Quantum physics from your (re-usable) cup at Lost Sheep, Canterbury

Coffee in Canterbury, keep cup

Finding the sheep. Lost Sheep coffee in Canterbury. Note the lighting.

I have long been looking forward to trying the Lost Sheep coffee pod in Canterbury. How would the reality compare to the friendly and knowledgable impression they give on social media? Being mostly a take-away outlet, what was their attitude to the disposable coffee cup problem? We had ensured that we had packed our keep-cups when we left London so that we could enjoy a coffee without having to use a disposable cup. Little did we know.

The sheep was visible as we approached the Lost Sheep coffee pod from the direction of the High Street. Adjacent to the pod, people were drinking their coffee while standing at the chip-board standing-bar nearby. In front of us in the queue, another customer was buying what appeared to be his usual coffee in his re-usable cup. The conversation between the customer and barista showing that cafés that help build communities do not have to come in standard formats. ‘Pods’ can work as well as cafés inside buildings (though the Lost Sheep has one of those too over in Ashford). The queue ahead of us enabled us to take more time to study the environment of the Lost Sheep.

Interestingly, a set of ceramic cups were placed above the espresso machine. Although we saw none in use, presumably this means that should you wish to enjoy your coffee at the bars, you can do so, even if you have forgotten your reusable. What a great feature for a take-away coffee place. The friendliness of this café was apparent as I presented my keep-cup for my long black. Commenting on the design of the cup (glass with a cork handling ring, perfect in size for the coffees I mostly drink), we continued to enjoy a short conversation about keep-cups and how nice the size was for the coffee. The coffee was amazingly fruity, a sweet, full bodied brew roasted locally in Whitstable. It was great to be able to enjoy this interesting coffee while wandering as a tourist in my old home-town.

Coffee Canterbury Sheep

Behind the sheep. At least it is easy to spot from all angles.

Before leaving the Sheep though, we did notice the lighting. A yellow hue from the lights immediately above the espresso machine with a whiter, harsher light from the luminescent strip light at the edge of the pod (a dull sunlight surrounding the rest of the outdoor space on this cloudy day). Coals are red hot, the Sun appears more yellow, how does colour vary with temperature? And how does this link to an old story that links quantum physics (very quickly) to your coffee cup.

How things absorb and emit light and electromagnetic radiation has been a subject of study really since white light was split into its different colours and then it was found that there was ‘invisible’ light beyond the blue and far from the red. It was known in the nineteenth century that things (which physicists tend to like to call ‘bodies’ for reasons that become clearer later) that absorbed all the light incident on them re-emitted the light unequally. As they absorbed all the incident light, they could be called a ‘black bodies’. People knew that the radiated light from a black body formed a spectrum that depended upon the temperature of the body. For most things that we encounter on earth, such as the coffee cup, their temperature means that they will emit more strongly in the infra-red, we can feel the heat coming off of them but we can’t see it. But as things get hotter they start to glow ‘red-hot’ and then if we heated them still further, they would glow with different colours.

The stars show this with the colour of the star being an indicator of the temperature of the star. Stars that are very hot shine blue, those that are cooler (but still thousands of degrees Celsius) appear to us as more white. Although these stars are emitting light at all frequencies, they show a characteristic peak in emissions for one frequency. The corresponding “black body spectrum” was very well known in the nineteenth century but the problem was that classical physics just could not explain it. Attempts were made to describe the curve but when it came down to it, if the energy (ie radiation) was described using classical physics, the shape of the curve could not be explained. While classical physics predicted the shape of the curve very well at long wavelengths (reds, infra-reds), there was a failure at shorter wavelengths. And not just a failure, it was a catastrophe: the theory predicted that an infinite amount of energy would be emitted at the low wavelengths. Clearly this is wrong, nothing can emit an infinite amount of energy and so for this reason, the problem was described as the “ultra-violet catastrophe“.

Sun, heat, nuclear fusion

The Sun is our nearest star and source of heat. But what links coffee to the Sun? It turns out a great many things of which this is just one. Image © NSO/AURA/NSF

A solution came when Max Planck changed the assumptions about how energy was emitted or absorbed. Rather than the continuous emission that was expected in classical physics, Planck reasoned that energy was emitted in discrete packets and that, crucially, these “quanta” were dependent on the frequency of the light being emitted. Planck’s formulation allowed for a mathematical description of the curve. Finally the shape of the black body spectrum could be explained, but it came at quite a cost; it came at the expense of classical physics. To use Planck’s formula meant abandoning some aspects of classical physics in favour of a new quantum model and it meant leaving the absolutes of classical mechanics and entering into a new statistical world. This change didn’t come easily even to Planck who had been motivated to study physics by the absolute answers that the theory of thermodynamics seemed to provide. He wrote, regarding his own black body theory:

“… the whole procedure was an act of despair because a theoretical interpretation had to be found at any price, no matter how high that might be”

In some ways, that feeling that you experience while warming your hands on a cup of steaming coffee while basking in the late afternoon sunshine is an intrinsically quantum experience. Neither the infra-red heat of your cup nor the colour spectrum of the sun could be explained using purely classical physics. So while taking time to appreciate the heat of your coffee, perhaps it’s worth remembering that this feeling that you are experiencing comes as a result of the same physics as determines the hot glow of stars and the cold microwave glow of the universe. The coffee heating your hands is indicating that the world is stranger than you may think, a quantum world being revealed to you all the while you sip your coffee.

Lost Sheep coffee is in St George’s Lane, CT1 2SY


A lawyer, an accountant and and emperor walk into a cafe…

Strata, geology

This is not a resonance in a coffee cup but the concentric circle pattern is similar to a resonance that you could frequently see.

Have you ever noticed concentric rings on the surface of your coffee, forming as the table under the coffee cup vibrates slightly? Perhaps you have seen more complicated patterns. You may have observed, as you have played with your coffee, that some patterns are more stable than others. The one that is formed from concentric circles is fairly easy to form and to see. A more complex one looks like a chequer board, you may perhaps of seen others. These patterns are what are known as ‘resonances’ on the surface of the coffee and they are the consequence of standing waves being set up on the coffee surface. Many people who have gone through an undergraduate physics degree will immediately be reminded of Chladni figures and there is a good reason for this. Ernst Chladni (1756 – 1827) was a pioneer in investigating such resonances, one of the reasons that he has been described as “the father of experimental acoustics”.

And yet Chladni was not a physicist in the way that we now think of the term. In fact, by training he was a lawyer, a consequence of following his father’s rather insistent ‘advice’. Obediently, Chladni had trained in law and had started working as a lawyer in 1782 when his father died. Chladni appears to have taken this event as an opportunity to start to investigate the scientific problems that he was actually interested in and so re-invented himself as an acoustician testing the theories of music developed by people like Bernoulli and Euler¹.

transmission lines, electrical noise

Like strings on a guitar. Resonances on a string can be used to make musical notes.

Did Chladni drink coffee in eighteenth century coffee houses while admiring the resonances in the cup? Sadly what comes down to us in history is not his coffee habit but his experiments with sand covered metal plates secured onto wooden rods. Chladni caused resonances on these plates by rubbing them with a violin bow. By exciting resonances similar to those you can see on the surface of your coffee, Chladni was able to test theories about the sounds made by curved metal surfaces (e.g. bells). Indeed, these experiments became so important to understanding acoustic theory that Chladni started a European tour demonstrating his plates and their relevance to designing musical instruments. It was presumably through one of these tours that he met an Emperor of the time, Napoleon Bonaparte.

But despite this great experimental progress, the mathematics used to understand these resonance patterns, was developed by another physicist with a non-typical career path, Friedrich Bessel (1784-1846). Bessel had trained as an accountant but with the good fortune of timing, he had apprenticed into an exports company. At this time, such companies would have been interested in the problem of longitude and so Bessel gained an opportunity to indulge his interest in astronomy. As a consequence of this work, particularly his work on the orbit of Halley’s comet, Bessel secured a job in an astronomical observatory and it was there that he started the work that would eventually lead us to be able to describe, mathematically, the resonances on the surface of your coffee.

Did Bessel drink coffee? Had he seen Chladni demonstrate his plates? We don’t know the answer to those questions and in many ways it is not relevant because Bessel’s mathematics did not concern such resonances at all. Instead, almost to underline the idea that everything is connected, particularly with physics and coffee, Bessel was working on the problem of how to calculate the gravitational attraction between multiple objects.

Kettle drum at Amoret

The note made by a drum is a function of the size and shape (therefore resonance pattern) of the drum and also the gas filling the drum. Would this drum-table sound the same if banged on Venus as on Earth?

Perhaps you remember from school Newton’s famous description of the gravitational attraction between two bodies as being F = GMm/r² (where F is the force, G the gravitational constant, M and m the masses of the two bodies and r the distance between them). That’s all very good but what if there were three bodies, or four, or…

It was this problem that Bessel was working on and by so doing he solved the problem of Chladni’s patterns. The maths that describes the many body problem also describes the way that these resonances form. Those patterns in your coffee are described by the same maths as allows us to calculate complex gravitational problems.

And so perhaps it is not quite correct to title this post as a lawyer, an accountant and an emperor walk into a café, but it would be fair to say that each time you catch those resonances in your coffee cup, the  influence and interests of these investigators of nature are infused within the brew.

You can find a sketch of Chladni entertaining Bonaparte with his metal plates here.

¹Harmonius Triads, Physicists, musicians and instrument makers in nineteenth century Germany, MIT Press, 2006


Coffee prints at Water Lane Brasserie, Canterbury

coffee in a friendly environment Canterbury

Drinks at Water Lane Brasserie, Canterbury

Making our way down the cobbled High St in Canterbury, into a side street within the old walled town and then following the black board signs for coffee, we found our way to Water Lane Brasserie on Water Lane. Although it is very close to the High St and even the bus station, somehow Water Lane Coffee feels quite hidden. We had decided to try Water Lane for a spot of lunch as we had read good things about the food and coffee. A friendly dog welcomed us into the café where a few groups of people were chatting or working on their laptops.

Various, slightly out of place, ornaments were dotted around the fairly large space. There was the Newton’s cradle in the window, the Fly agaric mushrooms near the sofa seats, the hand grinder and syphon brewer near the counter and, of course, the jenga sets on some of the tables. As various customers came and left, the friendly service suggested that this was a café in which relationships are built along with jenga towers. Corny analogies aside, it may have been tempting to focus a café-physics review on such pieces dotted around. However, it always seems that the more that you contemplate a place, the more rewarding the observations become (to yourself at least, whether they become more interesting to others is quite another matter).

mushrooms at water lane

A Fly agaric (Amanita muscaria) mushroom near the sofas. Learning about how to identify mushrooms is excellent training in noticing.

Our soup, which was indeed a lovely way to enjoy a light lunch meant that we had quite some time to look around the café. Just outside the window, a bird feeding area with hanging bird feeders had somehow attracted an ingenious moorhen that was cleverly balancing on a conveniently placed pole while grabbing food perhaps intended for smaller birds. Inside, punting equipment lined the walls as it seems that you can punt in Canterbury’s river now when it is warmer (is this a new thing? I cannot remember this from years ago when I used to be in Canterbury more regularly). On a shelf above the counter there were several beers with the logo “Canterbury Ales”.

By this time we were enjoying our coffee (long black) and soy hot chocolate. These were a great finish to the soup. Although there was no information about the roaster, the coffee was very drinkable, darker rather than fruity. As we moved the soup away, the indentations on the top of the (old card table) table became more obvious. Rather like footprints in the sand or fossils in London’s Portland stone. Evidence on a table top of coffee-drinkers-past. Could we gain much information from the imprints left on the table top? Firstly, this table has not just been used for playing cards, a fair few plates of food have been placed on it. Secondly, some very heavy small objects, given the shape of the footprint, perhaps vases, have also been put on the table in the past, was this used decoratively? It is difficult to know with any certainty what happened on this table but with a bit of extra information, such fossil footprints can be full of information.

coffee prints at Water Lane

The table top at Water Lane. What can you discern from the indentations that have been left?

When thinking about fossil footprints, as with the table, the first bit of information that can be gleaned from the fossil is the size of the animal (or object) that made them. So even in the absence of a skeleton fossil, it would be known that some dinosaurs were enormous. Last year a set of dinosaur footprints were discovered in Australia that were 1.7m large, a single foot larger than many humans are tall. Then there is the information that can be ascertained from multiple footprints, such as the idea that perhaps dinosaurs hunted in packs or at least, that some dinosaurs such as the Tyrannosaurus Rex moved in small groups, presumably for hunting. Elsewhere, the presence of different types of dinosaur footprints that seemed to move in different patterns suggested a hunt that occurred millions of years ago.

Tristan Gooley in “The Walker’s Guide to Outdoor Clues and Signs” suggests using more recent footprints to see the wildlife stories that have recently unfolded around you when you walk in the country*. He writes:

“Tracking is built upon these simple, logical principles. All four-legged animals lift and replace their feet in a set order and rhythm and this reflects their evolutionary heritage….. It will not be long before you come across two sets of tracks that are clearly related in some way. The two types of tracks, their character, the spaces between them, the habitat, the time of year and a host of other circumstantial evidence will reveal whether an animal was hunting another, scaring it off, playing with it or trying to mate with it. Here, following the track means reading the story.”

Returning from our day dreams and to the table at Water Lane, looking out the window it became apparent that a figure was staring back at us. Standing just on the other side of the river Stour, a short, stout, statue of a monk looked out from under the hedge around the church beyond the river. The old Greyfriars chapel dates from the thirteenth century, the home of the (then recently formed) Franciscans, named after St Francis of Assisi. Details of the history of this place are revealed in old graffiti around the venue. The monk on the river seemed to silently acknowledge the place’s history as the water ran by. What clues as to previous visitors are there in this friendly, quiet and contemplative café on the river Stour? What will be our imprint on the world when we leave it, as individuals, as a society?

Water Lane Brasserie is in Water Lane, Canterbury.

“The Walker’s Guide to Outdoor Clues and Signs” by Tristan Gooley, Hodder & Stoughton, 2014

*Not just the country. In many urban parks you can see the recent behaviour of geese, sea gulls and the dogs that chase them, or walking down a pavement tracking a dog that has just walked through a puddle. Hearing a story from the clues left behind needn’t just be a game left to country walkers and fossil hunters.


Freezing point

coffee and ice in New Cross on a wooden table

Isn’t it a fact that water boils at 100C and freezes at 0C?

Water boils at 100ºC and the ice in your iced latte is at 0ºC. These are facts that we think we know about water: it boils at 100ºC and it melts at 0ºC. A sharp observer may point out that these are pressure dependent and that if we were at the top of a mountain, the water would boil at a slightly lower temperature (I once had a student argue that this was a good reason to only ever drink green tea at high altitude). But if we are at ground level and it is a normal day, we will be fairly certain that the water for our coffees would boil at 100ºC and ice would form at 0ºC.

Yet these ‘facts’ hide some complicated physics and some oddities about our planet. Pure water, that is, water without any impurities in a clean vessel (such as a clean, scratch free glass) does not boil at 100ºC but at temperatures significantly higher than that. Nor does pure water freeze at 0ºC but at temperatures significantly below that. These are phenomena known as superheating and supercooling respectively and, if you are observant, you could see them occasionally in your coffee cup. To see why, and how, we need to think a bit more about how water freezes.

blue tits, mint water, mint infusion, mint leaves in water

If you put pure water into the freezer, you may find that it freezes at a temperature considerably lower than 0C

If you fill an ice cube tray with water and put it in your freezer, you would expect ice cubes to start forming at about 0ºC. We expect the freezing temperature to be the same as the melting temperature, that is the temperature at which the ice cubes would melt. And yet, if you make the water very pure (even distilled water would be a start) and put that in a clean, defect free container (such as a clean glass jar) in the freezer, the freezing process will not begin until much lower temperatures. It’s because the water has to crystallise and change state from a liquid to a solid and to start this process, there needs to be a seed, a surface on which the ice can form. Called a “nucleation site”, this seed could be a piece of dust, a small impurity in the water, a scratch on the surface of the container holding the water, or in fact anything that allows the bonds of ice to start to form. The same is true at the other end of the temperature scale. When the liquid water turns into steam, nucleation sites are needed so that the gas bubbles can start to form at those sites. In the absence of impurities in the water, the water will not boil until temperatures high above 100ºC.

Fortunately in tap water, or in your super-filtered water that you make your coffee with, there are plenty of such nucleation sites so the water boils and freezes at roughly the temperatures you’d expect them to. The same is not true however for clouds in the sky where some (high altitude) clouds have been shown to contain water droplets that are at -35ºC, well below the “freezing temperature”. Exactly why this occurs is still puzzling and a topic of research, but when you stop and think about it, how would you actually measure this temperature? If you supercooled a cup of water and then put a thermometer into it, the thermometer would provide a nucleation site and the water would immediately freeze. How can you measure the water’s temperature without a thermometer?

kettle, V60, spout, pourover, v60 preparation

You are unlikely to see superheating when you boil the water for your coffee in a kettle like this.

Recently a study reported in Physical Review Letters used a laser to measure the diameter of a series of supercooled liquid droplets by determining the energy of a resonance that depended on the droplet’s size. To calculate the temperature of the droplet, the authors then used the principle that as water evaporates, the droplet from which it is evaporating will become colder at the same time that it shrinks in size. Measuring the size of the droplet allowed them to calculate the evaporative loss and therefore the temperature of the drop. They double checked this new technique by measuring (with the same laser) the energy of a particular atomic bond in water that has a known temperature dependence (at higher temperatures). The temperature determined from the drop’s size corresponded with the extrapolation of the energy of this atomic bond and so the team were fairly confident that they had measured liquid water to very cold temperatures indeed. In fact, the authors suggested that it was still possible to have liquid water at 230.6±0.6 K which, in more every-day units corresponds to -42.55ºC, well below the nominal ‘freezing point’.

So pure, liquid, water can get very cold indeed. But could you ever see this in your coffee cup? Although you may like to try some experiments with freezing ultra-pure water, it is easier to see the phenomenon of superheating in your coffee. However, given the possibility of an accident, it may be safer to watch the effect on the video below. The idea is that if you put very pure water in a clean cup into a microwave, it is possible to superheat it well above 100ºC without it boiling, because there are no nucleation sites in the cup or the water on which the steam bubbles could start to form. When you take the cup out and put a nucleation site in (perhaps a spoon or maybe even instant coffee granules), the water will boil suddenly as a result of those new nucleation sites and can even explode. Obviously if you were anywhere near the water when this happened you could get seriously burnt and so it is probably safer to watch the Mythbusters do it with their robotic arm. Enjoy the video, enjoy your coffee, preferably far from superheated:




Seeing the light at Redemption Roasters

Coffee Bloomsbury

Redemption Roasters Cafe on Lamb’s Conduit St.

At the top end of Lamb’s Conduit Street there is an unassuming café in a fairly modern building at the corner of Long Yard. In recent weeks I had been hearing a lot about Redemption Roasters and their café. First came the review by Double Skinny Macchiato, then various comments on Twitter, in Caffeine magazine and finally, an article in the FT. In an ideal world, it seems to me that cafés can act as seeds towards forming a better society. Local and independent, a friendly place where you can chat with the baristas (or café owners), and so where communities can form and develop. All that I had heard about Redemption Roasters café fitted, in some way, into this ideal which meant that it was not going to be long before I headed towards Bloomsbury and tried this new café.

Plenty of seating could be found inside the café, with tables of two or four and benches around the space. The counter was immediately in front of us as we went through the door and the friendly barista took our order (long black and soya hot chocolate, what else?) while we took our seats. There were a fair few staff in the café when we visited, so many in fact that we weren’t initially sure who were staff and who were customers. Nonetheless, their joviality transformed the café’s fairly austere decor more into the feel of the welcoming space of a living room.

blue shadow, hot chocolate

A layered hot chocolate? No, just the reflection of the saucer in the glass.

Having taken our seats and started to look around, we found that much could be said about the science in this café. From the SMEG refrigerator and individual radiators to the light reflection off individual sugar crystals in a glass on the table. Moreover, when our drinks arrived, the reflection of the (blue) saucer in the hot chocolate glass made it appear as if the hot chocolate were layered. In fact it was an optical illusion caused by the way our minds process the colour blue in shadows, more on that in this great article about colour, Goethe and Turner. But it was to a different lighting effect that my thought train eventually turned. Above the counter are a series of hanging lights with angular shades over them. Above our table were LED bulbs inset into the ceiling.

The way that the LEDs above us had been placed produced two shadows from the spoon on the saucer of my cup. A dark shadow and a light shadow at a slightly different angle. One reason that LEDs have caught on as a light source is that they are more efficient and so better environmentally and cheaper financially. So you may think that LEDs are one way of reducing our (collective) environmental footprint. But does this work? According to a study that measured the outdoor light levels around the world from 2012 to 2016, the answer is no. It would appear that while on a local level, people are enjoying cheaper lighting, on larger scales (nationally, globally), this decreased cost is leading to us installing more lights. Consequently, on the global scale, the area of land that is lit has increased by 2.2% per year with very few countries showing a reduction or even a stabilisation of the amount of outdoor areas that are lit.

shadows from a coffee Redemption Roasters

Determining a presence by noticing an absence. The two shadows of the spoon came from the light bulbs inset into the ceiling.

Does this matter? Well, it is something that is affecting us, the way we view our world and the wildlife that we share our planet with and so it is something that we ought to be thinking about. In brightly lit areas of the UK, trees have been shown to produce buds up to 7.5 days earlier than in darker areas. Artificial light is causing problems for nocturnal insects and animals, with knock on effects for crop pollination. And when was the last time you looked up at the sky on a clear night and saw seven of the Pleiades let alone the Milky Way? How does it change our psychology and philosophical outlook when we can no longer gaze at the night sky with wonder and without the glow of streetlights?

Some astronomers have called for increased shielding of street lighting as a way for us to both enjoy well lit streets and be able to enjoy looking up at the night sky. Shielding such as that over the lights over the counter at Redemption Roasters café, where the light is efficiently directed downwards rather than be allowed to escape into the sky. Small steps that can make a big difference. It is interesting to notice that around central London at least, many newer lampposts are more efficiently shielded than older ones. Pausing for a coffee in Redemption Roasters café is a great moment to consider this problem and your reaction to it. Have you stopped to gaze at the night sky recently?

After leaving the café, I realised I had lost an opportunity to notice something else. Frequently, after visiting a good café, I will look up the area in my London Encyclopaedia¹ to see whether there is anything of interest historically in the area of the café. As expected, Lamb’s Conduit St was named after a conduit made from a tributary of the river Fleet restored by one William Lamb in 1577. But Lamb also donated 120 buckets for poor women of the area to use for collecting their water, which explains the statue of a woman with an urn at the top of the street. However what was also mentioned was that at the entrance to Long Yard (ie. very close to Redemption Roasters) there is an ancient stone inset into a wall with a description about the Lamb’s Conduit. Somehow I missed this though Double Skinny Macchiato evidently found it. So if you do visit Redemption Roasters café, and I would very much recommend that you do, as well as taking some time to savour the coffee and to notice the surroundings, please do look out for this elusive stone and if you find it, do let me know.

¹The London Encyclopaedia, Weinreb, Hibbert, Keay and Keay, MacMillan, 2008

Redemption Roasters Cafe is at 84 Lamb’s Conduit St, WC1N 3LR

Coffee and the world

Welcome to the first post of 2018, Happy New Year! But before embracing 2018, perhaps let’s take a moment to remember those things that we discovered in 2017 that connect your coffee cup (or brewing device) with the physics of what occurs in the wider universe. Here are some of the highlights for me this year, if you want to share your highlight, please comment in the section below.

latte art, flat white art

A properly made latte. But what if you add hot espresso to the milk instead of the other way around?

1) Latte layering

In mid-December a study was published in Nature Communications that explored the complex, but elegant, physics involved in making lattes (ok, not quite by the technique that you would hopefully find in your neighbourhood café but keep with this…). When a hot, low density, liquid (espresso) was poured into a hot higher density liquid (milk) contained within a cold mug, the competition between the density gradients of the liquid (vertical) and the temperature gradient from the cup wall to the liquids (horizontal) produced multiple layers of varying coffee/milk concentration in the cup. Too late for a 2017 Daily Grind article, this looks to be too good an experiment to pass by, hopefully it will appear on the Daily Grind in early 2018.


science in a V60

Could this V60 mystery now be solved?

2) Bouncing drops

November 2017 saw research published about what happens when a cold droplet falls onto a hot liquid (think milk and coffee). The temperature difference causes currents to be established within the droplet (and in the main liquid) that in turn create air flows between the droplet and the liquid bath that prevent the droplet from merging with the bath. The research can explain why it is that you can sometimes see raindrops staying as spheres of water on the top of puddles. It may also explain a puzzling phenomenon that I have seen while brewing coffee in a V60.


Vortex rings get everywhere.

3) Vortex rings in coffee

June 2017 and it is again about adding milk to coffee (why do I drink coffee black?). When one liquid (such as milk) is dripped into another (such as coffee), it is very likely that you will observe the milk to form “vortex rings”. These rings are related to smoke rings and have, in the past, been proposed as an atomic model. This year however it was suggested that these vortex rings could form as a type of magnetic nanostructure. Mathematically impressive, beautiful, perhaps quite useful and mathematically similar to something you can find in your coffee.


bloom on a v60

How do craters form?

4) Crater shapes

April 2017. What happens while brewing a pour over? As you drip water onto a granular bed (or, in coffee terms, ground coffee in a V60 filter), each drop will create a crater. The size and shape of the crater will depend on the density of the granular bed (espresso puck or loose grounds in a filter) and the velocity of the falling drop. Fast frame photography revealed how the shape of the crater changed with time for different scenarios.


Coffee bag genuinely home compostable

How it started.
The Roasting House bag before it went into the worm composter.

5) A home experiment

Perhaps not quite in the theme of the other four stories but this is an experiment that you can do at home. Some have proposed compostable coffee cups as a more environmentally conscious alternative to ordinary, disposable, coffee cups. But how “compostable” are compostable cups and compostable packaging? Between May and September 2017, #howlongtocompost looked at how long it took the Natureflex packaging (used by the coffee roasting company Roasting House for their ground coffee) to compost in a worm composting bin. This one worked quite well. Within 17 weeks, it had been eaten by the worms. In comparison, the “completely compostable” take away coffee cup is still in the worm bin (although considerably degraded) 37 weeks after the start of the experiment. If you are interested, you can follow #willitcompost on twitter. Will it finally compost? I’ll leave you to place your bets but you may decide that a link to Brian’s coffee spot guide to re-usable cups will be helpful.


What will 2018 bring? Certainly there will be more composting experiments as I have a coffee bean bag from Amoret coffee, 3 different compostable cups and a compostable “glass” to try with the worms. But in terms of the science? We’ll have to wait. Meanwhile, if you have a coffee-science highlight from 2017, please do share it either here in the comments section, on Twitter or on Facebook. Happy New Year to you all.






Hidden appearances at HoM

hot chocolate, soya, marsh mallow, HoM

Hot chocolate with marshmallows at HOM, Kings Cross.

In these long dark afternoons in the northern hemisphere, what could be better than a warming mug of lovely coffee in a bright environment? And so it was that we ended up at House of Morocco (HoM) on the Caledonian Road. Alerted by Brian’s Coffee Spot that Pattern Coffee had changed hands and become HoM we headed up to Kings Cross one damp afternoon in December to see how things had changed. Entering HoM is a strange mix of déjà-vu mixed with new. The pattern on the wall next to the window remains, as does the layout of the place. However it is also clear that much has changed since HoM took over.

There are murals and variously coloured cushions dotted around the café. Even in the darkness of the afternoon, the café was bright, but also crowded. We ordered a soya hot chocolate, a long black and a cheesecake and found a seat perched at a small table for two near the door (the only seat left at the time). The coffee, roasted by Terrone Coffee, was nicely balanced for the afternoon. But it seems that the hot chocolate and cheesecake combination were a real hit. The cheesecake was apparently very good (definitely worth a return visit apparently) while the hot chocolate went very quickly!

Inside the café, the windows were steaming up with the warmth of the inside. We over-heard that this was because of the coffee machine rather than any extra heating that had been installed. Does this suggest an alternative energy source? Coffee machine heaters to go with treadmill electricity generators in gyms?

all about pigmentation at HOM

Menu with sugar bowl and glazed tile at HOM, Kings Cross.

Meanwhile, the decoration was demanding my attention. A vividly coloured glazed tile supported a jar of sugar which was propping up a black and white menu. The menu had an illustration reminiscent of henna tattoos while above all of this balanced a peacock feather in a vase. Underneath the peacock feather was a poster advertising the “Phantom of the Opera”. The whole ensemble was suggestive of appearances and how they can be deceptive. The phantom of course wore a mask to disguise his disfigured face. But the peacock? The peacock is hiding something too.

Many of the colours that we see around us such as those making our coffee brown and making the tiles colourful are as a result of energy from the light being absorbed by the atoms in the substance (the coffee or the tile). This type of light absorption (and emission) can be connected with vortices in coffee as was discussed here. However the blues and greens in a peacock feather are different. If you look at the feather under a high powered microscope, you will find that the feathers are not dyed as such, in fact the natural colour of the feathers is quite dull. Made from keratin (as you can find in your fingernails) and melanin (responsible for the brown pigmentation of your skin, eyes and hair), the feathers do not seem blue at all. In fact it is the structure in the feather that is producing the colour rather than any dye that produces the colouration.

It turns out that there is a long history concerning our understanding of the colours of a peacock’s feather. It started with Robert Hooke who, in 1665 described the feathers of both peacocks and ducks and noticed that the colours he saw under an optical microscope were ‘destroyed’ by putting a drop of water on the feather. A little bit later and Isaac Newton was suggesting that the colouration was due to the thickness of the transparent bits of the feather. There’s a link here to coffee. Newton was suggesting that an effect similar to thin film interference (which causes the rainbow colours on the bubbles in a coffee) was causing the colours of the peacock feather.

appearances at HoM

Peacock feather and phantom poster with the top of a mirror. How does structure affect what is seen?

As our understanding developed through the centuries (and the microscopes became more powerful), it became apparent that while thin film interference (and multiple film interference) could cause some animals to appear as if they had certain colours, the peacock, along with some other animals, was a little bit more special. Rather than just being the result of reflection off an interface, the peacock’s feathers showed structure at the nanoscale (1/1000000 of a mm). The keratin and melanin in the feathers were arranged in a square lattice to form what is known as a ‘photonic’ crystal. The way this structure reacted with incoming light meant that only certain wavelengths were reflected from it. Depending on the size of the layering in the feathers, they appeared as blue, green or yellow.

Although a lot more is now understood about the factors, structural and chemical, that lead to colouration in all sorts of creature, be they butterflies or beetles, peacocks or pigeons, there is still more to discover, more to understand. The authors of the paper referenced here wrote

“In this paper, we describe a wide variety of structural colors occurring in nature and attempt to clarify their underlying physics, although many of them are not fully clarified.”

There’s clearly a lot more work to do before we can properly explain these “beautiful microstructures”.  And plenty of time to do so as we sit enjoying well made coffee and hot chocolate in a bright and warming café.

HOM can be found at 82 Caledonian Road, N1 9DN


Coffee and cream baubles – not just for Christmas

floating, bouncing drops

Drops of water can be stable on the water’s surface for many minutes if you put the water on a loudspeaker, more info on how to create these at home here.

You may have noticed them before: balls of liquid dancing on the surface of your coffee (or tea) that seem to last for ages before being absorbed into the drink? Perhaps you have added milk to your coffee and noticed that it took some time before the milk entered into the brew?

It turns out, there’s some very interesting physics that is happening whenever you add milk to your tea or when you are preparing a pour-over. It can link coffee to wine and to quantum mechanics. It is worth taking a closer look at these drops.

You may remember that you could use a loud speaker to make droplets of coffee bounce on a cup of the same. The vibrations in the cup meant that the air between the droplet and the drink never got squeezed out of the space between them. So, rather than coalesce, the drop jumped up and down on the coffee surface before finally disappearing under. This type of bouncing bauble has been shown to behave in similar ways to quantum particles in wave-particle duality. An analogue of quantum physics in the macroscopic droplets on the surface of your drink.

But that type of bauble required the use of a loud speaker (or some similar way of generating vibrations on the surface of the coffee). What if you could ‘bounce’ a drop of coffee on a cup of coffee without any external props like speakers? Well, it turns out that you can. In November 2017 a group of researchers showed how a temperature difference between a drop falling into a drink and the drink itself could result in the drop appearing to float on the surface of the drink for many seconds. The obvious example was cold milk into a cup of coffee (or tea). But I think that it may also happen in a V60 when you prepare a pour over, more on that below.

science in a V60

Bubbles of liquid dancing on the surface of a brewing coffee.

The idea is quite simple. If there is a temperature difference between the drop and the coffee, when the drop approaches the coffee, there will be thermal gradients across the drop/cup system. Surface tension is temperature dependent: the higher the temperature, the weaker the surface tension. Differences in surface tension across the surface of a liquid result in compensating liquid flows (one of the best places to see this is in a glass of wine, but there’s also a great party-trick experiment you can do to demonstrate it which is here). So, because there is a temperature difference across the surface area of the droplet (owing to the difference between the droplet and the cup), there will be liquid flows set up within the drop. These flows are like circulating vortices which draw the surrounding air into the gap between the drop and the cup and so prevent the existing air between the drop and the cup from escaping. If the air has nowhere to escape to, the drop can’t merge with the drink, in fact it ‘levitates’ for a number of seconds.

The authors suggest that this is a reason that you can often see rain drops staying on the top of puddles or ponds before being subsumed into the water, or why you can see the cream (or milk) stay as globules on the surface of your coffee (or tea). And so I wonder, could this also be the explanation for an odd phenomenon that I sometimes notice while brewing coffee in my V60. Perhaps you have seen this too? After some time, the new drops of filtered coffee impacting on the surface skit along to the edge of the jug. They stay as balls of coffee on the coffee’s surface for quite some time before becoming part of the brew. You can see a photo of some of these droplets above. Initially I thought that this was because the surface of the coffee had started to vibrate with the impacting droplets. But it is also possible that it could be this temperature effect. As the (brewed) coffee in the jug would be cooler than the water dripping into it from the filter, there would be a temperature difference between the droplet and the coffee but the reverse of the milk-coffee situation. The drop would be warmer than the coffee it’s dripping into. The authors of the study suggested that it was the magnitude of the temperature difference that was the key, not the sign of the temperature difference. So that would fit with the V60 observations seen previously. However how would you show which effect (vibration or temperature difference) is responsible for the behaviour?

Enjoy playing with your tea, coffee and V60s. Do let me know the results of your experiments. Is it a vibration thing or does the temperature difference have to be there to begin with? Let me know what you think is going on.

I am also grateful to Amoret Coffee for alerting me to this story in the first place through Twitter. If you come across some interesting coffee-science, please let me know, either here in the comments section (moderated, please be patient), or on Twitter or Facebook.




Focussing the sound at Spike and Earl

soya latte ginger beer

Soya latte and a ginger beer at Spike and Earl.

A few months ago, news came that the coffee roasting company Old Spike had opened a new café, Spike and Earl, down in Camberwell. Operating on similar principles to Old Spike, Spike and Earl aims to serve excellent coffee (and food and cocktails) with a social conscience. By employing those who have previously been homeless, Spike and Earl offers an employment (and training) route for people who may not easily otherwise have the opportunity. So although Camberwell is a bit of a trek, I was looking forward to trying this new place. As it was a late afternoon in November and the menu suggested that the dairy alternatives were only soya or oat, I decided to try a soya latte. (For any reader with a nut allergy, the current fashion of using almond milk means that you should always ask first if your cappuccino contains nuts). The baristas were friendly and confident in assuring me that they do not use almond milk (no danger of nut-cross contamination) but that their brownies did contain nuts (so I sadly had to pass on the brownie opportunity). My partner in these café reviews opted for a ginger beer.

There were a series of high tables with stools on the left hand side of the café. Presumably many people can therefore be accommodated when it gets crowded. However, at the time of our visit, it was fairly empty and we made our way to the rear of the café. Behind us, and behind closed glass doors, was a coffee roaster that we later discovered was part of the Old Spike roasting expansion. It’s always a nice touch to see coffee roasting happening as you drink but perhaps we needed to arrive earlier for that.

Bricks with holes Spike and Earl

Holes in bricks at Spike and Earl. Just a foot-hold or a suggestion for a great piece of engineering?

Drinks arrived together with complementary water and the soya latte was very smooth. Almost caramel like in the sweetness and very drinkable. It makes a pleasant change to have a latte once in a while. Light was playing tricks around the room as the sun was setting and the inside lights were becoming more prominent. But the striking thing about Spike and Earl was that the bricks used to support the tables and line the walls all had holes in them. On the wall running along the side of the café, (windows were on the other side), pot plants were placed in the holes giving the impression of the beginnings of a green wall. The holes in the bricks supporting the table meanwhile made an excellent footstool and were complemented by holes in the stools. A latte of course is largely made up of holes, or at least bubbles. The foam structure consisting mostly of air. How is it that some structures can be made better owing to what they don’t contain rather than what they do?

For example, if you imagine the difference between a latte and a cappuccino (but made out of metal rather than milk) that can be the difference between a successful tooth implant and a failure. We know from our coffees that bubble size can have a significant structural effect. But how about more fundamental properties, can the holes in bricks change things such as the way sound propagates?

Interior wall at Spike and Earl

More bricks with holes at Spike and Earl, this time with some plants escaping from them. The start of a green wall?

You may have heard about how different structures can be engineered to make materials “invisible” to certain frequencies of light. Imaginatively named “invisibility cloaks” are made by designing materials with patterns on them that change the path of an incident light beam. Because the effect on the light beam is due to the structure in the material rather than purely from the material itself, these materials have become known as ‘meta-materials’. When you remember that microwaves are a form of light, it is perhaps easy to see some of the applications of this research and one reason that it has attracted a lot of funding.

However there is an acoustic type of metamaterial that is far more similar to the bricks in Spike and Earl and that may find applications in medical imaging (ultrasound). Earlier in 2017, a team from the universities of Sussex and Bristol published a study about acoustic metamaterial ‘bricks’. Each brick had a differently shaped hole through the centre of it which delayed the incident sound wave by a specific phase interval (you can say it ‘slowed’ the wave). In order to work efficiently, the brick had to be of a height equal to the wavelength that the researchers were interested in and a width equal to half that wavelength. As they were investigating ultrasound, the bricks were therefore about 4.3mm square and 8.66 mm high.

By assembling the bricks together, the researchers found that they could steer a focussed beam of sound or even change the shape of the sound beam. This would have applications as diverse as targeting cancer cells with ultrasound to levitating a polystyrene bead. You can read more about their research here (or, if you have access to Nature Communications, their paper can be downloaded here).

soya latte Spike and Earl

Layering at the end of my soya latte. What would you think about?

Just for fun, assuming that the bricks supporting the table at Spike and Earl could be similarly turned into acoustic metamaterials, we could calculate the musical note that they would best work with. Estimating the brick at about 15cm square and remembering that is approximately  half the wavelength (λ/2) and using the speed of sound in air to be 330 m/s, we can calculate the frequency to be:

f = c/λ

f = 330/0.3 = 1100 Hz

Which is the musical note C#6 (with an explanation of nomenclature here).

As I finished my soya latte, strata of milk lined the cup. Reminiscent of the Earth’s layers or perhaps, metaphorically, our strata of understanding, there is certainly plenty more to ponder at this interesting new(ish) addition to the London café scene. So next time you are in Spike and Earl, do let me know what you end up thinking about, you never know where these thought trains may take you.

Spike and Earl is at 31 Peckham Road, SE1 8UB


Data overload at The Gentlemen Baristas

coffee Borough

The Gentlemen Baristas in Borough.

Borough is always such a great place to wander. Walking around the backstreets with their bits of hidden history. The other day, we had visited the market, wandered down Redcross Way past the old Crossbones graveyard and hit upon The Gentlemen Baristas on Union Street. It is difficult not to have heard about these Gentlemen and my visit there was long overdue and so, we wandered in to try this famous venue.

The shop front advertised itself as a “Coffee House”. A very accurate description and a nod to the Coffee Houses of the past. As it was shortly after lunchtime, it was very crowded with a diverse bunch of people and felt a little cramped at the counter. Nonetheless, the queue was quick and friendly baristas soon took our order allowing us to retire inside to try to find a table (no chance) or a stool next to a bar (successful). Around us, people were either chatting over their coffees or working on laptops.

While waiting for my long black (intriguingly described on their website as a “well mannered coffee”), I noted the various posters describing different types of screw head or parts of the human skeleton. Enough detail to be a phone distraction but surely there was more physics waiting to be seen in this convivial back room of a coffee house? A blackboard at the end of the bar, offered details of the wifi as well as a quote (slightly adapted) from PG Wodehouse about the benefits to friendship of a shared taste in coffee. On a shelf opposite the blackboard were a number of books including a thick book detailing coffee trading in years gone by. From the fact that the books were stacked horizontally, it would appear that they are not consulted often.

shelf books hats Borough

The lighting made photography difficult but you can see the books (and the hats) on this shelf at The Gentlemen Baristas

Sitting between this juxtaposition of wifi information and old books, caused me to pause. I have heard it said that we “know” more now than we have ever known in the past. That we have access to an enormous amount of knowledge merely through our phones. Is this correct?

On one level it is certainly un-arguable. Ninety percent of the world’s data in 2013 had been generated in the previous two years. If you need to find anything out, a quick duckduckgo (or if you have to, a google) will often lead to websites detailing all sorts of quirky bits of information. If we want to know the radius of the Earth or the size of an espresso grind, we no longer have to remember the answer, nor even really to have a feel for the answer, instead we can almost immediately find webpages that tell us (here and here).

And yet, this answer seems unsatisfactory. While there is an awful lot of information available to us at the tap of a phone, it is questionable whether that information translates to our own knowledge. Although collectively we can understand amazing things such as gravitational waves, individually we may struggle to explain how a toilet works. We need the plumber’s knowledge as much as we need that of the cosmologists. Does it matter who knows? What level of knowledge does someone need to have to say that they ‘know’ something?

coffee long black gentlemen baristas

Taking time to stop and think about what it’s all about. My coffee at The Gentlemen Baristas

Perhaps this appears a very strange cafe-physics review, where is the physics? But part of the rationale behind Bean Thinking is also to slow down and contemplate and it seems that The Gentlemen Baristas offers the perfect environment in which to do so. A café that mixes the new with the old, a space in which the practices of one can inform the other.

So to return the thought train to the area local to the Gentlemen: Writing in the second century AD, the Stoic philosopher Marcus Aurelius wrote

In death, Alexander of Macedon’s end differed no whit from his stable-boy’s. Either both were received into the same generative principle of the universe, or both alike were dispersed into atoms.

It is a quote you will probably find very easily via a search engine, or slightly less easily if you read his “Meditations”. But it is perhaps worth pondering, in what sense we ‘know’ what he was meaning. Strolling past the ribbons and messages memorialising the (estimated) 15,000 people who lay buried in the ‘outcast’ graveyard of Crossbones, what about our own attitudes to our modern outcasts? And perhaps more tellingly, our attitudes to those in positions of power or influence?

Perhaps it will take a lifetime of understanding our personal reactions to the poor, the prostitutes, the homeless and the powerful to really know what Aurelius meant. It certainly requires of us that we stop, pause and reflect on the knowledge that we come by. So it is far from obvious that it benefits us to use the wifi password rather than sit, slow down and contemplate. And where better to do so than in a friendly café with good coffee and seats to ponder the moment?

The Gentlemen Baristas can be found at 63 Union St, SE1 1SG



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