Brewing up on Dale Head today I was asked if anyone had ever brewed up on the top of Everest. It is not possible to brew a good cup of tea on Everest. I was taught this at school but such things have gone out of fashion in teaching because there is so much else that now needs including. Water boils when the molecules have enough kinetic energy and therefore momentum to overcome surface tension and the push of the air molecules above. At sea level, we call that 100 degrees Celsius. At high altitude, the air pressure is much lower so there is less to stop the escape of water molecules. Yes, water boils, because it all changes from liquid to gas, but now the temperature at which it does it is much lower. I think I remember being told 60 degrees Celsius. That's not hot enough for good tea, so I'm told by Mrs B.
