Boiling potatoes in their skins (Slideshow version)
Stage 6/6 :
Next the potatoes are left to cool in their cooking water until cold, then dried and weighed again.Result: the weight of the peeled potatoes has increased by 4 grammes each.
Conclusion "You should not leave potatoes to cool in the cooking water": it's true if they are peeled, otherwise they will absorb some of the water.
Remarks
Both true and false: It's not necessary to leave the skins on potatoes for boiling, peeled or unpeeled they do not absorb water during cooking.But you should not leave peeled potatoes to cool in the cooking water, because they will absorb water (about 7% in these tests). On the other hand, this "sponge" property of peeled potatoes might be an advantage when cooking them in something other than water, milk or cream for example, as they will absorb some of the good flavour.
And to drink?
We are going to boil both peeled and unpeeled potatoes together, weighed before and after boiling, to see if they have absorbed any of the cooking water.Next we'll leave the potatoes to cool in the cooking water, then weigh them again, to see if they have absorbed any water or not.