vacuum

Telling the time with an Aeropress?

Aeropress bloom, coffee in an Aeropress

The first stage of making coffee with an Aeropress is to immerse the coffee grind in the water. Here, the plunger is at the bottom of the coffee.

On occasion, it takes a change in our routine for us to re-see our world in a slightly different way. And so it was that when there was an opportunity to borrow an Aeropress together with a hand grinder, I jumped at it. Each morning presented a meditative time for grinding the beans before the ritual of preparing the coffee by a different brew method. Each day became an opportunity to think about something new.

Perhaps it is not as immediately eye catching as the method of a slow pour of water from a swan necked kettle of a V60, and yet making coffee using the Aeropress offers a tremendously rich set of connections that we could ponder and contemplate if we would but notice them. And it starts with the seal. For those who may not be familiar with the Aeropress, a cylindrical ‘plunger’ with a seal tightly fits into a plastic cylinder (brew guide here). The first stage of making a coffee with the Aeropress is to use the cylinder to brew an ‘immersion’ type coffee, exactly as with the French Press (but here, the plunger is on the floor of the coffee maker). Then, after screwing a filter paper and plastic colander to the top of the cylinder and leaving the coffee to brew for a certain amount of time, the whole system is ‘inverted’ onto a mug where some coffee drips through the filter before the rest is forced out using the plunger to push the liquid through the coffee grind.

clepsydra creative commons license British Museum

A 4th century BC Ptolemaic clepsydra in the British Museum collection. Image © Trustees of the British Museum

Immediately perhaps your mind could jump to water clocks where water was allowed to drip out of two holes at the bottom of a device at a rate that allowed people to time certain intervals. It is even suggested that Galileo used such a “clepsydra” to time falling bodies (though I prefer the idea that he sang in order to time his pendulums). With many holes in the bottom of the device and an uneven coffee grind through which the water (coffee) flows, the Aeropress is perhaps not the best clock available to us now. However there is another connection between the Aeropress and the clepsydra that would take us to a whole new area of physics and speculation.

When the medieval thinker Adelard of Bath was considering the issue of whether nature could sustain a vacuum, he thought about the issue of the clepsydra¹. With two holes at the bottom and holes at the top for air, the clepsydra would drip the water through the clock at an even rate. Unless of course the holes at the top were blocked, in which case the water stopped dripping, (a similar thing can be observed when sealing the top of a straw). What kept the water in the jar when the top hole was blocked? What kept it from following its natural path of flowing downwards? (gravity was not understood at that point either). Adelard argued that it was not ‘magic’ that kept the water in when no air could go through, something else was at work.

What could be the explanation? Adelard argued that the universe was full of the four elements (air, water, fire, earth) which are “so closely bound together by natural affection, that just as none of them would exist without the other, so no place is empty of them. Hence it happens, that as soon as one of them leaves its position, another immediately takes its place… When, therefore, the entrance is closed to that which is to come in, it will be all in vain that you open an exit for the water, unless you give an entrance to the air….”²

inverted Aeropress and coffee stain

The Aeropress inverted onto a coffee cup before the plunger is pushed down. Complete with coffee stain behind the cup where the inversion process went awry.

Now, we would argue that whether the water flows down and out of the Aeropress, or not, depends on the balance of forces pushing the water down and those pushing it up. The forces pushing the water down and out of the clepsydra, or Aeropress, are gravity and the air pressure above the water in the cylinder. Pushing it up, it is only the air pressure from below. Ordinarily, the air pressure above and that below the water in the Aeropress are quite similar, gravity wins the tug of war and the water flows out. In an enclosed system however (if the holes at the top are blocked), were the water to flow out of the bottom, the air pressure above the coffee space would reduce. This makes sense because, if no new air gets in, the same amount of air that we had before now occupies a larger volume as the water has left it, the pressure exerted by that air will have to be less than before. A reduced air pressure means a reduced force on the water pushing it down through the filter and so the force pushing the water down can now be perfectly balanced by the force (from the surrounding air) pushing the water up: the water remains in the Aeropress. The only way we get the coffee out is to change the balance of forces on the water which means pushing down the plunger.

But perhaps it is worth stepping back and imagining what the consequences could be of having the idea that the universe was just full of something that had to be continuous. You may find it quite reasonable for example to consider that vortices would form behind and around the planets as they travelled in their circular orbits through this ‘something’*. Such vortices could explain some of the effects of gravity that we observe and so there would perhaps be no urgency to develop a gravitational theory such as the one we have. There would be other consequences, the world of vacuum physics and consequently of electronics would be significantly set back. In his lecture for the Carl Sagan Prize for Excellence in Public Communication in Planetary Science, The Director of the Vatican Observatory, Br Guy Consolmagno SJ explored previous scientific ideas that were almost right, which “is to say wrong” (You can see his lecture “Discarded Worlds: Astronomical Worlds that were almost correct” here) If it is true that so many scientific theories lasted so long (because they were almost correct) but were in fact wrong, how many of our scientific ideas today are ‘almost correct’ too?

It makes you wonder how our preconceptions of the world affect our ability to investigate it. And for that matter, how our ability to contemplate the world is affected by our practise of doing so. They say that beauty is in the eye of the beholder. For that to be true, the beholder has to open their eyes, look, contemplate and be prepared to be shown wrong in their preconceptions.

What connections do you make to your coffee brew each morning? I’d love to know, here in the comments, on Twitter or over on Facebook.

 

* Does a connection between this and stirring your freshly brewed Aeropress coffee with a teaspoon trailing vortices stretch the connectivity a bit too far?

¹ “Much Ado about Nothing: Theories of space and vacuum from the Middle Ages to the Scientific Revolution”, Edward Grant, Cambridge University Press, (1981)

² Quoted from Adelard of Bath’s “Quaestiones Naturales” taken from Much Ado about nothing, page 67.

Something in the air at Mace by Coffee Chemistry Signature, KL

3D hot chocolate art on an iced chocolate, Mace, Mace KL, dogs in a chocolate

Drinking an iced chocolate with friends.

Perhaps Mace by Coffee Chemistry Signature in Kuala Lumpur should really have a “cafe-art” review rather than a “cafe-physics” review. Indeed, it was because of its latte art that Mace, which operates from a light and airy building in Damansara Uptown, Kuala Lumpur, had been recommended to me. With a comfortable interior and friendly staff, Mace is an interesting place in which to spend some time. But it is certainly the artistic endeavours that are the striking thing about Mace. Nor is it just ‘latte art’. The cakes at Mace arrive at the table decorated into an artwork. It is interesting that every visit to Mace will provide a different creation to enjoy, providing a place that you could return to again and again.

Nonetheless, this is a cafe-physics review website and there is also plenty of science to be found in latte art. For example, one of our drinks arrived with a 3D latte art sculpture floating on its surface. This piece requires manipulation of the rigidity of the milk foam, a topic that has been covered previously on the Daily Grind. However this time, it may be worth looking a little deeper into our frothy coffee: What makes a bubble?

The answer may seem obvious, inside the bubble is “air” with the bubble surfaces being formed from the water and proteins in the milk∗. But it is the question of what air is, and the implications of that, that is today’s Daily Grind.

Tweetie pie with a cake at Mace, KL

Cakes can be shared with cartoon characters at Mace

It appears that it was Empedocles (492 – 432 BC) who first recognised that air was a substance†. A thing that existed all around us. But it took until the seventeenth century and the invention of the air pump by Otto von Guericke (1602 – 1686) before people recognised that air was heavy. Guericke was responsible for the spheres of Magdeburg demonstration about the strength of a vacuum. He had fashioned two hemispheres of copper. Each hemisphere fitted very closely to the other. He then used his air pump to pump the air out of the spheres (ie. make a vacuum) and tried to pull the two hemispheres apart. Accounts vary but it is said that teams of 8-15 horses tethered to each hemisphere were unable to pull the spheres apart because of the vacuum created within the spheres†.

It was von Guericke’s air pump, together with the work of Boyle on gases and Torricelli’s invention of the barometer that prompted Francesco Lana-Terzi, SJ (1631-1687) to design an ‘air ship’. The idea was simple: If air had a weight and it is possible to make something lighter than air (by making a space inside a copper sphere a vacuum), then it should be possible to make something lighter than air such that it would float, just as objects that are less dense than water float. What differentiates Lana-Terzi’s design from previous fantasies about flight (such as Daedalus and Icarus) was that Lana-Terzi based his ideas on solid principles of mathematics and physics. He calculated how heavy the air was and balanced that with the amount of air that he would have to pump out of four hollow spheres of copper in order that they could lift a gondola full of people.

latte art by Mace, Eiffel Tower and hot air balloon

Art on a cafe latte at Mace

Although there were practical problems with Lana-Terzi’s idea of an air-ship based on four hollow copper spheres, his ideas were correct and eventually led to the development of the hot air balloon. And it is with the hot air balloon that we return to coffee, to Mace and find a connection with a London cafe. The artwork on my cafe latte was not, ‘latte art’ in the sense to which we have recently become accustomed. It was however very much art on a latte, with a scene featuring the Eiffel Tower depicted in chocolate. Just to the right of the Eiffel Tower and suspended in the milky sky was a hot air balloon, floating away exactly as Lana-Terzi had envisaged. Back in 1783, on the corner of Euston Road with Tottenham Court Road, there used to be a pub/coffee house called the Adam and Eve. It was renowned for its cakes and cream and its large tea garden. As far as I can work out, the tea gardens extended to around what is now Brock St and the site of a Beany Green. It was here, in 1783 that the balloonist Vincenzo Lunardi (1759-1806) “fell with his burst balloon, and was but slightly injured”‡. Fortunately for Lunardi, and for ballooning in general, it was only a slight setback. Lunardi went on to make a number of balloon flights, including the UK’s first successful hot air balloon flight.

So next time you are in Kuala Lumpur, why not spend a while at Mace imagining floating in on Lana-Terzi’s air ship gondola while you enjoy a gorgeously frothy iced chocolate. Who knows, one day Lana-Terzi’s air ship gondola may even feature on their latte art, I’d love to see that picture!

Mace by Coffee Chemistry Signature is at Damansara Uptown, Kuala Lumpur.

∗ On Food and Cooking, The science and lore of the kitchen, H. McGee, Unwin paperbacks, 1984

† History and philosophy of science, LWH Hull, Longmans, Green and Co, 1959

‡ Quote from London Coffee Houses, Bryant Lillywhite, 1963