Question

Working of pressure cooker

Answer 1

Answer:

Pressure cookers are fantastic tools. They develop the characteristic flavors and textures of foods so quickly that what is conventionally a long, labor-intensive process becomes one hardly more time-consuming than a casual sauté. Risotto takes six minutes instead of 25. An intense chicken stock takes only 90 minutes. You can even pressure-cook food in canning jars or in oven bags or FoodSaver bags rated for high temperatures–which means grits and polenta, for example, no longer require constant stirring to avoid sticking. The high temperatures inside the cooker also promote browning and caramelization, reactions that create flavors you can’t get otherwise in a moist cooking environment.

A pressure cooker is essentially just a pot with a semi-sealed lockable lid and a valve that controls the pressure inside. It works by capturing the steam that, as it builds up, increases the pressure in the vessel. The pressure increase in turn raises the boiling point of water, which normally limits the cooking temperature of wet foods to 100 °C / 212 °F (at sea level; the boiling point is slightly lower at higher elevations). Because the effective cooking temperature is higher in the pressure cooker — as high as 120 °C / 250 °F — the cooking time can drop substantially.

Take a look below at our cutaway photo from Modernist Cuisine at Home. The letters correspond to an explanation of each part of the pressure cooker.  (Refer the image attached)

1. High-pressure steam rapidly transfers heat to the surface of any food not submerged in liquid.
2. A spring-loaded valve is normally open so that air can escape. As heating begins, expanding vapor pushes this valve up, closing off the vent. (At very high pressures, it rises farther and reopens the vent to release excess steam.) The valve regulates the pressure inside the cooker to a preset level: typically 0.7 or 1 bar / 10 or 15 psi above atmospheric pressure; this value is called the gauge pressure. At these elevated pressures, water boils at 114 °C or 121 °C / 237 °F or 250 °F, respectively. As soon as the cooker reaches the correct cooking pressure, reduce the heat to avoid over-pressurizing it.
3. The sealing ring, typically a rubber gasket, prevents steam and air from escaping as they expand. This causes the pressure in the vessel to build as the temperature rises. Any food particles stuck in the seal can cause it to leak steam, so check and clean the gasket regularly.
4. The lid locks with a bayonet-style mechanism that pushes against the sides of the cooker. Frequent over-pressurization can damage this mechanism and render the cooker useless. Other designs use bolts that clamp around the outside.
5. The handle locks as well, to prevent the lid from opening while the contents are under pressure.  
6. There is too much liquid in this cooker. Generally, you should fill the pot no more than two-thirds full.
7. Water vaporizes into steam, increasing the pressure inside the cooker as it heats. Because the boiling point of water depends on pressure, it rises too, just enough to keep the water and steam temperature hovering around the boiling point for the higher pressure. The pressure continues to rise until it is stabilized by the valve.
8. Add enough water to the pot, either around the food or under a container of food elevated above the bottom of the pot, to enable plenty of steam to form.

Answer 2

Answer:

High-pressure steam rapidly transfers heat to the surface of any food not submerged in liquid.

A spring-loaded valve is normally open so that air can escape. As heating begins, expanding vapor pushes this valve up, closing off the vent. (At very high pressures, it rises farther and reopens the vent to release excess steam.) The valve regulates the pressure inside the cooker to a preset level: typically 0.7 or 1 bar / 10 or 15 psi above atmospheric pressure; this value is called the gauge pressure. At these elevated pressures, water boils at 114 °C or 121 °C / 237 °F or 250 °F, respectively. As soon as the cooker reaches the correct cooking pressure, reduce the heat to avoid over-pressurizing it.

The sealing ring, typically a rubber gasket, prevents steam and air from escaping as they expand. This causes the pressure in the vessel to build as the temperature rises. Any food particles stuck in the seal can cause it to leak steam, so check and clean the gasket regularly.

The lid locks with a bayonet-style mechanism that pushes against the sides of the cooker. Frequent over-pressurization can damage this mechanism and render the cooker useless. Other designs use bolts that clamp around the outside.

The handle locks as well, to prevent the lid from opening while the contents are under pressure.  

There is too much liquid in this cooker. Generally, you should fill the pot no more than two-thirds full.

Water vaporizes into steam, increasing the pressure inside the cooker as it heats. Because the boiling point of water depends on pressure, it rises too, just enough to keep the water and steam temperature hovering around the boiling point for the higher pressure. The pressure continues to rise until it is stabilized by the valve.

Add enough water to the pot, either around the food or under a container of food elevated above the bottom of the pot, to enable plenty of steam to form.