Categories
Coffee cup science General Home experiments Observations slow

Coffee ring bacteria

coffee ring, ink jet printing, organic electronics
Why does it form a ring?

We have all seen them: Dried patches of coffee where you have spilled some of your precious brew. The edge of the dried drop is characteristically darker than the middle. It is as if the coffee in the drop has migrated to the edge and deposited into a ‘ring’. It turns out though that these coffee rings are not just an indication that you really ought to be cleaning up a bit more often. Coffee rings have huge consequences for the world we live in, particularly for consumer electronics. Various medical and diagnostic tests too need to account for coffee ring effects in order to be accurate. Indeed, coffee rings turn up everywhere and not just in coffee. Moreover, the physics behind coffee rings provides a surprising connection between coffee and the mathematics of bacteria growth. To find out why, we need to quickly recap how coffee rings form the way they do.

When you spill some coffee on a table it forms into droplets. Small bits of dust or dirt or even microscopic cracks on the table surface then hold the drop in the position. We’d say that the drop is pinned in position.

artemisdraws, evaporating droplet
As the water molecules leave the droplet, they are more likely to escape if they are at the edge than if they are at the top. Illustration by artemisdraws.com

As the drop dries, the water evaporates from the droplet. The shape of the drop means that the water evaporates faster from the edges of the drop than from the top (for the reasons for this click here). But the drop is stuck (pinned) in position and so cannot shrink but instead has to get flatter as it dries. As the drop gets squashed, water flows from the centre of the drop to the edges. The water flow takes the coffee particles with it and so carries them to the edge of the drop where they deposit and form into a ring; the coffee ring. You can see more of how coffee rings form in the sequence of cartoons below and also here.

However in this quick explanation, we implicitly assumed that the coffee particles are more or less spherical, which turns out to be a good assumption for coffee. The link with the bacteria comes with a slightly different type of ‘coffee’ ring. What would happen if we replaced the spherical drops of coffee particles with elliptical or egg shaped particles? Would this make any difference to the shape of the coffee rings?

Artemisdraws
As water evaporates from A, the drop gets flatter. Consequently, the coffee flows from A to B forming a ring. Illustration by artemisdraws.com

In fact the difference is crucial. If the “coffee” particles were not spherical but were more elliptical, the coffee ring does not form. Instead, the elliptical particles produce a fairly uniform stain (you can see a video of drying drops here, yes someone really did video it). The reason this happens is in part due to a pretty cool trick of surface tension. Have you ever noticed how something floating on your coffee deforms the water surface around it? The elliptical particles do the same thing to the droplet as they flow towards the edge. (Indeed, the effect is related to what is known as the Cheerios effect). This deformation means that, rather than form a ring, the elliptical particles get stuck before reaching the edge and so produce a far more uniform ‘coffee’ stain when the water dries.

E Coli on a petri dish
A growing E. Coli culture. Image courtesy of @laurencebu

By videoing many drying droplets (containing either spherical or elliptical particles), a team in the US found that they could describe drying drops containing elliptical particles with a mathematical equation called the Kardar-Parisi-Zhang equation (or KPZ for short). The KPZ equation is used to describe growth process such as how a cigarette paper burns or a liquid crystal grows. It also describes the growth of bacterial colonies. Varying the shape of the elliptical particles in the drying drop allows scientists to test the KPZ equation in a controllable way. Until the team in the US started to ask questions about how the coffee ring formed, it was very difficult to test the KPZ equation by varying parameters in it controllably. Changing the shape of the particles in a drying drop gives us a guide to understanding the mathematics that helps to describe how bacterial colonies grow. And that is a connection between coffee and bacteria that I do not mind.

As ever, please leave any comments in the comments section below. If you have an idea for a connection between coffee and an area of science that you think should be included on the Daily Grind, or if you have a cafe that you think deserves a cafe-physics review, please let me know here.

Categories
cafe with good nut knowledge Coffee review General Observations Science history slow

Coffee as an art at Briki, Exmouth Market

exterior of Briki coffee London
Briki London on the corner of Exmouth Market

Traditionally made coffee always appeals to my sense of coffee history. Coffee made its way out of Ethiopea via Turkey and the method of brewing the finely ground coffee in a ‘cezve’ or ‘briki’ is one that goes back a long way. It’s therefore always interesting when a new cafe arrives on the scene that offers “Greek” or “Turkish” coffee on its menu. Briki, in Exmouth Market, opened in May last year and so it was only going to be a matter of time before I visited to try it out. Aesthetically Briki appealed to me as soon as I walked through the door. Spacious and with the bar along one wall, there are plenty of seats available at which to slowly enjoy your coffee. The cafe itself is almost triangular and the other two walls have windows running all along them. What better way to sit and enjoy the moment (and your coffee) than to gaze out a window? Still, given that I had gone to a cafe called ‘Briki’ and that it advertised “Briki coffee” on the menu behind the bar, it was obvious that I had to try the briki coffee. The coffee was rich, flavoursome and distinctive, well worth the time taken to savour it. There was also an impressive selection of food behind the counter and the dreaded “does it contain nuts” question was met with a friendly check of the ‘allergen’ folder. I was therefore able to also enjoy the lovely (nut free) chocolate cake. Briki definitely gets a tick in the “cafes with good nut knowledge” box on my categories list.

image from British Museum website
Folio 109b from an album of paintings showing Turkish sultans and court officials. Kahveci. A youth who serves coffee. He is holding a cup in each hand, circa 1620.
© The Trustees of the British Museum

However as I realised later, the coffee was not brewed in the traditional way but in a Beko coffee maker – a coffee maker specifically designed for optimising the brewing of Turkish coffee. The idea of the Beko is that it carefully controls and automates the entire brewing process so that you get a perfect coffee each time. But just how do you make a ‘perfect’ Turkish coffee?

A quick duckduckgo (it’s a mystery to me why has this verb failed to catch on while ‘to google’ is used so frequently) revealed two sets of instructions on how to make Turkish coffee. The first set, (including some otherwise very good coffee brewing websites) suggested ‘boiling’ the coffee repeatedly in the pot (cezve/briki). The second set, which seemed to be more specifically interested in Turkish coffee (as opposed to interested in coffee generally), were much more careful, even to the point of writing, in a very unsubtle way, “NEVER LET IT BOIL“. According to this second set of websites, the coffee in the cezve should be heated until it starts to froth, a process that begins at around 70C, far below the 100C that would be needed to boil it. Warming the cezve to 70C produces these bubbles and the lovely rich taste of the traditionally made coffee. Heating it to boiling point on the other hand destroys the aromatics* that form part of the flavour experience of coffee and therefore makes a terrible cup of coffee.

The contrasting instructions however led me to recall a discussion in Hasok Chang’s Inventing Temperature. Perhaps we all remember from school being taught how thermometers need two fixed points to calibrate the temperature scale and that these two fixed points were the boiling point and the freezing point of water. Perhaps this troubled you at the time: Just as with making coffee in a cezve, just how many bubbles do you need in order to say that the coffee (or water) is ‘boiling’? How were you supposed to define boiling? How much did it matter?

Cezve, ibrik, Turkish Coffee Creative Commons license
Cezve, image © http://www.turkishcoffee.us

It turns out that these questions were not trivial. There is a thermometer in the science museum (in London) on which two boiling points of water are marked. The thermometer, designed by the instrument maker George Adams the Elder (1709 – 1773) marked a lower boiling point (where water begins to boil) and an upper boiling point (where the water boils vigorously). The two points differed by approximately 4C.  So how is it that we now all ‘know’ that water boils at 100C? And what was wrong with Adams’ thermometer? The Royal Society set up a committee to investigate the variability of the reported boiling point of water in 1776. Careful control of the heating conditions and water containers reduced the temperature difference observed between different amounts of boiling. However, as they experimented with very pure water in very clean containers they found that things just became more complicated. Water could be heated to 120C or even higher without ‘boiling’. They had, unintentionally, started investigating the phenomenon that we now know as ‘superheating‘. Superheating occurs when water is heated to a temperature far above its boiling point without actually boiling. What we recognise as boiling is the escape of gas (which is usually a mix of air and water vapour) from the body of the water to its surface. In order to escape like this, these bubbles have to form somehow. Small bubbles of dissolved air pre-existing in the water or micro-cracks in the walls of the container enable the water to evaporate and form steam. These bubbles of gas can then grow and the water ‘boils’. If you were to try to calibrate a thermometer using very pure water in very clean containers, it is highly likely that the water would superheat before it ‘boiled’, there just aren’t the ‘nucleation’ sites in the water to allow boiling to start. The Royal Society’s committee therefore came up with some recommendations on how to calibrate thermometers in conditions that avoided superheating which meant thermometers were subsequently calibrated more accurately and superheating (and improved calibration points) could be investigated more thoroughly.

Perhaps viewed in this way there are even more parallels between Turkish coffee and physics. It has been written that “making Turkish coffee is an art form“. It is a process of practising, questioning and practising again. The Beko coffee machine automates part of the process of making Turkish coffee. When it’s done well though, Turkish coffee is far more than just the temperature control and the mechanics of heating it. There is the process of assembling the ingredients, the time spent enjoying the coffee and the atmosphere created by the cafe in which you drink it. Coffee as art in Briki is something that I would willingly spend much more time contemplating.

 

Briki is at 67 Exmouth Market, EC1R 4QL

“Inventing Temperature”, by Hasok Chang, Oxford University Press, 2004

*Although these aromatics are part of what gives coffee such a pleasurable taste, they decay very rapidly even in coffee that is left to stand for a while, it is this loss of the aromatics that is part of the reason that microwaving your coffee is a bad idea. A second reason involves the superheating effect, but perhaps more on that another day.

 

Categories
General Home experiments Observations Science history Tea

Caustic Coffee

A post that applies equally to tea, just swap the word “tea” for “coffee” throughout!

A cusp caustic in an empty mug of coffee
Have you seen this line?

Look deep into your coffee. Do you see the secrets of the cosmos being revealed? Well, neither do I usually but there is something in your coffee that could be said to have ‘cosmic implications’ and I’m sure it’s something that you’ve seen hundreds of times.

Now, admittedly it is easier to see this effect if you put milk in your coffee. Imagine drinking your (milky) coffee with a strong light source (the Sun, a lightbulb) behind you. You see that curved line of light that meets in a cusp near the centre of the cup? You can see various photos of it on this page. Yes, it is indeed the reflection of the light from the curved mug surface but it is far from just that. It is what prompted a professor at Duke University to say “It’s amazing how what we can see in a coffee cup extends into a mathematical theorem with effects in the cosmos.” To understand why, perhaps it is worth reflecting a bit more on our coffee.

The shape of the curve is called a ‘cusp’  and the bright edge is known as a ‘caustic’. It is fairly easy to play with the angle of the cup and the light so that you can see the first cusp curve but you can go further and create caustics that are the result of multiple reflections. Such multiple reflections can give heart shaped curves or “cardioids” so, in a certain sense adding milk to your coffee is good for (seeing) the heart.

caustic in a cup of tea or coffee
A cusp reflection is just visible in a cup of (soya) milk tea

Caustics were first investigated by Huygens and Tschirnhaus in the late 17th century. Mathematically, the cusp curve is termed an epicycloid, you can draw one by tracing the shape made by a point on the circumference of a circle rotating around a second circle, as this graphic from Wolfram mathematics demonstrates. There is a lot of maths in milky coffee. But just how is it that these curves reveal the “Cosmos in a cup of coffee“? It turns out that once you start to see caustics you start to see them everywhere. Caustics are not just going to be formed on the inside of your coffee mug, they can be formed by light waves getting bent by ripples on the surface of a stream or even by gravity, in a phenomenon known as “gravitational lensing”.  Gravitational lensing is when a massive object, such as a black hole or a galaxy, bends the light travelling past it so that it acts analogously to a lens in optics (but a very big one). It is this last type of caustic that prompted the headline quoted above. In a series of papers published in the Journal of Mathematical Physics, Arlie Petters of Duke University and coworkers calculated how light from distant objects was focussed through gravitational lensing and the effects of caustics. Their predictions (and in particular any exceptions to their predictions) could lead to a new way to search for the elusive dark matter, which is thought to contribute to much of the Universe’s mass. They are now waiting for the Large Synoptic Survey Telescope (LSST) to start mapping the sky in order to test their theories.

multiple caustics from multiple LEDs
Multiple light sources are being reflected in this cup.

Before concluding this discussion of cosmic coffee, it is worth taking another look at the mathematician Tschirnhaus. As well as maths, he was known for his philosophy and his chemistry. In fact, it seems that he was responsible for the invention of European porcelain. As noted elsewhere, it has been argued that it was the ability of Europeans to start making their own porcelain that explained the rapid rise in consumption of tea and coffee during the eighteenth century in Europe. Interestingly, one of the tools that allowed Tschirnhaus to succeed in manufacturing porcelain in Dresden where others elsewhere failed was his use of “burning mirrors” to focus the heat and to achieve higher furnace temperatures than were otherwise available. He was using those caustics that he and others had so thoroughly studied mathematically in order to produce the type of cup in which we most often encounter the easiest caustics. A lovely little ‘elliptical’ story on which to end this Daily Grind.

In order to see the caustics in your coffee, it is necessary that the coffee reflects the light incident on it. Meaning, you need to add milk to your coffee. I knew there had to be a good reason to add milk to coffee at some point. Please do share your photos of caustics in your coffee either here or on Facebook or Twitter.

 

 

Categories
Coffee review Observations Science history

Planet Earth is blue (or is it) at Ground Control, Clerkenwell

Ground Control, outside the cafe
Ground Control on Amwell St

Ground Control is a small little cafe on Amwell St. If you are in the Angel/Clerkenwell area it is well worth stopping by this interesting cafe which serves a variety of Ethiopian coffees. Of course they offer the normal espresso, Americano etc. type drinks but if you want to sample their coffee properly, I think it best to try one of their coffees prepared with a V60. Tasting notes are shown on the menu on the wall. Being fairly small, there aren’t that many tables, however if you are lucky enough to get one of the two tables at the window, you will find plenty around you to look at without resorting to checking your phone while you enjoy your coffee. Behind one of the tables at the window is a set of shelves with coffee beans (presumably for sale). Behind the other table is a picture of a lady holding a jug and a basket. Vibrantly coloured circular patterns form the backdrop behind her.

coffee mosaic, colour perception
The coffee mosaic at Ground Control

The picture (shown on the left) has a flow to it, you are almost drawn into the movement of the picture. This movement comes from the many, differently coloured, coffee beans that have been used to make the picture. Each bean is orientated slightly differently so that the lines through the bean flow with the picture, rather than the beans being mere individual pieces of a mosaic. The circular patterns, the lines of her shirt, all of these are produced by orientating coffee beans this way or that. The mosaic is also richly colourful. Many of the colours stand out, but some, arranged next to each other, appear more subdued. How do we see the colours of a picture? How much of our colour perception is due to the pigment of the paint, how much due to the lighting, and how much is due to the individual colouration of the neighbouring beans?

An artist known for his unusual use of colour was Georges Seurat (1859-1891). Seurat developed the technique of pointillism in which small dots of varying colours are painted next to each other. Viewed from a distance, the colour seen by the viewer may be quite different from the multitude of differently coloured dots perceived close up. As with the coffee bean mosaic, direction was given to Seurat’s work through the orientation of the painted dots. Seurat had based his technique on the state-of-the-art science of the day. One of the scientists whose work on colour theory influenced Seurat’s artistic development was Ogden N. Rood, a physicist who’s 1879 book “Modern Chromatics” he seems to have read (in its French translation)*. Rood had carefully distinguished between two types of colour mixing, that of mixing coloured lights and that of mixing pigments. Mixing pigments had been used by all of the old masters. It is the process by which paints are mixed to produce a new paint colour. Rood however showed that if small dots of colour were painted adjacently, when the painting is viewed from a distance such that the eye cannot distinguish the two dots individually but rather mixes them in the eye, the colour produced is that of mixing coloured lights, not coloured pigments. As he explained, colour mixing through adding light of different colours was an additive process, colour mixing through combining pigments was subtractive. More about colour theory and colour mixing can be found here.

Pointillism Seurat
Georges Seurat, 1859 – 1891
The Channel of Gravelines, Grand Fort-Philippe
1890, Oil on canvas, 65 x 81 cm, Bought with the aid of a grant from the Heritage Lottery Fund, 1995, NG6554
http://www.nationalgallery.org.uk/paintings/NG6554

In the late 1880s, Seurat was criticised for relying “unduly on scientific formulae”, though he himself seems to  have viewed his use of science merely as a guide, a way to help control the colour and light seen by the viewer*. The colours that we perceive can be affected by the colours they are adjacent to, as evidenced by many optical illusions. Yet even when everybody is looking at the same photo, we do not necessarily all see the same colour (I saw it as white and gold).

There is indeed a lot to the science of colour perception and some great fun that can be had with it. Seurat was aware of some of this and used science to understand how to best paint his paintings. Note how the (pointillist) border of the Seurat painting pictured on the right is a different colour at the top, do you think that affects how your eye perceives the top compared to the bottom of this painting?

Starting tomorrow, light and colour are to be combined in a three day “Lumiere festival” across London. The event looks as if it will take full advantage of the effects of different methods of colour mixing. If you are outside London, sorry! If you are lucky enough to be in London over the weekend, more details of what looks to be a fascinating science/art/experience event can be found here.

 

Ground Control is at 61 Amwell Street, EC1R 1UR

*”Seurat and the Science of Painting” by William Innes Homer was published by MIT press in 1964

Ordinarily I would have left the title of this post as a type of puzzle to see if anyone got the link (some posts on the Daily Grind have such puzzles, I’ve no idea whether I’m the only one who understands some of them). However, given that he passed away two days ago, here’s a rendition of David Bowie’s Space Odyssey (which is referenced in the title) sung by Cdr Chris Hadfield:

 

Categories
General Home experiments Observations Tea

Bouncing Coffee

floating, bouncing drops
Water droplets ‘floating’ on a bath of water (actually they bounce rather than float).

Perhaps you remember the video about how to ‘float’ coffee droplets on water posted on the Daily Grind a few weeks ago? The video featured an experiment that you could do at home in which droplets of water (or coffee, or even, if you were feeling adventurous, tea) could be made to stay as spherical droplets on the surface of a shallow dish of water for minutes at a time. Of course there were a few tricks: The water had soap added to it (10ml of soap to 100ml of water) and the shallow dish was on a loudspeaker which was playing music at the time. The whole experiment was very pretty. But hopefully as well as appreciating the aesthetics, you were asking ‘how’ and ‘why’? Why does the addition of soap mean that these globules of liquid appear to float on the liquid surface? And is the rumour you have heard about a connection with quantum physics true?

Well it turns out that people have known about these floating droplets for over a hundred years but why they behave as they do is still being investigated. It is another case of cutting-edge science appearing in your coffee cup*. So it’s worth taking a look at what is going on and why we needed to add soap and vibration for the droplets to remain stable on the water surface.

lilies on water, rain on a pond, droplets
When it rains, the rain drops don’t float on the pond

It seems to appeal to common sense and to everyday experience that if we drop a droplet onto a bath of water, the droplet will merge with the water and become part of the bath. After all, when we bring two drops that we have dripped on a table close to each other, at a certain distance between the two drops, they appear to touch and then rapidly merge into one big droplet (try it). And when it rains onto a pond, we don’t see lots of spherical droplets hovering over the surface of the pond! We know that it is the attractive van der Waals forces that bring the two drops together and then the effects of surface tension that minimise the surface area of the drops so that they become one big drop. So how is it that we can get a droplet to remain, as a droplet, on the surface of a bath of water?

How to bounce water droplets on a water surface

It could be said that the answer can be pulled out of thin air: Before the drops can merge, the air that separates them has to escape from the area between the droplet and the water bath. If the droplet can somehow be made to bounce back upwards before the air separating the droplet from the bath becomes thin enough for the two liquids to combine, the air could be made into a cushion to keep pushing the droplet upwards. This is why the experiment needs to be done with a vibrating dish of water, each time the surface vibrates upwards it is providing the drop with an acceleration upwards that overcomes gravity, like a miniature trampoline: The droplet is not floating, it is bouncing.

So why soap? We all know that the addition of soap decreases the surface tension of the water. But that is not why the addition of soap helps to stabilise the drops in this instance. No, soap has another effect and that is to increase the surface viscosity (and surface elasticity) of the water. Think about the air between the droplet and the dish. As the droplet bounces down (ie. the distance between droplet and water becomes a minimum), the air gets squeezed out of the layer between the droplet and the bath. On the other hand, as the droplet reaches its peak height, air will rush into the gap between the drop and the bath. If the liquid is not very viscous (eg. water), as the air rushes in (or gets squeezed out), it will combine with the liquid and form a turbulent layer on the surface of the droplet. If the viscosity is increased, the air cannot ‘entrain’ the liquid as the droplet bounces and so the drop keeps its shape more easily and is more stable. Soap increases the surface viscosity of the droplet and so helps with this effect. However soap also increases the surface elasticity and makes it harder for the air to flow out of the layer separating the drop from the bath. It is because soap does multiple things to the water (or coffee) that more recent studies have focussed on liquids with controllable viscosity but minimal surfactant effects, i.e. silicone oils. It is just that if you want it to work with coffee, it is easier to add the soap to get the experiment to work.

An “un-cut” video of coffee on water shows how tricky it can be to actually get these drops to be stable on the surface of the water.

Which leaves the quantum link. The experiment shown in the videos show single droplets (or droplet patterns) stabilised by vibrations caused by music. If instead of music you use fixed frequencies to excite resonances through the speakers, it is possible to get the droplet to resonate in a controlled way and, at a certain point, it will move. As the droplet moves, it appears to be guided by the vibrations of the liquid underneath the drop, it is a particle guided by a ‘pilot wave’. It turns out that such walking droplets show behaviour reminiscent of the ‘wave particle duality‘ found in quantum physics where particles (such as electrons and other sub-atomic particles) can be described both as particles and as waves. You can find a video describing the similarities between these bouncing droplets and quantum effects here.

 

* Ok, so you may not want to add soap to your coffee to see this effect but actually I first observed it in a milky tea. Adding milk to the coffee/tea would increase its viscosity which makes the observation of the bouncing droplets more likely. The ‘milk’ used in the video was actually soya milk which did not appear to increase the viscosity sufficiently to allow the droplets to bounce on the surface without soap.

Categories
General Science history slow

Ghosts of Christmas Past, the Devereux

Grecian, Coffee House, London Coffee House
The Devereux now stands where the Grecian once was

The Grecian is steeped in history. One of London’s early Coffee Houses, it counted Isaac Newton and Edmond Halley among its regulars. Today it is the site of a pub, “The Devereux“, owned by Taylor-Walker. The building itself dates from the nineteenth century though it is on the site of the old Grecian (a drawing of which can be seen on a wall inside the pub). In a sense, the Devereux is a continuation of the Grecian that once existed on this spot and it is for this reason that I’ve wanted to enjoy a drink at the Devereux/Grecian for a long time. What better time to do it than for a Christmas themed cafe-physics review?

The Devereux itself is a fairly spacious, comfortable pub, tucked down a little alley just off Fleet Street. It is strange to consider (while sipping on a glass of the 1730 pale ale) that it was here, just over 300 years ago, that the Grecian would host the after-meeting “pub outing” of the (then newly formed) Royal Society. Paintings and photographs of the Grecian and the Fleet St. area surround you, as you sit and enjoy your drink (they do serve tea and coffee too). Indeed, it is possible to almost feel the history of this place. I recalled reading a 1686 paper in the Philosophical Transactions by Edmund Halley in which he described a live demonstration, in front of a meeting of the Royal Society, of just how much water could evaporate from a heated plate of water in two hours. Halley was interested in this as part of the whole question of how rivers formed and where rain came from. I wondered whether Halley and his friends Newton and Sloane, retired to the Grecian after that meeting and sipped on hot coffee as they sat next to the cold windows which started to steam up on the inside.

Vegetable Lamb, Lamb of Tartary
The Vegetable Lamb in the collection of The Garden Museum

Reading about these early frequenters of this drinking establishment, it is hard to avoid the impression that they were driven by an interest in knowledge and knowing things. Of course the term ‘scientist’ had not yet been invented*. Science as in ‘scientia’ was still just Latin for knowledge, the men who gathered at the Grecian (and they were mostly men) were not “scientists” they were Natural Philosophers. Hans Sloane, another regular, was a great collector, finding curiosities from around the world and displaying them in his house. Most of his collection became the start of the British Museum but there is one curiosity of Sloane’s that I came across recently that is not to be found there at all and that is his “Vegetable Lamb”.

Vegetable Lambs were believed, in the seventeenth century to be, genuinely, part vegetable part animal. You can see from the photo that they do look fairly animal-like. According to the Garden Museum, these vegetable lambs originated in the Far East but now only two remain in the UK. The one that belonged to Hans Sloane (which is in the Natural History Museum) and the one that belonged to John Tradescant and that can now be found in the Garden Museum (now sadly closed until refurbishment is complete in 2017). Hans Sloane’s contribution was to show that this vege-animal was in fact purely a plant, a type of fern, which may make vegetarians everywhere breathe a sigh of relief. It was because these people were interested that they worked so hard in trying to understand the world around them. Which brings us, somewhat surprisingly, to one of the more recent famous patrons of what had by that time become, the Devereux.

Chesterton
The festive Chesterton bookshelf at the Devereux

GK Chesterton is not known for his scientific research. However, he did spend a great deal of time thinking and writing about all sorts of things. (It also appears that he spent a fair amount of time in the Devereux where there is an entire bookshelf of his books). A book of Chesterton’s essays “As I was saying” was published in the year of his death, 1936. Within that book is an essay “About the Telephone”. Chesterton was musing on a sentence that he had read in a newspaper that had troubled him: “The time will come when communicating with the remote stars will seem to us as ordinary as answering the telephone”. Chesterton wrote “Now if you could say to me: ‘The time will come when answering the telephone will seem to us as extraordinary as communicating with the remote stars…’ then I should admit that you were a real, hearty, hopeful, encouraging progressive.” I suspect that with our tendency today towards the fragmentation of knowledge and increasing specialisation, we would categorise the work of Newton and Halley, Sloane and then Chesterton in quite different compartments. Yet it seems to me that they share something in their work: an element of wonder and curiosity at the world. As Chesterton continued in “About The Telephone”,  “I am not objecting to the statement that the science of the modern world is wonderful; I am objecting to the modern world because it does not wonder at it.“

It sometimes seems hard for us to sit in a cafe on our own without using, or at least looking at, our telephones. Checking our email or the latest news on our telephones has become extraordinarily ordinary for us. Maybe this should be our New Year’s resolution: put our phone back into our pocket and consider, with Chesterton, Sloane, Halley and Newton, just how wonderful it is.

Happy Christmas & New Year to all

 

* The word science/scientist was first used in the sense that we now understand it by William Whewell in the nineteenth century.

“As I was Saying – a book of Essays by GK Chesterton” was published by Methuen&Co Ltd, 1936

The Devereux can be found in Devereux Court, just off Fleet Street, WC2R 3JJ

Categories
Home experiments Observations slow Tea

Coffee baubles

resonating coffee
Not the best image of a resonating coffee but you hopefully get the idea

Most people, at some point in their lives, must have pushed a take-away coffee cup across a table and watched as patterns form on the liquid surface. Sometimes these patterns seem to stand still, we’d say that they form ‘resonances’. On even rarer occasions, on dragging your cup across the surface, you may have seen coffee droplets jump out of the coffee and then dance on the coffee surface for a couple of seconds as the liquid vibrates.

Today’s Daily Grind investigates these ‘floating droplets’ with an experiment in time for Christmas: Decorate your coffee with coffee baubles.

To make these droplets form on your coffee in a controllable way you will need a few bits of equipment:

  1. A couple of loud-speakers with the woofers exposed
  2. Some sort of liquid soap (washing up liquid, hand soap, soap for hand washing clothes etc)
  3. Some water (or coffee but you will do horrible things to it)
  4. A shallow dish (I used the bottom of an old yoghurt pot)
  5. A “dropper”, a pipette or syringe would be ideal, a straw will probably work.

You can do this completely systematically, in which case you’ll also need a signal generator to provide a fixed frequency output to the speakers (I used “ScorpionZZZ’s Lab, Signal Generator Lite for iPhone). Or you can just go straight to the fun bit which is to make these droplets dance to music. It’s Christmas so it’s entirely up to you!

floating drops, resonances, speakers, kitchen top science
Balance a shallow dish on the woofer of a speaker. A roll of sellotape can be used to couple the vibrations of the speaker to the dish if necessary.

Balance your speakers on a flat surface and put the shallow dish so that it sits in good contact with the woofer. Because my dish was ever so slightly larger than the vibrating bit of the speaker, I ‘coupled’ the speaker to the dish with a roll of sellotape. Mix 10ml of soap with 100ml of water (this does not have to be exact but you may want to investigate just how much/little soap you can get away with). If you are using coffee rather than water, you will need to mix 10ml soap with 100ml coffee.

Pour about half the soapy-water into the dish and then turn the speakers on. If you are using a signal generator, watch what happens as you sweep the frequency from 10-200 Hz. Now, either choose a frequency which shows a nice resonance pattern on the water, or start playing the music through the speakers. Music with a good beat will work well (I watched drops dance to Tiesto, Blondie, and Josh Woodward’s “coffee”).

Drip a drop of the remaining soapy-water onto the resonating surface. A video of my playing with these droplets can be seen above. Although not all the drops will float, it is fairly easy to start to form patterns of flowers or rows of droplets and then it’s worth just playing.  How big a droplet can be made to float without collapsing? How many minutes can you get a drop to last before it sinks? What happens if you combine a drop of black (soapy) coffee with a drop of milky (soapy) coffee?

Have fun, and please do share your videos and photos of your experiments with me on Facebook or Twitter.

Disclaimers & Credits:

No coffee was wasted in the making of this video. A very good coffee from Roasting House was thoroughly enjoyed before the remnants were diluted and mixed with soap.

Inspiration & experimental details taken from Jearl Walker’s great article “The Amateur Scientist” in Scientific American, p. 151 (1978).

 

Categories
cafe with good nut knowledge Coffee review Science history

Hanging out at J+A Cafe, Clerkenwell

Exterior of J and A cafe (the bar is on the other side of the passageway)
Exterior of J and A cafe (the bar is on the other side of the passageway)

Tucked down a little alley, in the back streets of Clerkenwell is the J+A Cafe. Not just a cafe, but also a bar, J+A is a satisfying place to find, particularly if you happen to find it serendipitously. As you head down the alley, the café is on your right whereas the bar opens up on your left. The café is simply furnished, with bare brick walls adorned with a few impressionist paintings. There are plenty of seats at which to enjoy good coffee and home-made cake. Their website suggests that J+A specialise in Irish baking and so we dutifully had a slice of Guinness and chocolate cake with our coffees. Importantly, the dreaded “does it contain nuts?” question was met with a knowledgable answer and without the ‘frightened bunny face’ that I often encounter when I ask this question. J+A definitely gets a tick in the ‘cafe’s with good nut knowledge’ box on my website.

Lights were suspended from the ceiling, connected by wiring that was allowed to hang down, a section of electrical wire held at both ends and freely hanging. While I’m sure that this was done for aesthetic reasons (and certainly it works on that level), such hanging wires are in fact far more than merely pleasing to the eye. Such hanging wires were a mathematical puzzle just four centuries ago. Indeed, these simple hanging wires form curves that are so important they get their own name; they are catenary curves, from catena, the Latin for chain.

lights at J and A coffee Clerkenwell
Between each lamp, the electrical cord formed a catenary curve.

Galileo had thought that a wire hanging under its own weight and suspended at its two end points formed a parabola. A fairly simple curve that is easy to describe mathematically. It was natural for Galileo to assume that these catenary curves were really parabolic. He had earlier shown that objects that fell with gravity followed parabolic paths, and after all, the hanging wires did look almost parabolic. It fell to Joachim Jungius to show that the curve was not parabolic and then to Huygens, Bernoulli and Leibniz to derive the equations determining the form of the curve. Although the differences between the parabola and the catenary curves are subtle, they have profound consequences.

When a chain, or a wire, is suspended and allowed to hang under its own weight, it forms a catenary. Flipping this around, quite literally, a catenary arch will be self-supporting. This means that a vault made of a series of catenaries or a dome that is made into the shape of a catenary will be self-supporting with no need for buttresses. This property of the catenary curve was used by Antonio Gaudi in his designs of the Casa Mila in Barcelona and also by Christopher Wren. The famous dome of St Pauls is not a catenary, but it is not one dome either. It is in fact 3 domes stacked together. The outer dome is spherical (which is weak from a structural point of view) while the inner dome is a catenary. The dome between these two was designed, using the mathematics of the day, to support the impressive outer dome (more info here and here). Wren, was not just an architect, he was also a keen mathematician, there is maths, physics and beauty throughout many architectural designs.

Mathematics in the city reflected in the lights of J+A.

J+A is at 1+4 Sutton Lane, London EC1M 5PU

 

Categories
General Observations slow Sustainability/environmental

A drop in the Chemex?

Chemex, 30g, coffee
How do you prepare your coffee?

How do you prepare your coffee? Generally I’ll either use the Chemex or a French press. Often it will be the French press purely because it is, sadly, quicker. However, on those mornings that I do slow down to prepare a Chemex, I generally feel better for it. Not only does the coffee taste better, but those 5 minutes of preparing the coffee pay off as time for the mind to wander rather than just time spent waiting for the caffeine. When the Chemex is nearly ready, the fresh brew drips slowly from the filter onto the liquid below. Each drop produces a ripple pattern. At the start of the UN conference on climate change in Paris (COP21), we may well hear talk of some of our efforts being mere “drops in the ocean”. So it seems a good time to reflect on those “drops in the Chemex”. Just how much influence can a drop  have?

It is worth stopping for one moment to consider what is going on around us at this moment. As I write this, it is late November in the Northern Hemisphere. Taking a walk outside, I can see the last of the yellow leaves falling off the trees. In just a couple of weeks time, many of the trees will be bare. Why do the leaves fall from the trees? We could answer this question in a number of different ways. Biologically, the tree is forming cells at the joint between the leaf and the tree that will eventually enable the leaf to tear from the tree. As these cells are, in some way, responsible for the leaf falling off, they are called “abscission” cells. But even with these abscission cells, the leaf still needs something to force the leaf off. Often this is the wind which is why we get such an abundance of leaf fall on windy days. However there is another mechanism that can help a leaf to drop, and that is a curious interplay between the leaf and rain.

autumnal scene, red leaves, hydrophilic
The surface of the leaf changes from waterproof to ‘wettable’ over the course of the summer

In the spring, many species of tree, including Oak, develop a wax layer on the leaf. Perhaps you have been walking in the country and have needed to wax your walking boots before you go? The wax on the boots acts as a waterproofing for the boot, ensuring that your feet don’t get soggy. The wax on an oak leaf performs the same function for the leaf, it makes the leaf waterproof. Although this is not the only function of the wax. It seems that a waxy surface also slows the processes that dry out the leaf, prevents insects and pathogens attacking the leaves and may even play a role in affecting the way that the light is concentrated into the leaves for photosynthesis. Nonetheless, from the tree’s perspective, it is a significant advantage to have waterproof leaves. Imagine rain falling onto a waterproof surface. The drops of rain do not ‘wet’ the leaves but instead roll off. As the raindrops roll off, they take particles of dust and dirt with them. It is a tree’s way of cleaning itself. Waterproof surfaces are self-cleaning surfaces. Something that some scientists are now trying to replicate for man-made products.

hydrophobic leaves
Some leaves are more waterproof than others.

As the summer continues and the leaf gets older, the wax layer changes. The structure of the wax changes and erodes as the wind, weather and even pollution batter the wax layer. Just as with the hiking boots, the damaged wax layer results in a less waterproof leaf. The leaf becomes “wettable”. When a drop falls on a surface, the shape of the droplet is determined by how waterproof the surface is (more details here). A surface is termed “wettable” when the droplet becomes significantly flatter and coats the surface rather than forming a spherical drop that can roll off. Now consider each raindrop as it hits the different types of leaf. In the spring, the leaf is waterproof and the raindrops will roll off them. A drop of rain will cause the leaf to shake on its stem but then to return to its original position. It is ultimately not affected by a light rain shower. In the autumn when the leaves are no longer waterproof, the rain will start to stick to the leaf surface. Now when the leaf shakes, the wet leaf will not return to its original position but will bend slightly further downwards. As it continues to rain, the leaf will experience a greater torque and this means that it is more likely to fall off the tree. As each rain drop hits the leaf, the likelihood that the leaf will tear away from the abscission cells at the base of the leaf increases. Each drop has an effect.

This also has an important consequence for some of our technology. One renewable energy source that has been proposed for self-powering electronic devices harnesses the energy of rain. When rain falls on an array of cantilevers, it forces the cantilever to bend and to oscillate. This energy can be harvested ( that is, changed into a form that is useful to us) by using small piezo-electric devices (that convert movement into electricity or vice versa) at the  base of the cantilever. When a tree leaf is wet, the leaf joint experiences a greater torque which causes the leaf to ultimately tear from the tree. For the rain-energy harvesters, this is exactly what we want. The greatest energy obtainable from the cantilever system will be from cantilevers that can be made wet. Waterproof cantilevers would be a bad idea. A renewable energy that comes from rain would definitely be a positive development for UK energy production!

It seems that one coffee drop does indeed go a long way.

 

Categories
Coffee review General Science history

Something in the air at Mace by Coffee Chemistry Signature, KL

3D hot chocolate art on an iced chocolate, Mace, Mace KL, dogs in a chocolate
Drinking an iced chocolate with friends.

Perhaps Mace by Coffee Chemistry Signature in Kuala Lumpur should really have a “cafe-art” review rather than a “cafe-physics” review. Indeed, it was because of its latte art that Mace, which operates from a light and airy building in Damansara Uptown, Kuala Lumpur, had been recommended to me. With a comfortable interior and friendly staff, Mace is an interesting place in which to spend some time. But it is certainly the artistic endeavours that are the striking thing about Mace. Nor is it just ‘latte art’. The cakes at Mace arrive at the table decorated into an artwork. It is interesting that every visit to Mace will provide a different creation to enjoy, providing a place that you could return to again and again.

Nonetheless, this is a cafe-physics review website and there is also plenty of science to be found in latte art. For example, one of our drinks arrived with a 3D latte art sculpture floating on its surface. This piece requires manipulation of the rigidity of the milk foam, a topic that has been covered previously on the Daily Grind. However this time, it may be worth looking a little deeper into our frothy coffee: What makes a bubble?

The answer may seem obvious, inside the bubble is “air” with the bubble surfaces being formed from the water and proteins in the milk∗. But it is the question of what air is, and the implications of that, that is today’s Daily Grind.

Tweetie pie with a cake at Mace, KL
Cakes can be shared with cartoon characters at Mace

It appears that it was Empedocles (492 – 432 BC) who first recognised that air was a substance†. A thing that existed all around us. But it took until the seventeenth century and the invention of the air pump by Otto von Guericke (1602 – 1686) before people recognised that air was heavy. Guericke was responsible for the spheres of Magdeburg demonstration about the strength of a vacuum. He had fashioned two hemispheres of copper. Each hemisphere fitted very closely to the other. He then used his air pump to pump the air out of the spheres (ie. make a vacuum) and tried to pull the two hemispheres apart. Accounts vary but it is said that teams of 8-15 horses tethered to each hemisphere were unable to pull the spheres apart because of the vacuum created within the spheres†.

It was von Guericke’s air pump, together with the work of Boyle on gases and Torricelli’s invention of the barometer that prompted Francesco Lana-Terzi, SJ (1631-1687) to design an ‘air ship’. The idea was simple: If air had a weight and it is possible to make something lighter than air (by making a space inside a copper sphere a vacuum), then it should be possible to make something lighter than air such that it would float, just as objects that are less dense than water float. What differentiates Lana-Terzi’s design from previous fantasies about flight (such as Daedalus and Icarus) was that Lana-Terzi based his ideas on solid principles of mathematics and physics. He calculated how heavy the air was and balanced that with the amount of air that he would have to pump out of four hollow spheres of copper in order that they could lift a gondola full of people.

latte art by Mace, Eiffel Tower and hot air balloon
Art on a cafe latte at Mace

Although there were practical problems with Lana-Terzi’s idea of an air-ship based on four hollow copper spheres, his ideas were correct and eventually led to the development of the hot air balloon. And it is with the hot air balloon that we return to coffee, to Mace and find a connection with a London cafe. The artwork on my cafe latte was not, ‘latte art’ in the sense to which we have recently become accustomed. It was however very much art on a latte, with a scene featuring the Eiffel Tower depicted in chocolate. Just to the right of the Eiffel Tower and suspended in the milky sky was a hot air balloon, floating away exactly as Lana-Terzi had envisaged. Back in 1783, on the corner of Euston Road with Tottenham Court Road, there used to be a pub/coffee house called the Adam and Eve. It was renowned for its cakes and cream and its large tea garden. As far as I can work out, the tea gardens extended to around what is now Brock St and the site of a Beany Green. It was here, in 1783 that the balloonist Vincenzo Lunardi (1759-1806) “fell with his burst balloon, and was but slightly injured”‡. Fortunately for Lunardi, and for ballooning in general, it was only a slight setback. Lunardi went on to make a number of balloon flights, including the UK’s first successful hot air balloon flight.

So next time you are in Kuala Lumpur, why not spend a while at Mace imagining floating in on Lana-Terzi’s air ship gondola while you enjoy a gorgeously frothy iced chocolate. Who knows, one day Lana-Terzi’s air ship gondola may even feature on their latte art, I’d love to see that picture!

Mace by Coffee Chemistry Signature is at Damansara Uptown, Kuala Lumpur.

∗ On Food and Cooking, The science and lore of the kitchen, H. McGee, Unwin paperbacks, 1984

† History and philosophy of science, LWH Hull, Longmans, Green and Co, 1959

‡ Quote from London Coffee Houses, Bryant Lillywhite, 1963