Pressure cooker is a modern kitchen appliance that can cook almost any type of food in a very short time. It also saves a lot of fuel. Moreover, the nutritional constituents of the food are also not spoilt. Do you know how the pressure cooker helps in fast cooking?
We know that every liquid boils at a definite temperature at the normal atmospheric pressure. This temperature is called the ‘boiling point’ of the liquid. In the 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 the steam in order to maintain the internal pressure within the limit the vessel can bear. A rubber ring is fixed at the junction of the vessel and the lid which does not allow the steam to leak out. A thermally insulated handle is attached to the pressure cooker for handling it. 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 is why food gets cooked quickly inside the pressure cooker. 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 there is no risk of bursting.
If there is no hissing or whistling after the cooker has been kept on the oven for a sufficient time, the valve should be slightly shaken to see if the hole below is not choked. Before opening the lid the valve should be slightly lifted up with the help of tongs to allow the steam to escape.