In culinary school, it was drilled into us that the lid must be left off to avoid mushy, brown vegetables. Their explanation that acids trapped in the covered pot would turn the vegetables brown made enough scientific sense that we never thought to question it. Well, it's a good thing we have Cook's Illustrated...
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.
Related: Food Science: When Good Carrots Turn Green
(Image: Flickr member iLoveButter licensed under Creative Commons)
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I was always told that vegetables turn brown when you decide to peek, and then re-cover it. Once the lid comes off, it should stay off.
a follow-on question to this is whether we should cook vegetables by boiling them in the first place.
My girlfriend insists on cooking her broccoli in the microwave (essentially steaming them), claiming that boiling them removes all their nutrients. I like the texture better when broccoli is boiled for a little while, better than when it's nuked.
I think the veggies (or anything) would cook faster with the lid on, but you might also be more likely to forget about them and let them overcook if you couldn't see them.
good call -- why are we boiling vegetables?
i think potatoes and noodles are about the only things i boil.
I thought blanching means in and out in only ONE minute in boiling water not boiling. So lid on shouldn't even be an option.
Lid on might be an option if you want the water to return to the boil as quickly as possible, since you are working with mere moments.
We blanch veggies (boiling briefly and then dumping into ice water to stop the cooking) to partially cook them for use in salads or for stir-fries or even just taking crudites up a notch. If I want a veggie fully cooked, I steam it.
renata took the words right off my keyboard. ;)
vegetables brown when overcooked, period.
Well said renata! After all, blanching isn't the same as boiling.
Argh, those blindly repeated, silly cooking myths that just can't possibly serve any purpose, but that people do and insist on anyway. I am the kind of person who must know the why of everything. If it smells like it doesn't make sense, it probably doesn't.
Harold McGee's "On Food and Cooking" is another great resource for kitchen truth and the science behind it.
and yea, who boils vegetables anyway?