Originally Posted by GA Home Cook
Chief - Sorry to recorrect, but my degree is in Chemistry.
Question: What Temperature Does Water Boil?
At what temperature does water boil? What determines the boiling point of water? Here's the answer to this common question.
Answer: Short Answer: The boiling point of water is 100°C or 212° F at 1 atmosphere of pressure (sea level).
Yes, and my degree is in Electrical Engineering Technology, and yes, I had to take two classes of physics. You are correct in your assertation that water boils at 100' C at 1 atmosphere. But when the air pressure increases, the water has to be hotter to boil. Water boils when the vapor pressure exceeds the atmospheric pressure. Please see the following site for the formula - Water Vapor Pressure Boiling Point Equations Formulas Calculator
. In a pressure cooker, as temperature increases, the atmospheric pressure increases within the vessel. Therefore, more thermal energy is required to create enough vapor pressure to overcome the internal pressure of the air pressure. Hence, the water has to reach a higher temperature to boil. The same is true that as atmospheric pressure decreases, the boiling temperature is reduced. This is what creates gas embolisms in scuba divers. Under greater than 1 atmosphere conditions, the regulators on the the tanks increases the air pressure to compensate for the water pressure on the body. Under the greater pressure, the body fluids absorb more nitrogen from the air tank. If they ascend too quickly, the reduced water pressure causes the vapor pressure in their body fluids to exceed the pressure on their bodies, and gasses boil out, causing havoc. Another way to see this in action is to take a hypodermic needle, and immerse it into plain water. Quickly draw the plunger toward the tube end, creating a partial vacuum. Again, the lower pressure will decrease the atmospheric pressure with relation to the fluid's vapor pressure, and the water boils.
Water does get hotter in a pressure cooker. I also know that if my food is completely immersed in liquid, in the pressure cooker, then it is not subject to the steam, and is cooked entirely by the heat transfer from the water into the food. It still cooks much faster than in boiling water, and food particles break down to make the food more tender.
I have been in environments were super-heated steam was used (I worked on an aircraft carrier. Water vapor can reach temperatures in excess of 1000 ' F., while water will eventually reach a critical temperature and turn to vapor, no matter the atmospheric pressure. That super-heated steam will create enough pressure to launch an airplane, or jet. My pressure cooker is rated for 11.5 lbs. above 1 atmosphere, or about 30 psi., which will raise the boiling point to - about 150' F. at my elevation. According to this table - Pressure and Boiling Points of Water
, the boiling point of water at 11 lbs. of pressure is 250'F. at sea level.
So, the pressure cooker does indeed cause an increase in the water temperature inside the vessel before it will boil, thereby cooking the food more quickly, while the pressure breaks down food substances.
Seeeeeya; Chief Longwind of the North