I just wonder if my porridge would be ready any faster if I take the lid off my tupperware container.
closed as unclear what you're asking by Art Brown, Bernhard, Kyle Kanos, ACuriousMind, Brandon Enright Aug 29 '14 at 16:12
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If you put cooked porridge in a vacuum it will dry out i.e. lose all it's water. In fact this process is the basis of freeze-drying.
But what you're describing isn't putting the porridge in a vacuum. If you put a hot water/porridge oats mixture in a sealed box then exclude the air you actually have the water/porridge mixture in equilbrium with water vapour. The pressure of the water vapour will be the vapour pressure of water at whatever the temperature of the porridge is.
In any case, the absorption of water by the porridge oats is limited by the diffusion of liquid water into the starch grains in the porridge, and the vapour plays no part in this. So whether the box is sealed or not will have little effect on the cooking time. However with an unsealed box you may need to add extra water to make for the water lost by evaporation.