A Story with many layers, Clapham Junction

Story Coffee St John's Hill Clapham

The doorway to Story, or a story depending on how you look at it.

A “ghost sign” above the door to Story Coffee on St John’s Hill ensures that you know that you have arrived at the correct place. “Peterkin Custard, Self-Raising Flour – Corn Flour, can be obtained here”, only now it is coffee rather than custard that is sold in the shop beneath. The sign is an indicator to the many tales that could be discerned while exploring the coffee within. I had had a couple of attempts to visit Story Coffee (thwarted for a variety of reasons) before Brian’s Coffee Spot’s review appeared a couple of days after one of my attempted visits. Suitably re-motivated, another trip was attempted (address checked, closing times checked) and this time we were in luck. Although a pour over is listed on the menu, sadly this was not available on our visit and so I enjoyed a lovely long black instead (Red Brick, Square Mile) while looking at the cakes on offer. There was plenty of seating in which to shelter from the rain outside and many things to notice in this friendly café. In addition to the cakes and lunch menu, a box on the counter housed “eat grub” protein bars, protein bars made of cricket powder. Are insects the future for humans to eat protein sustainably?

glass jar at Story

Through a glass darkly?
The distortions produced by the refractive indices of air, water and glass and the shape of the glass produces interesting effects on our view through it.

The tables were well arranged for people to sit chatting while enjoying their beverages and it is always an excellent thing (from a personal point of view) to encounter a café with a no laptop (or tablet) at the tables policy. Complementary tap water was available in jugs placed on each table while it was also nice to note that Story branded re-usable cups were on sale from the counter. Many things we noted can be seen in the gallery pictures in the review on Brian’s Coffee Spot: the funky fans, the egg shaped light shades, the light introduced by the large glass window panes (though it was a much fairer day on Brian’s visit than on ours). Each had its contribution to a thought train, the way the glass water jar bent the light coming through, the concept of a Prandtl boundary layer in fluids (and its connection to both fans and coffee cups). Moreover there were hexagons, which for someone who has worked on the periphery of the graphene craze, are always thought provoking.

Apart from hexagons decorating the top of the stools, there were hexagons lining the counter made of cut logs, each showing the rings from the tree that was felled. Rather than a flat surface, these hexagons were made to be different thicknesses on the wall, rather like the hexagonal columns of the Giant’s Causeway. It is a subtle thing that may have implications for the space that is otherwise surrounded by flat, solid, walls. Such spaces can become echo-y and yet, the music and conversation in Story was not overly distracting presumably because features such as the uneven hexagonal wall reflected the sound waves such that they destructively interfered rather than echoed around the room.

every tree tells a story, but which story

A macroscopic crystal of hexagonally cut logs forms the side of the counter.

Each log in the hexagonal decoration was cut with its cross-section showing a number of tree rings. We know that we can age a tree by counting the rings (though each of these would be underestimated as they have been trimmed into hexagons post-drying), but what more do the tree rings, and the trees themselves have to tell us? The rings are caused by the rapid growth of large cells during spring followed by a slower growth of smaller cells as the year progresses. But this method of growth means that the cut logs have more to tell us than just their age. The spacing between the rings can tell of the weather the tree experienced during that year, were there many years of drought for example? Such clues, from the relative density of the tree rings, can help researchers learn about the climate in previous centuries, but conversely, reading the climate report in the rings can indicate in which year a tree was felled and so the age of a building for example.

coffee at Story

Many stories start with a coffee.

And then there is more, trees will grow at an average rate per year so that, as a rough guide, the circumference of a mature (but not old) tree increases by 2.5cm per year¹. There is therefore something in the idea that you can have a good guess at how old a tree is by hugging it. But this assumes that the tree is growing in its optimum conditions, far enough from any neighbouring trees so as not to be crowded into growing more slowly. So the absolute density of tree rings must also give a clue as to whether this tree was in a dense forest or an open clearing. Which is reminiscent of something else that living trees can tell you if you listen to them closely enough: trees will grow so that their leaves are exposed to the maximum amount of light. For us in the UK, this means that the crown of a tree will frequently tip towards the south (where the Sun is most often) and there will be more leaf growth (and consequently more branches) in a southerly direction². But again, we only see this if the tree has room to grow on its own, without the crowding, and competition, of too many neighbours. A solitary tree helps us to know which direction we are walking in.

empty coffee cup Story St John's Hill

While many coffees could also tell a story. It depends on how you read them.

Which all points to the idea that there are many stories being told all around us all of the time, the ones we hear depend on what we choose to pay attention to. So what about the story behind the ghost sign above the door? The Peterkin custard company was a venture by J. Arthur Rank in an attempt to start a milling company in the mould of his father’s (Rank Hovis McDougall, later bought by Premier Foods). The company failed and Rank went on to form the Rank Organisation that was responsible for many films made throughout the 40s and 50s as well as running a chain of cinemas around the UK. Truly a sign concealing many stories.

 

Story Coffee is at 115 St John’s Hill, SW11 1SZ

¹Collins complete guide to British Trees, Collins, 2007

²The Walker’s Guide to Outdoor Clues and Signs, Tristan Gooley, Hodder and Stoughton, 2014

 

 

 

 

Hear no evil… at the Inverness Coffee Roasters, Inverness

Coffee in Inverness

Inverness Coffee Roasting Company.

Hear no evil, see no evil, speak no evil, so the saying goes and so the monkey, that was sitting on the sofa at the Inverness Coffee Roasting company (and café) indicated. And while I would not like anything evil to be said on this website generally, today it will be taken to an extreme as this cafe-physics review will not say much at all. Not because the coffee was not good, my Americano was a lovely complex dark and very enjoyable brew. Nor because there weren’t things to write about, several avenues suggested themselves for a ‘cafe-physics’ type review. There were also plenty of things to enjoy nibbling on while sitting down in this warm and comfy environment taking in the surroundings. Chocolate from The Chocolate Place was clearly labelled (and so I could enjoy it confident that it was nut-free) with a good variety of interestingly flavoured chocolates. The chocolate/coffee combination always goes well and the salted dark chocolate indeed complemented the coffee. A variety of freshly roasted coffees were in jars ready for selling to the home-brewing crowd and I heard both people behind the counter discussing coffee tastes with different customers to ensure that they could properly recommend a coffee for each of them.

So why, if the coffee was good, the service friendly and the environment interesting am I not going to write much about Inverness Coffee Roasting Company? Well, largely because I had been on holiday and so the preoccupations of the days before would necessarily influence what I noticed about this little café. Although I could happily write about neolithic monuments and considerations about inter-generational solidarity in relation to the re-use of refuse heaps at Skara Brae (as building material) and our own use (or misuse) of refuse in our environmental behaviour today. And it could even fit into a cafe-physics review of this venue as a sign on the wall above the door invited everyone to join the Plastic Free Scotland movement. However, it is not really what a Bean Thinking cafe-physics review is about. The idea behind the cafe-physics reviews is that things are often connected in surprising and beautiful ways and we can generally only see the connections if we slow down and look for them.

hear no evil, see no evil, speak no evil

Monkey on a sofa, but there was much more to notice at the Inverness Coffee Roasting Company if you looked around you.

Therefore, while you may (or may not) prefer to read about my holiday considerations of all things thousands of years old, what I thought I’d do with this café review is suggest a few things that I noticed in the café, things that offered a variety of potential thought-trains and then see what you think, what you notice, what you see (or don’t see). Perhaps you will observe something in one of the photos that clicks into a thought train for you, perhaps you can look around you, wherever you are right now – and think about the connections you could make to things you sense there instead? But whichever you do, it is a great time to sit back with a coffee (or perhaps a tea), breathe in and take in your surroundings.

Back in Inverness, the first thing of course was the monkey. Eyes shielded with an arm, suggestive of those who would prefer not to see what is in front of them. Nancy MacLean in “Democracy in Chains” notes that a training in the humanities perhaps opens students to question their society more than other, more utilitarian, subjects may do. Is it hurt pride that makes me rebel against this idea? Can’t physicists question too?

Perhaps it is connected but a sign by the door, and an identical one by the sofa, was written on the glass front of a box of coffee beans: “in emergency break glass”. This suggested so many avenues for exploration to me, I wonder which occur to others?

Behind our seats, a lizard was painted on/engraved into a stone, suggestive of fossils, geology and how we collect evidence. But a second lizard suggested a different direction. An ornamental lizard was positioned as if climbing up the counter. How do lizards climb? What is it about their feat? What connects lizards to a coffee company? Above our heads and above the door, stereotypical of Scotland perhaps, loomed a deer head complete with antlers. But this one was different: it was made of coffee beans and string. How a bean based diet could replace a meat one? The nature of units and how it would not necessarily be sensible to measure the mass of a deer in units of coffee beans? The mind jumped. Jumping beans?

Deer head in beans

Bean there done that?
Gruesome ornament or vegan friendly?

Finally, the logo of the cafe which was featured on signs around the interior and exterior of the space: a flaming coffee bean. The Maillard process and the changes in coffee as it is roasted? The nature of heat/temperature and the manner in which we measure it? What we hear as fire burns, lightning bangs or on “the first crack” of roasting and what this tells us about our atmosphere, our planet and our coffee is made of?

Whatever you notice, please get in touch, either by Facebook, Twitter, leave a comment or send me an email. But one last thing on coffee thought trains that links to real trains and is perhaps reflective back onto what it means to pause and watch. We left Inverness the day after our visit to Inverness Coffee Roasting by train. Inverness station has a relatively steep (1:60) gradient for 20 miles on leaving the station. It is Scotland in autumn, it had been raining and leaves had been falling on the line. Five or ten minutes out of the station, our train to Kings Cross juddered and came to a halt. A signal failure apparently. As the driver re-started the train, it slipped backwards, and again. We weren’t able to get up the hill. And so we had to return into Inverness station. Once back at Inverness station, the guard came across the tannoy and suggested that the signallers had given us the go-ahead to ‘have another run’ at the hill to see if we could get up it this time. So we tried again, juddering and shaking to a stop a few hundred metres beyond where we had stopped before. Back to Inverness station it was. The ever hopeful guard came across the tannoy again: “Third time lucky, fingers crossed”. This time the train left the station faster, building up speed, moving along more quickly and powering out of the station. The carriage was silent, were we going to make it? Past the first point we stopped at, past the second, a bit further, the family behind clapped, the train continued then slowed down and shook, juddered and then sped up again. We were over the hill and on our way back to London.

A last consideration on the conservation of energy and its relation to coffee and thought trains? Or a metaphor for how we may not find those connections in that cafe come to us quickly but if we persist and keep noticing, we can go on a fascinating journey?

Do let me know your thoughts.

The Inverness Coffee Roasting Company can be found at 15 Chapel Street Inverness, IV1 1NA

Air raising

Small waves seen from Lindisfarne

How do clouds form? How does temperature vary with altitude, and what does coffee have to do with any of it?

You put a drop of alcohol on your hand and feel your hand get cooler as the alcohol evaporates, but what has this to do with coffee, climate and physics?

Erasmus Darwin (1731-1802) was the grandfather of Charles of “Origin of the Species” fame. As a member of the Lunar Society (so-called because the members used to meet on evenings on which there was a full moon so that they could continue their discussions into the night and still see their way home) he would conduct all sorts of scientific experiments and propose various imaginative inventions. Other members of the Lunar Society included Matthew Boulton, Josiah Wedgwood and Joseph Priestley. The society was a great example of what can happen when a group of people who are interested in how things work get together and investigate things, partly just for the sake of it.

One of the things that Darwin had noticed was that when ether* evaporates from your hand, it cools it down, just as alcohol does. Darwin considered that in order to evaporate, the ether (or alcohol or even water) needed the heat that was provided by his hand, hence his hand started to feel cooler. But then he considered the corollary, if water (ether or alcohol) were to condense, would it not give off heat? He started to form an explanation of how clouds form: As moist air rises, it cools and expands until the moisture in the air starts to condense into droplets, clouds.

hole in water alcohol

There are several cool things you can notice with evaporating alcohol. Here a hole has been created in a thin layer of coffee by evaporating some gin. You can see the video of the effect here.

As with many such ideas, we can do a ‘back of the envelope’ calculation to see if Darwin could be correct, which is where we could also bring in coffee. The arabica growing regions are in the “bean belt” between 25 °N and 30 °S. In the sub-tropical region of that belt, between about 16-24°, the arabica is best grown at an altitude between 550-1100 m (1800-3600 ft). In the more equatorial regions (< 10º), the arabica is grown between 1100-1920m (3600-6300 ft). It makes sense that in the hotter, equatorial regions, the arabica needs to be grown at higher altitude so that the air is cooler, but can we calculate how much cooler it should be and then compare to how much cooler it is?

We do this by assuming that we can define a parcel of air that we will allow to rise (in our rough calculation of what is going on)¹. We assume that the parcel stays intact as it rises but that its temperature and pressure can vary as they would for an ideal gas. Assuming that the air parcel does not encounter friction as it rises (so we have a reversible process), what we are left with is that the rate of change of temperature with height (dT/dz) is given by the ratio of the gravitational acceleration (g) to the specific heat of the air at constant pressure (Cp) or, to express it mathematically:

dT/dz = -g/Cp = Γa

Γa is known as the adiabatic lapse rate and because it only depends on the gravitational acceleration and the specific heat of the gas at constant pressure (which we know/can measure), we can calculate it exactly. For dry air, the rate of change of temperature with height for an air parcel is -9.8 Kelvin/Km.

contrail, sunset

Contrails are caused by condensing water droplets behind aeroplanes.

So, a difference in mountain height of 1000 m would lead to a temperature drop of 9.8 ºC. Does this explain why coffee grows in the hills of Mexico at around 1000 m but the mountains of Columbia at around 1900 m? Not really. If you take the mountains of Columbia as an example, the average temperature at 1000 m is about 24ºC all year, but climb to 2000 m and the temperature only drops to 17-22ºC. How can we reconcile this with our calculation?

Firstly of course we have not considered microclimate and the heating effects of the sides or plateaus of the mountains together with the local weather patterns that will form in different regions of the world. But we have also missed something slightly more fundamental in our calculation, and something that will take us back to Erasmus Darwin: the air is not dry.

Specific heat is the amount of energy that is required to increase the temperature of a substance by one degree. Dry air has a different specific heat to that of air containing water vapour and so the adiabatic lapse rate (g/Cp) will be different. Additionally however we have Erasmus Darwin’s deduction from his ether: water vapour that condenses into water droplets will release heat. Condensing water vapour out of moist air will therefore affect the adiabatic lapse rate and, because there are now droplets of water in our air parcel, there will be clouds. When we calculate the temperature variation with height for water-saturated air, it is as low as 0.5 ºC/100 m (or 5 K/Km), more in keeping with the variations that we observe in the coffee growing regions†.

We have gone from having our head in the clouds and arrived back at our observations of evaporating liquids. It is fascinating what Erasmus Darwin was able to deduce about the way the world worked from what he noticed in his every-day life. Ideas that he could then either calculate, or experiment with to test. We have very varied lives and very varied approaches to coffee brewing. What will you notice? What will you deduce? How can you test it?

 

*ether could refer to a number of chemicals but given that Erasmus Darwin was a medical doctor, is it possible that the ether he refers to was the ether that is used as an anaesthetic?

†Though actually we still haven’t accounted for microclimate/weather patterns and so it is still very much a ‘rough’ calculation. The calculation would be far better tested by using weather balloons etc. as indeed it has been.

¹The calculation can be found in “Introduction to Atmospheric Physics”, David Andrews, Cambridge University Press

 

 

Creating an impression at 2Love Coffee House, Clapham Junction

coffee, cake menu, Clapham Junction, monmouth coffee

The menu at 2Love in Clapham Junction and some of the coffee making equipment in the window.

There is a lot of coffee paraphernalia on display in the windows at 2Love Coffee House on St John’s Road near Clapham Junction. Reusable cups, filters, moka pots, Chemex’s etc. Stepping inside, a piano greets you while the counter is on the left. The wall behind the counter is lined with jars of different sorts of tea while the coffee menu is on a blackboard close to the window. Coffee is roasted by Monmouth and is also available to purchase for brewing at home. Moreover, the number of re-usable cups on display meant that I have to admit to a touch of reusable cup envy when I saw the variety of glass cups on sale, have I used my cup enough to justify a second*? One great feature about this café was the care that they have taken to specify the allergens in their cakes on the blackboard, it is a considerate touch for people with allergies. Although we didn’t enjoy a cake on this occasion, it is great to know that I can!

There is definitely a musical feel to the café, with statues of musicians on shelves around the shop and pictures of different singers on each of the walls. Although we managed to find a table, it was rather crowded with the amount of chatter and distractions in the café initially challenging my assumption that all cafés can offer a space to contemplate and consider connections. However, this brief doubt in the idea behind Bean Thinking did not last long. The change in direction started with our discussion over an Americano and a fruit juice: can there be a justification for not eating certain meats if you are not already vegetarian/vegan and if so, what is it? This didn’t seem to go down too well with the table adjacent to us. On the wall behind our table was a metal picture of a horse drawn cart where the figures had been raised out of the picture to form a 3D image. It was reminiscent of the patterns given for stone rubbing as a child. But it was also reminiscent of something else, something that shines a light on an area of manufacturing as well as, perhaps, our conversation about the ethics of meat eating.

Not quite a mirror at 2 Love

3D Metal picture, musician statue and poster at 2Love Coffee House, who is the fairest of them all?

It concerns Chinese (or Japanese) magic mirrors. Known about for millennia (and not just in China, Aulus Gellius (c125 – approx 180 AD) wrote of them in the second century¹), they are slightly convex mirrors made of bronze. One surface appears to be an ordinary mirror but on the reverse surface, images of mythology or special Chinese characters are cast in relief. A Nature paper of 1879 describes why they were considered ‘magical’:

“If a polished surface is looked at directly, it acts as an ordinary mirror, reflecting the objects in front of it, but giving, of course, no indication whatever of the raised patterns on the back; if however a bright light be reflected by the smooth face of the mirror onto a screen, there is seen on this screen an image formed of bright lines on a dark background more or less perfectly representing the pattern on the back of the mirror, which is altogether hidden from the light”.¹

You can see photos of such mirrors and their reflections here but how would such an image be produced? Apart from magic, the first explanations for the effect focussed on it being trickery on the part of the makers of these mirrors. Perhaps the image was patterned onto the front of the mirror using more dense (or less dense) material, covered with a thin layer of lead or tin and highly polished so that you would never notice it by looking at your reflection only by shining light at it? Maybe there was other trickery involved on the part of the mirror makers to deceive us into thinking we could see through the mirror to the back. Later researchers wondered if these mirrors really existed at all as few could be found when they searched for them amongst Japanese mirror workshops. And yet a few mirrors with this magic quality were found and subject to study in the late nineteenth century.

window display 2Love

How much is that cup in the window?
Some of the reusable cups on sale at 2Love coffee house.

The results showed that the image was not formed if projected too close to the mirror but only if the screen were held some distance away from the mirror’s surface. Moreover careful optical experiments showed that the image was formed by the surface of the mirror having thicker regions that were less convex than the rest of the mirror so that these reflected the light differently². Although the image at the back of the mirror had been cast and not stamped on the back, the stresses and strains formed by the pattern on the metal somehow propagated through the (thin) mirrors and produced distortions on the surface of the mirror. Even when highly polished, these minute distortions in curvature remained causing the reflection of the ‘magic’ image under certain lighting conditions.

The theory describing the optics behind the magic mirrors was described as a ‘beautiful fact’ in a fairly recent mathematical description. But exactly how the stress of the pattern at the back gets transferred to the surface of the mirror remains to be understood³. Nonetheless, the fact that imperfections on one side of a material can be revealed by the projected reflections from the surface of the other, a process known as “Makyoh imaging”, is now used to check the integrity of semiconductor wafers before they are used in the manufacturing of devices. A piece of physics based neither on magic, nor on trickery, that is useful for our computer based lifestyles.

When faced with something that seemed improbable, it is interesting that our first explanations were based on magic, deceit on the part of the one who made it or distrust of the phenomenon altogether. It was only by carefully studying something that was too easily dismissed that the beautiful physics and industrial relevance of the property was revealed. For me this has pertinence to the question of our own investigation into what we think about the world. Do we place too much weight in our judgement of what we do not understand merely based on our own experience of how things are? Do we need to look more carefully at what we thought we knew? Great pondering points for a visit to a café and confirmation that, provided you have good coffee and a nice chair to sit on, contemplation directions can be found no matter how popular the venue.

2Love coffee is at 89 St John’s Road, Clapham Junction, SW11 1QY

¹ “The Mirror of Japan and its Magic Quality” Nature, April 10 1879, p 559

² “The Magic Mirror of Japan, Part 1”, WE Ayrton and John Perry, Proc. Royal. Soc, 28, 127 (1878-79)

³ “Oriental Magic Mirrors and the Laplacian Image”, MV Berry, Euro. J. Phys. 27, 109 (2006)

*Although there are differences depending on what you take into account, lifecycle analysis done here, here and here suggest a break-even point of disposable to reusable cups from 15 to 100 re-uses. However, if you consider that part of the solution to our environmental problems involves breaking the consumerist mindset then perhaps, if it ain’t broke, no need to replace it.

 

Feeling the Earth move at Pritchard and Ure, Camden

Egg no pales, coffee, garden centre

Fried egg on cactus leaves. Cactus festival at Pritchard and Ure, Camden

Good coffee in a garden centre, in (nearly) central London, with some physics thrown in? Today’s cafe-physics review seems unlikely on several levels. And then it becomes even more unlikely as you realise that this garden centre and café are also a social enterprise where people “disadvantaged in the labour market” are helped back to employment through working here. All in all, Pritchard and Ure represent a great café to have come by.

Pritchard and Ure can be found in the gallery space of a warehouse type shop that houses the Camden Garden Centre. They serve Workshop coffee together with an extensive selection of alternative drinks and food. As it was lunchtime we enjoyed a spot to eat which gave me an opportunity to try cactus (it was cactus festival at the garden centre). Cactus leaves with re-fried beans and a cactus-water mocktail which came together with a reusable metal straw. The straws were being sold (together with brush straw cleaners) at the counter. After lunch there was a very well made long black (interestingly I was given the choice to have it either as a 6oz or an 8oz, ie. more or less water depending on whether I wanted more or less coffee taste) and resisted (somehow) one of the tempting cakes before having a wander in the garden centre.

equations art work coffee Camden

But are they real?
The equations are the writing on the wall at this cafe.

There are of course many things that you can notice and connect with/to in a garden centre. Plants, biosphere, windows and greenhouse effect, the carbon cycle, the nature of colour, the list could go on. In addition to all of these, to the left of the counter was an art piece on the wall with a list of various equations and comments. Were all these equations real? One thing in particular though in this café/garden centre was particularly mesmeric: the disco ball suspended as a pendulum from a beam across the ceiling. Initially we watched as the ball just glinted reflected light as it slowly swayed to and fro in its oscillation. It took 22 seconds to cover 5 oscillations while I estimated it was 7m in length. Knowing that there is a formula for calculating the period of oscillation I wondered, was my estimation any good?*

During the hour it took us to enjoy lunch, the position of the Sun moved in the sky so that the disco ball started to reflect an array of polka dots of light onto the walls surrounding us (you can see these in the photo). Owing to the combined rotation and oscillation of the ball it wasn’t too easy to measure the time period from these oscillations but about 4 seconds per swing (as I had obtained by merely watching the ball) seemed comfortingly correct. The sun slowly moved round and these dots danced until at some point the sun had moved far enough that the glitter ball was no longer in direct light. But had the Sun moved or the Earth rotated underneath it? We all know the answer (or at least we think we do), but we could use the pendulum to prove it (and to calculate our latitude).

discoball cafe

Disco ball pendulum together with polka dot reflected sunlight. The view from the gallery at Pritchard and Ure.

In various science museums around the world, different Foucault pendulums swing to and fro all day above circular patterns on the floor. The pendulums appear to rotate clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere thereby illustrating the rotating earth underneath the pendulum. The idea is of course that the pendulum continues to swing in the same plane as it was when it was started off but as it is swinging the earth is rotating underneath it giving an apparent rotation of the pendulum swing over the course of a day. If we were at the north (or south) pole, the period of one complete rotation of the pendulum through a circle on the floor would take 24h. As most of us are not at the pole (and Pritchard and Ure certainly is not), the period of complete rotation is lengthened by a corrective factor proportional to the sine of the latitude. Consequently, it is perfectly feasible for us to calculate our latitude by observing a pendulum swinging for long enough in the absence of any breeze.

It is a great piece of evidence for the rotation of the earth (and by implication the fact that the earth is not flat and that the sun is not going round the earth each day). It’s also a very simple (hiding some complicated maths) demonstration that anyone could set up if they wished to carefully do so. So next time you see a disco ball suspended as a pendulum in a café, you would have another reason to start singing “I feel the Earth, move, under my feet…”

Pritchard and Ure is in the gallery of Camden Garden Centre at 2 Barker Drive, St Pancras Way, NW1 0JW

*7 m is an over estimate of the length of the pendulum based on the period of the oscillation. A length of 7m would give a time period of 5.3 seconds, whereas 22 seconds for 5 oscillations is about 4.4 seconds for one giving a calculated length of just under 5m. More details about how to calculate this are here.

Exploring the sound of coffee

coffee at Watch House

We’re used to thinking about the aroma of coffee and how it looks, tastes, even how it feels, but what about how it sounds?

How much attention do you pay to your brewing coffee? You know the aroma, how the coffee blooms, you anticipate the taste and feel the warmth of the steam rising off the brew. But what about the sound? Admittedly this depends on your brew method, but what about the sounds as you filled the kettle or prepared a pour over brew? It turns out that the sound of dripping water was the subject of a recent paper in Scientific Reports.

Perhaps take time to watch a tap dripping into a bowl of water. Or maybe use this as an excuse to make another coffee by drip brewing. Each drop falling onto the water (or coffee) below first deforms the water’s surface then, as far as we can see, rebounds up with a splash of a returning drop or droplets. The phenomenon of what causes the characteristic sound of the drip has been investigated for over 100 years but in 1959 it was established using high speed photography that there were four key phases to any drip sound. First, the drop fell on the liquid, then a cavity formed just under the water surface and an air bubble formed just under that. Finally the water surface recoiled leading to a jet of droplets returning from the surface. It has been thought that the sound, that ‘plink’ of the dripping tap, was caused by that trapped air bubble expanding and contracting as it moved through the water under the water’s surface¹. But this has now been confirmed, along with some other interesting, coffee related, observations using ultrafast video recording (30 000 fps for most of the work, 75 000 fps for some of the extra details).

lilies on water, rain on a pond, droplets

Like the sound of falling rain? What causes the dripping sound of a tap?

The authors of this recent paper describe what must have been a fun experiment to do, dripping water into a tank below. You can see some of the videos of the droplet entering the water by scrolling down to the “supplementary information” in the paper. Two microphones (one above, one below the water surface) recorded the sound waves coming from the dripping ‘tap’ simultaneously with the video recording so as to match the timing of the sound with what was happening in the video. The microphone above the water surface largely recorded the same sound waveform as the microphone under the water with one crucial exception. When the authors lined the tank with MDF wood, the underwater sound was ‘damped’ quite quickly, in comparison the bare tank amplified the sound and so the sound wave took much longer to decay. Above the surface however, it didn’t matter whether the tank was lined or not, the sound signal remained the same. This may sound somewhat insignificant, but it means that it cannot be the sound created by the wobbly bubble itself merely propagating through the surface of the water. If this were the case, the microphone above the water surface should show the same signal as the microphone under the water’s surface. Instead the authors suggest that the oscillating bubble causes the surface of the water immediately above it to vibrate (in the bit that is depressed owing to the droplet having fallen into it) and it is this that we hear above the water surface.

science in a V60

Droplets on the surface of a brewing V60 may also form owing to a temperature difference between the dripping drops of coffee and the coffee ‘bath’ underneath.

It is a beautiful set of experiments but how can it link to coffee (apart from with the dripping)? It is in the way that it gives us the chance to experience our coffee with experiments involving more of our senses than just smell, touch and taste. Firstly, the study emphasises the connection between the drop’s diameter and speed to the sound of the drip (the best sounds are for drops between 1mm and 5mm diameter). This suggests that by changing the brewing parameters (whether you prepare your V60 in a jug or a mug or change the filter paper to a metal kone for example), you may hear a change in the sound of the drips. Do you? Secondly, it has been suggested that the sound that is formed is dependent on the temperature difference between the dripping drop and the water bath underneath. A temperature difference between drop and bath would also explain an odd phenomenon I noticed in the V60 a while back. Do you notice a difference in the sound of the brewing coffee when you prepare cold brew pour over as opposed to a standard breakfast brew? Lastly, the authors of this study found that they could suppress the sound of the plink by reducing the surface tension of the water bath that they were dripping water into. In their case they added washing up detergent to the bath. This seems an awful waste of coffee but is it possible that something intrinsic to our coffee brew could do the same thing? Oil will also change the effective surface tension of the water and different coffees (and different roast strengths) change the oil content of the brewed coffee. Have you noticed any change in the sound of the drips of the coffee depending on how dark a roast coffee you use?

It may not make ground-breaking science but it does offer us an opportunity to pay even more attention to our coffee. Does the sound of your coffee reveal the beauty of the physics at work just under its surface?

¹ Some history of the investigation into the dripping sound as well as the experiments can be found in: Phillips et al., “The sound produced by a dripping tap is driven by resonant oscillation of an entrapped air bubble”, Scientific Reports, 8, 9515 (2018)

Metrology and the Press Room, Twickenham

Press Room coffee Twickenham

The arrival of the pour over at the Press Room, Twickenham.

It is not often that I have an errand to run in Twickenham, but when one popped up just two weeks after reading Brian’s Coffee Spot review of The Press Room, it was obvious where we were going to have a coffee. The Press Room serves pour over coffees (along with a good selection of other drinks). It is always great to find somewhere that serves pour overs well and so I had no hesitation in ordering a Nicaraguan “Los Altos” prepared by V60. Hot chocolate was available as white, milk or dark chocolate and there were a number of alternative non-dairy milks on offer as well as a large variety of tea. A lovely feature of The Press Room is that they offer suspended coffees, the idea being that you buy a coffee now for someone later who may not otherwise be able to afford one. The total number of coffees (given/claimed) is recorded on a blackboard behind the counter. It was nice to see that at the time of our visit 800+ coffees had been paid forward (and just less than 800 claimed), suggesting that the Press Room is having a positive effect on its local community.

clock wall Twickenham coffee

The large clock on the wall at The Press Room in Twickenham.

A great thing about ordering a pour over is watching as the barista expertly prepares your coffee, taking the time to do this properly. To be fair, this is part of the reason that finding a café serving pour-overs is becoming more difficult. After a while, the coffee was brought over to our table together with a bowl ready for me to place the filter cone on it when I was ready to enjoy the coffee. After taking the obligatory photograph, and pondering when would be the best time to remove the filter from the top of the mug and place it onto the empty bowl, the clock next to us took our attention. It is a large time piece that dominates this corner of the room. It is revealing to consider how the accuracy and availability of clocks have changed the way we live as a society.

Considering measurement (of time and other things), I used to be in this area more frequently a few years ago when I worked on a project in collaboration with the National Physical Laboratory (which is down the road, on the same bus route that Brian’s Coffee Spot notes takes you to a few good cafés). Partly, NPL’s work is to ensure that we know how to measure things properly. Take the pour over I enjoyed at The Press Room. A known amount (perhaps 12 g) of coffee was weighed out before 200 g of water was poured slowly over the coffee. But how do you know that the 12 g measured at Press Coffee is the same 12 g as you measure at home? And while perhaps it may not be critical for the coffee culture (even the most extreme home-brewer does not need to know the amount of coffee they are using to the nearest 0.000 002%), knowing accurately how heavy something is can be extremely important. Hence the need for a standard kilogram (and a standard metre, second, Candela etc) so that we have a way of knowing that what you call a kg is the same as what I call a kg.

coffee bowl pour over

The coffee that escaped! But was it a measure of my patience or hesitation?

Oddly, the kilogram is the last fundamental unit still defined with reference to a physical object (the other fundamental units are seconds, metres, Kelvin, Amperes, Moles, Candelas). The kilogram reference block is a PtIr alloy kept at the International Bureau of Weights and Measures near Paris. However all this may change next year depending on a decision due in November 2018. If all goes to plan, from May 2019 all units will be defined with respect to natural constants such as the speed of light etc. For the kilogram, this has meant measuring mass relative to a magnetic force generated by a coil of wire in a device known as a Kibble balance. In this way, the kg can be defined with respect to Planck’s constant and an era in which we measured substances relative to known objects will end.

On a day to day level though, how much do these things matter to us? Sometimes the way we measure things affects how we view them (and therefore what questions we ask next). Take for example temperature. We are used to measuring degrees of ‘hot’, so on the centigrade scale 0ºC is the freezing point of water and 100ºC is the boiling point. But it wasn’t always this way. Celsius devised his original scale to measure degrees of cold so 0º was the boiling point of water and 100º was the freezing point (you can read more about that story here). It is arguable that changing to measuring degrees of ‘hot’ enabled us to more easily conceptualise the idea of heat as energy and the field of thermodynamics. Certainly for a while, considering the idea of ‘degrees of cold’ meant that some looked for a substance of ‘cold’ called “frigorific“¹. There’s a similarity here with the coffee at The Press Room, was the amount of coffee in the bowl used to hold the filter after I removed it from the mug a measure of my impatience before trying the coffee or my hesitation at testing the coffee? How we ask that question affects how we view the coffee and the café (for reference, I would take the positive interpretation: the amount of coffee in the bowl measures my impatience; I was eager to try the coffee).

droplets on the side of a mug

Condensation on the side of the mug. These droplets can reveal many aspects of physics, which do you think about?

Partly this suggests some of the ways in which language, and philosophy, underpin all science. It certainly suggests one further connection with this bright and comfortable café. Erich Fromm in “To have or to be”² considered an interesting linguistic usage that reveals our way of being. Do we “have an idea”, or do we “think”? Are we consumers or people with experiences? Do we wish to have, to acquire, to consume or do we wish to exist, to be. Our language affects how we perceive the world which in turn changes the language we use about it. Linguistically, depending on how we interpret the cafe’s name “The Press Room”, we either have a café that offers a space to read the latest news or one that is reflective of the coffee brewing process (specifically espresso); a space to get up to date or one in which to contemplate? The symbol of the café visible in the frontage of the shop and on the mugs suggests the latter, but maybe it is something we need to experience to truly know?

¹Inventing Temperature, Hasok Chang, Oxford University Press, 2008

²To have or to be, Erich Fromm, Jonathan Cape, 1978

The Press Room is at 29 London Road, TW1 3SW

(Im)perfect reflections on coffee

science in a V60

Have you noticed droplets like these dancing on your drip-brewed coffee?

With the recent coffees from Hundred House and Quarter Horse, there have been many opportunities to observe the coffee brewing in the V60 in the mornings. The steam rising from the filter paper, the different ways different coffees bloom and out-gas, the droplets that skim the surface of the coffee and bounce off the walls of the jug and then, of course, the many different effects with light. Watching the dancing droplets (an explanation of why they may dance is here), it is perhaps not immediately obvious that you could form a connection between these, the light reflections and an insight into something you may have noticed while passing through customs. And yet the connection is definitely there.

The connection is formed through a technique called Raman spectroscopy. Named after Chandrasekhara Venkata Raman (1888-1970) who discovered the Raman effect in 1928. As the ‘spectroscopy’ part of the name suggests, it is a technique that offers a way to identify different chemicals, or components, in a substance. For coffee it has been used both as a non-destructive technique to determine the kahweol content of coffee beans and hence help as a test for identifying rogue robusta in arabica beans and as a way of analysing the brewed coffee. But what is it, how does watching a brewing V60 help to understand it and why would you want to know about Raman spectroscopy while travelling through an airport?

beauty in a coffee, coffee beauty

A collection of bubbles on the side of the coffee. What happens when one of the dancing droplets collides with a group of bubbles?

Generally, it helps to begin with coffee and the link is the way in which the droplets bounce off the side of the jug. Brew a coffee and watch them (if you are a non-coffee drinker, you could try dripping hot water through a filter paper into a jug). When one of these droplets hits the wall of the V60 container, it generally bounces back with a trajectory expected for an elastic collision. Given the relative masses of the droplet and the jug, the speed of the reflected droplet is essentially unchanged (even if its direction is reversed). This is similar to what we would normally expect for light. We are used to considering light as waves but because of the wave-particle duality of quantum mechanics it is equally valid to consider light as a stream of particles called photons. As the photons hit a surface and are reflected off, they recoil with the same energy that they initially had, just like the droplets in the coffee. But now look more closely at the dancing droplets. Normally they hit the walls and not each other but just occasionally, they can hit either another droplet or a group of bubbles that have formed on the coffee surface. In these cases, rather than get reflected as before, the droplets transfer some of their energy to the collection of bubbles causing them to move and to wobble. And when the droplet is reflected back, it has a noticeably slower speed (and so we could say a lower kinetic energy) than when it initially danced into its collision. Where is the analogue with light?

When we think about a coffee bean, we probably think about something that is about 1cm oval, brown and quite solid. But if we zoom in, we find that it is made up of a collection of atoms bound together in molecules or, if we are thinking about a solid like salt, in a crystal structure. These atoms act as if they are balls connected by springs and so they wobble as would any structure of masses connected by springs. This is true whether the crystal is diamond or the molecule is caffeine, kahweol, cocaine or semtex (do you see where the customs part is going to come in yet?). Different crystal structures have different atomic arrangements meaning that they are effectively connected by springs of differing strength. If you build a mental model of masses connected with springs, you can see that changing the spring strength will change the vibration energy of the structure. So if now we think about the photons hitting such a structure, while most will bounce off as we saw with the droplet hitting the V60 wall, some photons will trigger a wobble in the crystal structure and bounce off with lower energy. It is a process analogous to the droplet hitting and bouncing off the collection of bubbles on the coffee surface.

Sun-dog, Sun dog

Sun dogs are caused by a different interaction between light and crystals. Rather than the inelastic scattering of Raman spectroscopy, Sun dogs are caused by the refraction of light by hexagonal platelets of ice crystals.

When a photon of light loses energy, it is equivalent to saying that the frequency of the light has changed (which is very closely related to what Albert Einstein got his Nobel prize for in 1921). So a photon that creates a crystal vibration and is scattered off with lower energy has a lower frequency (or longer wavelength) than it had when it first hit the crystal. Importantly, the energy lost by the photon is identical to the energy gained by the vibrating crystal and so by measuring the frequency change of the scattered light we have a way of determining the energy of the crystal (or molecule) vibration. As this energy depends on the way that the atoms are arranged in the crystal or molecule, measuring the frequency shift offers us a way of identifying the chemical under the laser light: kahweol or cocaine.

It is not an easy technique as you can guess from the V60 analogy. Only around one in a million photons incident on a solid will be Raman scattered. You need some pretty decent optics to detect it. Nonetheless, it is a powerful technique because no two chemical structures are the same and so it can be used to identify tiny amounts of smuggled material completely non-destructively. It becomes easier to understand how this elegant technique has become useful for many areas of our lives from customs, through to pharmaceutical development and even into understanding how fuel cells work.

Although it is stretching the analogy too far to say that you can see Raman scattering by watching the droplets on your V60, it is certainly fair to say that watching them allows you the space to think about what is happening on a more microscopic level as your bag is hand-scanned at customs. What do you see when you look closely at your brewing coffee?

 

As quick as (a) Quarter Horse

Dog and Hat, Dog & Hat, Hundred House, Quarterhouse coffee

The package from Dog & Hat with Hundred House and Quarter Horse. Is it a particularly contemplative dog with the monocle?

Links with science can be found everywhere, from the café to the coffee roaster. A couple of weeks ago a delivery from Dog and Hat coffee gave me an opportunity to explore the random thought paths that may occur if you stop to ponder your coffee at home rather than in a café. The first coffee, an Ethiopian from Hundred House prompted thoughts on star gazing. But the second coffee, a Mexican from Quarter Horse coffee was equally thought provoking.

Finding time to prepare a V60 and sit with the SCAA “flavor wheel” as a guide, I was rewarded with a sweet, well rounded and perfectly enjoyable brew. I found fruity notes of blueberry and cherry/pineapple though the tasting notes on the packaging say “green grape, toffee and cocoa”. Sadly I missed the cocoa but this offers a good excuse for another slow brew with the coffee wheel at hand.

Thinking about the name of the coffee, I started to consider how you could quarter a horse. Perhaps not a literal horse given the ethical considerations but rather an irregularly shaped volume. How would you divide, into equal portions, an irregularly shaped object such as a horse? It seemed related to the question of finding the shortest route between two locations, how would you calculate the best route to take from A to B? In the 1950s a computer scientist called Edsger Dijkstra (1930-2002) came up with an algorithm to calculate precisely this problem. Originally designed to show the shortest routes between 64 cities in the Netherlands, Dijkstra’s algorithm is now ubiquitous in our lives.

Quarter Horse but how would you

A close up of the Quarter Horse Coffee Bag.

One of the ways in which we have started to rely on such algorithms is in car GPS devices or even on our phones trying to navigate to our destinations. Or at least, many of us do. London taxi drivers however have been shown to have developed a different brain structure from the general population that means that, for them, Dijkstra’s algorithm may be unnecessary. A few years ago, a study compared brain scans of people who had been driving London’s “black cabs” for a number of years to those of us in the general population. A follow-up study followed three sets of people over several years. A control group of people in the general population and a second group of people who studied the “Knowledge”, the navigational test that London taxi drivers have to pass in order to become cabbies. The Knowledge tests the driver’s ability to recall tens of thousands of London’s streets and the prospective cabbie can be asked to navigate between two points anywhere within a 6 mile radius of Charing Cross. Typically it takes years to acquire the Knowledge and not everyone who starts on the Knowledge will pass (the pass rate is only about 50%). This means that this second group of people splits into two groups; those who studied and passed the Knowledge and those who studied but did not pass.

The studies proved illuminating. One particular part of the brain, the posterior hippocampus had a greater volume of “grey matter” (the brain processing cells) in taxi drivers who had studied, and passed, the Knowledge compared with the general population. Moreover, those that had been taxi drivers for longer, showed larger posterior hippocampi. The changes in the brain seemed to lead to the cabbies having not only better navigational ability than the general population but better memory for London based information. The study of the trainees moreover confirmed that these brain changes occurred as a result of learning the Knowledge, showing that our brains are adaptable and still able to develop well into adulthood. While the brains of all the study participants started off similarly, those that went on to pass the Knowledge had a larger posterior hippocampus than those who either didn’t study or studied but hadn’t passed. However it was not all good news for the cabbies. The growth of the posterior hippocampus seemed to occur at the expense of the anterior hippocampus in long serving taxi drivers (but not newly qualified ones). The improved memory for London based information shown by the taxi driving group was also accompanied by a poorer ability to learn other visual information/memory related tasks in those that passed the Knowledge compared to the general population.

taxi and motorcycle, London

London black cab drivers have been shown to have a larger volume of grey matter in the posterior hippocampus area of their brains, demonstrating that our brains remain adaptable well into adulthood.

Perhaps the ability of the cabbies to navigate quickly around London’s streets suggests a second connection with Quarter Horse. A Quarter Horse is a breed of horse that can sprint very quickly over short (less than a quarter of a mile) distances. Which goes faster, the cabbie with the Knowledge or us with our smartphones once we have plugged in our destination? We are reminded of the tale of the hare and the tortoise. But I think a different tale is more appropriate. A tale that in reality was only ever a snippet of an ancient saying but has been developed into tales by thinkers such as Isaiah Berlin and Ronald Dworkin.

“The fox knows many things but the hedgehog one important thing”.

What does this mean? It seems there is a connection here between coffee roasting and taxi drivers, between algorithms and personal development, between coffee science and writing about coffee science. Is this connection really there or is it a meaningless statement that leads us into blind alleys of coffee consideration? It may be time to stretch our brains, grow our grey matter a bit and contemplate. Am I a fox or a hedgehog and where do London cabbies and coffee roasters fit in?

Quarter Horse coffee is online at https://quarterhorsecoffee.com

You can find out more about the coffee subscription site Dog and Hat on their website https://dogandhat.co.uk

You can read more about the taxi driver study on the Wellcome Trust’s press release about it here.

Enjoy your coffee, have fun thinking, grow your grey matter.

 

 

A shocking coffee connection

There have been some fantastic thunderstorms in London lately. Perhaps nothing to rival thunderstorms in the tropics but for this region of the world they were quite impressive. One lightning storm in particular came very close. Thank goodness for lightning conductors! Perhaps the connection between lightning storms and coffee is not obvious. But maybe this is because you mop up your coffee spillages too quickly.

Reynolds, rain, waves, pond, raining

There are so many coffee-physics connections with rain and weather. It’s worth looking out for more.

The link is in the mess and the maths. It turns out that the maths describing water evaporating out of a drying coffee droplet is the same, in one crucial detail, as the maths describing the electric fields around a lightning conductor. If we want to see why this may be, we need to get a little bit messy and spill some coffee.

The question is how do coffee rings form? We know that to start with the solids in the coffee are distributed fairly evenly throughout the drink. It is the same when you spill it, initially a spilled drop of coffee looks like, well, coffee. But if you wait as this spilled coffee dries, you will find that a ring starts to form around the edge of the drop. How? How does a uniform coffee distribution when the drop is first spilled become a ring of coffee solids around the edge of the dried drop?

coffee ring, ink jet printing, organic electronics

Why does it form a ring?

A number of different aspects of physics feed into this problem but the one that is relevant to the lightning conductors concerns how the water in the drop evaporates. If you think about how a water molecule escapes (evaporates from) the droplet, it is not going to go shooting off like a rocket blasted out from the drop. Instead it will take a step out the drop then encounter a molecule in the air and get deflected to a slightly different path and again, and again, and so on. It follows the same sort of “random walk” that we know that the bits of dust on a coffee surface follow (and the same sort of random walk that provides a link between coffee and the movements of the financial stock exchange but that is a whole other topic).

Now think about the shape of that spilled coffee drop. If a water molecule were to evaporate from the top of the dome of the drop, it has a certain probability of escaping but it also, because its path is random, has a certain probability of re-entering the droplet. A water molecule at the edge of the droplet however will have a lower probability of re-entering the droplet purely on the basis that there isn’t so much of the droplet around it. Over many molecules and many ‘escape attempts’, this lower probability of re-absorption will translate to a higher flux of water molecules evaporating from the droplet at the edges. The water will evaporate ‘more quickly’ from the edge of the droplet than from the top of it.

artemisdraws, evaporating droplet

As the water molecules leave the droplet, they are more likely to escape if they are at the edge than if they are at the top. Image © @artemisworks

When this is written mathematically, the rate of evaporating water is related to the contact angle between the drop and the surface. The shallower the angle, the higher the rate of evaporation or equivalently, the greater the ‘flux’. It is this mathematical expression that is the same as for the lightning conductor if, rather than refer to an evaporating water flux we refer to an electric field. So the more pointy the conductor, the greater the field concentration around it. A shocking example of the idea that everything is connected.

Of course, there is much more to the coffee ring than this with physics that relates coffee rings to bacterial colonies, burning cigarette papers and soap boats. If you are interested, you can read more about how coffee rings form (including why a higher evaporation rate helps lead to a coffee ring effect) here. If on the other hand you want some well justified thinking time, go spill some coffee and watch as the coffee dries.

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