science philosophy

Connectivity

Shades of light and dark. How do we see shadow, colour, depth? How is it linked to the physics of coffee?
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The other morning, grinding coffee in order to prepare a V60 (the last of a fantastically complex Natural El Salvador from Amoret coffee), I was hit by the intense aroma of rich, freshly ground beans. It seems at the moment that we are surrounded by more vivid impressions of things that have, in reality, always been there, but that have previously been obscured by other features of our lives. Such things have been revealed by the changes to our lives that have come about as the result of the “lock-downs” needed to reduce the transmission of Covid-19. The birdsong that seems more dramatic and intense than before the traffic subsided. The colours of the trees as the spring light bounces off and filters through the leaves no longer surrounded by a misty haze of pollution (now suggested through its absence). And of course the smell of the coffee hitting our olfactory senses.

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Before this period of social distancing and self-isolation, I had been preparing for another in the series of Coffee & Science evenings at Amoret coffee in Notting Hill. The title of the evening had been “Space Coffee” and we were going to explore the connections between what happened in your coffee cup with features that you can see in the atmospheres of planets such as Saturn and Jupiter. Actually the connections are a lot wider than that and can be seen on the Earth too, but the atmospheres of Jupiter and Saturn have some very peculiar structures that you may not immediately think could possibly be linked to your coffee cup. One of the key people who worked on the science behind this was Hermann von Helmholtz (known as H2 to his friendsa). For the Coffee & Science evening, the important work of Helmholtz was on vortices and fluid rotations, but it turns out that he has more links with a coffee cup than that, connections that can even give us some food (drink?) for thought in this time of separation.

which will win, gravity or light
The world has not really been turned upside down, but certainly the way that we view it could be. An opportunity to re-assess our view points?
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Helmholtz made many contributions to the understanding of our world including how we see it. In addition to inventing the ophthalmoscope (in ~1850), Helmholtz was interested in the way in which we perceive colour and how we manage to see in 3D. Thinking about the way in which we see things like light and colour and developing on the idea that how we perceive our world is, ultimately, received in each of our own minds via our sense organs, Helmholtz compared the sensations of light and colour to symbols of language: ways in which we interpret the world around us. As Michel Meulders writes in his fascinating biography of Helmholtz (told from the view point of a medical doctor rather than a physicist)b, Helmholtz had

“…stated lyrically that we should thank our senses, which miraculously gave us light and colour as responses to particular vibrations and odour and taste from chemical stimuli. We should thank the symbols by which our senses informed us of the outside world for the spell-binding richness and the living freshness of the sensory world.”

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What does it mean that I should thank my senses for the way in which I smell, see and hear the coffee beans as they are ground?

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The connections between Hermann von Helmholtz and coffee are more than just the vortices that form, and more than the fact that Michael Faraday once served him cups of it while he was preparing lectures for the Royal Institutionc. We’ll be exploring those links over the next few weeks, from how we see coffee, through how we hear it and eventually to what ties it all together. Please keep checking back but also, do let me know what new sensory symbols you have perceived in this time of opportunity to attention.

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a “Worlds of Flow”, Olivier Darrigol, Oxford University Press (2005)

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b “Helmholtz: from Englightenment to Neuroscience”, Michel Meulders, MIT press (2010)

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c “Helmholtz and the British Scientific Elite: from force conservation to energy conservation”, David Cahan, Notes & Records of the Royal Society, 66, 55-68 (2012) doi:10.1098/rsnr.2011.0044

Coffee as an art at Briki, Exmouth Market

exterior of Briki coffee London

Briki London on the corner of Exmouth Market

Traditionally made coffee always appeals to my sense of coffee history. Coffee made its way out of Ethiopea via Turkey and the method of brewing the finely ground coffee in a ‘cezve’ or ‘briki’ is one that goes back a long way. It’s therefore always interesting when a new cafe arrives on the scene that offers “Greek” or “Turkish” coffee on its menu. Briki, in Exmouth Market, opened in May last year and so it was only going to be a matter of time before I visited to try it out. Aesthetically Briki appealed to me as soon as I walked through the door. Spacious and with the bar along one wall, there are plenty of seats available at which to slowly enjoy your coffee. The cafe itself is almost triangular and the other two walls have windows running all along them. What better way to sit and enjoy the moment (and your coffee) than to gaze out a window? Still, given that I had gone to a cafe called ‘Briki’ and that it advertised “Briki coffee” on the menu behind the bar, it was obvious that I had to try the briki coffee. The coffee was rich, flavoursome and distinctive, well worth the time taken to savour it. There was also an impressive selection of food behind the counter and the dreaded “does it contain nuts” question was met with a friendly check of the ‘allergen’ folder. I was therefore able to also enjoy the lovely (nut free) chocolate cake. Briki definitely gets a tick in the “cafes with good nut knowledge” box on my categories list.

image from British Museum website

Folio 109b from an album of paintings showing Turkish sultans and court officials. Kahveci. A youth who serves coffee. He is holding a cup in each hand, circa 1620.
© The Trustees of the British Museum

However as I realised later, the coffee was not brewed in the traditional way but in a Beko coffee maker – a coffee maker specifically designed for optimising the brewing of Turkish coffee. The idea of the Beko is that it carefully controls and automates the entire brewing process so that you get a perfect coffee each time. But just how do you make a ‘perfect’ Turkish coffee?

A quick duckduckgo (it’s a mystery to me why has this verb failed to catch on while ‘to google’ is used so frequently) revealed two sets of instructions on how to make Turkish coffee. The first set, (including some otherwise very good coffee brewing websites) suggested ‘boiling’ the coffee repeatedly in the pot (cezve/briki). The second set, which seemed to be more specifically interested in Turkish coffee (as opposed to interested in coffee generally), were much more careful, even to the point of writing, in a very unsubtle way, “NEVER LET IT BOIL“. According to this second set of websites, the coffee in the cezve should be heated until it starts to froth, a process that begins at around 70C, far below the 100C that would be needed to boil it. Warming the cezve to 70C produces these bubbles and the lovely rich taste of the traditionally made coffee. Heating it to boiling point on the other hand destroys the aromatics* that form part of the flavour experience of coffee and therefore makes a terrible cup of coffee.

The contrasting instructions however led me to recall a discussion in Hasok Chang’s Inventing Temperature. Perhaps we all remember from school being taught how thermometers need two fixed points to calibrate the temperature scale and that these two fixed points were the boiling point and the freezing point of water. Perhaps this troubled you at the time: Just as with making coffee in a cezve, just how many bubbles do you need in order to say that the coffee (or water) is ‘boiling’? How were you supposed to define boiling? How much did it matter?

Cezve, ibrik, Turkish Coffee Creative Commons license

Cezve, image © http://www.turkishcoffee.us

It turns out that these questions were not trivial. There is a thermometer in the science museum (in London) on which two boiling points of water are marked. The thermometer, designed by the instrument maker George Adams the Elder (1709 – 1773) marked a lower boiling point (where water begins to boil) and an upper boiling point (where the water boils vigorously). The two points differed by approximately 4C.  So how is it that we now all ‘know’ that water boils at 100C? And what was wrong with Adams’ thermometer? The Royal Society set up a committee to investigate the variability of the reported boiling point of water in 1776. Careful control of the heating conditions and water containers reduced the temperature difference observed between different amounts of boiling. However, as they experimented with very pure water in very clean containers they found that things just became more complicated. Water could be heated to 120C or even higher without ‘boiling’. They had, unintentionally, started investigating the phenomenon that we now know as ‘superheating‘. Superheating occurs when water is heated to a temperature far above its boiling point without actually boiling. What we recognise as boiling is the escape of gas (which is usually a mix of air and water vapour) from the body of the water to its surface. In order to escape like this, these bubbles have to form somehow. Small bubbles of dissolved air pre-existing in the water or micro-cracks in the walls of the container enable the water to evaporate and form steam. These bubbles of gas can then grow and the water ‘boils’. If you were to try to calibrate a thermometer using very pure water in very clean containers, it is highly likely that the water would superheat before it ‘boiled’, there just aren’t the ‘nucleation’ sites in the water to allow boiling to start. The Royal Society’s committee therefore came up with some recommendations on how to calibrate thermometers in conditions that avoided superheating which meant thermometers were subsequently calibrated more accurately and superheating (and improved calibration points) could be investigated more thoroughly.

Perhaps viewed in this way there are even more parallels between Turkish coffee and physics. It has been written that “making Turkish coffee is an art form“. It is a process of practising, questioning and practising again. The Beko coffee machine automates part of the process of making Turkish coffee. When it’s done well though, Turkish coffee is far more than just the temperature control and the mechanics of heating it. There is the process of assembling the ingredients, the time spent enjoying the coffee and the atmosphere created by the cafe in which you drink it. Coffee as art in Briki is something that I would willingly spend much more time contemplating.

 

Briki is at 67 Exmouth Market, EC1R 4QL

“Inventing Temperature”, by Hasok Chang, Oxford University Press, 2004

*Although these aromatics are part of what gives coffee such a pleasurable taste, they decay very rapidly even in coffee that is left to stand for a while, it is this loss of the aromatics that is part of the reason that microwaving your coffee is a bad idea. A second reason involves the superheating effect, but perhaps more on that another day.