Levers at higher altitudes

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rpavlis

#1: Post by rpavlis »

I am currently in Pagosa Springs, Colorado, elevation about 2200 metres. I brought my 1999 Europiccola with me with the 1974-2000 group with the reputation for overheating. This morning I made two shots up here.

The tendency to overheat is gone--completely. I waited about 15 minutes between shots by then at low altitude I would have been getting overheated shots. Everything was still fine. The espresso was boiling as it emerged, but since water boils here at about 92, it was not over extracted. The crema was partly disrupted by this, but the important thing is how espresso tastes, not what it looks like. Still there was substantial crema.

I did not attempt to make cappuccinos. I suspect there would be no problems.

It is apparent that getting much above this altitude would result in the boiling point of water getting so low that there would be poor extraction. I suspect also that the 1974-2000 group equipped La Pavoni machines and similar steam heated group machines are really the BEST, and probably the VERY BEST machines for high altitude where their overheating becomes about their ultimate virtue.

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[creative nickname]
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#2: Post by [creative nickname] »

Our family has a vacation home in Colorado at around 2500 meters above sea level. I make espresso up there using a 1976 Pavoni, and it is, as you say, the perfect tool in that environment. I find that slightly darker than usual roasts work best, however.
LMWDP #435

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hankbates

#3: Post by hankbates »

rpavlis wrote: It is apparent that getting much above this altitude would result in the boiling point of water getting so low that there would be poor extraction. I suspect also that the 1974-2000 group equipped La Pavoni machines and similar steam heated group machines are really the BEST, and probably the VERY BEST machines for high altitude where their overheating becomes about their ultimate virtue.
Excellent point.
I am not sure I would want to tinker with the pressure relief valve on a two switch machine, but you could adjust the pstat higher if so equipped.
This approach might be helpful on millennium machines which have no steam heating.

insatiableOne

#4: Post by insatiableOne »

well I am at 2689, wonder what that does to the different variables?

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drgary
Team HB

#5: Post by drgary » replying to insatiableOne »

Very interesting topic, and it makes me want to ask people asking dial-in questions about altitude, since it's potentially a critical factor.
Gary
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What I WOULD do for a good cup of coffee!

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another_jim
Team HB

#6: Post by another_jim »

What's the difference between altitude and a similar pstat (or relief valve) adjustment?

In a vacuum, a machine set at 1.2 bar gauge (2.2 bar absolute) would still show 1.2 bar, but be running at 1.2 bar in actuality; and as it rose in altitude it would run through this range of 2.2 to 1.2 bar absolute. Why is using the pstat to make the same adjustment different?

Cappas is another story -- I'm guessing steam pressure is a result of pressure difference, not absolute -- so the gauge pressure reading will determine pressure regardless of altitude (providing it's not high enough for the milk to boil while steaming :wink: )
Jim Schulman

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drgary
Team HB

#7: Post by drgary »

So, Jim, you're making the distinction between brewing inside a pressurized vessel compared to an open boiler. The takeaway is if you're brewing with a closed boiler, don't worry about it. If you're taking your Caravel to a mountain cabin, consider using a darker roast. Even if you see cooler water boiling out of the group, it's a different matter when you create a seal with the loaded portafilter and pressurized water enters from above. Since you texture milk to no more than 160F/about 70C, you would only need to reconsider steaming it if carrying your coffee kit above 18,000 ft./about 5500 m. Maybe this is why sherpas drink buttered tea?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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rpavlis

#8: Post by rpavlis »

Both pressurestats and the La Pavoni steam relief valve on the two switch models control the difference between atmospheric pressure and boiler temperature. Thus the boiler temperature is substantially lower in Pagosa Springs than in Miami, Florida, for a given setting.

However, the boiling point in an open container is lowered at higher altitude. It is about 92-93 at 2500 metres. If the liquid emerging from the machine be above this temperature it will boil and almost instantly be be cooled down to 92 or 93 degrees.

If one be much above 2500 metres I suspect we would be unable to maintain high enough temperature for proper espresso extraction.

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drgary
Team HB

#9: Post by drgary »

rpavlis wrote:Both pressurestats and the La Pavoni steam relief valve on the two switch models control the difference between atmospheric pressure and boiler temperature. Thus the boiler temperature is substantially lower in Pagosa Springs than in Miami, Florida, for a given setting.
I'm trying to interpret what's being said by Robert and Jim here. Thinking about how a pressurestat works, there's a spring-loaded membrane attached to a contact that can touch a microswitch. That switch is normally closed, meaning it transmits power to the heating element. It opens, disconnecting power, if it is touched by the spring-loaded contact. If the pressure outside the switch is lower, it will be a small influence compared to the resistance of the spring. In that case the pressure and temperature inside the boiler would be virtually the same at the different altitudes we're discussing.

Similarly a steam relief valve uses spring tension to hold it closed. It seems to me that the relevant pressure would be exerted from inside the boiler and the spring holds the closure in place. Differences in external atmospheric pressure should be small compared to the spring tension.

The salient question would be answered with a measurement of spring tension versus the lesser resistance of lower atmospheric pressure.

Robert and/or Jim, please correct me if I'm wrong.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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rpavlis

#10: Post by rpavlis »

Actually the atmospheric force is similar to that of the spring's force over the area of the pressure valve seat. Atmospheric pressure at sea level is 100000 Pascals. (newtons/m^2). At 2500 metres it is around 75000 Pascals. With the pressurestat set to exactly 1.0 atmosphere, or 100000 Pa and at sea level, the pressure inside the boiler would be 200000 Pa, with the atmospheric Force exerted on the valve seat equal to the spring force.

Pressurestats and pressure relief valves thus produce a DIFFERENCE in pressure between ambient and the boiler pressure.