How does a steam cooker use energy...where does it come from?

Question

Need help understanding pressure/pressureless steam cooking very confusing.....what's convection....I know it's alot....thanks

Answer 1

To get steam you heat water until it boils thus producing steam. How you add this heat depends on the type of stove or oven. Typical home appliances will use either gas or electricity for heating.

A pressure cooker is a sealed pot (air tight) with a special lid which contains a pressure gauge and a pressure limiting relief valve.

The items you wish to cook are placed into the pot and placed on the stove top. Heat is applied and the temp rises until the boiling point of water is reached. As steam is produced in the sealed pot the pressure inside rises. the properties of steam are such that the boiling point of water raises with pressure. In other words as teh pressure rises so does the boiling point of water. In a pressure cooker the pressure builds up so that the food is cooked under pressure. This allows cooking to be performed at a higher temperature without boiling, (or boils as much) because the steam is held inside the pot flavors do not have a chance to escape and the higher cooking temperatures used under pressure allow for faster cooking.


Steam cooking: The easiest way to use steam to cook an item (at atmospheric pressure NOT like a pressure cooker) is with a WOK. (you can use a pot with a lid) Because the lid of the pot or wok is not mechanically sealed, steam pressure cannot build up. So you may referr to this as pressureless steam. (Its really atmospheric pressure)

Steam cooking uses the steam produced by boiling water to cook. The steam is moist heat at 212F which will not dry out food. Also because the food is not being boiled in the water many of teh nutrients remain in the food rather than being washed away in the water. Steam cooking is also indirect heat, the stove heats the water not the food. It is the steam produced by the heated water which cooks the food. This means that food is less likely to burn and it limits the temperature the food is exposed to the boiling temperature of the water 212F / 100C

Convention Oven.

In a regular stove/oven the heat or a flame or electric element is at the bottom of the stove. Heat rises to the top of the oven. There are several racks in teh oven to place food at different levels, use a higher rack the food gets hotter as heat collects at the top of the oven
Place the food on a lower rack the food still cooks but slower as not as much heat collects in the lower part of the oven.

A convection oven works in a similar fashon to a regular oven except that a fan is used to mix the air. The mixing of the air in the oven prevents the heat from collecting at the top . In a convection oven the mixing of the air within the oven by the fan prevents having a temperature difference between the upper rack and the lower rack.

Foods placed in a convection oven on multiple racks will cook at the same temperature and rate. In a regular home oven food placed on different racks will cook unevenly as the upper rack sees more heat .

Convection ovens are available for the home but are mainly used in commercial / food service kitchens. Convenction ovens also cook food a little faster as the moving air keeps hot air in contact with the food, and the mixing of air cooks the food evenly eliminating the need for turning or swaping positions from rack to rack thus saving time....

Answer 2

The energy comes from the steam produced from the boiling water, as it re-condenses on the food. Condensing steam is a much more efficient way to transfer heat than the normal method of hot air circulation provided by a regular oven.

To produce the steam you have to input enough energy to evaporate water placed in the bottom of the kettle, which takes about 1000 BTU per lb of water.
This energy in the steam is then available to heat your food as the steam condenses into water again on the cooler surfaces of the food.

The higher the pressure of the steam, the more energy that you have to put into the water to turn it into steam, but the more energy the steam also contains as it transfers the energy back to the food.

In a normal pot or pressure cooker you depend on normal convection currents to circulate the steam inside the kettle.

Some of the new ovens come equiped with a fan that circulates the warm air over the food being cooked and provides for more efficient heat transfer and cooking speeds.