Pressure, Temperature, Volume!

October 14, 2010 | By | 6 Replies More

Warning – Science Geekery ahead!

Am I the only person in the world who gets that we can control for Boyle’s Law?

Moka Coffee Pot

(C) Creative Commons - photograph by Hans Chr. R., derivative work by Saibo

While reading a (Science Fiction) book, by a very respected author*, I encountered a scene where a character brews some coffee. Yum! I love coffee! But my delightful anticipation was immediately spoiled by the character’s complaints about how the low ambient pressure makes for lukewarm coffee!


Have people never heard of these amazing newfangled devices called pressure cookers? Heck, Europeans have had little stovetop espresso makers for many many years, that are essentially little one-shot pressure cookers! With the correct setup such equipment can produce strong, hot coffee regardless of the ambient pressure!

Whenever I come across such obvious stupidity it kills the story for me.

Get the little details right, people! Let me enjoy my stories and enjoy my coffee (regardless of ambient)!

* in defense of the Author, he is an older American, so can be excused for not really understanding the difference between coffee and the pale brown caffeinated beverage that shares that name in the States.


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Category: Entertainment, Science, Writing

About the Author ()

I’m a technophile with an enduring interest in almost anything real or imagined. I suffer fools badly, and love trashy science fiction, plot-free action movies, playing guitar, and baking (especially scones. You haven’t lived ’til you’ve eaten my scones. I’ve recently undertaken bread, and am now in danger of gaining in a matter of weeks the 60 pounds I’ve lost in the past 2 years). My wife & I are Scottish, living north of Atlanta, GA, with two children, one dog, and a growing collection of gadgets. I work for a living.

Comments (6)

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  1. Paul Hsu says:

    A pressure cooker may give you hot and flavorful coffee but as soon as you vent it, the coffee will boil and cool. How much it cools after boiling depends on ambient pressure. Thats why you have to cook things longer at high altitude. The lower ambient pressure causes the water to boil at a lower temperature.

    • Tony Coyle says:

      Paul – you are entirely right, but it does not cool 'explosively' – therefore I have a nice hot cup of coffee (essentially superheated according to ambient) long enough to enjoy the drink.

      Everything will cool after heating… the difference between boiling and non-boiling is in the vapor pressure (low ambient will impose a higher vapor pressure – which is why boiling water steams significantly more than merely warm water). Water heated above the liquid/gas phase transition temperature (the 'natural' boiling point at that pressure) will lose more energy per unit time through evaporative cooling than water below the phase-change temperature, but that cooling is still pretty slow in macro terms (unless you rapidly change the pressure/volume – such as in a bernoulli expansion valve).

      I could draw the phase change diagram – but I won't.

  2. Paul Hsu says:

    So to enjoy hot coffee at low ambient pressures, one must drink it while it is boiling away. Don't you think you might be wearing half of it in the process. How about super heating the coffee without boiling. Not likely, but if you could, this may happen.

  3. Ben says:

    I've recently quit coffee, but I still have dreams about it sometimes.

    When I visited London, I was appalled at how bad their teeth were.

    *In their defense they are Brits and they do not understand the difference between a toothbrush and a crumpet.

  4. Dan Klarmann says:

    I've recently had the chance to try coffee at many different elevations, like Salt Lake City at 4,200 feet (but coffee is actually forbidden in some parts of downtown), Topaz Lake, Nevada at about 6,200 feet, and Green River, Wyoming at 6,100 feet. The drip coffee in those places seemed fine to me (albeit too weak for my taste). Fortunately, espresso is widely available out there.

    But to avoid bitter coffee one should not pass water over 94C over the grounds. (Article from Scientific American, June 2002)

    According to the Water Altitude Boiling Point Calculator, 6,000 feet gives a boiling point of 94C.

    That's hot enough to scald the tongue, anyway.

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