Steaming is a moist-heat cooking method in which foods are cooked on a rack or in a steamer basket in a covered pan over, (NOT IN) simmering or boiling water (usually about an inch in depth). Steaming provides a gentle heat that is especially good for vegetables. Unlike boiling vegetables—which means immersing the vegetable in enough boiling water to cover—steaming vegetables usually keeps veggies crisper and is less likely to lead to overcooking. Steaming is also a faster method than boiling, since you only have to heat a small amount of water, as opposed to a whole pot. (However, actual boiling does cook the vegetables faster.)
To steam vegetables, you can use a wide variety of equipment. Steamer pots are specially designed for steaming; a perforated pot holds the item to be steamed and stacks on top of a solid pot that holds the water. A common alternative is a steamer basket, a folding metal basket that adjusts to fit in almost any pot.
Cooking times and preparations vary from vegetable to vegetable, especially depending on size. For larger vegetables that need to steam longer, check the water level occasionally, adding more if necessary. In general, steamed vegetables are done when they are tender but not mushy; you should be able to pierce the thickest part of the vegetable easily with a thin-bladed knife.
Some cooking times and tips for common vegetables include:
Artichokes: 20 to 40 minutes; artichokes are done when an inner petal pulls away easily and a sharp knife or skewer easily pierces the heart.
Asparagus: about 5 to 8 minutes; you can steam asparagus without any equipment—just stand them up in a pot with about an inch of salted water at the bottom and cover.
Beets: 30 to 45 minutes; drop the beets into ice water after cooking-drain, and peel.
Broccoli: put the peeled and sliced stalks in the steamer first, cover, and cook for 2 minutes before adding the florets, then cook for 5 to 6 minutes longer.
Carrots: 3 minutes for julienned carrots; 10 to 15 minutes for larger chunks of carrot.
Cauliflower: Break cauliflower into florets and steam as you would broccoli: Put the stalks in the steamer first, cover, and cook for 2 minutes before adding the florets; cook for 5 to 6 minutes longer. You can also cook the head whole, which will take 12 to 25 minutes, depending on the size of the head. The cauliflower should be slightly underdone when you remove it; because of its large size it will retain some heat and continue cooking slightly.
Corn: Kernels, 2 to 3 minutes; whole cobs, 8 to 10 minutes..
Green Beans: 4 to 6 minutes.
Potatoes: Peel and slice or cube potatoes 1/2 inch to 3/4 inch thick; steam 10 to 15 minutes.
Spinach: 2 to 3 minutes; you can put the spinach directly into a pot with about a tablespoon of water, and toss occasionally to steam evenly.
Read more information: http://www.bonappetit.com/tipstools/tips/2009/04/how_to_steam_vegetables#ixzz1M9hOkmd8