The computer is faster than pulling K&K out of the bookcase.

The mechanical p-stat will respond exactly as the spring relief valve to changes in altitude.

Over a good number of yeas I have watched this issue get seriously misinterpreted and cause some rather serious accidents.

-- A zero psi indication on the common pressure gauge is 14.7 psia or absolute.

-- Local atmospheric pressure is a function of local weather events and altitude. A Corrected barometer reading from the NWS/NOAA is not going to provide any reliable information for making the local boiler pressure-temperature conditions as the corrected reading is based on the physical point of observation and the physical data regarding that point is usually not available.

homeburrero wrote:For practical coffee boiler purposes I don't really need the barometric pressure.

OldNuc wrote:A Corrected barometer reading from the NWS/NOAA is not going to provide any reliable information for making the local boiler pressure-temperature conditions

FWIW, as a compulsive analytic I was curious at one time about just how much of a difference the local barometric pressure changes cause, and learned that the variability is generally within plus or minus 0.03 bar unless you are in an extreme and rare weather situation. Even in the midst of a record tropical storm it only drops 0.1 bar or so below normal, so there is little need to consider barometric pressure variations when thinking about coffee brew temps.

On another less geeky subject related to brewing at altitude I've noticed one post from Chris Tacy that found a benefit to adjusting his boiler pressure lower when moving to higher altitude. (This is contrary to what you might expect, which would be to adjust it higher to keep the same boiler temp.) An opposing example is from Martin, who moved from New York to Santa Fe, and keeps his brew temp high (and ignores the bubbly crema that comes at the end of a high altitude, high temp shot.)

Being the proud owner of a real glass mercury filled barometer there is not much change, nothing to bother considering anyway as you said. The only point of concern is going from a ~900 ft elevation into the western mountains at 6500ft+ elevation as the electro mechanical p-stat is going to shut the heat off earlier than you are used to.

I have been using the 1999 La Pavoni here at Pagosa Springs, Colorado, since Sunday. Today I let it warm up and then bled it and waited for 45 minutes. The espresso would have been very bitter at low altitude. Here it was great. Crema always looks different here. It is much more dense and solid.

I am now going camping for a couple of days. It will be stove top espresso then.

It is strange that there seldom is made mention of the behaviour of different espresso machines at altitude.

rpavlis wrote:... It is strange that there seldom is made mention of the behaviour of different espresso machines at altitude.

Probably not many people even think about it.

rpavlis wrote:It is strange that there seldom is made mention of the behaviour of different espresso machines at altitude.

And you have to wonder how many people drag their espresso machines around from location to location! Addicts do though!

There really wasn't that much mention of this when the World Barista Cup was in Bogotá (8300') in 2011.

Dano wrote:

There is 14 lbs of air above me,

Are you 1 square in in area?