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In the morning, I went to the fridge to drink some chocolate milk. At night, when I took out the same carton of milk, the packaging seems expanded, like some kind of air is inside. Explain please !

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Don't forget to accept answers by clicking the check-mark on questions for which you have received acceptable answers. :) –  leonardo Nov 11 '12 at 12:56

2 Answers 2

The likeliest culprit here is fermentation carried out by bacteria present in the milk. Fermentation of a sugar, for example glucose, releases carbon dioxide (a gas) :

C6H12O6 → 2 C2H5OH + 2 CO2

Since this reaction produces a gas, the gas builds up in the milk carton causing it to bulge. This is not, generally, a good sign, make sure to smell the milk before drinking it!

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There are probably several reasons. One that I can think of is that spoilage bacteria may have introduced gases that increased the pressure inside the carton. Probably that's why you notice the bulging.

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