How does high altitude affect brewing? - Page 4

Beginner and pro baristas share tips and tricks for making espresso.
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#31: Post by HB »

Trisha wrote:Okay, I'm missing something basic. How do you have temps above the boiling point of water without ending up with live steam again?
Eric's table shows the water's boiling point at different pressures; the boiling point increases as pressure increases, as described in wikipedia's definition of boiling point, excerpted below:
wikipedia wrote:The boiling point corresponds to the temperature at which the vapor pressure of the substance equals the ambient pressure. Thus the boiling point is dependent on the pressure. Usually, boiling points are published with respect to standard pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased ambient pressure up to the critical point, where the gas and liquid properties become identical.
Is that your question? Of course the boiling / flash point will change once the water exits the pressurized boiler / HX.
Dan Kehn

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#32: Post by Trisha »

I was looking at the temp in the portafilter, unpressurized.

I get terrific espresso with my home roast and the Elektra - but it took dialing down the pressurestat to 1.4 and yep, paying attention to the basics (no problem).

Being able to compensate for alittude in a boiler isn't an issue, I was getting tripped up by what I was interpreting as folks saying they get brew temps higher than the boiling point at their elevation. That's all.

. . . and cello sonatas flow through the air. . .

Matthew Brinski

#33: Post by Matthew Brinski »

Hey everyone,

I haven't posted in quite some time, but I have been keeping up with the boards. This post is basically to inform you that I was full of crap in regards to many of my earlier assumptions of difficulties with brewing espresso at high altitude (I'm at 8500 ft). I was convinced that because the local boiling point of water here is ~ 196F, I must maintain a brew temp below that so as not to expose the coffee to boiling water. I have always understood that espresso is brewed under pressure which results in raising the boiling point of water, but I was convinced that the initial infusion which was yet to come under pressure was causing sours and bitters due to the churning water and steam. I also had a theory that the initial steaming/boiling water was disrupting the integrity of the prepared coffee cake which would result in channeling every now and then. I WAS WRONG! What I discovered several months ago with the aid of a Fluke/Scace setup and naked PF was that I really had no idea how to manage the brew temp of my HX machine. I also had trouble with distribution of the coffee in the PF. I'm currently brewing espresso (and have been for months now) with temps of 199 to 203 with consistent success. Oh yeah ... and my brew pressures are 9 to 9.1 bar. I think it's easy for us to blame our brew troubles on things we can't control (like altitude) rather than the parameters that we can control such as dosing, DISTRIBUTION, temp management, etc., because those parameters require skill obtained by practice and experience.

ALTITUDE IS NOT A MAJOR PROBLEMATIC FACTOR IN ESPRESSO PREPARATION in my opinion. It matters, but not significantly.

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#34: Post by RegulatorJohnson »

MattB wrote:ALTITUDE IS NOT A MAJOR PROBLEMATIC FACTOR IN ESPRESSO PREPARATION in my opinion. It matters, but not significantly.
i agree.

i am in SLC ut (4500ft) for me the "water dance" / flash boiling ends at 203°. i have erics TC adapter it backs up this fact.

i sometimes think about it and realize it may be an advantage in some ways to be at altitude. doesn't it in a sense give a "ceiling" on how hot your water will be?

it seems like for a press pot or moka pot that the correct altitude would create a specific boiling point temperature. not that you would but would it not be possible to mathematically know what temp will be at what altitude? you could just boil the water and know its 198°.

i think im going to rent a hot air balloon and do some experiments.

2012 BGA SW region rep. Roaster@cognoscenti LA

Matthew Brinski

#35: Post by Matthew Brinski »

I see your point about the advantage of your altitude and its relation to your local boiling point. The problem I discovered with my altitude/boiling point is that with it (boiling point) being anywhere from 3 to 6 degrees lower than my target brew temp, I can't follow Dan's "water dance" routine. I say this because if I wanted to surf down to where the "water dance" ceases, I have to figure out the time for rebound to a target brew temperature. That isn't too difficult with trial and error, but what I discovered when I analyzed things with my Scace was that the rebound times were not consistent with consecutive extractions. They showed a trend of needing a longer rebound time as you continued through a series of extractions. I'm pretty sure that this is due to the small boiler and HX circuit which cannot maintain a temp stability when an attempt is made to surf BELOW the target temp and then rebound repeatedly. There is just not enough thermal mass to accomplish such a routine without trending downward in temperature. My solution was a series of Scace measurements with various flush/rebound intervals to establish routines for specific temperatures. With such a routine, the "water dance" never ends.


#36: Post by davefitz »

erics wrote:Just for anyone's reference, attached is a chart showing how temperature and pressure in a boiler are related as a function of altitude. Perhaps, yet another reason to PID a heat-exchanger equipped machine for making that transition from point A to point B.


All other factors being equal, high altitudes will reduce cooling flush requirements.

Saturated steam properties were taken from and data checked at random against Thermodynamic Properties of Steam by Keenan & Keyes. I'll be happy to send the MS excel file (of the chart) to anyone who wants it.

Edited: Added 9000 ft. elevation data since that was the OP's location, added 10000 feet and cleaned up chart a little.

Eric S.

This is kind of confusing.
Several members above (mteahan, HB, Ken Fox, Espresso Smith) have agreed that Altitude "DOES NOT" affect the water temperature in the boiler.
The chart you posted seems to disagree.
If I read it correctly, it says my espresso boiler (at 4500 ft) is several degrees cooler than a boiler set to the same pressure at sea level.

To me, this seems to be a question of whether the pressure gauge is relative or absolute.
If my pressure gauge says 1.1 bar, is that absolute, or is that the 'relative' pressure difference at my altitude???
Members above have indicated that this is an 'Absolute' pressure measurement, but your chart implies that the measurement is relative to my altitude.

Is there a trusted answer to this question?

Thanks to anyone who can elaborate, Dave

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#37: Post by SandBaggerOne »

Your altitude is going to determine to what the pressure reading in the boiler is compared, not the temperature of the boiler at a given absolute pressure, which is what I think the previous posters meant when they said altitude doesn't matter. However, your pressure gauge is reading 1.1 bar MORE than atmospheric pressure when it says 1.1. If this is a diaphragm gauge then it reads zero when the machine is off because there is zero pressure differential across the diaphragm. At sea level atmospheric pressure is 1.01 bar, while at 4500 feet it is .86 bar. So, at 4500 feet a reading of 1.1 bar means 1.96 total while at sea level it means 2.11. Let me know if I am crazy, but I think this is the correct answer. If you could get your machine up to a total of 2.11 bar in the boiler (gauge reads 1.25) then that should give the same temperature as a reading of 1.1 bar at sea level.


EDIT: Eric says the same thing below.
LMWDP #310

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#38: Post by erics »

Is there a trusted answer to this question?
Yes, and its called "science" :) ; Gage pressure + Atmospheric Pressure = Absolute Pressure. The temperature of the water, at the water/steam interface, is a function of the absolute pressure within the boiler as shown in the references I previously provided and in the charts I prepared.

And, just to add a little more to the thread, the boiler pressure (and thus temperature) varies over time as a function of the pstat actions. Here is a sample chart:

The temperature of the water within the boiler is not constant, either with time or with position, but this gets pretty smoothed out by the time it exits the dispersion screen.

Eric S.
E-mail: erics at rcn dot com

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#39: Post by barry »

and if you use a PID, then you can toss the PSIG/PSIA charts. ;)


#40: Post by liteonphotography »

it changes shot times.... but drip shouldn't affect much