Category: General

Categories
Coffee cup science General Observations slow

Coffee & Contrails (II)

vortices in coffee
Vortices forming behind a tea spoon being dragged through coffee.

Drag a tea spoon through your cup of coffee (or tea). Start by dragging the spoon slowly, then faster. Initially, the coffee flows around the spoon smoothly then, as you speed up, small vortices appear at either side of the spoon. Pull the spoon out of the coffee, and the vortices continue to move together through the cup before bouncing off the sides. Such vortices form whenever there is a speed difference between two layers of fluid (gas or liquid), as there is around the spoon being dragged through coffee. It is this effect that is the second connection between the physics of coffee and contrails.

Of course it is not giant tea spoons in the air but aeroplanes. Behind each aeroplane is a series of vortices trailing behind the wings. These vortices do not (normally) cause the contrails, the reason that they form was discussed in Coffee & Contrails (I). However, the vortices do cause some interesting effects in the contrail that we can, occasionally, see.

wake vortex, contrail, coffee in the sky
In this contrail there is a set of protuberances at regular intervals along the lower edge.

As the plane moves through the air, the speed of the air going over the wing is greater than the speed of air under the wing. As well as leading to vortices forming behind the wing, this speed difference results in an air pressure difference (the air pressure under the wing is greater than the air pressure above the wing). The pressure difference (below and above the wing) pushes the plane upwards, or, perhaps more technically, ‘creates lift’ and enables the plane to fly. If you want a good demonstration of the fact that a higher air speed leads to a lower air pressure, get two pieces of flat A4 paper and hold them in front of you such that you are looking through the small gap between them. Now blow into the gap separating the two sheets; they will join together. The reason that they do this is that the air pressure for fast moving air (as you blow) is less than the air pressure for static air (around the paper) and so the difference in air pressure pushes the two sheets together.

Shadowy contrail
Look carefully for another interesting contrail optical effect. There are two contrails here, an obvious one cutting straight down the photo and a second contrail moving more horizontally across the photograph. The second contrail can be seen more clearly by its shadow.

On a clear day, if the air in the higher atmosphere is relatively humid, you will see lots of persistent contrails. These contrails last for a long time in the skies and can drift with the wind. Occasionally at the edge of such a contrail you will see regular protrusions from the contrail, almost as if waves are forming on the contrail and producing white horses in the sky (see picture above). Initially I had hoped that this was a manifestation of the Kelvin-Helmholtz instability however the actual explanation is still quite fascinating. It seems that these protrusions are the result of the “wake vortices“, the vortices that form behind a plane just as the coffee forms vortices behind your spoon. I find it quite impressive to realise that high in the sky, these contrails are showing us that the atmosphere behaves just as if it were a cup of coffee. A definite case for which a coffee is a telescope for viewing the world.

Please leave any comments in the comments box below. If you think of any other connections between the physics of coffee and contrails please share them either here or on my Facebook page.

Categories
General Tea

On nuclear fusion and making tea

tea bag, tea cup, diffusion, turbulence
How not to prepare tea

Although largely a coffee drinker, occasionally I will order tea in a café. When I do so, one of my pet hates is being served a cup of hot water with an individually wrapped tea bag sitting on the saucer beside it. Quite apart from the unnecessary environmental cost of individually wrapping tea bags, there is the problem with the resultant cup of tea. Hot water poured onto tea (preferably in a pot) allows the tea to infuse by a mixture of turbulence, convection and diffusion as the hot water swirls around carrying the tea with it. A tea bag placed into hot water on the other hand relies on infusion by convection and diffusion only and so takes a lot longer to brew. Oddly enough, there is at this moment, a major scientific project being built in the south-west of France that has the opposite problem. The aim of the project is to generate electricity by nuclear fusion in extremely hot clouds of gas that are confined into the shape of a doughnut. To achieve this, they must reduce the turbulence within their doughnuts. Unlike the tea, nuclear fusion seems to require diffusion and convection to prevail over turbulence.

Supplying the growing energy demands of the planet is a major problem for us all. How can we simultaneously generate the electricity that we want while limiting our carbon dioxide emissions to levels that will cause minimal damage to our planet? Renewable energy is part of the solution, some have argued that nuclear fission could be another part of the solution (all of our current “nuclear” power plants run by nuclear fission). The “ITER” project in the Provence-Alpes-Côtes d’Azur region of France aims to demonstrate the feasibility of nuclear fusion to supply our energy needs instead.

Sun, heat, nuclear fusion
The Sun is powered by nuclear fusion. Could we generate electricity on Earth with a fusion generator? Image © NSO/AURA/NSF

Unlike nuclear fission which works by exploiting the decay of radioactive elements, nuclear fusion ‘fuses’ elements together to produce energy. Gazing up at the sky you can see thousands of nuclear fusion generators: Each star (including our Sun) produces light and heat, by nuclear fusion. First the stars fuse hydrogen into helium (as our Sun does now), then, as the star ages, the heavier elements combine until finally iron is formed in the core of the dying star. All the elements found on our planet and elsewhere in space have, ultimately been formed in the core of a star (or in reactions as the star dies in a final explosion). Every atom in us has been formed by such reactions in stars and so it is very true to say “from dust you came and to dust you will return”, the dust in question being star dust. If we can exploit it on Earth, nuclear fusion offers a method of providing energy with no long term radioactive by-products and limited carbon dioxide emissions. It is a possible, but very long term, route out of our quandary about energy generation.

doughnut tokamak
A photo to demonstrate “doughnut shaped” was probably unnecessary, but it did provide a good excuse for an unhealthy breakfast.

So why can’t we start using it immediately? A clue comes from the fact that the nuclear fusion reactors that we know of (stars) are very hot and relatively dense. It is not easy to smash two hydrogen atoms together such that they fuse, it requires them to have a lot of energy (ie. be very hot) and be quite close together. To build a nuclear fusion reactor requires us to heat a gas until it becomes a ‘plasma’ which means heating the gas to temperatures of around 150 million ºC. At this temperature we need to confine the plasma with very high magnetic fields so that it does not hit the walls of its container and it turns out that the best way to do this is to manipulate the plasma into a ring doughnut shape. This doughnut confinement, known as a ‘Tokamak’ has become the standard way of confining the plasma. At the moment, we cannot keep the plasmas hot enough for long enough (the current record is 6min30 sec confinement) for fusion to generate more energy than is required to form the plasma in the first place. One of the things limiting the lifetime of the plasma is the fact that the plasma cools down and one of the things that cools the plasma down is the turbulence in the plasma carrying the heat energy from the centre to the edge of the doughnut. Increasing the time it takes for the heat to escape from the centre of the doughnut to the outer edge is one of the challenges facing the ITER team. Just as with the pot of tea, were the cooling by diffusion and convection only, the plasma would take a lot longer to cool down. Understanding the turbulence inside the plasma is one of the challenges facing the team at ITER.

Our method of making tea can tell us a lot, not just about the problems for nuclear fusion generators, but also about diffusion and turbulence generally. It is worth pondering that brew a little more deeply next time you make your pot.

 

Categories
Coffee review General Science history

Getting some perspective at Skylark, Wandsworth

Skylark Wandsworth
A sunny day at the Skylark on Wandsworth Common

It is late spring in the northern hemisphere and when the weather is fine, what better way to spend it than with a coffee in the middle of Wandsworth Common at the Skylark Cafe? With a number of tables outside and, if the weather turns bad, several more tables inside, Skylark is a lovely place to spend some time while wandering in West London. On the day that we were there, Skylark was frequented by a large number of families however, it was a Saturday afternoon and so it is quite possible that on a week-day it will be a bit quieter. The coffee is roasted by Caravan and they have an interesting array of cakes inside, but it was the plants on the tables outside that caught my attention. Each table had a pot of thyme on it, but the thyme smelled of lemon. Perhaps it was lemon thyme, but something that looks like one thing and smells of another is a nice introduction to this week’s Daily Grind which is all about appearances, reality and perspective.

The thyme was growing in a metal flower pot which reflected the wooden table top. From the photo (below, left), it is clear that the pot is cylindrical but if we stop and think about it, how do we actually know that? The image is two dimensional, no third dimension is possible through a computer screen. What clues in the picture tell you that the pot is cylindrical? The bending of the lines of the table top? This is a pattern that we have learned, we have found from experience that something that is circular will bend straight lines in this way.

perspective, flower pot
What shape is the flower pot?

How we see things and what we think we are seeing was a subject that bothered George Berkeley (1685-1753). How can you know that anything external to yourself is real? Everything you touch, everything you see, hear, taste or smell is, ultimately, a response in your brain to a stimulus. It is not easy to prove that anything ‘outside oneself’ really exists. Indeed, Berkeley argued for the theory that what was ‘real’ was only the sensations in your mind. The theory was famously challenged by Dr Samuel Johnson (1709-1784) who used to drink coffee at the Turks Head in Gerrard St. in what is now Chinatown. Johnson hurt himself by kicking a stone, while saying of Berkeley’s theory: “I refute it thus“. Does Johnson’s sore foot really refute the theory though? How can we avoid Berkeley and find our world again?

Writing about science at the turn of the twentieth century, Pierre Duhem (1861-1916) argued that “All the time we view scientific theory as an attempt at an explanation, we will be limited in what we consider an acceptable explanation by our metaphysical beliefs. Only by accepting that theory is in fact a description, a cataloguing, do we free ourselves from all but the primary metaphysical belief that the world exists“. In other words, in order to ‘do’ science we have to rely on (at least) two beliefs a) that the world outside exists, b) it is consistent, that is, governed by laws that are knowable. Neither of these premises can be ‘scientifically’ proven, instead they lie at the base of our belief system, even if we do tend to take them for granted. It is far easier after all to live in the world, if we assume that it exists.

Americano, Caravan coffee, Skylark, Wandsworth
Coffee at the Skylark

None of this should stop us doing science. Whatever we are investigating with our experimental (or theoretical) tools it is beautiful and the more that we understand the mathematics that describe the world, the more beautiful the world outside becomes. I cannot prove, scientifically, that the world outside exists, I could possibly argue that it does based on philosophical ideas but I will never be able to prove it. I understand that the pot on the table at Skylark is a three dimensional cylinder because of the way that the light is  bent on reflection and from my, admittedly intuitive, understanding of perspective. Perhaps we also need some perspective in appreciating what we can, and cannot, prove with science.

 

Skylark Cafe is on Wandsworth Common.

Quote taken from “The Aim and Structure of Physical Theory”, Pierre Duhem, 1910.

Categories
Coffee review General Observations Science history

Molecular reality at the Turkish Deli, Borough

“Just as the air is more dense at sea-level than on a mountain top, so the granules of an emulsion, whatever may be their initial distribution, will attain a permanent state where the concentration will go on diminishing as a function of the height from the lower layers, and the law of rarefaction will be the same as for the air” (Jean Perrin)

Turkish Deli, Turkish Coffee
The Turkish Deli, Borough Market

I have long had a fascination for the history of coffee and the different styles of brew. So it should be no surprise that I went to try The Turkish Deli in Borough Market for the Daily Grind. Very close to Monmouth, the Turkish Deli serves Turkish-style coffee and a delicious looking array of Turkish delights. Although quite far from the brew bars and single estate coffee types of some cafés now in London, Turkish coffee nonetheless offers the opportunity to slow down and appreciate the moment. Perhaps even more so than an espresso, since you are forced to wait for the coffee to be ready. The coffee is presented to you, straight from the Ibrik, in a small cup with a fantastic looking crema on top of it. At this point you are told that you will have to let it settle for at least four minutes before even thinking about starting to drink it. Indeed, the person in front of me in the queue was advised that he could “sit down, watch the world go by” while waiting for the crema on the coffee to turn a very dark (black) colour, indicating that the coffee was finally ready.

before settling, Turkish coffee
Waiting for the coffee to be ready

If you take sugar in your coffee you have to add it right at the start, before the coffee is warmed to the point of boiling (though it is not boiled). The reason is fairly obvious if you think about it. Turkish coffee has a large amount of sediment, this is the reason that you need to leave it for four minutes for the sediment to ‘settle’. Adding sugar during this settling time would mean that you would need to stir the coffee which would disturb the sediment and prevent it from quickly settling. Instead, you either take your coffee sugar-less or you add your sugar before starting this settling process.

Jean Perrin, (author of the quote at the start of this week’s Daily Grind) used the gradient of sediment in a different liquid (gamboge – a bright yellow paint pigment) to confirm the existence of molecules, just over one hundred years ago. He was exploring Brownian motion, the seemingly random motion of bits of dust, sediment etc, on the top of the coffee cup which had been explained in terms of “molecules” in the coffee (or water, or paint), hitting the bits of dust on the surface. Jean Perrin (1870-1942), realised that if Brownian motion was being caused by molecules, they would not just be causing the movement of the dust (and sediment) on the surface, it would be a three dimensional effect. Measuring the gradient of sedimentation would be a way to prove the molecular theory of Brownian motion and, simultaneously, to prove the existence of molecules.

Turkish coffee
The surface of the coffee reminded me of a coastline, itself connected (mathematically) to Brownian motion

Imagine a bit of sediment in the middle of the liquid (it could be a Turkish coffee, for Perrin it was the paint). That piece of sediment is going to be pulled down by gravity but in addition, it is going to be pushed up by molecules from below and down by molecules in layers above it. This is the bit that is related to Brownian motion. We know that even after leaving it for a long time, much of the sediment is still suspended mid-way up in the cup. It follows that the total forces acting downwards on the sediment (from gravity and the molecules above it) must be the same as the total force acting upwards (from the molecules below).

This means that the mass of sediment held at any particular level in the coffee must decrease with height. If the size of each piece of sediment is identical (which was ensured by Jean Perrin in his paint but is not the case for the Turkish coffee), then the number of pieces of sediment held aloft in the coffee/paint would decrease with height from the bottom to the top. All Perrin had to do therefore was to count (with a microscope) the number of bits of sediment as a function of height in order to test whether the molecular theory for Brownian motion was correct.

Turkish coffee, Borough market, sedimentary, sedimentation
The sediment at the bottom of the cup, don’t drink this bit!

To obtain statistics, Perrin and his assistants would count 11000 particles in one emulsion and repeat this experiment 1000s of times, but his patience paid off. By 1910, (only a few years after starting his observations), Perrin could claim that “the molecular theory of the Brownian movement can be regarded as experimentally established, and, at the same time, it becomes very difficult to deny the objective reality of molecules”. In 1926 he received the Nobel prize in recognition of this work.

Returning to the coffee, it is a very good drink with which to slow down and watch the world go by, perhaps while pondering molecular reality. When you get towards the bottom, do not drink the sediment but do take time to appreciate the mouthfeel and flavour as you drink this beverage that, in many ways represents an early chapter in the coffee story and one that continues to be made very well at the Turkish Deli.

The Turkish Deli is in Borough Market, Stoney Street, London, SE1 9AA

Quotes taken from “Brownian Movement and Molecular Reality”, Jean Perrin, 1910

Categories
Coffee cup science General

Setting the standard for coffee brewing

Chemex, 30g, coffee
A Chemex, how much coffee do you need to make a good cup (or two?)

Serious coffee drinking requires a serious attention to preparation. Various online guides (such as this one from Ineedcoffee.com) specify the ratio of water to coffee that you need and some will dictate the exact quantity of coffee that you should grind ready for your brew (30g for a standard, 500ml Chemex). Different brew methods require different amounts of coffee. Some will insist that the correct ratio of coffee to water is essential for a good coffee. So how can we ensure that 30g of coffee is really 30g? How do I know that what you measure as 30g is what I measure as 30g? It is a question that reveals a fascinating answer. The measurement of mass, the definition of the kilogram, is the only unit of measurement left for which we still use a physical standard as the reference.

This means that there is a physical lump of metal (it is actually a platinum-iridium alloy) that is sitting in a lab somewhere (Paris) against which all our definitions of mass are referenced. If you were to weigh out 1 Kg of coffee, your scales would, ultimately, be referencing this 1Kg lump of platinum-iridium in Paris. My scales reference the same standard and so we can be sure that, assuming our scales are accurate, your 30g is equivalent to my 30g. Many years ago (in 1884), forty replicas of this standard of measurement were made and distributed throughout the world. The idea was that rather than have to always refer to the Parisian standard, there would be a more local ‘standard’ that people could refer to. The problem of course is that the standards diverge, they have to be regularly re-calibrated so that the Kg in Paris weighs the same as the Kg in London (well, just outside London in Teddington, at the National Physical Laboratory).

gold weights, standard weights, not Kg
A set of gold weights from China in the British Museum collection. © Trustees of the British Museum

The reason appears to be because the standards get dirty. The surface of the metal adsorbs contaminants from the air which make the standard seem heavier. Admittedly, this may not be by much, only perhaps tens of μg, but over many tonnes, this small difference is going to add up. And if you trade in commodities (such as coffee beans) and are paying by weight of coffee then such differences, in large amounts, may be costly. So what is the solution? One method involves finding new ways to clean the standards so that they are contamination free. A more long term solution is to move away from measuring relative to a physical standard at all. After all, length is no longer measured with reference to a stick in a lab but with reference to the distance that light travels in a certain amount of time. Research is now being done into exactly this in metrology labs around the world. At some point in the not to distant future, it is very likely that the Kg will be defined with reference to an electrical measurement, for example, rather than with reference to a physical block of metal. For the meanwhile, we have to hope that the standards labs around the world keep their blocks of metal very clean otherwise, how would we ever expect to get the correct amount of coffee in our Chemex?

Comments always welcome, please click the link below to add a comment.

Categories
Coffee review General Observations

Reflections at Knockbox, Lamb’s Conduit Street

Knockbox, Knock box, coffeeKnockbox coffee is on the corner of Lamb’s Conduit Street and Dombey Street. It is a small place and we had to go twice in order to get a seat, though the compensation is that there are views all around the cafe (it being on a corner). I enjoyed a very good americano, made using Workshop coffee. Complementary jugs of mint infused water were dotted around the cafe which is always a nice touch. Sadly, I tried Knockbox just after lunch and so didn’t try any of the edibles on offer. This does mean however that I will just have to go back to try them at some point (and of course, to enjoy another coffee).

There were a lot of things to notice around Knockbox that day. There were the air bubbles in the water that had become stuck around the mint leaves. There were the light bulbs (that you can see through the windows in the picture). And there was the espresso machine: A gleaming piece of machinery that sat majestically on the counter. Looking at the espresso machine it was impossible not to be struck by the reflections from the surface. The reflections are not only testament to how much the staff at Knockbox must polish the machine; how reflections work is the subject of today’s Daily Grind.

espresso machine, metal, reflection
The gleaming espresso machine at Knock box

The interaction of materials with light is one of those fascinating areas that reveal physics at its most fundamental. I’ve often taught undergraduate physics students who are looking forward to learning about quantum mechanics because it is “weird”. This is true, quantum mechanics can be quirky, but electromagnetism (which is about light) can be just as odd. To get such elegant and surprising physics out of what is essentially all classical, nineteenth century theory, is one of those joys about learning about (and teaching, using and experiencing) this subject.

However, to return to the espresso machine and light.  How light interacts with objects reveals how the electrons are distributed in the material which in turn tells you something about the atoms that make up the espresso machine. (For how to experience electrons in your coffee, see Bending Coffee, Daily Grind, 26 Nov. 2014). As the electrons are electrically charged, they respond to light which is, ultimately, an oscillation of electric (and magnetic) field. Electrons in a metal are shared in an “electron sea” between all the atoms in the metal. Consequently, when light falls on a metal surface, the electrons can respond to the electric field oscillation of the light and they re-emit the light backwards as a reflection.

ImpFringe, #ImpFringe, Fox's Glacier Mints, linearly polarised light
Sugar rotates linearly polarised light. The ‘device’ above is made from layers of Fox’s Glacier Mints and 2 linear polarisers (eg. a pair of polarised sunglasses). Photographed at ‘Lit Up’, an Imperial Fringe event held at Imperial College London, that was free to the public.

On the other hand the electrons in the atoms of the plastic of the grinder (or the glasses on the top of the espresso machine) are held firmly to each atom. Therefore most of the light that we see will go straight through these substances with each atom acting to propagate the light forward but not able to completely block it for a reflection. Coffee beans too contain electrons that are held in place by the atoms in the molecules that make up the bean. Unlike the glass though, the electrons in coffee beans are held in atomic bonds that happen to have an “excitation energy” that is at a visible light frequency. Rather than let the light through, they absorb certain colours of light (more info in the Daily Grind here). The result is the opaque, deep brown of the coffee bean.

This year is the international year of light, a year which is intended to celebrate our understanding of light. There are so many light based processes occurring all around us at every moment. Why not stop in a cafe and see how many you can spot in your coffee cup?

Categories
Coffee review General Observations

The Corner One, Camden

20 Oval Road, Corner One
The Corner One in Camden

While browsing London’s Best Coffee, I came across a recommendation for The Corner One in Camden. The Corner One is tucked away on a side street near Camden Lock. What a great recommendation. The café itself is quite small and could be described as ‘cosy’. As the name suggests, it is on a corner, meaning that there are plenty of window seats on which to perch while enjoying your coffee. We ordered an Americano and a Flat White (Nude roastery) and couldn’t resist trying their muffins (which were very good). The atmosphere in the café was relaxed and, in a nice touch, dotted around the room were a variety of potted plants.

The strangely leaf-less plant at the Corner One
The strangely leaf-less plant at the Corner One

After a while, our attention was drawn to one plant in particular that had no leaves on it, although the flowers themselves seemed very healthy. This observation reminded us of the importance of plant life (and leaves) in the global environment and the fact that this week, diplomats from 200 countries are meeting in Geneva to edit the text agreed at the Peru climate summit. Their aim is to get the text into a form that could become a legally binding agreement at the climate talks to be held in Paris in December.

Plants are an essential part of the ecosystem of our planet. They absorb carbon dioxide and produce oxygen during photosynthesis. Another important contributor to the world’s oxygen supply are algae, as I became aware when I went to a recent Café Scientifique at the Royal Society (free and open to all). Dr Sinead Collins of Edinburgh University was describing her work on algae and what may happen to them as the oceans become more acidic. (The audio recording of the evening is available here). Ocean acidification is a consequence of increasing CO2 in the atmosphere. As CO2 dissolves in the sea water, it forms carbonic acid thereby increasing the acidity of the oceans (for more information click here). This increased acidity affects the ocean’s plant and animal life in ways that we are only just starting to understand. The evening emphasised how important it is to address the issue of climate change before it is too late.

latte art, flat white art
What the plant lacked, the coffee made up for

During the meeting, Collins mentioned that she preferred the term “global weirding” to “global warming”. The term does indeed convey the fact that a large greenhouse effect would make the weather system highly unpredictable rather than merely ‘warmer’. We should expect odd weather if we continue to pump CO2 and other greenhouse gases into the atmosphere. It is critical that the draft text currently being discussed in Geneva is agreed in Paris this year. We need a legally binding agreement to reduce our greenhouse gas emissions. Already our aim is very low; to reduce global greenhouse gas emissions to a quantity that would limit the global temperature increase to not more than 2°C higher than pre-industrial levels. Even so, this modest aim occasionally seems too high.

Let’s hope that the diplomats in Geneva this week and then the world leaders in Paris from 30 Nov – 11 Dec, agree to limit our CO2 emissions to that we can continue to enjoy our coffee.

The Corner One can be found at 20 Oval Road, NW1 7DJ.

Categories
General Science history slow

Of worms and grind

coffee ground, grind, composting
What do you do with your used coffee grounds?

What do you do with your finished coffee grounds? Feed them straight to the plants? Donate them to Biobean to be transformed into fuel? Or perhaps turn them into compost with a worm bin? Ground to Ground is a website dedicated to sharing information about what can be done with old grounds. My preferred option though is the worm bin. Each Chemex of coffee grounds gets put out into the “can-o-worms” compost bin ready to be transformed into compost and plant fertiliser.

I had thought that there could be very little connection between my worms (so to speak) and the Bean Thinking website. However, I recently came across an anecdote about Charles Darwin that, to me at least, unites some of what Bean Thinking is about with my can-o-worms.

can-o-worms, worms, coffee grounds, composting
The top layer of my worm bin. You can just see some coffee grounds but it is mostly cabbage.

Darwin’s last book was “The formation of vegetable mould through the action of worms” published in 1881. After Darwin’s death (in 1882), Edward Aveling (1849-1898) wrote about meeting Darwin years earlier. In “Charles Darwin and Karl Marx: A Comparison” (1897), Aveling wrote: “I remember, in my youthful ignorance, asking Darwin why he dealt with animals so insignificant as worms. I shall not forget his reply, or the look that accompanied it. ‘I have been studying their habits for forty years’.”

By studying what to others looks insignificant, Darwin had made huge progress in our understanding of worm behaviour. This has led to our current knowledge about the contribution of worms to the ecosystem and the benefits of composting our coffee grounds, both for our plants and our planet. It strikes me that we can all benefit from slowing down and noticing what seems insignificant.

Perhaps you do something unusual with your old coffee grounds? Maybe you have noticed something about coffee grounds and worm behaviour. Whatever it is, do let me know in the comments section below.

Categories
Coffee cup science Coffee review General Observations slow

Rain drops at Notes, Covent Garden

Notes Covent Garden, rain, puddles
No one wanted to sit outside when we visited Notes at Covent Garden

It was a cold and wet afternoon in early January when I finally had the opportunity to try Notes (Covent Garden branch). Inside, there were plenty of places to sit while warming up and drying off enjoying a coffee. Although it seems small from the outside, inside, the branch feels quite open, with the bar immediately in front of you as you come through the door. One of the attractions of Notes to me, was the fact that I knew that they served different single estate brewed coffees. I think I tried a “La Benedicion” coffee, or at least that is what I seem to have scribbled in my notepad. We took a stool-seat at the window to look out at the rain as my coffee arrived in a 0.25L glass jar. It is always nice to try different single estate coffees and generally, if I know that a café serves single estate coffees I will seek them out to try them for the Daily Grind.

The reflection of the Notes sign board in a cup of tea
The reflections in a cup of tea

Watching the rain form puddles outside, my thoughts were turned to the reflections bouncing off the water in the puddle. It struck me that the appearance of puddles depends on the water molecules behaving both as individual molecules and as molecules within a group. The rain creates ripples in the puddle which can only occur because each molecule is (weakly) attracted to the other water molecules in the puddle, forming a surface tension effect. A ripple is a necessarily collective ‘action’. On the other hand, the reflection of the lights from the street is the response of each individual water molecule to the incoming light. The reflected image is made from the response of many individual molecules. Reflection is more of an individual molecule thing.

Warning sign, train, turbulence
Such turbulence should be familiar to anyone who has stirred a cup of coffee.

I continued thinking about this when I got home where it occurred to me that there was another connection between rain and coffee. It is often said that “rain helps clear the air”, or something similar. Yet this is not quite true. If you have a coffee in front of you at this instant, take a moment to drag a spoon through it. Note the vortices that form behind the spoon. Such vortices form around any object moving through a fluid. In the case of the coffee it is the spoon through the water. For the rain, as the rain drop falls through the air it creates tiny vortices of air behind it. Just as with the coffee spoon, the size of these vortices depend on the speed and size of the falling drop. These vortices pull and trap the atmospheric dust bringing it down to earth more quickly than rain alone could do. The air is cleaned more by this ‘vacuum cleaner’ action than by the ‘wet mop’ of the rain itself.

I’m sure that there are many other coffee-rain connections that you can make if you sit in a café as I did on a rainy day. Let me know your thoughts on this or indeed, on anything that you notice and think interesting while sitting in a café. There is so much to notice if we just put down the phone or close the laptop while enjoying our brew.

Edited to add: Sadly, this article was posted just as Notes Covent Garden was closing down. Notes still has branches at Trafalgar Square and in Moorgate and is opening new branches in Kings Cross and Canary Wharf in February I believe. Hopefully they will all serve single estate brewed coffee and have good window seats from which to observe the rain when it falls.

Categories
Coffee cup science General

Getting my teeth into some latte art

LatteArt_CoffeeworksEach year, in the UK, there are approximately 160 000 hip or knee replacements. Additionally, many of us will have a dental implant during our lifetime. How is this linked with coffee? The answer lies in the differences between a latte and a cappuccino.

To support the artwork that can be seen on many a latte, the milk foam used for the drink is a fine “micro-foam”. It is quite a soft structure. On the other hand a cappuccino is more rigid, being made out of a larger foam structure. The different way that a barista froths the milk for a cappuccino compared to a latte means that the peak structures that can be formed in the cappuccino, are far more difficult to create in a latte, the cappuccino has more of a “meringue like” froth.

Joint replacements and dental implants were traditionally made from solid metal. This meant that the majority of the load that was put on the joint (by walking or chewing for example) was carried by the implant. It is thought that this was one of the reasons that joint replacements and dental implants eventually failed; the bond between the bone and the implant became progressively weaker in a process called “aseptic loosening”. In recent years there have been many improvements to joint replacements/implants so as to avoid these problems. One such improvement is to manufacture the implant out of a metallic foam instead of solid metal.

Cappuccino showing peaks in the foamJust like a latte or a cappuccino, the way that the metal foam responds to stress (and its rigidity) is dependent on many factors including the size of the bubbles in the foam and exactly what the foam is made from. (Imagine comparing a cappuccino with a soya milk cappuccino). By manipulating the structure of the metal foam, an implant can be made that behaves almost exactly as bone does when stress is placed on it. Together with the inherently stronger bone-implant bond created by the bone growing into the ‘bubbles’ of the implant foam, this is thought to reduce the risk of implant failure owing to ‘aseptic loosening’.

I am indebted to Michaela and Juan of Poppy’s Place for patiently showing me the art (and science) of making coffee. With good coffee (from Climpson & Sons) and knowledgeable barista-teachers, it is a place that I am sure that I will return to very soon. Michaela and Juan assured me that if I would like to see a properly rigid milk foam I should order a “babyccino”. There are however limits to the amount that I am prepared to ‘suffer for my science’ and the babyccino is it. If you would like to properly investigate the effect of bubble structure on the ability of an implant (dental or otherwise) to take stress, I suggest you compare a latte with a babyccino. If, like me, you like your coffee, a cappuccino will definitely suffice.