"Newps" wrote in message news:86dqb.113533$Fm2.101588@attbi_s04...


Well water does not freeze until 0 degrees C at any pressure we pilots
will see.

And yet at 5000 feet you need to adjust how you bake because of the
different boiling point of water.

Freezing and boiling are different processes. Freezing is not much
affected by pressure. Boiling on the other hand is DEFINED in terms of
pressure. It's the point where atmospheric pressure equals the vapor pressure.
At 5000' (and altimieter setting 29.92), the boiling point is only 202 degrees
The liquid water never can get above the boiling point, so the temperature
of the food stays cooler and hence it takes LONGER to cook things that
are boiled.

However, the reason baking instructions change is only partially the boiling
point. In baking the food rises due to leavening (yeast, baking powder, etc...)
This process (amount of leavening used, temperatures, etc...) is generally
set for sea level pressures. At higher altitudes, these recipes tend to
over-rise. Adding addional flour or other adjustments to the recipe
compensate for this.

Freezing (of water) is affected by pressure, but to raise the freezing point requires
rather severe decrease in pressure. Between 0 and 5000 feet the frezing point
difference is less than a degree.