see the phenomenon of inflating milk cartons explained in The Last Word (8 April). You can have similar fun at breakfast time by taking a cold bottle of milk 鈥� the kind with a foil cap delivered to the door in the UK 鈥� from the fridge, pouring a little onto your cereal and replacing the cap securely. A little while later, when the air in the bottle expands as it warms up, the foil top will shoot into the air with a quite impressive pop.
Presumably this phenomenon also explains why, having taken my baby鈥檚 milk from the fridge and warmed it, when I come to test the temperature by inverting the bottle over my wrist the milk shoots all over the kitchen unless I first unscrew and re-screw the lid to release the pressure.
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Claire Webster, Winchester, Hampshire, UK