Steaming is normally associated with Asian or Chinese cuisine. The tools needed for the process are cheap and easily assembled. For example, the ubiquitous wok in Asian homes can be easily converted to a steamer. This may explain why it is a popular technique in many homes.
The best way to understand steaming is to see it as cooking without direct contact with a strong heat conductor, unlike stir frying in the wok or braising in a pot. Steaming is about cooking in low heat. Air is a poor conductor of heat. The Western equivalent is cooking in an oven, which generally uses the same principle but without the inclusion of water. Thus, you can steam a cake and bake a fish!
Through contact with steam, the food is cooked evenly throughout. This is why in steaming, you do not need to turn the food over mid-way to cook its other side.
The science of steaming is simple. Water (liquid) that boils off into a gaseous state (steam) contains high heat energy. This latent heat of vaporization hits the food and cooks it. Steam, by definition, is actually invisible. The ‘steam’ you see is mist – droplets of water that are suspended in or mixed with air. Of course, when there is steam, you see the mist. But my point is, what you do not see is actually where the heat is and this is what cooks the food. You want to cook the food in the steam which you do not see – under the mist rather than in it.
This explains why wok covers are dome-shaped. The dome holds the mist and ensures that the food is cooked below the mist and not in it. The shape also allows for condensed water droplets to slip back into the water below. For this simple reason, the plate you use to steam the food must be smaller than the circumference of your wok. By experience, you will know that if your plate is too big, it will collect more condensed water.
The exception is the bamboo steamer. The gaps in bamboo steamers allow the mist to escape. In fact, bamboo steamers are superior because less water condenses onto the food than when metal covers are used. This is why paus (buns) are best steamed using bamboo steamers. Wet buns are disastrous.
Bringing it altogether, steaming has these advantages:
1. Foods which come out best using the slow and low method are suited for steaming.
2. It is harder to overcook the food as the cooking process is gentler.
3. It is suited for odd-shaped food where you want the heat to be evenly applied across its surface (e.g. fish and rice dumpling).
4. It is considered a healthier way of cooking as there is less oil involved.
5. Steaming is similar to using the oven; you don’t need to attend to it as it cooks. This is why steaming is very useful when you need to cook various dishes simultaneously.