Brewing Espresso at Altitude

There has long been discussion about what happens when you brew espresso somewhere at relatively high altitude. This has become, and will become even more, relevant as the WBC is taking place in Bogota this year. Bogota is the third highest capital city in the world, some 2625 metres above sea level (approx 8,600ft).

At this altitude water will boil at 91.2°C/196.2°F – below the 93.5°C/200°F that the Aurelias will be set to. What follows is mostly personal opinion 1, coupled with a possible experiment that might answer some questions.

When we’re brewing espresso the system is under pressure (9 bars mostly), rather than the much lower atmospheric pressure. One of the unique aspects of brewing under pressure is that water is able to dissolve a lot more CO2 than it usually can at atmospheric pressure. When the coffee liquid leaves the basket we see that it is unable to retain that CO2 which forms bubbles that get trapped by various surfactants as a foam: crema.

People will often remark that at altitude the coffee acts like it hasn’t had a chance to rest/degas. The espresso tends to have very large bubbles, and lacks strength – often disappearing very quickly. This is, of course, similar to brewing very fresh coffee (up to 48-96hrs post roast) at sea level.

What doesn’t make sense to me is that surely CO2 would be more likely to be drawn from the coffee bean when stored at low pressure than at higher pressure?

My guess (and it is a guess) is that the pressure change from the bottom of the basket to atmosphere is much larger than normal when brewing at altitude. I would guess that the saturation point for CO2 in water at 2625m is significantly lower than the saturation point at sea level. The liquid loses more gas, and we see this as bigger bubbles. With foams in liquid the strength is dependent on bubble size (the smaller the stronger – think good milk foam), so these larger bubbles of crema will disappear faster.

What does this mean for competitors? Here is my advice:

Bring scales. I know a lot of people don’t like it (though I don’t really understand why), but your espresso volume is going to be radically different for an identical flow rate at sea level. Know your brew recipe before you come, and before you start freaking out about how things taste, check whether you are brewing on spec. Espresso is a recipe that is based on weights and flow rates. Going by eye is tough. I’ve tried, when I was there in 2007, and it took a while before things made sense!

Pulling shots in Bogota

Another question remains – should espresso be aged longer for brewing at altitude?

This is a good question, and one I think we need to do a few experiments on. Ageing espresso will certainly reduce the amount of CO2 left in the coffee beans, but surely at the expense of some loss of pleasing aromas and the potential development of negative flavours. I’d like to run a two way experiment, but it needs participants who have access to coffee machines at different altitudes.

Take two bags of espresso from the same roasts/blending batch. Store one at sea level, store the other at high altitude. Ideally in similar temperatures. After 10 days bring both back down to sea level and observe variations in volume for a fixed weight of coffee, liquid and brew time. Based on my amateur theorising above – there should be no detectable differences, or – if anything – the coffee stored at altitude might have less crema/volume when brewed.

Then take two bags of identical espresso and store both for 10 days at sea level. Then brew one at sea level and one at altitude. Record variations in volume for fixed weight of coffee, liquid and brew time.

This way we’ll know whether the issue is ageing of brewing. I would predict that when brewed identically the high altitude espresso should be just as delicious as the low altitude one – but I am very happy to be proven wrong.

One aspect to consider is when the brewing liquid might reach boiling point. If someone is pulling very fast shots, where the brew water doesn’t lose much heat to the coffee – then I’d expect to see some issues towards the end of the shot as the exit liquid from the basket will be very close to boiling, if not boiling at high altitude. Properly brewed espressos shouldn’t (in theory) see the same problem. Anyone have video of a naked portafilter at high altitude?

Comments, thoughts, accurate science and brutal critiques of the above welcome!  Thanks to Brent Fortune for setting my brain off!

  1. Warning: Amateur Science Alert!  ↩︎

34 Comments

  1. We were brewing near 10,000ft at the Roasters’ Guild Retreat a few years back. That was lots of fun, especially with the chopped portafilter. The crema cone that forms under the basket seemed to cut off immediately upon stopping the brew cycle, with the cone dropping, intact, into the cup. Very very strange to see. We had some very good espresso, but blends that required higher temps (above, say, 200F) seemed to struggle.

  2. We were brewing near 10,000ft at the Roasters’ Guild Retreat a few years back. That was lots of fun, especially with the chopped portafilter. The crema cone that forms under the basket seemed to cut off immediately upon stopping the brew cycle, with the cone dropping, intact, into the cup. Very very strange to see. We had some very good espresso, but blends that required higher temps (above, say, 200F) seemed to struggle.

  3. We were brewing near 10,000ft at the Roasters’ Guild Retreat a few years back. That was lots of fun, especially with the chopped portafilter. The crema cone that forms under the basket seemed to cut off immediately upon stopping the brew cycle, with the cone dropping, intact, into the cup. Very very strange to see. We had some very good espresso, but blends that required higher temps (above, say, 200F) seemed to struggle.

  4. Much of my experience with espresso is at 7200ft asl. I would argue (though with no scientific proof) that coffee degasses slower at a higher elevation and that is the cause of the observations that you’ve made. Especially with lighter roasts, I find that it is nearly impossible to get beautiful crema from coffee that is less than two, sometimes three weeks past roast (currently I’m making espresso with a coffee roasted on 1/3 and it’s delicious!). Also, on the point of roast profile, I notice that espresso that we roast for production at this elevation, big bodied, sweet, full coffee, tastes over roasted and carbony when brewed at sea level with higher temperatures.

    Back to crema, once the coffee has had adequate time to settle down, I notice that the crema consistency is similar to when brewed at sea level, color and texture are there. What is not there is the retention, the emulsion loses its integrity rapidly, and one is left with a black topped espresso in a matter of seconds. This problem gets worse with fresher coffee. I have experimented a bit with coffee roasted at sea level and brewed at elevation, and it seems that if it is properly degassed at sea level, then brought to elevation it will pull great shots, conversely, the coffee that I bring to sea level to pull shots with must be degassed for three weeks at elevation before I bring it down.

    Degassing vs. Brewing… I think this is where I loose my confidence. We have an Aurelia Competizione, and when we installed it it was set to competition standards. This exacerbated the issues that we find with our espresso (lack of crema retention, bigger bubbles in crema). Also, at these temperatures, we were getting a very acetic taste from any espresso. We have tuned it down to about 194 degrees F, and we are able to get beautiful and delicious shots with no problem. I don’t know why it needs to be cooler, but in my experience it does.

    Please excuse the rambling, I’ll post a video of a naked portafilter extraction tomorrow.

  5. I will dive into commentary and responses tomorrow. I just want to summarise and clarify the above post:

    - Crema definitely appears quite differently at altitude.
    - I believe this is because of the low pressure affecting the brewed espresso
    - I don’t believe altitude affects the actual extraction
    - I believe that crema is an unreliable visual indicator of quality or shot size at altitude.

    More tomorrow!

  6. This may come off a bit uneven, but I’ll drop a little coin into the pile anyway.

    I had the opportunity to judge the Colombian Barista Championship this past October in Bogota, which gave us the unique perspective of actually seeing what the WBC might experience this June.

    One of the difficult parts of doing judges calibration and judging is that you may not “know” the coffees being used. Typically, you’re using whatever is at hand and trying to make it work. Most of the discussion that I’ve heard for Bogota revolves around altitude and aging of coffee. Since I mostly worked with coffees I was unfamiliar with, it is difficult for me to offer insight on the effects of altitude or the aging time for coffees at altitude – and being in-country for 10 days doesn’t give much of a baseline either.

    However, based on the observations of other judges who were actually paying attention to that, it seems that the altitude slows the degas/aging process. My guess is that the lower atmospheric pressure exerts less pressure on the beans and the CO2 emits at a slower rate – kind of like pricking an inflated balloon with a pin and pressing on it at varying pressures to force the air out of the balloon. However, that is strictly anecdotal and not based on any serious research or theory.

    Having judged in Bogota, one might expect that the altitude would wreck havoc on the competitors. Not so, I say. In fact, I experienced some very nice espresso shots.

    While the higher altitude means a lower boiling point, I seriously doubt this affects the water path in the espresso machine. Bear in mind that the espresso machine, all the way to the portafilter basket, is a closed system. The machine maintains its own internal pressure exclusive of the atmosphere outside the water path.

    Does the altitude diminish the crema? Again, I seriously doubt it. While I can no longer remember specifics, I do not recall giving a “1″ or lower for visual espresso during the entire championship. Seems that proper technique still delivers even with whatever impact the altitude plays.

  7. We have had a very similar discussion about this very problem. In South Africa we have 2 regionals at the coast, and one at altitude, 5500ft, and people are constantly concerned about how the different water boiling points will effect the coffee.

    Just remember that boiling point is just the point in which the water will change state from a liquid to a gas. Does that mean that this 2deg difference in temp, from say 91 and 93 deg c, will effect the coffee? I don’t think so, like what Jay C said, the machine is a sealed unit.

  8. So, basically, brewing espresso is a closed system that doesn’t allow for atmospheric pressure to affect it; the only effect is in the degassing of the beans?

    This may be a little off topic, but of much concern to me lately:
    How does atmospheric pressure affect manual pour-overs (mostly in pre-infusion I’d imagine)?

  9. As far as boiling point I think it is very interesting that it is theoretically possible that espresso coming out of the spout could be loosing shot volume to water vapor.

    I also find it interesting that the CO2 dissolved in the espresso should be less in a lower pressure environment. I wonder what the impact of this loss in acidity will have in taste (if any) and if the coffees people choose for there espresso blends will be changed because of this.

    As fare as degassing goes would it matter if you degassed the coffee in a bag or in the open? Theoretically at higher altitudes a bean left in the open air should degas faster yes? Perhaps it is the bag that is causing the slower degassing. Would this lack of outside pressure on the bag be the reason peoples coffees are degassing slower at higher altitudes?

    on an unrelated note it i took fresh roasted coffee underwater then brought it up too fast would it get the benz?

  10. I’d certainly like to echo Jay’s comment that excellent espresso can be produced at altitude if one knows how to achieve it. While at high altitudes I’ve seen excellent and very normal looking extractions, “fresh” coffee is a hilarious disaster — the pull is more of an upside-down geyser. As noted above, the resulting crema is extremely unstable (maybe due to the violent precipitation of CO2 after the coffee leaves the portafilter) and pouring attractive cappuccinos is (I’ll boldly say) quite impossible.

    I do also want to echo and perhaps reinforce the comments that it doesn’t seem to make sense for either of these to be true:

    - “Offgassing is slower at high altitudes”:

    With respect, Jay’s balloon example doesn’t quite work — the reason air is forced out of a balloon faster when you prick it is because you are reducing the volume of the balloon and compressing the air inside, thus increasing the pressure relative to that outside and causing an increase in flow.

    Does the bag have any effect on degassing? The pressure inside the bag should still always be lower than it would otherwise be at low altitude. Once CO2 pressure inside a bag becomes slightly greater than outside the one-way valve should see CO2 passing through. The consequence of this is that internal pressure shouldn’t be considerably higher than outside the valve and it doesn’t seem to make sense that it would ever be higher than it would be at low altitude.

    All that is to say that I don’t see how offgassing would be slowed at higher altitudes. The extracellular pressure should always be higher than inside the cells, resulting in an increased rate of offgassing.

    - “The extraction temperature should be influenced by the ambient air pressure”

    As far as I can tell the espresso machine and portafilter are a closed system and I don’t see how ambient pressure would influence the extraction. Unless the pressure below the portafilter effects the flow rate of water through the portafilter? I’m not sure how a small change on the outside would influence the flow rate when it is resisting a pressure up to 9 times as great. Surely the flow rate has more to do with the coffee and gasses inside the portafilter than the ambient pressure?

    If I’m right about these two ideas (I don’t claim to be, I just claim to not have seen a convincing argument to the contrary) then it seems the only difference is in how the gasses behave once the coffee leave the portafilter. The problem must be in the violent precipitation of CO2 when the coffee leaves the portafilter. Naturally, allowing the coffee to degas more completely would help to resolve this problem (and would give the impression that it is simply taking longer for the coffee to degas).

    Any rebuttals to these thoughts would be welcome.

  11. I agree that degassing should theoretically be faster at higher altitudes. As far as bags go if the beans where to off gas faster initially this would push O2 out of the bag faster. This O2 would usually have time to react with the coffee. In short, the lower pressure allows the coffee inside a bag to reach an anaerobic state faster thus slowing the overall rate at which the coffee stales.

    Questions;

    Is there noticeably more steam when water comes out of a grouphead at higher altitudes due to the decrease in escape velocity of the water molecules?

    Is the temperature of the espresso leaving the bottom of the portafliter spout below 91.2C?

  12. The key thing to rule out is that the espresso machine ‘would not be able to get to a temperature above that of which the surrounding atmospheric pressure allows’. As everyone said above the system is closed.

    Degassing should in theory happen quicker at higher altitude. As we know for gas to escape from the bean then the pressure on the inside must be higher than on the outside. So if there’s even lower pressure on the outside in theory the beans should loose CO2 quicker. You could easily mimic the effects at sea level with out having to go up a mountain by putting a very small amount of beans in a large strong bottle and pumping some of the air out.

    I think the real concern should be of any coffee preparation that doesn’t included any espresso machine or any other closed system. In these situations the temperature of the water will be determined by the atmospheric pressure.

    The only thing to possibly think about with espresso brewing at altitude is how the coffee extracts and meets the air from the portafilter. If the water is above that of which the atmosphere allows it will of course rapidly boil (turn to steam).

    Which brings me to an interesting point, what is the temperature of the water exiting the portafilter? It it doesn’t loose pretty much all its temperature in excess of what the atmosphere allows it will rapidly boil which will give you two decisions. Either you accept a lower volume with the same timing as you would get at sea level or you extract for longer to make up for the lost water that boiled off? But this is only a real problem if a significant amount of water will boil off, if its just a small amount then your shot volume should be similar. If it is a problem how does the flavour change between the two different shots?

  13. The key thing to rule out is that the espresso machine ‘would not be able to get to a temperature above that of which the surrounding atmospheric pressure allows’. As everyone said above the system is closed.

    Degassing should in theory happen quicker at higher altitude. As we know for gas to escape from the bean then the pressure on the inside must be higher than on the outside. So if there’s even lower pressure on the outside in theory the beans should loose CO2 quicker. You could easily mimic the effects at sea level with out having to go up a mountain by putting a very small amount of beans in a large strong bottle and pumping some of the air out.

    I think the real concern should be of any coffee preparation that doesn’t included any espresso machine or any other closed system. In these situations the temperature of the water will be determined by the atmospheric pressure.

    The only thing to possibly think about with espresso brewing at altitude is how the coffee extracts and meets the air from the portafilter. If the water is above that of which the atmosphere allows it will of course rapidly boil (turn to steam).

    Which brings me to an interesting point, what is the temperature of the water exiting the portafilter? It it doesn’t loose pretty much all its temperature in excess of what the atmosphere allows it will rapidly boil which will give you two decisions. Either you accept a lower volume with the same timing as you would get at sea level or you extract for longer to make up for the lost water that boiled off? But this is only a real problem if a significant amount of water will boil off, if its just a small amount then your shot volume should be similar. If it is a problem how does the flavour change between the two different shots?

  14. AI want to note that I did everything I could to rewrite my high school class schedule to avoid physics and calculus! Because of this, I’m interested in asking questions to help clarify my understanding.

    “the reason air is forced out of a balloon faster when you prick it is because you are reducing the volume of the balloon and compressing the air inside, thus increasing the pressure relative to that outside and causing an increase in flow. ”

    Without a true grasp of the concepts involved, doesn’t the lower atmospheric pressure provide less of a “squeeze” on the balloon/bean, causing a reduction in the flow rather than an increase?

    “The pressure inside the bag should still always be lower than it would otherwise be at low altitude. Once CO2 pressure inside a bag becomes slightly greater than outside the one-way valve should see CO2 passing through. The consequence of this is that internal pressure shouldn’t be considerably higher than outside the valve and it doesn’t seem to make sense that it would ever be higher than it would be at low altitude.”

    I think that the only time we would find the interior bag pressure to be greater when there was some restriction or malfunction to the one-way valve. I imagine that everyone involved has dealt with “inflated” coffee bags – I’m presuming that this “inflated” bag is an indication of a pressure greater than atmospheric?

    “All that is to say that I don’t see how offgassing would be slowed at higher altitudes. The extracellular pressure should always be higher than inside the cells, resulting in an increased rate of offgassing.”

    Isn’t the term “extracellular” meaning the pressure outside the cell/bean? If so, wouldn’t atmospheric pressure greater than cell/bean pressure actually contain the bean gases – much like holding a cooked steak in a clarified butter bath prevents the meat from “bleeding out”?

    All of that said, I’m personally relying on Ian’s observations as he served as a tech judge in Colombia and is much more informed regarding the extraction of espresso and steam performance of milk. As a sensory judge, I was too busy writing to notice Ian’s areas of responsibility and focused solely on what was placed in front of me.

    What I can state is that we were presented with some great (and not so great) coffees during the entirety of the competition. While the pressure question is a good one, it is not insurmountable and I’m hoping that the competitors don’t get too bogged down in technical minutiae trying to definitely define the effect of Bogota’s environment on their coffee.

  15. AI want to note that I did everything I could to rewrite my high school class schedule to avoid physics and calculus! Because of this, I’m interested in asking questions to help clarify my understanding.

    “the reason air is forced out of a balloon faster when you prick it is because you are reducing the volume of the balloon and compressing the air inside, thus increasing the pressure relative to that outside and causing an increase in flow. ”

    Without a true grasp of the concepts involved, doesn’t the lower atmospheric pressure provide less of a “squeeze” on the balloon/bean, causing a reduction in the flow rather than an increase?

    “The pressure inside the bag should still always be lower than it would otherwise be at low altitude. Once CO2 pressure inside a bag becomes slightly greater than outside the one-way valve should see CO2 passing through. The consequence of this is that internal pressure shouldn’t be considerably higher than outside the valve and it doesn’t seem to make sense that it would ever be higher than it would be at low altitude.”

    I think that the only time we would find the interior bag pressure to be greater when there was some restriction or malfunction to the one-way valve. I imagine that everyone involved has dealt with “inflated” coffee bags – I’m presuming that this “inflated” bag is an indication of a pressure greater than atmospheric?

    “All that is to say that I don’t see how offgassing would be slowed at higher altitudes. The extracellular pressure should always be higher than inside the cells, resulting in an increased rate of offgassing.”

    Isn’t the term “extracellular” meaning the pressure outside the cell/bean? If so, wouldn’t atmospheric pressure greater than cell/bean pressure actually contain the bean gases – much like holding a cooked steak in a clarified butter bath prevents the meat from “bleeding out”?

    All of that said, I’m personally relying on Ian’s observations as he served as a tech judge in Colombia and is much more informed regarding the extraction of espresso and steam performance of milk. As a sensory judge, I was too busy writing to notice Ian’s areas of responsibility and focused solely on what was placed in front of me.

    What I can state is that we were presented with some great (and not so great) coffees during the entirety of the competition. While the pressure question is a good one, it is not insurmountable and I’m hoping that the competitors don’t get too bogged down in technical minutiae trying to definitely define the effect of Bogota’s environment on their coffee.

  16. > what is the temperature of the water exiting the portafilter?

    Some data on that subject is posted here:
    http://www.home-barista.com/tips/brew-ratio-vs-brew-temperature-t6731.html

    The executive summary: exit temperature varies brewing ratio. It
    will obviously also vary with brew water temperature. In my
    experiment, average “lungo” exit temps finished up about 8F less
    than brew water temperature. Average “ristretto” exit temps
    finished about 16F less than brew water temperature. Those
    numbers translate to something like 4 and 9 degrees respectively
    for you Celcius devotees.

    Given these numbers, I don’t think most baristas will have espresso
    exit temperature above boiling. Remember that espresso is a fairly
    concentrated solution of various compounds, and these solutes
    RAISE the boiling point of the liquid.

    I believe most of the outgassing people have observed in making
    espresso at altitude is due to what others have already mentioned:
    CO2 is less soluble in water at lower ambient pressures, so it
    bubbles out of the espresso faster than usual as the liquid exits the pf basket.

  17. > The extracellular pressure should always be higher than inside the cells, resulting in an
    > increased rate of offgassing.

    I don’t understand this sentence at all.

  18. Won’t the adding of solubles to the water lower its boiling temperature even more? I don’t think the boiling point is a huge factor i just find it interesting. i agree that the largest contributing factor is CO2 solubility.

  19. With all the my talk about bags i really just wanted to bring to light that the valves where most likely designed to work at standard temperature and pressure and any environment outside these parameters might have some effect on their operation.

  20. No, it’s the opposite: boiling point is raised slightly.

  21. Meant to say, “exit temperature varies WITH brewing ratio.”

  22. Hey Jay – let’s see if I can iterate further on what I was thinking. Sorry to turn this into a classic “dissect and respond” post but it seems to be a useful format.

    “Without a true grasp of the concepts involved, doesn’t the lower atmospheric pressure provide less of a “squeeze” on the balloon/bean, causing a reduction in the flow rather than an increase?”

    This would probably be true in the case of squeezing a balloon. I don’t think coffee beans are “squeezable” to any meaningful extent. It’s unlikely air pressure can compact the beans enough to increase pressure on the inside. The more significant factor is going to be the pressure differential between the inside of the bean and outside — gas will flow from an area of high pressure to low pressure until it reaches equilibrium. This is why degassing should occur more rapidly — there should be the same pressure inside the cells after roasting and reduced pressure outside.

    “I think that the only time we would find the interior bag pressure to be greater when there was some restriction or malfunction to the one-way valve. I imagine that everyone involved has dealt with “inflated” coffee bags – I’m presuming that this “inflated” bag is an indication of a pressure greater than atmospheric?”

    I think I meant to suggest that there may be a slightly higher pressure in the bag than outside on a functioning bag. It won’t be much higher, but it has to be at least slightly higher for gas to want to flow from inside to outside. I’d say you’re right that if there is a significantly higher pressure inside the bag then it’s likely an anomalous case of valve malfunction.

    “Isn’t the term “extracellular” meaning the pressure outside the cell/bean? If so, wouldn’t atmospheric pressure greater than cell/bean pressure actually contain the bean gases – much like holding a cooked steak in a clarified butter bath prevents the meat from “bleeding out”?”

    Apart from saying it sounds mouthwatering, I can’t comment on the steak analogy. I’m not sure what would be happening there but it sounds interesting. Someone with more knowledge of osmosis would have to comment on how much an impact “like” molecules would have on the flow rate. My assumption would be that it wouldn’t have an impact but I’m not sure.

    It’s worth echoing that it’s entirely possible to make outstanding espresso in Bogota — but gas management will play a significant role in success.

    Does anyone know of any resources that detail exactly how our one-way valves are designed and built? Just curious.

  23. > wouldn’t atmospheric pressure greater than cell/bean pressure actually contain the
    > bean gases – much like holding a cooked steak in a clarified butter bath prevents
    > the meat from “bleeding out?”

    Yes, bean gases would be contained IF atmospheric pressure were greater than the bean’s internal pressure. But actually, the reverse is true: roasting creates very high internal bean pressures, and it takes many days (or weeks) of degassing before the internal pressures come down to near-atmospheric levels.

    OTOH, Illy makes the claim that their rigid, slightly pressurized storage tins prevent a certain amount of “bleeding out,” to use your phrase. Supposedly their technique keeps (1) more coffee oil inside the bean and (2) more aromatic compounds dissolved in that oil. Obviously, their claims are highly partisan and controversial.

  24. fwiw, I’m fairly confident there has been some research into degassing rates with the result that beans apparently do not degas faster in a reduced pressure environment. It’s in Ukers or Sivetz, iirc.

  25. I make espresso at 9,500′ now… , before that just 8,500′. I get used to that high altitude, the cofee smells and tastes better. Jim is absolutely right about everything he mentioned. Its my experience.

  26. Since the main driver for degassing is the difference between the bean internal pressure and the environmental pressure, it stands to reason that a reduced pressure environment HAS to increase the degassing rate. OTOH, since the bean internal pressures are many, many times the environmental pressure, a modest decrease in environmental pressure isn’t going to have a big effect until much of the degassing has already occurred. Perhaps the research you remember just couldn’t detect a very small change in the degassing rate (and perhaps, for practical purposes, it’s not a significant change).
    .

  27. This is an interesting thread! From a roasting angle here is what I can add:

    If you were to roast at sea level, then truck it up a large mountain immediately afterwards, it will lose C02 more quickly than at sea level. Since pressure is being built inside of the bean as it ages in the first few days, moving it into an environment with fewer molecules will naturally diffuse any gases out of the bean and into the atmosphere pretty quickly.

    If it had been roasted, let sit, and then slowly walked up the mountain, who knows. It may age normally.

    Coffee *roasted* at high elevations will last a little longer, due to the lack of 02 in the air, but since the C02 produced from roasting would be relative, I doubt it loses c02 at any quicker or slower rate than coffee roasted at sea level.

    It would be great if you could roast up there – since high altitude is gold for coffee roasters. The diffusion of vapor into the thin air creates conditions where you can really control your roast. Happens here in Portland sometimes when its frozen, but most of the time you are battling water molecules in your air because of constant rain.

    Coffee does indeed taste better up there for the same reasons – there are so few molecules in the air, so your olfactory gets pretty sharp. That is assuming you aren’t on a frozen peak and your nostrils have turned to frozen straws.

    I have no idea about crema – would it be that the lack of gaseous elements make thin, weak bubbles in general?

    I love discussions like this because it makes me want to take some coffee up to Mt. Hood

  28. From a chemist’s point of view (…mine, that is) the things that make most sense above are:

    - since the machine being a semi-closed system in which water pressure is carefully controlled, atmospheric pressure should not affect the product

    - “…theoretically possible that espresso coming out of the spout could be loosing shot volume to water vapor” does make sense, hence resulting in a slightly more concentrated espresso

    - …but the above might also possibly give a slightly MORE RAPID COOLING of the coffee on its way out of the portafilter (because the evaporation process takes energy; think of the cooling you feel when you pass a rapidly running stream or river because water evaporation takes energy from the surroundings)

    - CO2 solubility is a rather complex matter because it’s among those gasses which react with the water producing carbonic acid. Hence, it differs radically from most other gases (e.g. oxygen, nitrogen). Lower atmospheric pressure WILL probably result in faster CO2 release from the brew, but these might not be directly proportional to each other

    - soubility of CO2 is highly pH dependent (acidity). More acidic –> loer solubility. A simple experiment is when you put a lemon slice in your soda: pH drops and you see the CO2 bubbles coming

    - I agree with Ian about the balloon analogy (and most of the other comments as well, really): lower ambient pressure should promote CO2 release from the beans. Think of the extreme situation in which you put the beans in a vacuum chamber: this should certainly result in CO2 loss from the beans, and lower atmospheric pressure is simply one small step in that direction.

    - Aandys’ comment seems reasonable: the pressure difference should not make a great difference until the internal and external pressures are close to converge, and at the end point, when inside pressure = atmospheric, the pressure inside the beans should be lower (but I guess these beans never reach this point before being brewed).

    - lower atmospheric pressure should result easier bubble release from the drink when brewed, and notably larger bubbles being formed compared to higher-pressure conditions. Low pressure allows for bubbles to grow more rapidly

    The biggest problem here is: which effects might make a difference and which are of marginal importance? The points above might all be correct, but some might have little or no bearing on the product whereas other might, relatively, have a larger impact.

    One question that comes to mind is my experience on bringing coffee on the plane home: lower cabin pressure makes the bags deflate completely, resulting in vacuumed bags (one way valve). I guess this woud promote degassing and hence result in my coffee reaching it’s peak earlier than if I went home by car?

  29. Es increible, ver como granos de cafe son afectados por elementos de la naturaleza, tal como la altura, clima, edad de reposo, caracteristicas densitrometicas del grano, etc.  Es un placer para mi ser y formar parte de este mundo tan maravilloso, donde la vida es cada vez una caja de sorpresas…

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