There is a certain fallacy in the wisdom of steaming green vegetables, a cooking method that is very much in favor these days. Steaming is really only best for green vegetables that are straight out of the garden, or at least no more than two or three days from being picked. Steaming heightens a fresh vegetable’s natural sweet flavors.
However, the delicate sweetness of a fresh vegetable changes soon after it is picked, and within several days is replaced by a stronger, sometimes bitter taste. (This is particularly true of broccoli and spinach.) Steaming will only accentuate this off taste, and therefore I do not recommend its use for older vegetables.