On food and cooking the science and lore of the kitchen ( PDFDrive ) 1476

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,vaporizeandbecomesteam,andform
regions that are less dense than the
surrounding liquid. (The small bubbles that
formveryearlyonarepocketsofairthathad
been dissolved in the cold water but became
lesssolubleasthetemperaturerose.)Because
all the pan heat at the boil goes into
vaporizing the liquid water, the temperature
ofthewateritselfstaysthesame(p.816).It’s
onlyslightlyhigheratafull,rollingboilthan
inagentlybubblingpot,andwillnotgetany


higher until the phase change from liquid to
gashasbeencompleted.
TheBoilingPointDependsonElevation 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.Theboilingpointofanyliquiddepends
ontheatmosphericpressurebearingdownon
its surface: the higher the pressure, the more
energyittakesforliquidmoleculestoescape
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
cookat200ºthanitdoesat212º.Evenalowpressure weather front can lower the boiling
point, or a high-pressure front raise it, by as
muchasadegreeortwo.
PressureCooking:RaisingtheBoilingPoint