Author Archives: kayatesriseup-net

Tales from the worm bin

the cup before the worm bin

How it all began.
“Completely compostable”
But how compostable is it?

It is hard to believe but it was one year ago this week that the composting experiment that became #willitcompost started. The idea was to test just how “compostable” a coffee cup described as “completely compostable” really was. The problem is that “compostable” has a legal definition but it is not one that you or I may immediately recognise. Legally for a take-away coffee cup to be described as compostable it has to completely disappear within 6 months in an industrial composting facility. Industrial composting is quite different from home composting. In the former, the temperature is kept at (58±2)ºC while in my composting worm bin, it can get very cold indeed.

As has been written about elsewhere, in the absence of better industrial composting facilities, there is very little virtue involved by swapping a disposable cup for a compostable one, to combat the problem of waste it would be far better to remember your re-usable. However, what if you had a composting bin at home? How long would it take the cup to compost? And even, would it compost?

So every week for the past 52 weeks, I have posted a photo of the cup, composting away, in the worm bin. It seems clear that although it will eventually compost, more than 52 weeks is a long time to wait and not practical if you are drinking multiple take-away coffees.


51 weeks later, the lining and part of the rim of the cup are still in the worm bin. Clearly the worms have better things to eat.

In the meanwhile, other questions have been raised. What about other coffee packaging such as the bags for roasted coffee beans? What about the compostable “glasses”? Can anything be done to speed up the composting of the cup?

Last month, the opportunity came to start a new experiment testing these questions. A compostable coffee roasting bag from Amoret Coffee (which was reviewed on Bean Thinking here) was placed in the second shelf of the worm bin together with a cup, a compostable “glass” and a section of food packaging. The cup and the ‘glass’ were cut in half before being placed in the worm bin. One half of each was left as it was but the other half was soaked in (initially boiling) water for 12 hours. The idea of this was that part of the problem that has slowed the composting of the original cup was the lining that is designed to hold hot liquids without leaking. If we could somehow weaken that lining before placing it in the worm bin, perhaps the composting process would be accelerated?


A roasted coffee bag, a cup (split in two, see main text), a compostable glass and some food packaging, but will they compost?

Starting in late March provides the best chance of a quick composting process due to a particular aspect of worm behaviour. Although the composting worms will continue to eat the waste put into the composting bin throughout the winter, they do slow down quite a lot. If you have a worm bin, you may notice that the amount of waste that you can put into the bin decreases during the winter months. On the other hand, as the weather improves, the worms seem to eat everything very quickly so, to provide the best conditions for composting, the weather has to be reliably warm (or at least, not freezing).

Rather than once a week, updates will be approximately once per month both on social media and in the Bean Thinking newsletter. So keep your eyes on #talesfromthewormbin on twitter or subscribe to the newsletter. Do we really take our environmental responsibility seriously by using compostable packaging or, ultimately, is a more radical approach to waste, single use packaging and consumerism necessary?

Pushing it at Lever and Bloom, Bloomsbury

Lever Bloom coffee

Lever and Bloom under a blue sky.

Does a take-away need to be rushed? A coffee so quick that there is ‘not enough time to prepare a flat white’? Are we always so preoccupied with the distractions of our day that we consume our coffee merely for the pleasant caffeine kick that it provides?

Lever and Bloom in Bloomsbury is a great example of why this does not have to be, indeed should not be the case. Since 2015, Lever and Bloom have been operating out of a cart on Byng Place close to UCL and a number of other research institutes. The character of the surroundings really does affect the space and both times I have been to Lever and Bloom I have either met interesting people in the queue or overheard snippets of intriguing conversation about history I know nothing about.

Coffee Bloomsbury reusable coffee cup

Long black in a keep-cup and telephone box in Byng Place.

It is easy to spot the coffee cart in the corner. Firstly, it is bright red and quite eye catching but secondly because of the queue forming in front of it. Don’t be put off though, the queue moves very quickly so you won’t wait long even if you are in a rush. Queueing however does give you an opportunity to peer into the cart. Space is used extremely efficiently. with each piece of equipment  apparently having its own perfect home. It reminded me of a childhood game of trying to fit in as many objects as possible into a matchbox. A cabinet on the table in front of the cart displays cakes including cinnamon rolls (sadly sold out by the time I arrived in the afternoon). It was also nice to see the number of people ahead of me in the queue who were using re-usable cups.

The lever of the name refers to the (Izzo Pompei) lever espresso machine that is used on the cart. It was fascinating to watch the ground beans being carefully tamped and the lever being pulled to prepare the espresso. Although there is some debate as to the optimum water pressure needed for preparing an espresso, the standard pressure is 9 Bar; water is pushed through the tamped grinds at nine times the atmospheric pressure at sea level. Watching these espressos being prepared reminded me of preparing ceramic samples of an interesting magnetic material a few years ago. We were interested in the electrical properties of a class of materials called manganites. To prepare the materials for measurement we first had to grind the pre-cursor powders (but with a pestle and mortar, no burr grinders) and then, after a couple of further preparatory steps, press them into a pellet ready for firing in the oven. The machine used for pressing the pellets had a lever, not dissimilar to that on the espresso machines and yet, the pressure that we used for the pellets was roughly 1000 Bar. This high pressure was needed so that dense pellets of manganite material would be formed when we heated it in the oven (typically at 1200 ºC). Just as a good espresso depends on the pressure and then the temperature and time of extraction, so the properties of the pellet would be affected by the pressure and then temperature and time of firing in the oven.

Portland Stone fossils

Fossils in Portland Stone. It is astonishing what is revealed when you slow down and notice the buildings around you.

Similar effects affect the rocks of the earth, something that is particularly visible in the area around Lever and Bloom. A geological walking tour around Byng Place, Tottenham Court Road and towards the British Museum illustrates this particularly well. Behind Lever and Bloom, the church of Christ the King is built from Bath Stone. An oolitic limestone, this type of rock is formed of compressed sand and bits of shell. Much as the manganite samples of my study before they were fired in the oven but of a more interesting colour. Heading towards Gower St and the impressive UCL building is made of Portland Stone. Another limestone, this building material is a goldmine for urban fossil explorers. Continuing the walk, on Tottenham Court Road, the Mortimer Arms pub is fronted by quartzite while Swedish Green Marble adorns 90 Tottenham Court Road. Quartzite and Marble are both types of metamorphic rock, formed by pressing together different precursor materials at high pressure and temperature. Other types of marble can be seen on the tour, suggesting the influence of pressure and temperature of formation on the rock structure as well as the type of precursor rock.

It would seem that such a walking tour is perfectly timed for a longer style of coffee, perhaps a latte (in a re-usable cup of course) from such a centrally located place as Lever and Bloom. And of course, assuming you are using a re-usable, there is even more to ponder. The pressure and temperature during the manufacture of the re-usable cup would have affected the properties of the cup (or in my case, glass).

Let me know if you spot any interesting rocks or fossils during your time at Lever and Bloom but whatever you do, I hope that you can enjoy your coffee and then slow down to enjoy it a bit more.

Lever and Bloom is at Byng Place, WC1E 7JJ

Coffee and a horse box at Blue Tin, Oxfordshire

coffee Nuffield Oxfordshire Blue Tin

The cafe is in here. The new farm shop at Blue Tin.

Blue Tin is not an easy café to find, one that you can wander into just off the street. In fact, although it serves coffee and cake, Blue Tin is not really a café at all but a friendly place for a drink attached to a farm shop. Open to walkers and passing cyclists, horse riders and drivers, Blue Tin seems to be almost in the middle of nowhere. Approximately 4km by road from Nuffield, Blue Tin can be found just off a single lane country road. You will know when you actually arrive at the farm because of the sign and the box advertising fresh eggs (complete with honesty box for when the shop is closed).

We first came across Blue Tin (when it was a shop in a shed rather than a shop/café in a building) while walking in the area. There are some good walks in the area which can be very pretty when the bluebells are out and so it is well worth combining a visit to the café with a walk in the Oxfordshire countryside. Despite only opening in December 2017, the café associated with Blue Tin has put a lot of effort into ensuring that their coffee is ethically sourced, great tasting and locally roasted. The coffee is roasted by Horsebox Coffee and is of course also available to purchase in the shop. The espresso based drinks use the Dark Horse espresso blend (though I wasn’t sure whether this was occasionally rotated when the seasonal espresso is available). We had an Americano and a latte. The Americano indeed had the chocolate notes described on the coffee bag, while the milk of the latte really complemented the espresso base. Cakes are also available though we didn’t try on this occasion.

Provenance Information Blue Tin, old board, no coffee info

On the wall of the cafe is a schematic showing where each product sold in the shop originates. Seen here is the earlier version that does not include the coffee (roasted within 5 miles). Everything is local and the meat is particularly local having been brought up in the farm next to the shop.

There is plenty of space to sit down inside and contemplate the shop while enjoying your coffee in this welcoming environment. The arrangement also gives you time to consider the farm and space for your mind to wander. One place my mind was wandering that day was to the importance of our beliefs in our decision making, even while they are informed by science.

For example, it is often said that we could significantly help climate change by becoming vegetarian or including one meat free day per week in our diet. In a 2013 paper, the authors calculated the emissions associated with farming, producing, packaging and storing 66 categories of food item that were sold in a (modelled) medium sized supermarket. In order to calculate this various assumptions about the produce had to be made¹.

To summarise the paper (though it is well worth taking the time to read it), the study suggested that avoiding meat altogether could reduce our individual carbon footprint due to food by 35%. However even introducing a meat free day (combined with a switch to poultry rather than beef and significant reduction in the amount of food we waste/packaging used) could introduce a reduction of 26%.

Horsebox coffee Oxfordshire

Americano, Latte and shop. The coffee-space at Blue Tin farm shop, Oxfordshire

Does the science therefore “say” that we should all go vegetarian? It is worth looking more closely at the paper and considering our own belief systems. In the report, beef had a total CO2 equivalent emissions of 25.13 Kg per kg of food¹. One suggestion of the authors was to swap beef for poultry. Poultry has a total emissions of 4.05 Kg CO2 equivalent per Kg. But looking through the table of calculated emissions for each food type, “spirits and liqueurs” had a total emissions of 3.16 Kg CO2e per Kg. Perhaps (hopefully) you could say you would take a long time to drink a kg of spirits, but even wine has 2.41 Kg CO2e per Kg. As a rough estimate, 1 bottle of wine (750 ml) is 3/4 Kg, so the bottle of wine with dinner is contributing roughly equivalently to the shared roast chicken. There are nutritional arguments for eating meat. Can we say the same of drinking wine? What of coffee? (not included in the table I’m relieved to say!)

The study shows the quantity of emissions associated with each type of food stuff. It does not show us how to act. Each decision we make (eliminate meat/go teetotal/all things in moderation) is based on what we believe about the world. Even the idea that it would be a good thing to reduce our greenhouse gas emissions in order to try to limit climate change is a moral one, not a scientific one. These decisions depend on what we think is ‘good’, what is ‘bad’, what life is about. In short it depends on our beliefs about the world and our place in it rather than purely the facts. These are philosophical, or dare I say it, even religious questions. Science can inform us of the damage that we are doing but it cannot help us to decide whether that matters, nor even if it does matter, what we should do about it.

Interior of Blue Tin with flower

You won’t need the sugar. Another view of the cafe at Blue Tin.

Whether we decide to buy better quality² meat less frequently, go vegan or even do nothing are not decisions that we are making entirely based on the science. Although informed by the science they are nonetheless based also on our existing beliefs about the way the world is and the way the world should be. We may decide for example that, while we should reduce our consumption of “cheap” beef/imported lamb, we should take care to buy more expensive meat from somewhere that takes care of their animals throughout the farming (and slaughtering) process but eat it less often. Depending on the rest of our diet, this could similarly reduce our food-related greenhouse gas emissions (if for example we mostly ate vegetarian with occasional meat consumption). We may similarly decide that eating meat is intrinsically wrong and so go entirely vegetarian.

These are choices we make, informed by the science but based on our ideas of morality. They are not easy choices nor are they choices we will necessarily agree with each other about. To make these choices requires time set aside to think about what matters to us, about what we believe in. And this means that there is no intrinsic conflict between science and religious belief any more than there is a conflict between science and the decisions we make in general. We need science to inform our beliefs but we need also to recognise the role of our beliefs (conscious or subconscious) in our decision making.

In short, we need to slow down, pause and really think about things. And where better to do so than in quiet and comfortable places with good coffee (and cake) such as Blue Tin?


¹Interestingly, the authors assumed that for beef, the effective emissions were increased owing to deforestation and land clearance that is associated with beef production in some places. If this is not accounted for, the effective emissions from beef are still calculated to dwarf much of the other food stuffs but not by quite so much. The footprint would therefore be less for beef raised on an existing local form, slaughtered and purchased locally. Similarly, the ‘vegetarian’ diet that was modelled by the authors contained dairy (with similarly high emissions as beef).

²Again ‘quality’ is a subjective term that cannot be easily ‘scientifically’ quantified, instead it is argued based on what we believe ‘good’ means. Do I mean that the animal had healthy conditions during life? Was well cared for? That it tastes good? That I could speak to the people who farmed the animals? I’ve left it deliberately slightly ambiguous here.

Blue Tin Produce is at Garsons Farm, Ipsden, OX10 6QU

Coffee (beans) in the blood?

Brazil nut effect

A green bean ‘floating’ in coffee grounds. When you pour your beans into your grinder, do they behave like a liquid flow or do they have their own type of ‘granular’ flow?

When you first learn about liquids, solids and gases, you may learn about the fact that a solid keeps its shape whereas a liquid flows. A solid is rigid and can be moved as one block whereas a liquid will spread and change shape. Solids can be stacked up like bricks though this is not true of liquids.

A slightly unfair question is then put to you. What about sand? (Or, in the context of this website, what about coffee beans?). A pile of beans will initially stack but as the pile builds, avalanches will occur to prevent the tower being too vertical. When you pour your beans into your grinder hopper, the beans will level out, in much the same way as the eventual coffee will in the cup. Do the collection of coffee beans move more as if they are a liquid or a solid?

Clearly to some extent the question is wrong, the beans represent their own class of structure but perhaps a better way of asking the question would be, how do a collection of coffee beans flow? It is a question with consequences beyond the coffee hopper. From pharmaceuticals to civil engineering projects and beyond, understanding how granular materials flow is an important topic.

Beans on a plate. The aspect ratio of the coffee bean is similar to that of the particles used in a new study to analyse granular flow.

And yet it has apparently been difficult to analyse this problem owing to the difficulty in tracking individual coffee beans (tablets or particles of cement) as they are pushed in one direction or another. A start was made nearly 20 years ago when a team at the University of Chicago used Magnetic Resonance Imaging (MRI, yes, the same MRI as you get in hospitals) to image individual mustard and poppy seeds as they flowed between two cylinders. The imaging allowed researchers to track the position and velocity and packing density of the seeds as they moved around the cylinders. Then, last year a new study used X-ray tomography to watch individual particles in a rectangular box as they were subjected to being pushed at various pressures in different directions. This, more recent study used plastic ellipses with a minor axis of 6.35mm and an aspect ratio of 1.5. Sadly, not real coffee beans but a fairly large plastic equivalent. While the aspect ratio will of course vary from varietal to varietal and even bean to bean, the coffee beans in my hopper at the moment have an aspect ratio of 1.3 (and a minor axis of 4.5mm) which makes them pretty close to the plastic used in the study.

Brew&Bread, latte art Sun, KL latte art

The structures in milk allow the milk to be ‘frothed’ and so enable latte art. They also make milk an example of a complex fluid.

By tracking each bean, the study discovered that such granular collections moved as if they were “complex fluids”. Which is all very well but does makes you wonder, what is a complex fluid? Is coffee a complex fluid?

Does the definition help? The definition on the Physics (APS) website says that: complex fluids “can be considered homogeneous at the macroscopic (or bulk) scale, but are disordered at the “microscopic” scale, and possess structure at an intermediate scale.”. What does that mean? Well, it seems to mean that complex fluids contain things that are larger than the molecules that make up the liquid and so affect how the fluid flows. Milk has long chains of proteins and fats (which give it the foam like qualities when it is frothed in a cappuccino) and so is a complex fluid. Chocolate and blood are other complex fluids as are emulsions and gels. Pure water would not be a complex fluid and my guess is that coffee (which contains water molecules and various molecules associated with the coffee itself) is also not a complex fluid. Were you to have a latte or a cortado though, the milk would transform your coffee into a complex fluid. Although I much prefer to keep my coffee simple, it would seem that there is more to the saying “you have coffee in your blood” than it would at first appear, particularly as regards the coffee beans. It may be time for some experimental tests of coffee bean (and coffee or latte liquid) flow….

Time standing still at VCR, Kuala Lumpur

VCR chalkboard

A trip down memory lane via a new cafe. VCR in Bangsar, KL

One of the first science-based talks I gave was about how VCR tapes worked. Depending on how you viewed it (and whether you had to listen), this was either an achievement given that I was at school and didn’t really understand magnetism nor magnetoresistive devices, or a thing to be suffered through (for much the same reasons). So when I learned that a new café called VCR had opened in Bangsar in Kuala Lumpur, it prompted a series of fond (and a few embarrassing) memories.

Moving on, it is clear that this second branch of VCR (the first is in Pudu, in the main part of KL), aims to provoke such memories of times past. From the name of the wifi to the pulleys behind the counter and the wooden screen at the back of the café, various details around the café pull your memory in different directions. However the coffee is very much in the present. With three types of coffee available to try as a pour over as well as the standard espresso based drinks, this café has a lot to offer. The coffee is roasted by VCR themselves in their Pudu branch. There is also an extensive food menu with an interesting Chawan mushi as well as an intricate avocado toast (topped with pomegranate seeds, toasted quinoa and feta).

coffee at VCR Bangsar

Coffee and pour over jug. But is the number 68 or 89?

The friendly baristas were happy to advise on which coffee to match with which brewing device (though there seemed a marked preference for V60s on the days I visited). In total I tried 4 pour-overs, one with the Kalita Wave and the others by V60. These coffees were all excellent but very different. A couple were fruity, one was sweet and full bodied, one reminded me a bit of the local fruit durian, not I hasten to add because of its taste, but because the aroma from the cup was so different from the flavour of the drink. It was a great privilege to be able to try these different coffees consecutively and to really experience the variety of flavours in coffee. Great care was taken while making the pour over before it was brought over to the table, together with a jug of water, it also seemed to me that the baristas kept a discreet eye on me afterwards to ensure I enjoyed the coffee. So it was a good experience to have had the opportunity both to enjoy one of those pour overs and to observe the people and the surroundings of VCR when I had to wait for 1 hour for someone with no phone and no book. If you get the opportunity to do this I would very much recommend it. Find a comfortable café, order a coffee and then sit, without distractions, and watch what your mind notices and where it wanders for an hour.

An obvious place for a mind to wander would be to the mechanism of tape recording (and why mini-disks are the superior recording medium for the elegance of the physics involved). However, in an hour a mind wanders far further than the name. Supporting the cakes (and a display case for the 2nd place award of the brewers cup), was a table with a concertina type decoration around its edge. Was this a nod to the Kalita Wave brewing device? This is a significant difference between the V60 and the Kalita Wave: the ridges (or wave pattern) on the filter of the latter. How does coffee flow past these ridges? Does this difference in flow dynamics make a difference to the taste of the coffee?

variables grind size, pour rate, pour vorticity

It seems that there would be a lot of physics to observe in the fluid flow in a Kalita Wave filter.

A few weeks previously a friend had made a (lovely) coffee with her Kalita Wave. It was interesting to note the different dose of coffee she used and the way the grinds built up in the ridges (compared with my ‘normal’ V60). Why do the grinds end up in the ridges? Why is there a layer of dust on the blades of a fan? Why do some corners of a building collect more dust or leaves than others? Are these questions related and does it change the flavour of the coffee in the Kalita?

In fact, there are many subtleties in understanding how fluids move around solid objects. One of these is that at the interface of the fluid with the solid, the fluid does not flow at all, there is a stationary layer. Known as a boundary layer or Prandtl boundary layer (after the person who first suggested their existence, Ludwig Prandtl), realising these layers existed revolutionised the field of aerodynamics. The problem had been how to model the drag experienced by a solid object in a fluid flow. Although perhaps only of academic interest in terms of the flow of coffee around a Kalita filter or a spoon, by the end of the nineteenth century and particularly, with the invention of airplanes, how to calculate fluid (i.e air) flow around a solid (i.e. wing) object became very important for practical reasons.

vortices, turbulence, coffee cup physics, coffee cup science

Another cool consequence of boundary layers:
Vortices created at the walls of a mug when the whole cup of coffee is placed on a rotating object (such as a record player).

Prandtl introduced the concept of a boundary layer in 1904. The idea allowed physicists to treat the main body of the moving fluid separately to the layer, very close to the solid, that was dominated by friction with the solid. This meant that the Navier-Stokes equations (that are used to describe fluid flow and ordinarily do not have an analytical solution) are simplified for this boundary layer and can be quantitatively solved. Although simple, by the 1920s Prandtl’s layer (and consequently the solvable equations) were being used to quantitatively predict the skin friction drag produced by airplanes and airships.

The boundary layer allows us to understand how vortices form behind cylinders or around the corners of buildings. I suspect a mix of the boundary layer, turbulence caused by the coffee going over many of the ridges and the brick like stacking/jamming of the coffee grains would combine to explain the difference in the grind shape around the Kalita Wave and the V60 filters. What this does to the flavour of the coffee and whether better brewing would involve more agitation, I will leave to Kalita Wave coffee lovers to investigate. And when you do, I would love to hear of your results, either here on Facebook or Twitter.


A tense moment for a coffee…

capillary bridge

A bridge formed by water between a cup and a cafetière.

Each and every coffee represents an opportunity to uncover an unusual bit of science. Sometimes the connections between what happens in your cup and the wider world are fairly obvious (e.g. the steam above your coffee and cloud formation), but sometimes the connections seem a little more obscure. On occasion, your observations may lead to philosophical speculations or stories from history. Every coffee is an opportunity to discover something, if you just slow down and ponder enough.

It was with this in mind that I looked at my freshly made French Press coffee a few weeks ago. I had positioned my cup very close to the cafetière such that a small water bridge had formed between the cup and the cafetière (see photo). Such “capillary bridges” have been studied for a couple of centuries and yet there is still more work to do. Caused by the surface tension of the water, understanding the way these bridges form and the shape of the surfaces produced is important for fields such as printing and powder processing. Yet it is only in the last 150 years or so that we have started to understand what surface tension is. Moreover, much of the pioneering work on this subject was done by an amateur scientist who just noticed things (and then designed some very clever experiments to discover more).

Agnes Pockels (1862-1935) is now regarded as a surface science pioneer but in 1891 she was a complete unknown. Although she had wanted to study physics, she was prevented from going to university because she was female. Consequently, all her study of the subject had to be through her brother Friedrich’s books and letters. It is not known what prompted her investigations but from 1880 she had been experimenting with a device to measure the surface tension of water. The device used a sliding weight to measure the force required to pull a 6mm diameter wooden disk off of the surface of a trough of water.¹ The design of this device was so successful that, a few years later, Irvine Langmuir adapted it slightly in order to study the surface of oils. He went on to receive the Nobel Prize for his work in 1932. Yet it is a device that could also be built in your kitchen, exactly as Agnes Pockels did².

reflections, surface tension

The effects of surface tension can be seen in the light reflected from a coffee

Pockels measured the surface tension of water contaminated by oil, alcohol, sugar, wax, soda crystals and salt (amongst other things)¹. She discovered how the surface tension of the water could be affected by pulling the surface or introducing metal objects onto it. She discovered the “compensating flows” that occurred between regions of different surface tension (you can see a similar effect with this soap boat). Yet all of this remained hidden from the wider world because Pockels was unable to publish. Not having access to the contemporary literature about surface tension and moreover unknown, unqualified and female, no journal would look at her work let alone publish it. Nonetheless, she was clearly a brilliant experimentalist and capable physicist.

Things changed when Pockels read a paper by John William Strutt (Lord Rayleigh) in about 1890. Rayleigh was quite the opposite of the unknown Pockels. As well as his work on sound, electricity and magnetism and the (co-) discovery of Argon, Rayleigh is known for his work on understanding why the sky is blue. (Which is another phenomenon that you can see while preparing your coffee if you drink your coffee with milk.) In his paper on surface tension, Rayleigh had come to similar conclusions as Pockels’ work but Pockels had gone further. Unable to publish herself, she instead wrote to Rayleigh, in German, detailing her experimental technique and results. Rayleigh responded by forwarding her letter to the scientific journal Nature together with an introductory paragraph:

“I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behaviour of contaminated water surfaces. The earlier part of Miss Pockels’ letter covers nearly the same ground as some of my own recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels’ experiments.”¹

Coffee Corona

You may have seen white mists form over the surface of your coffee (seen here by the rainbow effect around the light reflection). But what are they and how do they form? This is still not really known.

Rayleigh’s introduction and Agnes Pockels’ letter were published in Nature on 12 March 1891. The paper enabled Pockels to publish further results in both Science and Nature as well as in other journals. In 1932 she received an honorary doctorate in recognition of her work.

It seems that this coffee-science story has two main messages. The first is to emphasise how much we gain by ensuring everyone has access (and encouragement) to study physics (or indeed whatever subject they are motivated by). What would we have lost if Agnes Pockels had not had the books of her brother and made the decision to write to Rayleigh? But the second message is that Agnes Pockels managed all this, at least initially, by merely noticing what was going on in the liquids around her. Being curious she designed and built a piece of equipment that enabled her to measure what she was intrigued by and by taking a systematic series of data she discovered physics that was unknown to the wider community at the time. So the question is, what do you notice when you look at your coffee? How does it work, what can you discover?

Please do share any interesting physics that you see in (or around) your coffee either here in the comments section below, on Facebook or on Twitter. Tea comments would also be welcome, but whatever you do, slow down and notice it.


¹Rayleigh, Nature 1891, 43, 437-439, 12 March 1891 (full text here)

²Reference to the kitchen is here.

Waiting for the drop at Kurasu, Kyoto (Singapore)

Kurasu Kyoto Singapore, coffee Raffles City

The sign towards the entrance at Kurasu Kyoto, Singapore

Kurasu Kyoto, in Singapore, was recommended to me as a great place to experience pour-over coffee. Although they will serve espresso based drinks too, it is the pour over coffee for which they are famous. The Singapore branch is at the front of a shared working space in an office block. Entering from the street, you have to go up one level before the smell of the coffee will guide you to the café.

Ordinarily, coffee chains would not be featured on Bean Thinking. However, despite it’s name, this is a ‘chain’ of only two outlets, the original branch in Kyoto, Japan and this one in Singapore. The menu featured several coffees with their differing tasting notes together with a few other drinks. Coffee is shipped from Japan weekly as well as being locally roasted in Singapore. It is very much a place to enjoy your coffee while sitting on the comfortable chairs before getting back to work (or perhaps, a place to meet potential colleagues over a refreshing cup of coffee). And it is highly likely you will enjoy your coffee which is prepared for you as you wait.

coffee machine, V60 Kalita

The bar and some of the coffee equipment in the cafe space at Kurasu Kyoto Singapore

There is no hint of automation here. Each cup of coffee is prepared carefully and individually by the barista behind the bar. V60 or Kalita, it was somewhat mesmerising to watch the pour over being prepared, rhythmically, carefully, by hand. Indeed, automation seems almost alien to this place where the act of making coffee is truly artful. Once prepared, the coffee is brought to your table in a simple ceramic mug for you to taste for yourself and see how your tasting notes compare.

As I was watching, two thoughts occurred to me, the first of a directly scientific nature, the second more about our society. Firstly watching the barista slowly prepare the pour over, it is difficult not to be reminded of the pitch drop experiment.

You may remember the story from 2013 and then again in 2014. Two experiments that had been set up in 1944 and 1927 respectively finally showed results. The experiments were (indeed are, they are still going) very similar and concerned watching pitch (which is a derivative of tar) drop from a funnel. Pitch is used to waterproof boats and appears to us almost solid at room temperature although it is actually a liquid but with an extremely high viscosity. To put this into perspective, at room temperature coffee has a viscosity similar to water at about 0.001 Pa s, liquid honey has a viscosity of about 10 Pa s, but this tar has a viscosity of 20 000 000 Pa s. The experiments involved pouring this tar into a funnel and then waiting, and waiting, for it to drip. Both experiments seem to drip only approximately once a decade but until 2013 (and 2014 for the other experiment), the actual drop had never been seen. Both experiments are now building their droplets again and we await the next drop in the 2020s.

Imagine waiting that long for a drip coffee.

coffee Kurasu Kyoto Singapore

Apparent simplicity. The coffee at Kurasu Kyoto Singapore

But then a second thought, there is currently a lot of angst, particularly about automation and our environmental and/or political situations, as if they are something from outside ourselves being imposed upon us. To some extent it is true that we are not in control over many things happening around us. But in our feeling of powerlessness, are we resigning more than we ought to of our responsibility for the power that we do have? It was something that deeply concerned Romano Guardini in his essay “Power and Responsibility”¹. To use the example of automation and the pour over. Guardini argues that people become poorer as they become more distant from the results of their work (e.g. by automating the pour over coffee with a machine). And that the better the machine, the “fewer the possibilities for personal creativeness”¹ that the barista would have. For Guardini, this has consequences for the human being for both barista and customer. The barista clearly loses the element of their creativity when preparing a pour over with a machine but the customer too is affected by the loss of a personal contact, possible only through individually created things. Rather than celebrating each other as individuals we become consumers with tastes “dictated by mass production”¹ and people who produce only what the “machine allows”. To respond to the challenges of our contemporary society involves discovering where we each have responsibility and exercising it, no matter how small or large that responsibility seems (to us) to be.

Which is somehow resonant with the interview that one of the Kyoto based baristas at Kurasu Kyoto gave that was recently circulated by Perfect Daily Grind. Asked what was her preferred brewing method, she replied it was the V60 because of the control that the individual barista could gain over the flavour of the cup merely by tweaking some of the details of the pour. A knowledgable art rather than a technology. And it is precisely this knowledgable art that you can see carefully and excellently practised in the Singapore branch.

Kurasu Kyoto (Singapore) is at 331 North Bridge Road, Odeon Towers, #02-01

“Power and Responsibility” in “The End of the Modern World”, Romano Guardini. ISI books, (2001)


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.