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How does a pressure cooker work?

Pressure cooker is a modern kitchen appliance that can cook almost any type of food. It saves time, fuel and above all preserves the nutritious content of the food. Do you know how the pressure cooker does all this? We know that all liquids boil at a definite temperature under normal atmospheric pressure, which is known as the ‘boiling point’ of that liquid. In case of water, it is 100°C. It is observed that with the increase of pressure, the boiling point of the liquid also increases. Similarly, reduction in the pressure lowers its boiling point. It is this phenomenon that prompted the invention of pressure cooker. Pressure cooker is essentially a vessel of stainless steel or an alloy of aluminium. It has a lid fitted with a safety valve at its top to let out excess steam to maintain the internal pressure within the safety limits. A rubber ring is fitted between the container and the lid to prevent steam from leaking and build up pressure inside the cooker. The cooker is fitted with a thermally insulated handle. The food to be cooked is put in the vessel along with some water and the lid is closed. When the vessel is heated, the steam so formed increases the pressure inside the vessel. As the pressure increases, the boiling point of water also increases and it reaches up to 130°C. This helps to cook the food quickly. When the steam pressure inside the cooker increases beyond the required pressure, the control valve is automatically lifted up, allowing the excess steam to escape. Thus the pressure inside is regulated and kept with the safety limits. If there is no hissing or whistling sound after the cooker has been kept on the oven for some time, the valve should be moved slightly to check if the vent is not choked. Also before opening the lid, it should be ensured that there is no pressure inside the cooker, if there is pressure inside the cooker, the valve should be lifted up slightly with the help of tongs to allow the pressure to escape.

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