and maintain a particular cooking temperature, and reproduce the same temperature reliably Thermostats, thermometers, and our senses are all fallible So one of the great advantages of water as a cooking medium is that its boiling point is constant — 212ºF/100ºC at sea level — and it’s instantly recognizable The sure sign of boiling water is bubbling Why? When the water in a pan is heated near boiling, molecules at the bottom, where the pan is hottest, vaporize and become steam, and form regions that are less dense than the surrounding liquid (The small bubbles that form very early on are pockets of air that had been dissolved in the cold water but became less soluble as the temperature rose.) Because all the pan heat at the boil goes into vaporizing the liquid water, the temperature of the water itself stays the same (p 816) It’s only slightly higher at a full, rolling boil than in a gently bubbling pot, and will not get any higher until the phase change from liquid to gas has been completed The Boiling Point Depends on Elevation The boiling point of water is constant given a constant physical environment, but it varies from place to place and even in the same place The boiling point of any liquid depends on the atmospheric pressure bearing down on its surface: the higher the pressure, the more energy it takes for liquid molecules to escape the surface and become a gas, and so the higher the temperature at which the liquid boils Every 1,000 feet/305 meters in elevation above sea level lowers the boiling point about 2ºF below the standard 212ºF (or 1ºC below 100ºC) And food takes longer to cook at 200º than it does at 212º Even a lowpressure weather front can lower the boiling point, or a high-pressure front raise it, by as much as a degree or two Pressure Cooking: Raising the Boiling Point ... varies from place to place and even in the same place The boiling point of any liquid depends on the atmospheric pressure bearing down on its surface: the higher the pressure, the more energy it takes for liquid molecules to escape...higher until the phase change from liquid to gas has been completed The Boiling Point Depends on Elevation The boiling point of water is constant given a constant physical environment, but it... energy it takes for liquid molecules to escape the surface and become a gas, and so the higher the temperature at which the liquid boils Every 1,000 feet/305 meters in elevation above sea level lowers the boiling point about 2ºF below the