Every theorist (read that theoretical physicist) knows that without coffee there is no physics. Well, kind of. Every time I visit another physics department, after I am shown my office and how to get my computer connected to the web (also indispensable for physics), I am taken with reverence to the local coffee machine and I am explained with great detail on how it is supposed to be operated. Coffee seems to be the lubricant of good ideas.
So there it is. Now, no physics yet. Look carefully back and you will see that I have talked about physicist’s habits, but not really about physics.
So I thought it would be nice to describe how some really nifty coffee machines work. After all, there is a lot of physics in there that is worth expressing, and then it seems that they work by magic.
What I have in mind are some Italian Espresso machines. These are the simplest machines. They have no moving parts. You add water at the bottom, coffee grounds in the middle, you put them in a stove or some other source of heat, and a few minutes later you have coffee on the top.
Abstract Coffee maker rendition
So I drew a schematic of the machine, indicating the parts of it. There are no moving parts per se. The idea of how it works is simple, not magic. You heat the water at the bottom. Once you have injected enough heat in the bottom, you form a cloud of water vapor. Evaporating water costs heat. If you keep on applying heat, you get more water vapor, and the pressure of the water vapor rises. Once you have enough pressure, it pushes the water below it. The water is not very compressible, so it looks for a way out, and it finds it going upwards. There, the water is met with an obstacle. The coffee grounds. To get through it has to percolate. (Remind me to talk about percolation some other time). During this process it collects all the goodies from the coffee grounds. After it percolates, it keeps on rising. It still rises because the pressure from below has not ceased. So the coffee climbs and climbs, until it meets the exit and is collected on the upper compartment. The bonus: the upper compartment is cooler so it does not boil the coffee, which would make it taste horrible.
Voila! You have great coffee and a physics lesson. Some other time I will write a bit of the equations regarding this.
Shores of the Dirac Sea 
“A Mathematician is a machine for turning coffee into theorems” — Paul Erdos
I believe that the coffee machine you depict is explicitly banned by one of the sections of the Geneva Convention–at least, without a note from your mother, or from Alberto Gonzales.
Personally, I prefer tea. The physics is simpler: just diffusion, no water vapor required (though it works best if the water is actually boiling). And it’s yummy. (You do have to drink about three times as much to get the same caffeine, though.)
If we mandated that the water in the percolator always had to move up, then it’d be directed percolation, and your espresso would be in the same universality class as Reggeon field theory, right? š
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I love coffee. Or, more precisely, I love caffeine. But it’s getting to summer now in the southern hemisphere which means it’s getting hot, which in turn means that I’m starting to prefer an ice cold red bull rather than a steaming cup of coffee to get my kick. Which is unfortunately not as cost effective as coffee as they don’t serve red bull free at tea time. What to do!
[…] I just stumbled across a cute post on the blog “Shores of the Dirac Sea” about the importance of coffee in physics. …the caffeine is always there. What is sure is that physicists drink coffee regularly and […]
…a long-time CV reader.
You’re starting it off right with the coffee post.
What program did you use to draw that pic??
Hi Tim:
I used Adobe Illustrator. It took me a while to find the font that would look good.
It’s kind of a cute picture. You might consider tossing it on wikimedia commons…
I agree coffee is really the lubricant of good ideas.
Paradoxically, I find hot coffee in summer to be either cooling or at most neutral, while teas seem to be heating. I can’t say anything about iced coffee, though, which I have always considered to be an abomination.
Ok, I’ll subscribe based on this post alone.
BUT! Let’s have a touch more physics! In fact, anyone who uses such archaic ‘stove top espresso’ machines knows they are not all created equal. In fact, according to their physical dimensions, they will only generate enough pressure to force a certain percentage of the initial water load through the ground coffee before the entire apparatus heats enough to boil the coffee and ruin it. This ‘efficiency’ will be a relation of geometrical properties of the machine and the temperature profile of the applied heat. You often need to tweak the water load and the temperature profile to achieve good results.
How easily can we divy up this parameter space into ‘good’ and ‘bad’ machines, based on thermodynamic properties of ideal gases?
And you missed the pressure regulator valve that keeps the machine from blowing up.
Andre, it depends if they make the iced coffee with ice or ice cream. The ice cream one is the abomination.
Actually, the best “iced coffee” i came across was when I was on holiday in the Canary Islands, which are owned by Spain. I ordered a “Cafe con hielo” – literally, coffee with ice, and they brought me a tumbler filled with ice cubes and a shot of espresso. It was fantastic!
[…] of phone calls and then everything was fine. Phew! I had a lovely afternoon with the local folks, drinking coffee (remember how important it is) and just talking fun things, some physics, some not. We went for the […]