My wife and I have this debate all the time:
1) I say you can leave the lid off and even if the broth reduces, you can just add water back and still have equally good broth
2) She says that you have to leave the lid on and just let the broth boil down to the right amount
I was convinced that I was right, but then just saw a recipe for shio broth that says you cannot do 1). It's just not the same. Yet scientifically, I would have thought all that's boiling off is water, so adding water back should be fine. But thinking about it more, maybe there are aromatics that boil off also?
So, I thought I'd throw it to the Chowhound community...