Why is the cooking time reduced in the pressure cooker?

When the pressure is normal the cooking items absorb less heat and so the cooking time is high. When the pressure is high the cooking items absorb more heat faster and so the time to cook the cooking items reduced. For instance, water boils at 100 0C at 1 atmospheric pressure for a certain period of time (boiling time). When the pressure is increased the water boils at increased temperature (more than 100 0C) and the boiling time is increased. From this we can understand that when the pressure is increased the heat to be supplied is more but the cooking time is reduced. The name of the pressure cooker itself explains that cooker cooks at some high pressure. So closing the lid of the cooker we don’t allow more steam to escape and thus the pressure of the cooker increases. The heat spreads much faster and the cooking also is done faster than normal cooking.

Why is the cooking time reduced in the pressure cooker?

Why is the cooking time reduced in the pressure cooker?

 

          When the pressure is normal the cooking items absorb less heat and so the cooking time is high. When the pressure is high the cooking items absorb more heat faster and so the time to cook the cooking items reduced.

For instance, water boils at 100 0C at 1 atmospheric pressure for a certain period of time (boiling time). When the pressure is increased the water boils at increased temperature (more than 100 0C) and the boiling time is increased. From this we can understand that when the pressure is increased the heat to be supplied is more but the cooking time is reduced.

          The name of the pressure cooker itself explains that cooker cooks at some high pressure. So closing the lid of the cooker we don’t allow more steam to escape and thus the pressure of the cooker increases. The heat spreads much faster and the cooking also is done faster than normal cooking.

Explanation:

          In school our physics teacher may told us water boils at 100 0C. In our exams we may studied this fact. But do you remember one extra point in that fact.

“The boiling point of the water is 100 0C at 1 atm pressure.”

(atm – the unit of pressure in atmospheric air term. 1 atm is the pressure of the atmospheric air at sea level. Also 1 atm = 1 bar)

           Have you ever pondered at the point “at one atmospheric pressure”!

Yes, this is the point we should consider for understand the answer for our question.

The table of the boiling point of the water at different pressures:

Pressure

Boiling Point of Water

Boiling Time

0.1 bar

45.60C

The time is higher

0.5 bar (half pressure-1/2 bar)

81.50C

The time is high

1 bar (1 atm)

100 0C

The time is normal

2 bar

1200C

The time is less

8 bar

1700C

The time is even more less.

 

          From the table and figure we understood it better that when the pressure of the surrounding medium (atmospheric air in open cooking and steam in the pressure cooker) increases the boiling point (boiling temperature) increases and the cooking time is reduced.

When the pressure of the surrounding medium reduces the boiling point reduces and the cooking time is increased.

Pressure is inversely proportional to cooking time. If the pressure increases the cooking time decreases. If the pressure decreases the cooking time increases. 

Natural Example:

          When we cook rice in an open vessel at our home it takes some time to cook.

But when we cook the same at any mountain it will take more time to cook.

What is the reason?

          The pressure of the atmospheric air is 1 bar at sea level. So the cooking time is normal. The pressure of the atmospheric air is 0.78 bar at 2.13 km above sea level. So the cooking time is increased.

          But if we use pressure cooker at our home or at mountain the cooking time is almost same.

How is it possible?

          Pressure cooker is closed using gasket and gas a release valve. We pour some water inside the pressure cooker. While we heat the pressure cooker the water gets converted into steam. The steam tries to escape outside but there is no way except the small hole in the release valve. So the pressure of the steam increases inside. This makes the heat to distribute very fast. When the heat is distributed very fast the item is cooked fast and the cooking time is reduced.

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