Question

give notes on pressure number 1. how does it apply 2.advantages 3.disadvantages 4.how is pressur made.

Answer 1

Advantages

Foods cook much faster with pressure cooking than with other methods (except for small quantities in microwave ovens). Pressure cooking requires much less water than conventional boiling, so food can be ready sooner. Less energy is required than that of boiling, steaming, or oven cooking. Since less water or liquid has to be heated, the food reaches its cooking temperature faster. Using more liquid than necessary wastes energy because it takes longer to heat up; the liquid quantity is stated in the recipe. Pressure cookers can use much less liquid than the amount required for boiling or steaming in an ordinary saucepan. It is not necessary to immerse food in water. The minimum quantity of water or liquid used in the recipe to keep the pressure cooker filled with steam is sufficient. Because of this, vitamins and minerals are not leached (dissolved) away by water, as they would be if food were boiled in large amounts of water. Due to the shorter cooking time, vitamins are preserved relatively well during pressure cooking.[16]
Several foods can be cooked together in the pressure cooker, either for the same amount of time or added later for different times.[15]Manufacturers provide steamer baskets to allow more foods to be cooked together inside the pressure cooker.
Food is cooked more quickly in a pressure cooker because at the higher pressure (1 bar/15 psi), the boiling point of water rises from 100°C (212°F) to 121°C (250°F). More importantly, the temperature of the steam also rises to 121°C (250°F), at which point it is called super-heated steam. This super-heated steam (that is, steam under pressure) is able to transmit its thermal energy to the food at a dramatically increased rate. The higher water temperature has little effect on cooking time, it is the steam that is doing the work. One may consider a steam locomotive. The big tank of boiling water (the boiler) is only the source of the steam. It is the steam itself that does the work of driving the pistons and moving the locomotive forward. Not only is this steam energy transmitted quickly to food, it is also transmitted rapidly to any micro-organisms that are present, easily killing even the deadliest types that are able to survive at the boiling point. Because of this enhanced germ killing ability, a pressure cooker can be used as an effective sterilizer for jam pots, glass baby bottles, or for water while camping. In fact, the autoclave, used in hospitals to sterilize surgical instruments, is really just a more precise and technical version of the ordinary pressure cooker.

Disadvantages

Pressure cookers are considerably more expensive than conventional saucepans of the same size. The additional gasket (sealing ring) requires special care when cleaning (e.g., not washed with kitchen knives), unlike a standard lid for a saucepan. Food debris must be cleaned from the gasket after every use. The gasket/sealing ring needs replacing with a new one about once a year (or sooner if it is damaged e.g. a small split). A very dry gasket can make it difficult or impossible to close the lid. Smearing the gasket sparingly with vegetable oil alleviates this problem (using too much vegetable oil can make the gasket swell and prevent it sealing properly). A gasket that has lost its flexibility makes bringing the cooker up to pressure difficult as steam can escape before sufficient pressure is generated to provide an adequate seal; this is usually a sign that the gasket needs replacing with a new one. Oiling the gasket with vegetable oil may alleviate the problem temporarily, but a new gasket is often required. Pressure cooker manufacturers sell replacement gaskets and recommend their replacement at regular intervals e.g. annually. If the pressure cooker has not been used for a long time, the gasket and other rubber or silicone parts will dry out and will likely need replacing.
In order to inspect the food, the pressure cooker needs to be opened, which halts the cooking process. With a conventional saucepan, this can be done in a matter of seconds by visually inspecting the food. As a result, accurate timing is essential for the recipe e.g. with an audible timer.
The increased weight of conventional pressure cookers makes them unsuitable for applications in which saving weight is a priority, such as camping. Nonetheless, small, lightweight pressure cookers are available for mountain climbers (see Use at high altitudes).
A minimum quantity of liquid is required to create and maintain pressure, as indicated in the manufacturer's instruction manual. More liquid is required for longer cooking times. This is not desirable for food requiring much less liquid, but recipes and books for pressure cookers take this into account .

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