Science history

Noticing at Artisan, Ealing

coffee Artisan Ealing

A good coffee is a solid foundation for any afternoon’s noticing.

A cafe-physics review with a difference. In that, it’s not so much a review as an invitation. What do you notice in a café?

Last week, I had the opportunity to try Artisan’s Ealing branch. Although I had found a lot to notice on my previous visit to the East Sheen branch, I had a very specific reason for visiting the Ealing location of this small chain of four cafés. The coffee (espresso) was reliably good. Smooth and drinkable in a friendly atmosphere. Just as with the café in East Sheen, there were a good selection of edibles at the counter and plenty to notice. The light shades were immediately outstanding as something to notice while a framed ‘hole in the wall’ provided a conversation point. The café was very busy and while there was plenty of seating with many tables, we were still lucky to have got a table for two near the back. Behind us there was a lesson going on in the coffee school while on the wall was the calendar for the space booking downstairs. And it was this that I had come here for.

A couple of months ago, Artisan announced that this space would be available to rent to provide a friendly space (with coffee) for the meetings of local small businesses or charities. This stayed in the back of my mind for a while as it came about at roughly the same time as an idea for Bean Thinking.

Lampshades at Artisan Ealing

First the obvious. Immediately striking, these lampshades could provide several avenues for thought.

There are a couple of us who are interested in meeting, about once a month, to discuss science. As ‘science’ is quite a big subject, we thought we would limit it to science that is associated with coffee or with the café at which we are meeting. Perhaps readers of this website may realise that this is not such a restriction, it is quite easy to connect coffee to the cosmic microwave background radiation of the Universe or to chromatography and analytical chemistry. If we were to meet in a location such as Artisan, there should be plenty more food for thoughts. The lampshades prompted me to consider what made substances opaque or transparent? Where is the link to coffee and methods for measuring the coffee extraction? The hole in the wall suggested thoughts about the algorithms behind cash machines. I’m sure that there is plenty more to notice if we take the time to see it.

And so this is an invitation. Would you like to join us in exploring what we each notice about the science of our surroundings? The plan would be to meet once a month, probably starting late January 2019 or early February (date and location to be confirmed). An afternoon on the weekend is probably better than an evening and we’d probably stay for an hour or two. You do not have to be a practising scientist to come along indeed, it would be great if we could have people from a variety of walks of life. The idea is not (necessarily) to answer scientific questions that we each may have but instead to explore the science behind the questions, to find the connections that form our ideas of the universe. To really notice our surroundings and our coffees (tea drinkers would also be welcome). As a consequence of this, mobile phones/laptops etc. will be discouraged during the afternoon. We’d like to notice things around us and not be distracted by what a search engine suggests about it; if we think a search engine could help us, we’ll use it after we’ve left and come back the following month to discuss the issues further. So, if you are curious, would like to explore what you notice and can tolerate keeping your phone on silent and in your pocket for an afternoon, please do come along, it would be great to meet some of you.

menus and lampshades in Artisan

You may like to look more closely at this photo. How are the menus supported? What does that tell us about the history of science?

In order to understand whether there would be any interest in this idea and to hear your input about the format, content, location, time etc. I have set up a mailing list for these cafe-science-spaces. Please do sign up to the mailing list to hear the latest announcements concerning these events and also to email me back to contribute your opinion. You can sign up to the mailing list using the sign up form below. Alternatively, if you don’t want to sign up to the mailing list but do want to hear more, I will be advertising the events on Twitter and Facebook so please do feel free to follow me there.

 

Please enter your email address here if you would like to hear about future Bean Thinking events.

 

A post in need of a Curator(s) Coffee, Fitzrovia

espresso Curators

A deliciously intense and fruity espresso from the ‘specials’ menu at Curators Coffee.

Curators Coffee in Margaret St in Fitzrovia has been there for years. A great location just off of Oxford St, with plenty of seating and good coffee, and so it is perfect to pop into, unless you are like me and avoid the Oxford St area as much as possible. Which perhaps explains the rarity of my visits. I first popped into Curators Coffee a couple of years back (before the laws on allergen information came in) when I remember enjoying a lovely long black but couldn’t have a cake because the people behind the counter that day couldn’t tell me which (if any) cakes contained nuts. At the time, I sat upstairs and noticed the graphene type arrangement of hexagons around the back of the space and the Bramah’s 300 years of coffee makers book in a rack at the back. I had wanted to return to properly cafe-physics review the place at a later date (and try the cake) but circumstances (and Oxford St avoidance) meant that I never got round to it. Until very recently.

This time, I noticed that there were three single origin coffees available to try as espresso. Glancing at the tasting notes it was a fairly quick decision: “chocolate”. And although this time I had just had lunch and so passed on the cake, it appears that the espresso choices regularly rotate, offering an incentive to come back again and try something new. Although the café is quite large, with plenty of seating, it seems that it is also very popular. And so there were no spaces remaining upstairs. Fortunately, there were more seats downstairs and so, taking our table number with us, we made our way down the stairs and found a table at the window, as if it was waiting for us.

UFO in Curators Coffee Fitzrovia

A UFO reflected in the window? Why? What? Why (again)? It is small details such as this that reward you as you put down your smart phone and notice your surroundings.

Perhaps it is obvious that a café called Curators should have art work adorning the walls. That, and the spotlights that highlighted the work immediately caught our interest, (although it was odd to see that one of the rows of spotlights was almost devoid of bulbs). The exhibition downstairs seemed to have a tilt towards street art and a couple of decorated aerosol cans were on the windowsill priced at £15 each. Was this the time to consider why an aerosol gets cooler as you spray the walls with it?

Outside the window, a staircase leading up to the street outside had railings in straight lines leading up towards a blue sky. Inside, a space craft was reflected in the window.

Indeed, on checking again, there was a spacecraft, like a cartoon of a stereotypical little UFO, drawn onto the wall behind my accomplice’s head and reflected in the window next to it. What could it mean? Regardless of whether some UFO incidents are associated with visitors from other planets, there are a large number of scientific thought trains we can take when considering a UFO reflected in a window. To start with, how likely is it that we are alone in the universe or that there are many other intelligent life forms in other planetary systems?

The question has been answered on the basis of probability for many years. But recently, we have been finding more planets orbiting stars and crucially, more planets that are in the ‘habitable’ zone around other stars. Assuming that life elsewhere needs similar conditions to the earth’s in order to thrive, the idea of life elsewhere is becoming increasingly real.

canali Curators Coffee

If you see straight lines such as this, it is fairly sensible to infer that they were built by an intelligent life-form. Can you see canals on Mars?

Closer to home, there were even suggestions that Mars may support flowing water, thought to be a host for bacteria based life. And although these interpretations of the flow patterns observed on the Martian surface have more recently been contested (could they instead be flowing sand?), we continue to send probes (such as the Insight probe that landed recently) to the red planet to investigate its geology. Did Mars once host life?  Mars of course has a resonance in science fiction for being the planet hosting extra-terrestrial life. HG Wells imagined the Martians landing just south of London, and eventually being killed off by exposure to bacteria on earth that they had not experienced in their Martian habitat. Could life on Mars suggest a (tenuous) further link to this café on Margaret St?

Perhaps one reason that people started to imagine (intelligent) life on Mars came about because of an interesting mistranslation of an astronomical observation. While gazing at Mars in 1877, Schiaparelli noted ‘canali’ on the Martian surface. The correct translation of this in this context into English is “channels” but what the observation came to be known as was “canals”. Canals imply an intelligent builder, and hence life on Mars. Later observers also saw these ‘canals’ and a popular myth was born. It is a useful lesson for us all, sometimes how we see something can be influenced by the language we use to describe it.

soya hot chocolate, Curators

We photograph our coffee, and share it with our online friends. But would putting down our phone in a cafe be worth something for the planet as well as for ourselves? How many batteries do we need?

And then one final thought train, prompted by photographing the cafe with my mobile phone. The whole probability argument rests on two assumptions. The first is that there are other planetary systems (which we are finding). The second is that life is fairly easy to start, or at least, that the chances of producing life are not restricted to one planet a short distance away from the Sun; we are not unique. As yet we don’t know whether this assumption is justified but discoveries such as the deep sea hydrothermal vents challenge our preconceptions about the requirements for life and suggest that life could start more than once, and so could very well start on other planets, not just ours. In these vents, bacteria are known to convert what we think of as toxic chemicals into energy in a process known as chemosynthesis without the need of sunlight or other ingredients that we had thought essential to life. Could similar hydrothermal vents on other planets host new life forms?

And in a related way, what is going on with these vents? Is new life being created even now in the deep sea? In which case, what do we think about deep sea mining? If our aim is to reduce our carbon dioxide emissions by using more re-usable objects and renewable energy sources, we will require more batteries and batteries require (among other things) cobalt. If we are all to keep using mobile phones to photograph cafés, we too need the batteries which rely on these elements. A number of companies have realised that there is a vast untapped resource under the sea if only we could dredge it up. This may be easier or ultimately cheaper than recycling the old batteries. It may destroy a few hydrothermal vents or stir up the sea bed but what concern is that to us if we can gain access to more cobalt to allow us to have more batteries to allow us to all be ‘greener’.

Indeed, of what concern is that to us?

Curators Coffee is at 51 Margaret St, W1W 8SG

The universe and a coffee cup

a heat sensitive coffee mug

Now you see it….

Ordinarily, this week would be the turn of a cafe-physics review but circumstances have meant that this will be postponed by one week, sorry. So instead, a question. How does your coffee cup resemble the universe?

A few years ago, I was given a heat changing mug that revealed the constellations when the coffee within it was hot (and went black as the coffee was finished/went cold). Although this is not the way that the universe resembles a coffee mug, the science behind these mugs is quite interesting and they do provide a clue to the connection. The answer (or an answer, you may think of more) is in the way that the mug emits heat.

On a cold day with a hot coffee, I can be fairly sure that by putting my hands quite close but not touching the cup, I can feel the radiated warmth. Infrared waves helping prevent my fingers from becoming numb. Although there is air around the cup (even physicists don’t drink coffee in a vacuum) and so there will be heat transferred from the cup to my hands via conduction and convection, a large amount of the heat my hands receive will be radiated. It was by watching a candle flame between himself and a stove that Carl Wilhelm Scheele (1742-1786) inferred the presence of the infrared. For a coffee temperature of 60ºC (333 Kelvin), the cup would emit a range of light with a peak in intensity at a wavelength in the infrared of around 8.5 μm, about the length of a grain of espresso grind. The way that objects radiate heat is well known. Called a “black body spectrum”, all things radiate a spectrum that can be approximated to it, whether the object is a coffee cup or the universe, the difference is over what frequency range (or wavelength) the object radiates and where in the spectrum the light intensity peaks.

cold mug

Now you don’t.
The same cup as above but photographed when it is at room temperature not when it contains hot liquid.

Coffee emits light (in the infrared) at 8.5 μm because it is about 60ºC. A ‘red hot’ iron rod, still emits light in a spectrum that peaks in the infrared but appears more red than my coffee cup because the peak in the radiated intensity has decreased closer to the red region of the visible spectrum. The universe emits radiation over the same sort of blackbody curve but the spectrum emitted by the universe peaks at a wavelength of around 2cm, much longer than the coffee cup and well beyond the infrared. In fact, the universe is emitting light in the microwave region. The longer wavelength means that the universe is a lot colder than a cup of coffee. About 330º cooler in fact because the temperature of the universe is a chilly 2.7K (or approximately -270ºC).

The presence of this microwave ‘background’ was first detected in the 1960s. Further experiments in the 1990s with the COBE satellite and more recently with the Planck satellite have confirmed the almost perfect uniformity of the blackbody spectrum. No matter which direction you turn your microwave antennae to, you pick up the same background spectrum, peaking at about 2cm, all around the universe. This means that the background temperature of the universe is the same in all directions that we look, it is uniform. Indeed, it took until the sensitivity of the Planck satellite and more recently the WMAP data to show that the universe had any variation at all. And when it was revealed, it was a difference of about one part in a million. If we compare this to our coffee we can see from the lines of light that dance on the bottom of a tea cup that there is significant temperature variation within the cup. Even a difference of one degree would lead to a shift in the blackbody spectrum of the coffee cup by a few parts in a thousand: the background temperature of the universe is far more uniform than the temperature of your cup of coffee in fact the shift seems to be of the order of 0.0002º.

But, apart from an interesting curiosity why would we want to measure the temperature of the universe or know the uniformity of a cup of coffee? One reason is that knowing the current temperature and its likely cooling mechanism, means that we can calculate how long the universe, or coffee, has been cooling. If I were to drink a cup of coffee that was cooler than about 60ºC I would know that either it has been prepared much earlier and left on the counter top or that it had been prepared using water below the optimum brewing temperature. If I note from the lines of light crossing the bottom of the cup that there is a lot of convection going on in my tea cup with cells of different temperature, I could think that it is either a very cold day or that I didn’t warm the cup before I poured the coffee or tea into it.

NASA image CMB

There is even more information in the background if we start to look at the polarisation of the microwaves. The Cosmic Microwave Background showing the minute temperature fluctuations and polarisation directions. Image credit ESA/Planck Collaboration

Knowing the temperature of the universe allows us to check theories of how the universe formed (and therefore how it cools) by calculating its age and seeing if this matches with the age deduced by other means (by looking at the oldest star clusters for example). While looking at the minute temperature variations across the universe is also a test of the theories of the universe’s formation.

There are clearly differences between the universe and a mug of coffee, even a mug that shows the constellations of the stars, not least the fact that the coffee cools into the universe but the universe’s cooling is different having nothing to cool into. Nonetheless, it is remarkable that the same physical laws and mathematics that describes your cooling coffee cup can be used to describe our entire universe. So sit back, take a deep breath, and enjoy the universe through your coffee cup.

 

21 years of the coffee stain

dried coffee stains, alcohol and coffee

Happy 21st birthday to the coffee stain. But there is still much for us to learn 21 years after the first paper on the coffee stain was published.

On the 23rd October, 1997, a paper was published in the journal Nature titled “Capillary flow as the cause of ring stains from dried liquid drops.” The title is in the dry style that scientific papers can be written. An alternative title could have been “How coffee stains form”*. Perhaps you would think, surely someone had known how coffee stains formed before 1997? And maybe you would go on to think: certainly 21 years later in 2018, we’d know all there was to know about the coffee stain? I hope that readers of Bean Thinking would not think “who cares about coffee stains?”, but I wonder whether it was the combination of disinterest and assuming that someone somewhere surely knew how they formed that meant it took until 1997 for anyone to ask the question: well how do they form?

Coffee is a very popular drink among scientists, though even this does not explain how popular this paper has become. A paper’s popularity can be measured in ‘number of citations’ which tells you how many times other authors have found this piece of work important enough to reference it in their own published paper. As of early November 2018, this paper has been cited nearly 3300 times. Why? Well, there seem to be at least two reasons. Firstly, it turns out that the coffee stain effect is of enormous technological relevance; it may even have been used in the manufacture of the device you are using to read this website. But secondly even now, 21 years later, we still don’t understand what is going on, there is still much to learn and some of it is some very subtle and very beautiful physics.

the droplets ready to dry

What happens when you form coffee stains using drops containing two liquids (alcohol and water) compared to just one (water)?

Very recently for example, a new paper was published in Physical Review Letters. This one was titled “Density-driven flows in evaporating binary liquid droplets“. Another exciting title, another time we’ll retitle it for the purposes of this post: “what happens when you mix alcohol with a coffee type suspension, dry it at different angles and film it drying.” Arguably this time the given title is more succinct. Why does it make a difference if you add alcohol to your coffee rather than just drink it straight (the coffee, not the alcohol)? And what happens to the resulting coffee stain?

Maybe of an evening you’ve been relaxing with a glass of wine, or something stronger, and noticed the “legs” rising up the glass. Their formation and appearance is due to the differing surface tensions between alcohol and water and the fact that alcohol evaporates more easily than water, you can read more about that effect here. The point is that because of the difference in surface tension between alcohol and water, you get a flow of liquid from areas of low surface tension (higher alcohol content) to high surface tension (high water content). And it was this that had been thought to drive coffee stain formation in droplets which were a mix of liquids, water and alcohol for example. But how do you isolate this effect from the other effect in which alcohol evaporates more quickly than water and so there are changes in density and buoyancy of the droplet?

pendulant droplets

Drying droplets upside down. The things we do for coffee science.

To answer this you could add n-butanol to the water (or coffee) rather than alcohol. Just like ethanol based alcohol (the sort you may get in gin), n-butanol has a much lower surface tension and lower density than water but unlike alcohol, it evaporates much less readily than water. So, in a water-butanol mix it will be the water that goes first, while exactly the opposite will happen for an alcohol-water mix. In a drying droplet, the liquid evaporates most quickly from the edge of the drop. Therefore, after an initial, chaotic stage (imaginatively called stage I), you will end up with a droplet that is water rich around its rim in the alcohol-water mix but n-butanol rich around the droplet edge in an n-butanol-water mix (stage II). This suggests a way that you can distinguish the flows in the drop due to surface tension effects from those due to the differences in density between water and alcohol/n-butanol.

How would you test it? One way would be to compare the droplets evaporating as if you had spilled them on the table top with droplets evaporating ‘upside-down’, as if you had tipped the table by 180° after spilling your coffee. You can then watch the flow by taking many photographs with a camera. In this way you would be able to test whether it was surface tension flow (which should be in the same direction within the drop whether the droplet is upright or suspended) with gravity driven flow which should be opposite (the drop is upside down after all).

schematic drops upright and upside down

A cartoon of the flow found in droplets of alcohol and water mix. When upright, the flow is up through the centre of the drop and down the sides. This is expected for both surface tension based flows and flows due to gravity. When upside down, the flow is still upwards through the centre of the drop but this time the drop is upside down. So this is what you’d expect if the dense water at the edge of the drop flowed downwards (gravity based) but not if the flow were dominated by surface tension effects which should be the same, relative to the drop-interface as if the drop were upright.

The authors of the study did this and found that the flow in upright drops of alcohol-water was opposite to that in n-butanol-water drops. This is what is expected both in surface tension dominated flow and in gravity dominated flow. But, when the drops were inverted, the flow within the droplet did not change absolute direction, instead it changed direction relative to the substrate (it may be helpful to see the cartoon), in both droplet types. Expected for a gravity driven flow (dense liquids move downwards), this is exactly the opposite to what would be expected with surface tension driven flow. It is sensible to conclude that the flow in drying droplets containing two liquid types is dominated by gravity, or as the authors phrased it “density-driven flows in evaporating binary liquid droplets”.

dried upside down drops

The resultant coffee stains of drops that had been suspended upside down. They seem fairly similar to the upright ones with the exception of the central dot in many of the stains. The arrow shows some coffee that spilled down the surface as the tray was flipped over.

While the authors did a lovely job of watching the flows within the droplet, what happened to the the actual coffee stain? It could prompt us to do an experiment at home. How does adding alcohol affect the appearance of a coffee stain if the drop is upright compared to if you turned the drops all upside down? What happens if the droplet is not held upside down but instead at an angle to the vertical? There are many ways you could play with this result, see what happens, have a glass of wine and see if that gives you any insight into what you see with your coffee. As ever, have fun and if you do get any interesting results, please do let me know here, on twitter or over on FB.

 

*The dry scientific author in me wants to point out that although catchier, the title “how coffee stains form” does not actually capture the extent of the physics nor what the paper was about (the fact that this happens more often than just in coffee) and the given title was much better. The coffee drinker in me thinks yes, but, surely we could make it all about coffee anyway…

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

 

 

 

 

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.

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?