As we approach the end of the year, it is a good time to notice the changes in the weather. If you are in the northern hemisphere, the nights grow longer as the days grow colder. If you are in the southern hemisphere it is the opposite. And yet around the world, we have things in common. There may be days when it is more cloudy and days when there is a heavy dew (or even in some places a frost) on the grass. But what has this to do with coffee?
It’s to do with some experiments that you can do at home or on your way to work. And, in particular, with two effects you can see in your coffee cup.
To start with the dew, perhaps you’ve noticed the condensation around the rim of the cup or the coffee pot when you brew the coffee and the hot steam condenses onto the cold mug around it. Condensation happens because the temperature of the mug is lower than the ‘dew point’ of water at that humidity and pressure. Below the temperature of the dew point, the water vapour will condense into the liquid droplets that we then see dotted around the mug.
It is a similar effect on the grass: the temperature there is lower than the point at which the water vapour in the air starts to condense out of the air and so you get dew. William Charles Wells published his “Essay on Dew” in 1814. The result of more than two years of careful observation, Wells found that dew formed only under certain weather conditions and only on certain space (sky) facing surfaces. Wells’ results can be used to show that the space around the earth is much colder than the surface of our planet. His results (together with some back of the envelope calculations) can therefore also be used to show that the Earth is in a delicate balance and has a natural greenhouse effect. As the weather changes this year and you notice the dew, can you see how Well’s could come to this conclusion?
The second coffee experiment we could do at this time of year is to see whether pollution affects our steaming take-away coffee. While generally it’s always a better idea to sit in a cafe and take the time to enjoy your coffee, there are occasions when a take-away is necessary. Just as with the dew, clouds start to form when the air temperature drops below the dew point. However, water droplets in the air are unstable to evaporation and so as soon as a pure water droplet is formed, it will evaporate unless it has a diameter larger than about 0.1 µmª. This may seem small and yet to spontaneously form a droplet with this diameter would take the accumulation of several million water molecules (I will leave it to you to do the estimate!). This represents a very improbable occurrence and yet we can see that clouds are everywhere, how can this be?
The answer comes from the dust. Fortunately we are a dusty planet and these bits of dust in the atmosphere act as ‘nucleation’ points for water to condense onto. This makes the condensation of water into droplets much more likely and so clouds – which are an accumulation of droplets – can form.
Which brings us back to the coffee. If clouds require dust in order to form droplets, and the steam above your coffee is a grouping of water droplets, does it not make sense that your coffee should be steamier next to a polluted road than in the middle of a park (for the same temperature coffee)?
It’s an idea that I’ve never been able to test but the shift to colder weather here offers a(nother) perfect opportunity.
Does your coffee steam more when you take it away from a city cafe?
I look forward to hearing about the results of your experiments, in the comments here, on Twitter or on Facebook.
ª Introduction to Atmospheric Physics, Andrews, Cambridge University Press, 2008
There is a very vibrant speciality coffee scene in Berlin with plenty of excellent cafes offering an interesting variety of coffees and pour overs. A city break of just a couple of days is nowhere near enough to even start to scratch the surface of the city. Coupled to that, we arrived during the Berlin coffee festival so many cafes were participating in public cupping and tasting events. So much to explore. But if you are rushing around, can you really stop and notice things?
How can you experience a place when you travel? Carl Jung pondered this very point when thinking about Rome, he wrote:
“I have travelled a great deal in my life, and I should very much have liked to go to Rome, but I felt that I was not really up to the impression the city would have made upon me…. I always wonder about people who go to Rome as they might go, for example, to Paris or to London. Certainly Rome as well as these other cities can be enjoyed aesthetically but if you are affected to the depths of your being at every step by the spirit that broods there, if a remnant of a wall here and a column there gaze upon you with a face instantly recognised, then it becomes another matter entirely.”*
We may not all have the sensitivity of Jung towards visiting a place but it can nonetheless be illuminating to reflect on the sentiment. This is particularly true of a city like Berlin where the remnants of walls are an ever present reminder of the dangers of ideologies, as well as the ease with which they can seize us.
How do you visit a cafe so that you can appreciate the space beyond the aesthetic? We visited several cafes including Brammibal’s Donuts, Common Ground, Oslo Kaffeebar, the Refinery and Roststatte. We also attempted a visit to The Barn (Mitte) but it was sadly too crowded on our visit. Each cafe revealed something unique and each was memorable for its own reasons. The lovely pour-over at Roststatte, the long black with character at the Refinery, the vegan doughnuts during a heavy rain shower at Brammibals. And yet we know how many cafes we missed (as you can see in this guide here or here).
And yet, what stood out as something to stop you in your tracks? What can you sit and dwell with as you savour your coffee? In hindsight, it is interesting that the connections at Oslo Kaffeebar were both very much connected with nature. It was not the wood lining of the cafe and the plentiful wooden furniture around the cafe but the spiders web style tiles on the table and something we saw at the window.
The tiles on the table at the Oslo Kaffeebar were a regular array of spider’s webs. Each identifiable immediately as a web and striking for its regularity. The surprising uses of spider’s silk have featured on Bean Thinking before in a cafe that sadly no longer exists, but it was the regularity of the webs that prompted thoughts about the effect of different drugs, sadly including caffeine, on the behaviour of spiders. But it was a visitor to the outside of the cafe that struck us. A bird, silhouetted against the light, was perched on the (vertical) brick wall outside the cafe. What was it doing there? After it flew off, it was back, again in the same awkward perch but then it darted into the corner that the window made with the brick wall exterior to the cafe, could there be a nest there? The decline of bird species in our world as industrial scale farming has replaced hedgerows with monotonous fields of crops is well documented. But there is more to the bird-human interaction than that. Some bird species have adapted to the way we have traditionally built our houses, the problem being that modern building methods and renovations can threaten their ability to share our space. Other bird species have evolved to adapt to the way humans want to interact with birds with Great Tits for example apparently evolving longer beaks to make it easier for them to access the food put in bird feeders. What do these considerations reveal about evolution and our place in the world?
On the other side of the Tiergarten, the pink tiling of Brammibal’s Donuts contrasted with the teal tiling that had been ubiquitous on the U-bahn line 5. The teal tiling somehow highlighted how even strictly utilitarian architecture nonetheless evokes an emotional response. In addition to considering how this challenges our understanding of architecture as representative purely of form, it can prompt a question: is a utilitarian philosophy consistent with an environment that allows science, (and the pursuit of knowledge for curiosity’s sake) to flourish**? (a question with repercussions for our own, consumerist and atheistic society). To what extent is our scientific development dependent on the prevalent attitudes of our culture? To be somewhat hyperbolic about it, is it possible to continue to do science, as we have traditionally understood it, in a consumerist society that demands constantly new entertainment (itself a form of consumerism)? Do we not replace ‘science’ with ‘technology’ and replace those questions that ask about our place in a world of reality and truth with questions that ask how we can better manipulate our world (where truth and reality as such no longer matter)? And what, in turn, does that do to our understanding of humanity’s place in the universe and so back to our cultural outlook?
We are then left with a couple of questions for ourselves. When travelling, can we allow the space to affect us with, as Jung says, “the spirit that broods there”, or do we take ourselves, imposing our own lens on another space? Can we open ourselves to encounter and is it not urgent, lest walls arise in our minds as well as our countries? I do not have any answers to such questions, but the cafes of Berlin, of London, and of many other places around the world would be a great place to ponder them.
**The question really is, if we consider that the best thing for society is to maximise the happiness of the maximum number, this could tend to promote the sort of science that produces results, technology or devices quickly. This short-term investment in science is contrary to the ideal of funding science for the sake of knowledge and arguably against the idea of being able to investigate the world as it is as opposed to merely developing the technologies that we can use. Is this true? Does it matter?
Last Tuesday saw the first of what will hopefully be an autumn-winter series of “coffee & science evenings” at Amoret Speciality Coffee in Notting Hill. These evenings are designed to be conversational; spaces where people can get together and chat about the strange things that they have observed in their coffee (or perhaps the common things that link to stranger things).
The event last Tuesday was in the latter category. We have all seen milk frothed, and noticed how it is different in different milk types (cow and plant), or seen how some foams seem to age while some seem to last forever. But why are some foams stable while others age? And what is the additive in the “Barista edition” oat milk that encourages better foaming and is connected with the foams that you can sometimes see washed up on the beach after a stormy sea?
We were joined for the evening by Prof. Jan Cilliers of the Earth Sciences department at Imperial College. Why would a professor of Earth Sciences be interested in foam? Well, part of his research involved understanding the use of foams in the froth flotation technique of mining. You can read more about that here. How does it link back to your cappuccino? You can watch some more milk foams age to investigate.
Finally we had the foam line up. Sadiq Merchant of Amoret prepared a series of 8 milk foams using homogenised full-fat milk, non-homogenised full fat and semi skimmed milk, the non-homogenised full fat milk that is used at Amoret, a lactose free milk, coconut milk, oat milk and oat milk Barista edition. The differences were fascinating. That the semi-skimmed milk produced a good stable foam was explicable with its fat-protein content, but why did the lactose-free milk foam so much? Regular oat milk performed fairly poorly: a foam that quickly aged and returned to liquid, but the barista edition oat milk did not last too long either. After 15 minutes there was considerable ‘ripening’ of the microfoam into larger bubbles (as you can see in the photo), but will most coffee drinkers be aware of this? Many of us will have finished our coffee within 15 minutes and be ordering our next one!
Our next event on 22 October focuses more on the espresso part of the coffee. What makes a good crema? What are the connections between pulling an espresso and soil science, what can we learn about irrigation and soil ‘health’ by thinking about coffee? What about the grind size distribution? And can we make a connection between pulling an espresso and an old method of measuring blood pressure? (though the question here is not really can we, that answer is yes, the question is should we).
If you are in London, do come along on Tuesday 22nd October, you can sign up for that particular event here or sign up to the events list (to hear of future events) here. If you are not in London but still want to join the conversation, you are welcome to add comments here, head over to Facebook or see you on Twitter.
Hidden Coffee is inside Camden Road station. But this is no ordinary station-cafe, because of what lies within, perhaps you could say, ‘hidden’, from the view from the street. A few tables outside barely suggest the fairly large area inside. You can choose from a variety of the usual types of coffee or enjoy a coffee on pour-over while you sit down to ponder your surroundings. We also had a vegan, gluten free, nut free banana bread, which does make you wonder what was in it, but which went very well with the single origin Guatemalan coffee I had on pour over.
The space suggests that it used to be a pub, or that it is open at night, however the signs clearly indicate that Hidden Coffee is closed by 5pm. Because looking inside, it is clear that there is a vault extending into an area screened off from the main cafe, plenty of space that must have been used by the restaurant that existed here before Hidden opened recently. Mosaics on the walls of the vault glint in the reflected light from the cafe and the roof curves intriguingly back into a large, inaccessible, space. There is currently an art exhibition at the cafe featuring pictures of local buildings.
The vault is a consequence of the train line overhead, now part of the overground system. The vaults being a way of providing the strength needed to support the railway line above but also giving space for shops and businesses beneath. This could take you onto a consideration of how architecture assists in distributing load, or the idea and limits of deductive reasoning and its reliance on an idea of shared, knowable truths (we know there are train lines over head partly because of our familiarity with this form of architecture, partly because we walked through a door next to a train station). Or you could notice the glinting mosaics and wonder about the chemistry of the pigmentation in each of the pieces.
Looking out the window while drinking my coffee though I noticed the pine cone decoration on the railings. Several thoughts suggested themselves. How do squirrels remember where they hide their winter stocks? And related to that, how does memory work: why can I never remember the tasting notes of the coffees I enjoyed if I don’t write them down (only that I liked the coffee)? Why were the railings so obviously re-purposed? They are either not original or they have been adapted to incorporate a concrete step beneath them? And how do pine cones work?
The pine cone opens in response to dry weather to expose the pine kernels and closes in response to more humid weather so as to protect the seeds. But it was only back in 1997, that researchers used electron microscopy to see the structure of the cones and to measure the response of different types of cell to controlled humidity. They found that the response of the cells to humidity depended on the winding of cellulose structures around the cell. If the cellulose was wound with a high winding angle, the cell tended to elongate in humid conditions. Conversely, the cells having cellulose aligned more along the cell length (a low winding angle) didn’t elongate so much in response to humidity. The effect of coupling these two cell types together was to create an analogue to a bimetallic strip which bent in response to humidity rather than temperature.
It is reminiscent of a device I once read about, created perhaps by a member of the Lunar Society. The designer had cut a series of discs out of a small log of wood and joined them loosely together (presumably with a type of resin) so that they formed what would have appeared as a wooden caterpillar. On the front disc, he (and if it was a Lunar Society member it would have been a he) put a hook facing backwards on the bottom of the disc. A similar hook was placed on the back disc. When the humidity increased and the wood expanded, the caterpillar extended and hooked forwards. As the humidity decreased and the caterpillar shrank again, the back of the caterpillar would move towards the front forming a ‘self-propelling’ model caterpillar.
Unfortunately I can no longer find the reference to this device so if you know who invented it or where it is referenced please do let me know. In the meanwhile, enjoy the effects as the days turn humid/dry as we change seasons, and perhaps contemplate a hidden coffee while you do so.
Hidden Coffee is in Camden Road (overground) station, 33 Camden Road.
When people ask, what is Bean Thinking about, they often get the reply, it’s about “the universe in a cup of coffee”*. And it is perfectly true, much of the physics of the coffee cup is mirrored by the physics of the universe: you could think about the Black body radiation and the Cosmic Microwave Background, or the steam from the cup and cloud formation, but what about General Relativity? Could it really be that physics such as that of General Relativity mirrored in a coffee cup?
It could, perhaps, initially appear a ludicrous idea. Einstein’s theory of General Relativity explains the gravitational attractions of massive objects such as stars and planets through the curvature of space-time. And although what occurs on the planetary scale must also be valid on the scale of the coffee cup, we would surely expect classical, Newtonian physics to dominate here. But that would be to neglect the equally ludicrously named “Cheerios effect” and a paper that was published in Nature Communications earlier this month.
The cheerios effect is the phenomenon that you may have noticed on your tea or coffee whereby two floating objects on the surface are attracted to each other (and named after observations of the effect in a breakfast bowl). Two bits of a dropped biscuit come together or two bubbles bounce to form a pair. The effect occurs because both objects dent the surface of the drink by bending the surface of the liquid through surface tension effects. Consequently, the two objects don’t float on a flat coffee surface but a curved one and when they get close enough together, the surface tension effects bring the objects together into one big indentation rather than two smaller ones.
On the face of it, this has similarities with the ‘cartoon version’ (or schematic) of the idea of gravity in general relativity. Each massive object (ie. any object with mass) bends the space-time around it, the more massive an object, the more the space-time is bent. This has the effect of seeming to bend light and leads to gravitational attraction. And yet there are very many differences. A liquid surface is 2D, planets clearly move in at least 4D, the way the surface bends owing to surface tension is surely not the same as the way that space time bends owing to its distortion through massive objects. It could go on only it turns out that some of the maths is quite similar: the surface is distorted proportional to the mass of the object in a cup of coffee, the attraction between the objects is a product of both masses (as it is with gravity). Indeed, it has even been proposed that studying the cheerios effect could be a way of gaining insight into some of the problems of general relativity. But there was always a catch: Friction.
On the surface of a coffee, although the floating object is bending the surface proportional to its mass, it is in some sense in contact with the fluid. When the object moves, there is a frictional resistance to the movement caused by the object’s interaction with the coffee. This makes it quite different from the situation in space. And so you would have been correct in your suspicion that general relativity would not be easily found in a coffee cup, but only for reasons of friction.
Which is where the recent Nature Communications paper comes in. Rather than float objects on coffee, the researchers floated silicone oil droplets on liquid nitrogen. Being a liquid, the nitrogen is subject to surface tension effects just like coffee, but being a very cold liquid (196 C below freezing point), it shows a second effect when the (room temperature, ie. warm) oil droplets are floated onto it: the inverse Leidenfrost effect.
Again, you may have seen the Leidenfrost effect while frying eggs (or tofu if you’re vegan). When the frying pan is very hot, drops of water sprinkled into the pan will immediately vaporise in the layer between the pan and the droplet causing the drop to dance around the pan as if it is flying. The inverse Leidenfrost effect is, perhaps unsurprisingly, the inverse of this. When the liquid is very cold and a hot object is introduced to its surface it will instantaneously vaporise meaning that the hot object on the surface will skip over the cold liquid, without friction.
The reason that this is relevant to the idea of general relativity in a coffee cup is that this bending of the surface of the liquid nitrogen, coupled with the inverse Leidenfrost effect effectively levitating the drops means that you have a warped liquid surface, like the bending of space-time, but the floating object moves with absolutely no friction, because there is no contact between it and the liquid beneath. Clever.
And so what happens when you introduce two droplets to the nitrogen surface? How do they interact? Well, they attract each other and can even orbit each other like planets until, as the friction effects start to grow even in this system, the drops cease behaving as planets and can collide. It is a fascinating observation but one with relevance to biological self-organisation rather than an immediate extension to general relativity. That will be for another study, perhaps one with super-cold brew coffee.
So, the universe in a cup of coffee? Perhaps. But sometimes not strictly literally.
When Bean Thinking started, it was always going to be about coffee and yet, Katsute 100 is definitely a tea place. Not only that, but the idea was to see how the physics that we use to describe our universe is mirrored by the physics of the coffee and in a cafe, the physics of the every-day. On the other hand, the whole point of Schrodinger’s cat is to demonstrate how aspects of quantum mechanics are absolutely unlike our everyday experience: a cat both (and neither) dead and alive? And yet, without giving too much away, today’s cafe-physics review is absolutely this – a review of a tea house that features the famous thought experiment. How far Bean Thinking has moved!
Katsute 100 is a welcoming, and peaceful, Japanese tea place in Angel. With a full tea menu and some really great desserts, it is definitely a good place to spend half an hour, maybe more, watching the coming and going and exploring the tea. And there is certainly a lot of tea to explore, different tasting notes revealing themselves as the tea cools, the carefully placed tea pot and tray adding to the experience.
The shop itself is fairly narrow, decorated in sympathy with the Georgian age of the shop itself and with a view into a garden at the back. Japanese tea making equipment is displayed (and for sale) on the various wooden cabinets around the shop. My tea had been buttery (exactly as it had been described in the tasting notes) and the Ichigo Daifuku I had had with it was a fascinating exploration of texture. There were some Japanese art works on the wall and it was then that I saw my first one: a cat. Not a real one of course but one of several decorative cats that are, almost hiding, around the shop. The word “Katsute” has nothing to do with cats apparently meaning “once”, but nonetheless, a few cats do pop up here and there. And even where cats don’t pop up, there are drawers in the wooden cupboards that seem much like boxes, is there a cat there in the box? Is it dead, alive, both, neither? What does this even mean? And is it connected to Katsute, “once”, after all?
Looking carefully at my teapot, three grooves were carved into the spout allowing the tea to flow out. Each stream of complex flow interferes with the neighbouring stream to present an aesthetic of flowing liquid to match the sound and flavour of the tea. And of course it is reminiscent of an experiment that is key to the unfamiliarity of quantum physics: the double slit experiment.
When light (of a single wavelength, such as from a laser) is shone at a sheet with two holes in it, the light that has travelled through shows interference fringes and patterns. Indeed, it is one of the experiments that went to establishing the theory that light was a wave (and not, as Newton among others had thought, a stream of particles). The situation is quite different if you tried to pass particles through two slits, imagine a sieve with two holes and a stream of coffee beans travelling towards it, we’d expect each bean to go through one hole or the other, not both. In classical physics that’s what we would expect too and yet, when sub-atomic particles (such as electrons) were aimed at two slits and made to travel through them they interfered with each other, as if they were not particles but waves. But other experiments had shown conclusively that they were also particles and indeed, when each individually hit the detector it did so as a single spot, as a particle. Particles and waves? What was going on?
In fact it was a result that had been predicted: Louis de Broglie had shown, theoretically in 1923, that all particles should have wave-like properties and simultaneously, that all waves should have particle-like properties. We should expect that under certain circumstances, light, electrons, neutrons etc, even atoms, should behave as particles and under certain other circumstances (such as the double slit experiment) as waves. But there was an important catch. The electron travelling through a double slit will behave as if it is a wave, passing through both slits and interfering with itself to produce the characteristic “diffraction pattern” of a wave but only if we do not try to look at it to see which slit it really passed through. If we try to detect which slit the particle has travelled through, we can indeed find that some of the electrons travel through one slit and some through the other but when we look at the resulting interference pattern it is gone! What we are left with is the (classically expected) pattern of two particles going through two slits exactly as if they had been very small coffee beans. (You can see a video of Jim Al-Khalili explaining this peculiar result here).
What is going on? To a certain extent, this question is part of the reason that quantum mechanics can seem so strange. We can’t really ask what is going on, or rather, if we ask, we cannot expect to get an answer! We can describe what happens and we can make predictions based on the mathematics that we use to describe the processes. Our technology and our understanding of physics has developed hugely because we can describe how things will behave. But we will stumble if we try to understand what is really going on behind these processes. As Feynman said in lectures he gave to physics undergraduates:
“We cannot make the mystery go away by ‘explaining’ how it works. We will just tell you how it works. In telling you how it works we will have told you about the basic peculiarities of all quantum mechanics.”§
And so things remain enigmatic. Questions that appear to show paradoxes such as the problem of Schrodinger’s cat* continue to puzzle and intrigue us. Is the cat dead or alive? Can the cat be both? Is the cat an observer and what role does the observer have in physical measurements? What does this imply for the fabric of reality? And is there a connection back to the name of this cafe, “once”?
You perhaps should not expect to find any answers in Katsute 100, but pondering these things with a good cup of tea may help advance your understanding. It will certainly help advance your mood if you are in need of some peaceful, thoughtful, time out.
Katsute 100 is at 100 Islington High St, N1 8EG
§ Feynman Lectures on Physics Volume III, 1965
*The story of Schrodinger’s cat is that a cat is placed in a box together with a small amount of radioactive source material. The box is then closed and we cannot see inside. The amount of radioactive material is such that in one hour it has a 50:50 chance of decay. If the material decays radioactively, it triggers the release of a vial of poisonous gas which would kill the cat. Our mathematical models of quantum mechanics suggest that, until it is measured, the radioactive material is in a ‘superposition of states’: it has both decayed and not decayed; the cat is both dead and alive. Only when we open the box after an hour and thereby measure the state of the radioactive material does the cat, at that point, ‘collapse’ into a state that is either dead or alive.
We delayed our visit to Under the Willow Tree by a day because we noticed that the cafe was closed on Monday afternoons owing to “Sing and sign” sessions for the local community. What a brilliant idea and the sort of community engagement that makes a neighbourhood cafe particularly special. Definitely a cafe to visit.
Coffee is by Grumpy Mule while the tea is by Ero’s. There is a good selection of pastries on the counter and food for brunch/lunch on the menu. The only problem was that there was no sign on the frontage of the cafe to tell us that we’d arrived, we guessed based on the postcode and the fact that this was the only place serving this sort of coffee in the area.
The cafe is definitely child-friendly. With a children’s play area at the back and toys on the shelf by the water, there is plenty for kids to do while their parents enjoy some time with a coffee. Although there are also tables away from the play area if you wanted a coffee away from the kids. A table towards the back of the cafe is suspended by rope perhaps making you think of swings, or tree houses, while the rest of the cafe is fairly minimalist, focussing you on the coffee and the play.
It is no bad thing to focus on play and indeed, it could offer a first physics connection, or at least materials science, with this cafe, in the form of the English Willow needed to make cricket bats for Test cricket. The fibres within the wood provide the toughness needed to prevent the wood from splintering as the ball hits the blade.
But keeping with the Willow tree, the remarkable thing about it is how it bends down to the water’s edge, providing shade and shelter for all manner of wildlife. There is another type of deciduous tree in a London park that hangs across a footpath, lazing in a manner similar to that of the willow at the water’s edge. And although it is perfectly possible to walk underneath it on part of the path, I find it perhaps more respectful to bow to the tree as I walk underneath. Walking the path at different times of the year, it is noticeable that the amount I need to bow increases as winter moves into spring and summer. The weight of the leaves pulls on the branches pulling them down.
As the tree has horizontal branches hanging over the path, it is not a simple case of Hooke’s law (where the amount the tree stretches down is directly proportional to the gravitational force of the leaves acting on the branches). But nonetheless, it does give you an indication of the collective mass of the leaves.
The fact that the tree dips down towards the path when it has leaves and moves up away from the path each winter, implies that the tree branches are acting within the elastic limit. That is, that the response of the branch to a load is still reversible. If the stress becomes too much, the extension of the tree will become plastic rather than elastic and the branches would not return to their original position. The elastic limit will vary from wood type to wood type and with different materials. Sometimes we would want elasticity and so we’ll choose one wood type, sometimes rigidity and so another. One reason that willow is a good wood for cricket bats is also this elasticity: the elasticity of the wood as the ball hits it being determined by small pockets of air in the bat.
There is a similar balance that may occur in your coffee cup if you enjoy a cappuccino. The difference between a pourable foam and one that stands ‘peak like’ on the cup. The ability of the barista to pour and draw the latte art requires a foam that is fairly stiff but still pourable. This is quantified by measurement of the “yield stress” of the froth. The yield stress is the minimum shear stress needed for a liquid or foam to start to flow. So to make latte art, you would need a foam that is stiff enough to hold the design, that is, it has lots of little bubbles that make the foam more firm. But at the same time that the foam is not so stiff that it does not pour (so you need to ensure that you have a lot of liquid milk content within the foam). The yield stress increases as the foam drains and so a good, pourable foam can be achieved by forming lots of smaller bubbles (thinner channels between the bubbles = slower drainage) and pouring it fairly quickly after foaming. But if you wanted to make 3D art of the form in the photo, you would want foam of a different stiffness, a different type of elasticity. You would probably want a drier foam.
In a sense, it is interesting to note that much that determines the response of a substance is about the voids within it rather than purely the material it is made from. Perhaps there is an analogy back to the cafe there: much that makes a coffee shop is the atmosphere created by the cafe rather than purely the coffee and pastries that are stocked. Or maybe that’s one step too far, and we need to go back to ponder and play Under the Willow tree while we enjoy our coffee, foamy or not.
Under the Willow Tree is at 114 Green Lanes, N16 9EH
In Paradiso, Canto II, Dante asks Beatrice about the Moon: “what are the dark marks on this planet’s body that there below, on earth, have made men tell the tale of Cain?”*
On Earth below, it is perhaps the brightness of the milk in the latte art that we notice in our coffee. But it is in fact precisely the contrast that we notice, both on the Moon and in our coffee.
What causes this contrast in the coffee and how does it link back to the Moon? Watching videos of, or if you are lucky to be close enough, baristas making latte art, you may be struck by the skill of the barista to form the milk into complex patterns and art. Swans, tulips and other designs appear on the surface of the drink with seemingly simple oscillations of the hand. And yet, if you’ve ever thought about attempting this art, you will appreciate how hard it is to design this contrast. How does the first pour of the milk lead to a significant uptake of the coffee (and hence a brown colouring), while the second part of the pour is dominated only by the milk and hence the shapes appear?
It must be partly a turbulence effect. The initial milk pour is from a significant height which would churn up the coffee meaning that the suspended particles in the coffee then get caught in the spaces between the bubbles in the milk’s microfoam. The second part of the pour is from a lower height which leads to a reduced mixing between the two liquids.
Yet this is only part of the story. Another perspective on it could be to consider the ‘albedo’ of the drink. The albedo is a measure of how reflective a surface is, so highly reflective surfaces (milk bubbles, ice sheets) have a higher albedo and less reflective surfaces (the coffee liquid, the earth’s surface) have a lower albedo. Part of the visibility of the latte art comes from this difference in reflectivity between the pattern part and the base part of the coffee.
In Earth science this has consequences for climate change: if the ice (high albedo, highly reflective) melts and reveals earth or sea (lower reflectivity, lower albedo), more sunlight is absorbed by the Earth and consequently you get local heating and locally accelerated ice melting. This may have consequences more globally in terms of climate change.
For Dante, it explained the colouration of the Moon. As his guide Beatrice explained to him: different parts of the Moon shone differently depending on their composition**.
Which takes us to another connection between science and art. It is recognised that, in European science history at least, Galileo first realised that the ‘dark marks’ on the Moon’s surface indicated that there were mountains and craters on the Moon. He was able to do this because he saw the Moon through a telescope and deduced that the patches were shadows. But when we think about this, it can’t be the whole story. While a telescope magnifies a distant object we still see, effectively, a 2D surface. We see the mountains on the Moon in the shadows because we know they are there. But how did Galileo know? Indeed, another astronomer at the same time was looking at the Moon through a telescope and could deduce only “strange spottedness”. What was the difference between Galileo and Thomas Harriot that allowed the former to see what the latter could not?
It has been suggested that it was Galileo’s artistic training that meant that he recognised the shades of light and dark as shadowsª. His practise at chiaroscuro drawing meant that he knew how to render depth using light and darkness in 2D images. When he saw the Moon, he could recognise the mountains. Another scientist, not familiar with how to render depth in painting, may instead see latte art on the Moon.
There are many ways in which our different backgrounds benefit each other and in which it benefits us to work as teams rather than individuals. There remain some though where the right combination of knowledge of both art and science combined with a particular skill at rendering them, can result in brilliant coffees, or astonishing discoveries, through connecting dots that otherwise could not be seen.
*The Divine Comedy, Dante Alighieri, Paradiso, Canto II. It is interesting here that Dante uses the word “planet” for the Moon, something that we would not do now. In a way it emphasises how our descriptive language changes with time and therefore how there may still be hope for Pluto’s rehabilitation.
** It is interesting here though that Beatrice’s answer to Dante is given to him only after she has convinced him through two experiments that his own explanation for the patches of the Moon was wrong.
ª Styles of Knowing, Chunglin Kwa, Pittsburgh Press, 2011
A short while back while preparing a V60 and watching the coffee level slowly rise to “4 cups” (just about what is needed in the morning for one person I think), I started wondering about rain gauges and how we measure the rainfall. While the first rain gauge was recorded in India in the 4th Century BCE, their design was still being optimised well into the 20th Century. We clearly need to know and agree how to measure rainfall, not just for agricultural reasons, but also for our understanding of the climate. But, more fundamentally, being able to measure quantities precisely and accurately, as well as being able to agree on what we measure seem to be fundamental to any advancements in science. We are perhaps struck by the number of people who have contributed to our knowledge of the world, either directly or indeed indirectly through getting it ‘wrong’. How many times have wrong ideas contributed to an advance in, what we consider at the moment to be, the right ideas?
And then there is the kettle that you may have boiled to prepare the coffee. Hidden by familiarity, the bimetallic switch that ensures that the kettle turns off as the water boils is a fairly recent invention. While the development of our understanding of the perfect brewing temperature for coffee is a mixture of the work of the coffee professionals and the development of the thermometer, itself a journey into science and philosophy.
An over-looked item? It can be instructive to consider how many people have worked to optimise this ‘ordinary’ kitchen object.
Indeed, when we consider the number of people who have contributed to our ability to enjoy our morning coffee it is striking. From the roaster to the farmer, the trader to the inventor: pausing to consider these things may perhaps emphasise to us our dependence on (and growth in) society rather than our individuality. But then, if we extend our thoughts to the insects and agriculture that enable the coffee plants to thrive, we may come to an awareness of our dependence on the planet; a recognition that “we are profoundly united with every creature….”¹ Does this awareness have an influence on how we behave in and as a society?
In “Styles of Knowing”, Chunglin Kwa argued that just as the forms and styles of painting are responses to the social circumstances, so are styles of knowing². He argued that:
How do our attitudes affect the science we do, and our perception of the coffee we drink? The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler
“[The humanists] strong emphasis on the vita activa [rather than the vita contemplativa] probably contributed to a scientific mentality aimed at sweeping aside obstacles, making decisions, and then taking action, rather than focussing on consensus, like the medieval scholastics. For humanists, it was the will that mattered.”
It seems that in our society as we encounter ever more distractions, there are always more ways for us to believe that we are busy and therefore useful. Does our embracing of this ‘busy life’ contribute to some of the issues that we define as problems? Do we gain control over some of the issues by taking responsibility for parts of them rather than avoiding them? What would happen if we stopped to contemplate our world, maybe just for 30 minutes each day? We could even do it while we journey into the world revealed by our coffee mug. Would it affect the way that we do science, think about society or drink our coffee?
There is a great deal of depth in a cup of coffee. Four cups is not enough. Do let me know where your mind wanders.
¹Laudato Si’, Pope Francis, 2015
²Styles of Knowing: a new history of science from ancient times other present, Chunglin Kwa, University of Pittsburgh Press, 2011
What’s in a name? A hundred impressions and assumptions, an idea that to know somebody is to know their name? And so it was that The Italian Coffee Club thew me. Towards the Uxbridge Road end of Shepherd’s Bush Market, The Italian Coffee Club is in a wooden lined chalet. A few tables outside and some prominent signage leave you in no doubt as to the fact that coffee is served here. A sign asks if you would like to try the signature Italian blend, while another informs you that the aroma of the coffee “comes from here”.
Which goes part the way to explain why I was surprised when I walked in. Inside, a number of chairs and tables line the, fairly narrow, space leading to the counter. Towards the counter are various large jars of freshly roasted coffee beans ready for retail. Perhaps this should have given me a clue to check my assumptions. The roasts were varied with a good choice of origins, including several single origin. The coffee menu offered the usual choices and…. V60s of any of the various coffees that they sold (sadly I noticed this only after I had ordered an Americano). The coffees are roasted by The Italian Coffee company and include several direct-trade relationships. Although I had the “signature” Italian blend on the day, I did purchase 200g of the La Abuela washed Colombian to take home with me as beans. La Abuela means grandmother and apparently this coffee farm (which is one of those with which The Italian Coffee club has a direct trade relationship) is run by an 80 year old lady growing coffee that scores 83+ in the speciality quality score.
Looking around this chalet/cafe, the first thing that caught my attention was a sign about “smelling the aroma”. This immediately conjured up thoughts as to how it is that we actually perceive smells. In some ways an incredibly basic sense, in others, something that we still do not understand. It also prompted me to think about anosmia (smell blindness) and its allegorical relevance to my assumptions as I had entered the cafe about the coffee I would find.
The jars of coffee were the sort of transparent bottle with a rubber seal, reminiscent of vacuum physics. A (presumably decorative) manual coffee grinder at the bottom of the shelves could have prompted thought trains about automation and whether the coffee making process is improved by the uniformity of grind obtained by industrial grinders or the imperfections (but connections) that we would have through a fully manual brew (I think it may depend on what we mean by ‘improve’).
And then I looked down at my coffee and noticed a hair floating on top of it. I knew it was mine because it hadn’t been there originally and it was of the right length and colour. But I could tell it was there due to the indentations on the liquid surface around the hair, much as you can see the indentations around the feet of a pond skater. How much force was the hair exerting on the surface of the coffee to make such indentations? And when would it ‘fall through’?
The surface tension of the coffee is caused by the water molecules in the liquid being attracted by the other water molecules into the coffee but not having anything above the surface to balance that force. Consequently, there is a net attraction for the molecules at the surface into the coffee and a ‘skin’ is formed on the surface, rather like an elastic sheet. This ‘skin’ takes a certain force to break it, which can be measured and which is called the ‘surface tension’. My hair, about 5cm long, as a typical human hair, weighs about 168 micrograms. Which means the gravitational force acting on it is F = mass x gravitational acceleration = 1.68 microNewtons. Expressed as a Force per unit length, this works out as 34 microNewtons per meter. In comparison, at 60 C, the surface of water requires a force of https://www.engineeringtoolbox.com/water-surface-tension-d_597.html0.067 Newtons per meter to break through it. My hair would be no match: the surface tension supports the hair.
As this is a coffee blog, what if we took the example of a coffee bean and, neglecting for one minute any other considerations, calculated the force it exerts on the water/coffee. Beethoven’s 60 beans of coffee had a mass of 9 g. So one bean has, roughly, a mass of 0.15 g. Each bean is about 1cm long and so it exerts 0.15 Newtons per meter on the water surface. Certainly enough to break it: so we could use coffee beans to measure surface tension. A novel purpose for the coffee bean, but I prefer my more traditional approach of grinding and drinking it.
Which took me back to the Colombian, La Abuela that I purchased from The Italian Coffee Club and tried, at home, as a V60. Sweet and syrupy, with cherry fruit: an enjoyable coffee for some time to ponder.