Never ones to accept a kitchen myth at face value, the team at Cook's Illustrated blanched a series of vegetables with the lid both on an off. Not only did they find that the pH level of the water in all the pots were the same (meaning that the acid was equally "trapped" in both pots), but the vegetables all turned out bright green and tasty regardless of being covered.
We'd like to give this experiment a try ourselves next time we need to blanch some vegetables. We also feel a little like clipping this out of the magazine and sending it to our old school!
• This tip comes from the May/June issue of Cook's Illustrated, currently available on newsstands.