It traps DMS which is also something you don't want._Edge said:No, the lid is just in case I need to carry the thing -- I often have to carry it back inside in the winter because I don't have a utility sink in my garage (where I brew). I don't want to carry it with the lid off in case I stumble a bit -- boiling wort in my lap. If I put the lid on and let it cool just a few degrees it creates a seal.
Also brewing with the lid on traps sulfurs (I've heard).
