Steam can be used to cook food and it has been the most efficient way of cooking anything from soft vegetables to hard meat. Pressure cooker works on this principle.
The most important parts of a pressure cooker are the rubber ring and the valve on the top of the cooker. The rubber ring that goes between the pot and the lid takes care that no air escapes from inside the container. The valve on the top helps hold the steam and release it at proper time with a whistle ensuring that pressure does not reach dangerous levels. If both or one of these parts are worn out, pressure would not be able to build up inside the pot and the food will not be cooked properly.
In order to cook food, all that a pressure cooker does is to build pressure by heating water continuously. As a result water is able to get much hotter without escaping outside. When it turns into steam, the moisture-laden air is hotter than the steam that would come outside. The trapped steam transfers its energy to the water in the food. Now water being a good conductor of heat begins to force heat into the food. The steam applies uniform pressure to all surfaces of the food and that leaves the food un-smashed. Also fewer nutrients are lost because nutrient-rich steam condenses inside the pressure cooker instead of being lost in the air.
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