Category: Science history

Categories
Coffee cup science General Home experiments Observations Science history Tea

Is sixty the old forty?

Lundenwic coffee
What is the ideal temperature at which to serve coffee?

What is the optimum temperature at which to enjoy a cup of coffee?

A brief check online for the “ideal” serving temperature for coffee suggested a temperature of around 49-60ºC (120-140ºF, 313-333K) for flavour or 70-80ºC (158-176ºF, 343.1-353.1K) for a hot drink. In my own experiments (purely to write this article you understand), I found that I most enjoyed a lovely coffee from The Roasting House (prepared by V60) at around 52ºC. My old chemistry teacher must have been one who enjoyed the flavour of his coffee too. His advice for A-level practicals was that if we wanted to know what 60ºC ‘felt’ like, we should consider that it feels the same on the back of our hand as the underside of our cup of coffee. So, for argument’s sake, let’s say that we serve our coffee at the upper end of the flavour appreciation scale: 60ºC.

But, have you ever stopped to consider what 60ºC means or even, how we arrived at this particular temperature scale? Why do we measure temperature in the way that we do? While there are interesting stories behind the Fahrenheit scale, today’s post concerns the Celsius, or Centigrade, scale. Indeed, we use “degree Celsius” and “degree Centigrade” almost interchangeably to mean that temperature scale that has 0ºC as the melting point, and 100ºC as the boiling point, of water. It is one of those things that has become so habitual that setting 0ºC at the freezing end and 100ºC at the boiling end seems obvious, intuitive, natural.

thermometer in a nun mug
Careful how you drink your coffee if you repeat this experiment!

And yet the temperature scale that Anders Celsius (1701-1744) invented back in 1741 did not, initially, work this way at all¹. Celsius’s scale did indeed count from 0ºC to 100ºC and was defined using the same fixed points we use now. But rather than counting up from the melting point, Celsius’s scale counted up from 0ºC at the boiling point to 100ºC at the freezing point. Rather than degrees of warmth, Celsius’s scale counted degrees of cold. So, in the original Celsius scale, the serving temperature of coffee should be 40ºC: Sixty is indeed the old forty*.

Which immediately begs a question. Why is it that we count temperature up (the numbers get higher as it gets hotter)? A first answer could be that we view that temperature is a form of measurement of ‘heat’ and that heat is an energy. Consequently, something cold has less energy than something hot, “cold” is the absence of “heat” and therefore what we should measure is “heat”. This means that our thermometers need to indicate higher numbers as the temperature gets hotter, and so we are now counting the correct way. While this is good as far as it goes and certainly is our current understanding of ‘heat’, ‘cold’ and temperature, how is it that we have come to think of heat as energy and cold as the absence of heat? It was certainly not clear to scientists in the Renaissance period. Francis Bacon (1561-1626) considered that cold was a form of “contractive motion” while Pierre Gassendi (1592-1655) thought that although ‘caloric’ atoms were needed to explain heat, ‘frigoric’ atoms were also needed to explain cold.

effect of motivation on experience of pleasure while drinking coffee
How heat, rather than visible light, is reflected provides clues as to why we measure temperature ‘up’.

One experiment that helped to show that heat was an energy (and so lent support to the idea of measuring temperature ‘up’) was that of the reflection of heat by mirrors. In the experiment, two concave mirrors are placed facing each other, some distance apart. Each mirror has a focal length of, say, 15 cm. A hot object is placed at the focal length of the first mirror. At the focal point of the second mirror, is placed a thermometer. As soon as both objects are in place, the temperature indicated by the thermometer increases. If the mirror were covered or the thermometer moved away from the focal point, the temperature indicated decreases again to that of the room. It is an experiment which can easily be demonstrated in a lecture hall and which fitted with a view point that cold is the absence of heat.

However, around the same time as this initial demonstration, Marc-Auguste Pictet did another experiment, the (apparent) reflection of cold². The experiment was as before but in Pictet’s second experiment, a flask containing ice replaced the hot object. On repeating the experiment the temperature indicated by the thermometer decreased. Covering the mirror or moving the thermometer from the focal point of the mirror resulted in the indicated temperature increasing again. Just as ‘heat’ was reflected in the mirrors, so too (seemingly) was ‘cold’.

So, the question is, how do you know what you believe you know about heat? Are there experiments that you can design that could help to disprove a theory of ‘frigoric’? And how do you explain the experiments of Pictet? Reader, it’s over to you.

 

*Within ten years of Celsius’s death (of tuberculosis in 1744), his colleagues Martin Strömer and Daniel Ekström had inverted Celsius’s original temperature scale to the form we know today. A similar scale designed by Jean Pierre Christin was also in use by 1743³.

¹”Evolution of the Thermometer 1592-1743″, Henry Carrington Bolton, The Chemical Publishing Company, 1900

²”Inventing Temperature”, Hasok Chang, Oxford University Press, 2008

³”The science of measurement, a historical survey”, Herbert Arthur Klein, Dover Publications Inc. 1988

 

Categories
Coffee review Science history

In their Elements at Bean Reserve, Bangsar, KL

coffee in Bangsar at Bean Reserve
Bean Reserve, Bangsar, Kuala Lumpur. Note the logo on the window.

The first thing that struck me as I entered Bean Reserve in KL was the geometry. Somewhat hidden along a street behind Jalan Maarof, Bean Reserve offers a quiet space amidst the bustle of Bangsar. The 2D representation of a 3D object that is Bean Reserve’s logo is somehow mirrored in the choice of the tables and chairs that are contained in the cuboid space of this café. Triangular tables are arranged to form larger, quadrilateral tables. Circular stools nestle underneath square tables. Light streams into the café from a large window on one side of the room. The other side features a sliding door that was occasionally opened, revealing the desks of The Co, a co-working space that shares the building of Bean Reserve.

Although we only tried the drinks (an exceptionally fruity long black and a very cocoa-y iced chocolate), there looked to be an interesting selection of edibles on offer, with a bottle of chilli sauce stored behind the counter. Soy milk was available if you prefer non-dairy lattes and there were a good range of drinks on offer from nitro-cold brew to iced chocolate, just what can be needed in the heat of KL! Coffee is roasted by Bean Reserve themselves (who are both a café and a roastery), thereby providing the residents of (and visitors to) Bangsar with a seasonally varying range of great, freshly roasted coffee.

geometry at Bean Reserve
Triangular tables and circular stools.

The different geometrical features in the café immediately suggested Euclid to my thoughts. Written over 2300 years ago, Euclid’s The Elements was, for many years, the text book on geometry and mathematics. It is said that Abraham Lincoln taught himself the first 6 books of The Elements (there are 13 in total) at the age of 40 as training for his mind¹. Working from 5 postulates and a further 5 common notions, Euclid describes a series of elegant mathematical proofs, such as his proof of the Pythagoras theorem. And so, it may be appropriate that there is one more geometrical connection between the ancient Greeks and Bean Reserve: That sliding door that connects the café to the working space of The Co.

The space, occupied by The Co, behind the sliding door seems to be much larger than the café. But how much larger is it? Double the length? Double the volume? This is similar to the problem that perplexed the Delians. The idea is simple: Find the length of the side of a cube that has a volume exactly double that of a given cube. It is thought that the problem may have been formulated by the Pythagoreans, who, having succeeded in finding a method of doubling the square (see schematic), extended that idea to 3D. Could a simple geometrical method be used to double the cube? (There is of course the alternative legend about the problem having been given to the Delians by the Oracle)

A geometrical method for finding the length of a square with twice the area of a given square… now for 3D

It turns out that this is a tough problem, but one that may again have relevance for our world today. While researching this café-physics review, I came across a book by TL Heath² that had been published in 1921. In his introduction he wrote:

“The work was begun in 1913, but the bulk of it was written, as a distraction, during the first three years of the war, the hideous course of which seemed day by day to enforce the profound truth conveyed in the answer of Plato to the Delians. When they consulted him on the problem set them by the Oracle, namely that of duplicating the cube, he replied, ‘It must be supposed, not that the god specially wished this problem solved, but that he would have the Greeks desist from war and wickedness and cultivate the Muses, so that, their passions being assuaged by philosophy and mathematics, they might live in innocent and mutually helpful intercourse with one another’.“

 

 

Bean Reserve can be found at 8 Lengkok Abdullah, Bangsar, 59000 Kuala Lumpur, Malaysia

¹History of Mathematics, An Introduction, 3rd Ed. DM Burton, McGraw-Hill, 1997

²A History of Greek Mathematics, Thomas Heath, Oxford at the Clarendon Press, 1921

 

Categories
General Home experiments Observations Science history slow Tea

Reflections on physics and coffee

BeanThinking started as a way of slowing down and appreciating connections, often between a coffee and the physics of the wider world but also in terms of what can be noticed in any café. Perhaps, for this first post of 2017, it’s worth spending five minutes looking at your coffee while you drink it to see what you notice. Here are a few coffee connections that occurred to me recently:

reflections, surface tension
Reflections on a coffee.

Parallel lines and surface reflection: The parallel lines on the ceiling of a café were reflected in a long black. Surface tension effects on the coffee meant that the reflections were curved and not at all parallel. A piece of dust on the surface of the coffee was revealed in the reflection by the curved reflections of the ceiling. Astronomers can use similar effects (where images of a star appear in a different location to that expected) to infer the presence of dark objects between distant stars and their telescope. This gravitational lensing can be used to detect quasars or clusters of galaxies.

 

 

 

layering of coffee long black
Layers of coffee

Layering of crema as the coffee is consumed: The coffee stain effect and this layering of the crema suggests a connection between a coffee cup and geology. It used to be my habit to take a mug of tea with me when I taught small groups of undergraduates. In the course of one of these tutorials, a student (who had been observing similar layering in my tea mug) said, “You drink your tea faster when it is cooler than when it is hot”. Full marks for observation, but not sure what it said about his attention during my tutorials! Similar observations though can help geologists estimate the age of different fossils.

 

interference patterns on coffee
Bubbles in coffee

Bubble reflections: An old one but the interference patterns caused by bubbles on the surface of the coffee are full of fascinating physics. The fact that the bubbles are at the side of the cup and seem to be grouped into clusters of bubbles may also be connected with surface tension effects (although there is a piece of weather lore that connects the position of the bubbles to the weather. If anyone ever does any experiments to investigate this particular lore, I’d love to hear about them).

 

 

Coffee, Van Gogh
Art in a coffee cup

Van Gogh’s Starry Night: The effects of vortices and turbulence caused the crema of a black coffee to swirl into patterns reminiscent of this famous painting by Van Gogh. As a result of posting this image on Twitter, @imthursty sent me a link to this preprint of a paper submitted to the arxiv: the connections between Van Gogh’s work and turbulence. A great piece of coffee combining with art and science.

 

So many connections can be made between tea, coffee and science and the wider world, I’d love to see the connections that other people make. So, if you see some interesting physics, science or connections in your coffee cup, why not email me, or contact me via FB or Twitter.

 

Categories
Coffee cup science Coffee review Observations Science history

Water wheels and coffee engines at Artisan, East Sheen

Artisan, East Sheen LaneArtisan, on East Sheen Lane, is one café in a small chain of coffee shops in West London (four cafés at the time of writing). Although there was plenty of seating inside, most tables were already taken when I arrived shortly after lunch suggesting that this is a very popular local café. There are many details to notice in this friendly corner shop coffee house. Firstly, the counter, on the left as you enter, was decorated as if supported by a door fixed on its side, one of many quirky features. When it arrived, my black Americano came with a most fantastic crema on top which cracked to reveal the coffee beneath, appearing as if it were a meandering river. Adjacent to my table was a sliding door, presumably leading to the toilets, that had a counterweight hanging from its side, I’m sure that could have led to a series of thoughts on Greek science and Archimedes.

There was also plenty to notice on the counter itself, a sign for two tip jars suggested you either tipped in one or the other depending on whether you wanted to “see into the future” or to “change the past”. As with previous ‘honesty box’ type experiments, it would be fascinating to know which box gets more coins and whether this correlated with external events in the East Sheen area and around. Still, I digress. Also on the counter was a wheel, a bit like the wheel of the Wheel of Fortune TV show. In this café, the wheel offered different coffees or cakes rather than prizes. As the wheel is spun, it is slowed by friction acting against pins that stick out from the circumference of the wheel. When learning about angular momentum and wheels in physics we always assume the ideal of a frictionless wheel without losses. We assume that it spins forever. The wheel in Artisan was quite far from this ideal, the whole idea being that the friction eventually stops the wheel and the pin points to your ‘prize’. So how do we reconcile these two ideas of the wheel? How efficient can water wheels be? And how efficient can engines be?

counter held up by sideways door
The counter and wheel at Artisan, East Sheen

This was a question that occupied Sadi Carnot (1796-1832) (named after the Persian poet Sa’di of Shiraz). Carnot was interested in how to optimise steam engines. Although steam engines were being engineered to be increasingly efficient, Carnot realised that people still did not understand what the maximum efficiency of a steam engine could be. Carnot worked on the principle that heat was a fluid (caloric) and so steam engines could be understood analogously to water wheels. Even though we no longer have this understanding of heat, Carnot’s ideal engine is still relevant for today. He discovered that, for an ideal engine (that is an engine that works without frictional losses etc.), the maximum amount of work that you could extract from the engine depended only on the temperature difference between the maximum working temperature and ambient temperature of the engine (not on the details of the engine such as whether it used steam as its working fluid). In practise this means that a steam turbine (which operates between approximately 543 °C = 816 Kelvin and 23 ºC = 296 Kelvin) has a maximum efficiency of 64%. Were you able to design a frictionless engine made from a cup of coffee (typical drinking temperature 60 °C = 333 K), it would have a maximum efficiency of around 10%

Coffee at Artisan East Sheen
A meandering coffee river and Physics World (November 2016)

Of course, a real engine made from a cup of coffee would encounter frictional losses etc. which would reduce its efficiency. So while we may think that an efficiency of around 10% is not that bad (particularly if we’re making the coffee anyway), once we’ve allowed reality to enter into our calculations, the actual efficiency is much lower. This is probably best summarised as: The best use of coffee is in drinking it, and where better than Artisan coffee if you find yourself in East Sheen (or Putney, Stamford Brook or Ealing)?

Artisan Coffee is at 139 East Sheen Lane, SW14 8LR

 

Categories
Allergy friendly cafe with good nut knowledge Coffee review Home experiments Observations Science history

Bend it like sugar at Muni, Fulham Road

Muni Coffee, near Chelsea and Westminster hospital
Muni Coffee on Fulham Road

The area around Fulham Road and Chelsea & Westminster hospital is one that has long been fairly empty of speciality coffee establishments. Then, in June this year, Muni opened up on Fulham Road (just over 200 m from the main entrance of the hospital, in case you are visiting and looking for a good café nearby). Muni’s website emphasises its social mission, knowing the farmers they trade with by name and introducing Filipino coffee to the UK. Inside, there are plenty of tables (with more outside if you are visiting in warmer times). There is a menu on the wall behind the counter to your right as you enter, but I missed the listing of the Pandan iced tea (which would have been very interesting to try) as I was obviously not paying enough attention and instead opted for my default trying-a-new-cafe coffee, a black Americano.

My sometimes companion in these reviews had a soya hot chocolate while I was very confident to enjoy one of the (lovely) salted caramel brownies because Muni lists all the ingredients for all of their cakes on a tablet device at the counter and so I was encouraged to double-check the ingredients list to see that there was nothing vaguely nut-related in it. A very good feature and this cafe definitely gets a tick in the “cafes with good nut knowledge” category on the right (as well as the new allergy-friendly category). As mentioned, the coffee is imported directly from the farmers in the Philippines, and roasted by Muni in North London. The black Americano I tried was fruity and flavoursome, while the beans I purchased and prepared later using a V60 produced a sweet and floral brew, perhaps with blueberry notes (but with no tasting notes on the packet, I’d be interested to see if others agree with me on this, please let me know in the comments section below).

coffee cake Muni
Coffee and nut-free salted caramel brownie at Muni

On the ceiling, wooden beams had cracked and aged creating a lovely aesthetic and taking me on a thought trail that involved aeroplane engines and heat process treatments. But then I noticed something else. As it was getting dark, the cars passing by on the busy Fulham Road were mostly using their headlights and this meant that, every so often, the edges of the windows around the door changed these headlights into a spectrum of colour. Flashes of blue, red and green as each car passed. It reminded me of Newton’s experiments in which he used a prism to first separate sunlight into its various colours before recombining it with another prism into white light. An effect that led me to think about an instrument that has been advertised as a tool to creating better coffee: the coffee refractometer.

Some of the same physics links Newton’s prism with the coffee refractometer. Perhaps you remember “Snell’s law” from school. The equation describes how much deviation light experiences as it passes from one medium (air) to another medium (glass or coffee). Light travels at different speeds through different media and the refractive index can be thought of as an indicator of the degree to which each medium slows down the light.

the door at Muni
The window at the side of the door at Muni. Rainbows of colour were produced by the headlights of cars as they went by.

For the prism, the important detail is that light is composed of many colours (which means in this context, many wavelengths) and not all wavelengths are slowed to the same degree. This means that the refractive index of the glass prism is slightly different for red light than it is for blue. Consequently, the spectrum opens up as the white light travels through the prism.

For the coffee refractometer, the important point is slightly different. Water containing dissolved solids has a slightly different refractive index than pure water. Measuring the deviation of a light beam through a drop of coffee therefore gives an idea of the concentration of “total dissolved solids” and so a guide to the extraction of coffee from the grind that you have achieved. The difference in refractive index is however quite small, if the measurements here can be relied upon, while water has a refractive index of 1.333 (at 20ºC), a well extracted coffee showed a refractive index of 1.335. We can calculate how much difference this makes to the angle that the light is deflected: Assuming light enters the drop at an angle of 30º, the angle that light is refracted in water is 22.03º, while in the coffee it is 22.00º. A small effect that would be quite difficult to measure unless you had a refractometer.

However, there is an ingredient in some people’s coffee that bends light enormously: sugar (though I do hope that no one reading this uses it in the quantities needed for the experiment below). The refractive index of water is very dependent on the total concentration of dissolved sugar it contains. Therefore you can do a really cool experiment in which a sugar solution (which has more concentrated sugar at the bottom than the top) can be seen to bend the path of a laser beam. All the equipment can be easily found at home (or purchased for not too much from hardware/office equipment shops). Let me know if you try the experiment how you get along (and if you decide to try using a refractometer to enhance your coffee brewing experience). The video was shared on youtube by the Amateur Astronomical Spectroscopy group (CAOS).

Muni coffee is at 166 Fulham Road, SW10 9PR. Just around the corner on Drayton Gardens, is the blue plaque for Rosalind Franklin who used to live at an address there.

 

Categories
Coffee cup science Coffee review Observations Science history

Ripples in the Knowledge Quarter at Pattern, Kings Cross

Pattern, coffee, Kings Cross, Kings X
Pattern Coffee, Kings Cross

In 2018, the Institute of Physics will move to Kings Cross and into what is being called the “Knowledge Quarter”, an area incorporating the British Library, the newly opened Francis Crick Institute and the University of the Arts, among others. Coffee houses have, in the past, been integral to the development of knowledge, places where scientists, artists and the generally interested would meet to discuss new ideas or groundbreaking results. So what about the cafés in Kings Cross? Where will tomorrow’s scientists, artists and the generally interested meet?

Knowing that I would be in the Kings Cross area a couple of weeks ago, I looked up the Kings Cross coffee guide by doubleskinnymacchiato and decided, for not-quite-random reasons, to try Pattern on this occasion. I had been forewarned that the first thing that I would notice would be the colourful patterns on the wall. A good call, that was indeed one of the first things you notice as you walk in. Secondly though were the hat-lampshades on the bulbs over the table at the window (visible in the photo on doubleskinnymacchiato’s review). As anyone who has met me in autumn/winter may appreciate, the lampshades immediately made me feel right at home. It was fairly crowded when I arrived in the late-morning and so I shared the bench in the window with a couple of people who seemed to be discussing history/philosophy and how to write properly referenced argumentative essays. The Americano I had ordered was brought over and, slightly self-conscious to photograph it while sharing the table, I just had to enjoy and savour the well made coffee. There is, perhaps, almost too much to notice at Pattern. But something behind me caught my eye, something that connects coffee, patterns and this café: An old style dial telephone, fixed to the counter.

telephone, dial, coffee Kings X
Patterns in the cord, patterns in the telephone. An unusual feature at Pattern, Kings Cross.

Although the history of the invention of the telephone is quite controversial, the bit that reminds me of coffee is not so contentious, it is to do with how the telephone works. Let me explain.

In the gallery the “Information Age” at the Science Museum in London, it is argued that the commercial success of the telephone was driven by the invention of the carbon microphone, simultaneously invented by David Hughes (1831-1900) and Thomas Edison (1847-1931). It is the Edison version that prompts me to think of espresso. Edison’s microphone worked by packing a cylinder of carbon granules between two metal plates. In my mind I think of Edison’s carbon microphone as similar to a perfectly tamped coffee block in a filter basket. In the microphone, one plate was fixed, the other was flexible and acted as a diaphragm. When somebody spoke into the microphone, the diaphragm would vibrate causing the carbon granules to move alternatively closer together and further apart. Carbon conducts electricity and so the resistance of the microphone changed if the carbon granules were closer together or further apart. The sound waves impacting on the diaphragm were being perfectly translated to electric current patterns that could be transmitted through the telephone lines. The packing of the carbon granules would need to be optimum to transmit the sound, just as the pressure used to press the espresso tablet needs to be just right, enough contact between coffee grains to prevent the water flowing straight through without producing a good coffee, but not so much that the water cannot percolate through the coffee tablet and what should be a lovely espresso becomes over extracted. The ground coffee pressed into the filter basket at Pattern must have fitted this optimum density very well. A well poured espresso revealing that they had achieved that optimum balance between compression and space in the espresso tablet. Good coffee, interesting physics, I’m sure the Institute of Physics will be pleased when it eventually moves to its new home with such great coffee neighbours.

IoP poster in Kings Cross
Physics is everywhere! (But coming to Kings Cross)

Although slightly off topic, a cafe-review considering telephones would not be complete without including the story about Erasmus Darwin, the Devil and his “speaking machine”. Erasmus Darwin (1731-1802) was a fairly portly man who worked hard. So it was inconvenient for him to have to go from his study to the kitchen when he wanted something to eat. Being a bit of an inventor, he installed a speaking tube in his home that connected his study to his kitchen. Desmond King-Hele in “Erasmus Darwin, A life of unequalled achievement”* described what happened next:

“One day a local yokel who had arrived with a message for Darwin, was left alone in the kitchen. He was terrified when a sepulchral and authoritative voice from nowhere demanded ‘I want some coals’. Such a request could only come from the Devil, he thought, wishing to stoke up hell’s fires. The man fled and would not come near the house again.”

The poor local may have been bewildered by the number of telephones and ‘voices from nowhere’ that surround us now. If you’re reading this in a café, why not look around you, notice some strange connection (the very lateral ones can be particularly fun to ponder), and then let me know what you have seen. It’s always interesting to hear the science, history and connections that people notice as they sit in cafés around.

Pattern Coffee is at 82 Caledonian Road, N1 9DN

*Desmond King-Hele, “Erasmus Darwin, A life of unequalled achievement” was published by Giles de la Mare Publishers, 1999.

Categories
Coffee review General Observations Science history slow

Science & Religion at Rag & Bone Coffee, Westminster

Rag&Bone, Rag & bone, coffee Victoria, coffee Westminster
Rag & Bone Coffee in front of St Matthew’s Church.

Can a coffee cart provide the time and space for reflection and enjoyment of a coffee just as a sit-down cafe can? In seeking an answer to this question (as well as on a quest to find more great coffee in the Victoria/Westminster area), I turned up at Rag & Bone coffee on Great Peter St. It was quiet when I arrived in the courtyard of St Matthew’s Church, and the barista took time to make me a lovely, fruity and full bodied Americano (with beans roasted by Old Spike Roastery). Obviously, there is no seating around the bar but, the church behind the cart is open everyday and offers a rare quiet spot in Victoria to sit and reflect, should you want to do so, before you buy your coffee of course! Sadly, as this is a cart and not a sit-down cafe, the cups provided are disposable, but there is nothing to stop you taking your keep-cup along in order to enjoy your coffee. Just behind the cart, a crucifix above the door of the church caught my eye. And that got me thinking about something, perhaps slightly tangential to the ordinary cafe-physics reviews of Bean Thinking, why do some people imagine there is a conflict between religion and science?

I could see how there could be a disagreement if a religion took an overly literal interpretation of a text (as can happen with disputes over evolution). Or if someone used science as an argument against ‘belief’ while failing to appreciate that science too is based on belief (albeit beliefs that we are most likely just to assume as facts without questioning: particularly that our world exists and that it can be understood). But outside those extremes, and if we look at the motivations of both religion and science, it is surely that both religion and science aim to discover or value truth. If both sincerely follow that aim there can be no real conflict, for truth cannot contradict itself.

Earth from space, South America, coffee
One planet. One home.
The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler

Instead the investigations of one can inform the other and help both to advance our understanding of the world. Take for example the urgent issue of climate change. Scientists, using science as a tool, can investigate and highlight areas of concern for our planet (increasing CO2 levels, rising sea temperatures, a probable increase in extreme weather events, etc) but strictly speaking, as a tool it can go no further. If a scientist then urges us to do something to mitigate climate change, they are not speaking as a ‘scientist’ but as a human being; a human being who is informed by ethical concerns. It would be perfectly logical for someone to recognise that climate change is happening while holding that there is no obligation on our current generation to do anything about it. We may find such an opinion objectionable but that is the crux of it, we have introduced values to the discussion in the form of ‘right and wrong’ and ‘good’. We have moved beyond the remit of science. Religions have had millennia to consider the human condition and what constitutes ‘good’ or ‘right’. For us to combat climate change we need not just the evidence that it is happening, but an idea of a better, or more ‘just’ world. Ethical systems are of course possible without religion, but discussion informed by religious concern can help to change ‘concern for our planet’ into the concern for and protection of ‘our common home‘.

Artemisworks photography, rosary and keyboard
Prayer beads on a keyboard.

Then there is a link between religion and science that brings us right back to Rag & Bone Coffee and St Matthew’s church yard. When St Matthew’s was built back in 1849, the area surrounding it was squalid, conditions were so bad, the area towards Victoria St. was known as the “Devil’s Acre“. The Dean of Westminster, and the new vicar of St Matthew’s recognised that, to help people out of poverty, drastic steps would need to be taken and one of these was to improve education. The Dean of Westminster died soon after St Matthew’s was built but his wife, Mary Buckland, who was also a palaeontologist, wanted to continue his work with the poor. In order to improve the conditions for those living in the slums in the Westminster area, “Mrs Buckland” established a coffee house on Old Pye St, that was cared for by the Revd. Richard Malone, vicar of St Matthew’s. The coffee house was a place where lectures were given and a library was set up. The church and people in the scientific world, worked together to help the poor of the area positively change their living conditions.

The coffee house eventually had to close but, perhaps it could be said that, in a sense, the presence of Rag & Bone coffee in the courtyard of St Matthew’s, continues this work. Although times have changed, and the area is no longer a slum, there is a different form of poverty, people who are time-poor and harassed, working in the offices that now surround the church. In this sense, Rag & Bone Coffee offers not just refreshment, but a brief time-out from the daily grind for the people who now pass by this space. As making coffee is both an art and a science, perhaps we can also say that here too, science and religion work together, with coffee, to make the world a better place.

Rag & Bone Coffee can be found in the courtyard of St Matthew’s Church, Great Peter St. SW1P 2BU.

 

Categories
General Home experiments Observations Science history Tea

Coffee and Pluto

Three billion miles away, on an object formerly known as the planet Pluto (now sadly demoted to the dwarf planet Pluto), there exists a plain of polygonal cells 10-40 km across, extending over a region of about 1200 km diameter. Last year, the New Horizons mission photographed this region and these strange shapes (see photo) as the probe flew past Pluto and its moon Charon. But what could have caused them, and perhaps more importantly for this website, can we see the same thing closer to home and specifically in a cup of coffee? Well, the answer to those questions are yes and probably, so what on Earth is happening on Pluto?

Plutonian polygons
What is causing these strange polygons on the surface of Pluto. Image © NASA

Pluto moves in an highly elliptical orbit with an average distance to the Sun of 5.9 billion km (3.7 billion miles). Each Pluto year is 248 Earth years but one day on Pluto is only 6½ Earth days. As it is so far from the Sun, it is very cold on Pluto’s surface, somewhere between -238 to -218 ºC. The polygons that were photographed by New Horizons are in the ‘Sputnik Planum’ basin where the temperatures are at the lower end of that scale, somewhere around -238 ºC. At this temperature, nitrogen gas (which makes up 78% of the Earth’s own atmosphere) has not just liquified, it has solidified; turned into nitrogen ice. These polygons are made of solid nitrogen.

But solid nitrogen is a very odd type of solid and in fact, at the temperatures on Pluto’s surface, solid nitrogen is expected to flow with a very high viscosity (like an extremely gloopy liquid). And it is this fact that is the clue to the origin of the odd polygons (and the link to fluids like coffee). Pluto is not just a cold dead rock circling the Sun, but instead it has a warm interior, heated by the radioactive decay of elements in the rocks making up Pluto. This means that the base of the nitrogen ice in the Sputnik Planum basin is being heated and, as two groups writing earlier this summer in Nature showed, this leads to the nitrogen ice in the basin forming convection currents. The warmer nitrogen ‘ice’ at the bottom of the basin flows towards the surface forming convection patterns. It is these nitrogen convection cells that appear as the polygons on the surface of Pluto.

Rayleigh Benard cells in clouds
Rayleigh-Benard cells in cloud structures above the Pacific showing both closed and open cell structures. Image © NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

Of course, convection occurs in coffee too, we can see it when we add milk to the coffee and watch the patterns form or by observing the dancing caustics in a cup of tea. So why is it that we see stable polygons of nitrogen on the surface of Pluto but not coffee polygons on the surface of our coffee? The first point to note is the time-scale. Although the polygons on Pluto are moving, they are doing so much more slowly than the liquid movement in a cup of tea or coffee, at a rate of only a few cm per year. But secondly, the type of convection may be different. Although both of the papers in Nature attributed the polygons on Pluto to convection, they differed in the type of convection that they considered was happening. McKinnon et al., suggest that the viscosity of the nitrogen on Pluto is much greater on the surface of the basin than in the warmer interior and so the surface flows far more slowly. This leads to cells that are much wider than they are deep. We would not expect such a drastic change in the viscosity of the coffee between the (cool) top and (warm) bottom of the cup! In contrast, Trowbridge et al., think that the cells are Rayleigh-Bénard convection cells,  circular convection cells that form such that the cells are as wide as they are deep. This sort of convection is seen in a coffee cup as well as in the sky on cloudy days: On the Earth, clouds often form at the top (or bottom) of Rayleigh-Benard cells, where hot humid air meets cold dry air (more info here). But to form cells that you can see in your coffee (such as are on the surface of Pluto) you would need the coffee to be in a fairly thin layer and heated from below. You would also need some way of visualising the cells, either with an infra-red camera or with powder suspended in the liquid, it would be hard I think to see it in coffee alone. However, you can see these cells in cooking oil as this video shows:

As well as providing the link to the coffee, the different types of convection on the surface of Pluto hypothesised by Trowbridge and McKinnon have consequences for our understanding of the geology of Pluto. If the cells are formed through Rayleigh-Bénard convection (Trowbridge), the basin has to be as deep as the cells are wide (meaning the basin has to be 10-40km deep with nitrogen ice). If McKinnon is correct on the other hand, the basin only needs to be 3-6 km deep. It is easy to imagine that an impact crater could cause a shallow crater such as that needed for McKinnon’s mechanism. A deeper crater would create another puzzle.

If you do manage to heat coffee (or tea) from below and form some lovely Rayleigh-Bénard cells while doing so I’d love to see the photos or video. Please do contact me either by email, Facebook or Twitter. Otherwise, if you just enjoy watching the patterns form on your coffee, it’s worth remembering that there could be an entire cosmos in that cup.

Categories
cafe with good nut knowledge Coffee review Observations Science history Sustainability/environmental

Counting the caloric at Jaz & Jul’s Chocolate House, Chapel Market

Jaz Jules chocolate house
Jaz and Jul’s, The Chocolate House on Chapel Market

The London coffee houses of the seventeenth and eighteenth centuries have entered history as Penny Universities, places of debate and centres of news. Together with the (scientifically based) Grecian, there was Jonathan’s in Exchange Alley (origin of the stock exchange) and Lloyd’s on Tower Street (associated with insurance). But along side these coffee houses there were the chocolate houses, Whites and Ozinda’s on St James’ St and the Cocoa Tree in Pall Mall. White’s in particular developed such a reputation that it features in Hogarth’s The Rake’s Progress (which can be seen at Sir John Soane’s museum).

So it is an interesting bit of history repeating to find Jaz & Jul’s, a chocolate house on Chapel Market. The interior here is very far from Hogarth’s rendering of White’s. Here, light fittings hang from the ceiling like drops of chocolate about to melt into the café while photographs of cocoa plants and farms adorn the walls. Moreover the emphasis on social responsibility, including in sourcing, mean that this establishment is worlds away from the debauched shenanigans at White’s. Their coffee is roasted and supplied by Monmouth while the cakes are hand made and, needless to say, very chocolatey. The light and fluffy chocolate-Pimms cake arrived with my coffee presented on a plate and matching cup that reminded me of a mint-chocolate-chip ice cream.

Interior of Jaz and Jules Chapel Market
The chocolate counter at Jaz and Jul’s

The side of the counter was tiled to resemble a bar of chocolate, which immediately reminded me of the physics and chemistry of chocolate crystallisation. However, the physics connection of this cafe-physics review is a bit more lateral than that. Soon after I had enjoyed my incredibly chocolatey cake at Jaz & Jul’s, a study was released which showed that Britons were significantly under-reporting their daily calorie intake. Could it be that the obesity epidemic is a result of us eating too much rather than merely exercising too little? Apparently, rather than consume the (recommended) levels of 2500 kcal for men and 2000 kcal for women, many people were eating up to 3000 calories per day. Everything in moderation of course and there was plenty of room in my own calorie count for that great piece of cake (honestly). But the word ‘calorie’ turns out to have a connection with chocolate in a more unexpected way.

Calorie comes from the Latin, calor, meaning heat which in turn hints at how we used to think about heat itself. While we now think of heat as energy, which is why it doesn’t even strike us to equate the ‘energy’ in the chocolate cake with the number of kilo-calories in it, this is not how heat was always viewed. In fact, in the eighteenth century, about the time of the old chocolate houses, heat was thought of as a type of fluid, caloric. Caloric was thought to be able to flow in and out of all substances. When something got hot it was because the caloric flowed into it, when something got cold, it was because the caloric had leaked out. Caloric theory was in many ways very successful in understanding heat and heat processes. For example, the theory easily explained thermal expansion, if a fluid had to flow into something in order for that thing to warm up, then surely, the fluid has to occupy some space, the object must expand to hold it!

Mint choc chip cutlery
Coffee with the Chocolate-Pimms cake.

One area that was tricky for caloric theory though was the fact that friction could cause something to heat up. Such heat generation is crucial for our extraction of chocolate. Once harvested from the plant and cleaned, the cocoa bean is first roasted then shelled to leave the cocoa ‘nibs’. These nibs are then ground more finely. As they are being ground, the friction caused by grinding is enough to cause sufficient heat to melt the cocoa butter in the nibs which is then extracted and retained for later use*. How could you explain this heating if you thought of heat as a fluid? The traditional explanation was that as the two objects rubbed against each other (in this case, nib and stone grinder), the caloric fluid would be squeezed out, it would appear as if heat had been generated.

Benjamin Thompson, Count Rumford (1753-1814), disagreed with this explanation of heat. In the course of a colourful career he had been involved in manufacturing cannons in Bavaria. Rumford had noticed that a lot of heat was generated each time a cannon shaft was bored out. The heat produced continued as long as the grinding continued. If the heat were due to the cannon leaking caloric, surely there would be a point at which the cannon stopped getting any hotter. Yet this did not happen. Rumford suggested (correctly) that instead what was happening was that the energy generated by the boring was being transferred into the metal of the cannon, causing microscopic motion.

Although the heat as motion/energy idea eventually caught on, caloric in some ways still survives in the name that we give to our food energy intake. And so we can return to the cake, could it be that spending time thinking about the caloric in the cake can justify the calories consumed eating it? Sadly the jury is out on whether thinking counts as calorie counting exercise. It seems that the brain’s energy consumption is already so great (at 20% of our resting metabolic rate), that intense thinking does not add too much to the energy consumed by the brain. So we’ll need another excuse and I don’t think we have to look far. The coffee and chocolate at Jaz & Jul’s is delicious enough to justify a significant chunk of your daily calorie count, just based on considerations of taste. Everything in moderation!

 

Jaz and Jul’s is at 1 Chapel Market, N1 9EZ

*”Chocolate: A Global History”, by Sarah Moss and Alexander Badenoch, published by Reaktion Books, 2009

 

Categories
General Science history

Super cold brew

Cold brew coffee with ice
Cold brew coffee served with ice. Image from pixabay.com

How cold do you drink your cold brew? Poured over ice? As an experimental physicist who works with liquid nitrogen (& helium), I was initially quite intrigued to learn of nitro cold brew coffee. Could it be coffee that somehow uses liquid nitrogen to fast-cool it, what would that do to the taste? You would expect liquid nitrogen (at -196ºC) to rapidly cool the coffee below its freezing point, after all, it is how Heston Blumenthal makes ice cream. To make a drink-able cold-brew with liquid nitrogen would require great skill, especially given the potential health risks. It would be another situation where you may well ask yourself, “what’s the point?”

However, it turned out that the reality was far more mundane, gaseous nitrogen is passed through cold brew coffee to create a drink with a silky mouthfeel. A smooth drink that comes straight from the tap just like stout. Such a drink is going to behave as an ordinary liquid and chilled only to the point that it is kept in the vat. The novelty would presumably come from the mouthfeel introduced by the many tiny bubbles distributed through the drink. Just as with water, if you cooled the nitro-brew below its freezing point it would solidify and form coffee cubes. No real difference to get excited about. But what if there was a very different sort of liquid, a “super liquid”, that didn’t behave like water, coffee or even liquid nitrogen but one that could leak through solid cups?

Superfluid helium is such a liquid. Like water, oil or even liquid nitrogen, when you cool helium (the same gas that is in party balloons)∗, it becomes an ordinary (but very cold) liquid at -269ºC. But unlike those liquids, when you cool it further, below -271ºC, it does something very odd indeed. It becomes a superfluid in which the liquid moves with zero friction or equivalently, zero viscosity (honey is very viscous, water is very much less so).  And it is because of these properties that it can do some astonishing things such as stream through cracks in containers that were thought impermeable (see the video at 0:52m), or even climb the walls of the container it is in (1:13m)!

 

To explain the behaviour of superfluid helium it is necessary to use quantum mechanics. Indeed, Fritz London (1900-1954) is said to have described both superfluidity and superconductivity (which happens in solids) as “quantum mechanisms on a macroscopic scale”. At the heart of the theory of superfluidity is the idea that the helium atoms fall into the lowest energy ground state possible, a Bose-Einstein condensate. To form a Bose-Einstein condensate, the particles (atoms of helium) have to  be bosons rather than fermions. All particles in nature can be categorised as either bosons or fermions. The difference between the two types comes from another quantum property of particles, the spin. Spin is related to the angular momentum of the particles and, this being quantum mechanics, can take only discrete values, either whole number or half integer numbers.

cold brew, doublemacbex
Another photo of cold brew coffee, this time from Bex Walton (flickr) – note the condensation around the rim, much could be said about that. Image CC licensed.

Bosons are particles with integer values for spin, fermions are particles with half integer values. Most of the elementary particles you will have heard of are fermions: electrons, protons, neutrons, they’re all fermions. Some particles however, such as the photon (the particle of light) are bosons. Helium 4 atoms are effectively composite bosons, because of the combination of 2 protons, 2 neutrons and 2 electrons that make up the atom. When you add their individual (half-integer) spins, you will get an integer spin, hence a boson not a fermion. The distinction is important because while bosons can share a lowest energy state (the Bose-Einstein condensate), fermions cannot. Quantum mechanically, no two identical fermions can share an energy level (the Pauli exclusion principle), so you can never get to a state where all the fermions are in the lowest energy state. There are practical, every day consequences of this for us, such as the way metals such as copper conduct electricity and heat, the fact that the electrons in the metal are fermions turns out to be crucial for us to understand how metals ‘work’. In contrast, the fact that the helium atoms are in the lowest energy state in super-fluid helium means that the ‘liquid’ behaves very strangely indeed.

We seem to have come a long way from the idea of a cold coffee. But perhaps next time, if someone offers you a “super cold brew” take a moment to think of the physicists who get to play with some real super cold superfluids†. Hope you enjoy the video.

 

*Technically it is Helium 4 that becomes superfluid at 2.2 K (-271ºC). The rarer isotope, Helium 3, does not become superfluid until much lower temperatures and even then, the superfluidity has some very special properties.

†Although I do get to work with liquid helium (and although it is mostly helium 4), I work at the relatively ‘hot’ temperatures at about -269C. At this temperature the interest is not so much in the liquid helium itself but its use as a coolant for other materials.