Author: beanthinking

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Coffee cup science Home experiments Observations

Aroma and batch brew

Isn’t it great to find a lovely, freshly brewed, hot cup of aromatic coffee in a quirky little café? Which bit do you enjoy most? That special aroma as you inhale the steam above your cup before sipping the coffee to compare the taste with the smell?

2-furfurylthiol
Representation of 2-furfurylthiol. Amazing what can be found (briefly) above your coffee cup.

As you may imagine, a fair bit of research has gone into working out which chemicals are responsible for that just brewed aroma (for a review see here). More than 800 volatile chemicals have been identified as key to the aroma of coffee of which the most important for that freshly roasted and brewed coffee smell seems to be 2-furfurylthiol. Although it has a complicated name, it’s got a fairly simple chemical representation (shown right). Responsible for the “roast-y, sulphur-y” smell in freshly brewed coffee the problem for us, and for 2-furfurylthiol, is that it is not very stable. In fact, in experiments in which a freshly brewed coffee was stored in a thermos flask to keep it warm, the concentration of 2-furfurylthiol in the space just above the coffee decreased by more than 50% within 20 minutes of storage. After an hour, the concentration of 2-furfurylthiol had decreased to less than a quarter of its original amount and shortly after that, it was gone completely (study can be found here). (Other volatile aromatics decreased similarly (here)).

So if you were to brew a coffee, put it in a flask to keep it warm and then drink it within 20 minutes, you will have lost more than half of the lovely coffee smell. And if, heaven forbid, you were to take it from its thermos 1hr after brewing, almost all those wonderful aromatics would have decayed away.

Lundenwic coffee
This was not a batch!
Could you taste the difference between freshly made drip brewed coffee and batch brew?

Why is this important? Well, it’s about batch brew. You may have noticed that batch brew is increasingly popular in many cafés. Offered as a way of getting a filter coffee ‘freshly’ prepared for you without the hassle of actually having to have the filter made there and then. Different establishments try to get around the inevitable aromatic loss by changing the batch every 30 minutes or storing it in a ‘low oxygen’ environment, but is this enough? Do we need some blind taste-tests on batch brew?

A problem is that the decay of 2-furfurylthiol is not just due to oxidisation. Sadly for us, its decay seems to be intimately tied to other qualities that we appreciate in the coffee, the melanoidins (that make the coffee brown) and other chemicals formed during the roasting process (the phenols and the quinones). So even in a low oxygen environment, that aromatic 2-furfurylthiol is going to react with the other chemicals that make coffee great to make batch brew less great.

weather, bubbles, coffee, coffee physics, weather prediction, meteorology
It’s all in the 2-furfurylthiol. That fantastic coffee aroma is due to a number of unstable aromatic compounds that rapidly decay after the coffee is brewed.

That’s the theory. Clearly many cafés have taste-tested the batch brew and found that it doesn’t make enough difference to be concerned about. And in practice there are many other factors that may make a batch brew better than a fresh drip coffee you can make at home (though it would be great if someone could point some of these out for me!), what we need is a citizen science type taste test. A blind test of the same bean, prepared as a fresh filter and a cup at the end of the storage life of the batch. They will most likely have different temperatures so this would need to be considered, either by pouring very little of each (so the fresh-filter cools quickly), or waiting for 5 minutes for your cup of fresh-filter to cool to the batch temperature. Do they taste the same? Do they smell the same?

So this is a call for some science experiments “in the field” (and seemingly for everyone to drink more coffee). If you enjoy a cup of “batch” and are a regular at a café, please do drop me a note to share your blind taste-test experiences. If you are a café, any tips you have as to how to store warm coffee for longer than 20 minutes without compromising the aroma would be very interesting to hear (though if you find a café storing batch for longer than approx. 30 minutes, I would seriously consider going somewhere else!). And if you just drink coffee at home, why not get involved too, prepare a filter coffee that you store in a thermos and another a bit later ‘fresh’, get someone to help you so that you taste them ‘blind’ and let me know what you think. The comments section below is always available, otherwise I can be found on Twitter and Facebook and will happily debate there.

Enjoy your coffee!

 

Categories
Coffee cup science Coffee review General Home experiments Tea

The idea of a coffee at A Wanted Man

“We cannot do without a view, and we put up with an illusion, when we cannot get at a truth“.

A wanted man, Chelsea, coffee cup
A wanted man becomes visible under thin coffee.

A Wanted Man on Chelsea’s Kings Road is unusual in many respects. Firstly, never before have I been to an espresso ‘canteen’, but then, neither have I had a coffee in a café that is part coffee-shop part waxing salon. While both wax based hair removal and coffee rely on bees, this is surely not the connection between these two enterprises. Nonetheless, once your coffee-loyalty card is full, you can choose: free brow shape, bikini wax or coffee. The coffee comes from Common Man Coffee Roasters in Singapore so it would be interesting to know how it was transported to Chelsea in order to retain its freshness, surely each batch is not flown in? On our first visit, we had a rich and smooth long black, a lovely aromatic banana bread and a good hot chocolate (with soy milk). There is plenty of seating in the front of the café and some more towards the back near the bar which was all fairly empty on our first visit but far more crowded (with singly-occupied tables) on my second visit (see below).

As I drank my coffee, hidden wording became visible at the bottom of the cup. “A wanted man” appeared beneath the coffee when the coffee was sufficiently thin. By tilting the cup, this “critical” thickness could be estimated, as you can see in the photos. Ah-ha I thought, the physics bit of this cafe-physics-review will be easy! The absorption of light (which we could measure by the visibility of the writing at the bottom of the cup) is directly proportional to the thickness of the absorbing liquid, the coffee. This is the Beer-Lambert law which describes how light is absorbed through substances such as coffee in which there are molecules and bits of sediment that absorb light (which is ultimately why coffee appears brown). Could I experimentally verify this bit of the Beer-Lambert law by somehow quantifying the visibility of the wording as a function of cup-tilt angle?

a tilted coffee cup at a wanted man
Absorption is a function of thickness and concentration

Before I had thought that far, I had finished the coffee, however the second part of the Beer-Lambert law could be tested by having another coffee on a separate occasion. The other part of the Beer-Lambert law states that the absorption (that’s the (in)visibility of the wording on the cup in this case) is also directly proportional to the concentration of the absorbing molecules/sediment. This makes sense, weak coffee is far more transparent than overly extracted coffee. On my second visit, the coffee tasted slightly stronger, a bit different from my memories of the first occasion. Did the “A wanted man” become visible at a different tilt angle? I would guess – or perhaps that should read ‘hypothes-ise’ – that the angle on the second occasion would have to be lower (that the coffee would have to be thinner generally).

However, while sipping my coffee (before getting to the tilt-angle-test) and looking around the second time I noticed that all along the wall where previously there had been plenty of empty tables, each one was now singly occupied by somebody using a laptop, a phone/tablet or in one case, both of these items together. This second time, my mind started wandering into more social issues, while looking at our screens and immersed in social media, are we able to see more or less, than our less absorbed fellow citizens? Does social media clarify the detail or cloud important aspects of our understanding?

Beer-Lambert applied to twitter and Facebook
Does social media do this to you? The light absorption of a coffee is determined by the thickness of the coffee and concentration of absorption sites within it.

After considering these two points, it became clear that in some ways they are connected. Admittedly a loose connection, and not one that is strictly scientific but perhaps it’s worth ‘running with it’ for a bit and seeing if it leads anywhere. Just as with the Beer-Lambert law with coffee, the more ‘interacting sites’ (or absorption sites) we encounter on social media, the harder it is to see through to the bottom. Twitter, Facebook etc. can be enormously helpful for widening our networks and learning about new things. But, as has been frequently pointed out elsewhere, they can also become quite unhelpful when we are in an “echo chamber” or when we think that points can be made in mere soundbites. Is it possible that the more absorbing and reflecting sites that we encounter, the harder it is to see anything to any greater depth? What we need is time-out, for self-reflection and for considering points made by others, on Twitter, Facebook and elsewhere.

Perhaps the best way to end such a post is with a long quote by somebody else. In fact, the same person (and in the same book) as was quoted at the beginning of this article. Perhaps it would be something to consider while we drink our coffees and hover over the ‘retweet’ or ‘share’ button. Are we helping to probe the depths of our cup by the links we share, or are we merely adding to absorption sites in soundbites in our networks?

“It requires a great deal of reading, or a wide range of information, to warrant us in putting forth our opinions on any serious subject; and without such learning the most original mind may be able indeed to dazzle, to amuse, to refute, to perplex, but not to come to any useful result or any trustworthy conclusion. There are indeed persons who profess a different view of the matter, and even act upon it. Every now and then you will find a person of vigorous or fertile mind, who relies upon his own resources, despises all former authors, and gives the world, with the utmost fearlessness, his views upon religion, or history, or any other popular subject. And his works may sell for a while; he may get a name in  his day; but this will be all. His readers are sure to find on the long run that his doctrines are mere theories, and not the expression of facts, that they are chaff instead of bread, and then his popularity drops as suddenly as it rose.“

John Henry Newman, The idea of a university.

A Wanted Man can be found at 330 Kings Road, London

Categories
Coffee cup science General Home experiments Science history Tea

Reading tea leaves with Einstein and my great-grandmother

tea pot science
It’s not just tea, Einstein is famous for some other physics too

Ask anyone what Albert Einstein is famous for and you’ll probably (hopefully) hear that he came up with the theory of relativity (special and general). Perhaps you may also be told that he came up with a little theory explaining the photoelectric effect for which he won the Nobel prize in 1921. Maybe, if you have read this website before, you will know that he contributed to our understanding of Brownian motion, which is a phenomenon that is frequently found in a coffee cup. But it turns out that Einstein wrote another paper, far more important than any of these others, which was about tea. Or at least, I suspect my great-grandmother would have found it more important than any of these others as it coincided with a special hobby of hers, reading tea leaves.

It seems that my great-grandmother used to enjoy reading tea-leaves. Whether it was something she had learned as a child or merely used as an interesting trick to perform at family functions, stories of her examining the patterns formed by swirling tea leaves in a cup have come down to us in younger generations. Einstein too had noticed the patterns formed by the tea leaves in the cup and had observed a problem. The problem is this: If you drink a cup of (inadequately filtered) loose leaf tea and stir it, the tea leaves collect in a circle in the middle of the base of the cup. At first this may appear counterintuitive. When we stir things, don’t things fly outwards towards the edge of the cup rather than inwards to the centre of the circle? Why is it that the leaves collect in the middle?

Thames, NASA image
How do rivers erode? What causes a river to meander? The meandering Thames, photographed by NASA, Image courtesy NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

For Einstein, this tea leaf problem was connected to another phenomenon, the erosion of rivers. But it turns out that the problem is also linked to issues found in beer brewing and blood tests, and it seems, in how to poach an egg. To see the solution and therefore the connections, we need to think a bit more about how water flows. One of the brilliant lines in Einstein’s paper starts “I begin with a little experiment which anybody can easily repeat.” This experiment is to obtain a flat bottomed cup of tea with some tea leaves at the bottom of it. Now stir the tea and watch how the leaves settle, Einstein continues “the leaves will soon collect in the centre of the bottom of the cup“.

The explanation is connected with the fact that at the walls of the cup, the liquid (tea) is being slowed down by the friction between the walls and the tea. Secondly, as the tea is stirred, the surface of the tea becomes concave with a distinct dip in the centre of the swirling tea. The result of all this is that a secondary rotation is set-up where the tea flows down the sides of the cup, along the bottom and then back up in the centre and once more to the sides (have a look at the diagram, some things are easier with pictures). As they are carried along with the water, the tea leaves move towards the centre of the cup but then, being too heavy to rise again with the tea up to the centre of the cup, they stay on the bottom forming a circular patch of tea leaves.

adaptation from Einsteins paper
The secondary circular flow set up in a tea cup when it is stirred leads to a circular deposition of tea leaves (figure adapted from Einstein’s 1926 paper).

When you think about how water flows as it goes around a bend in a river, you could perhaps imagine a similar secondary flow being set up but this time from the inner edge of the bend to the outer edge and back down (so, like half a tea cup). As the water is going to be moving fastest at the outer edge, just before it plunges down towards the bottom of the river in this secondary cycle, any river erosion is going to be most noticeable on the outer edge of the bend.

It seems the effect is also used in beer brewing in order to introduce a greater concentration of hops into the brew, and to separate different types of blood cell in blood tests. So this just leaves the poached eggs. How do you poach eggs? If you have a proper poacher perhaps you get neat eggs each time but for those of us without them, poached eggs tend to be a messy cooking project. But worry no longer! Just as tea leaves collect in the centre of a tea cup, so will the egg if you ensure that your pan of boiling water is swirling around the central axis before you put your egg in. Cooking helped by physics, perfect.

For reasons of full disclosure, I should emphasise that I have only recently found this suggestion for cooking eggs ‘theoretically’ and not yet tested it. So, if you were looking for reasons to drink loose tea, or wanted to poach an egg without a poacher, perhaps you could try Einstein’s little experiment and let me know how you got on, I’d love to hear your tea leaf readings and see your poached egg results.

Categories
Coffee cup science Coffee review Observations Science history Tea

Coffee innovations at MacIntyre, Angel

MacIntyre Coffee AngelOne motivation behind Bean Thinking is to explore those connections that can be found when we stop to really look around us. Whether your interest is in history, philosophy or science, something in a café will prompt a train of reflections that can lead to interesting and surprising thought journeys. This is surely true for anybody in any café, if we just take the time to slow down. But, I admit a prejudice: while I had heard great things about the coffee in MacIntyre, when I had glanced in from the bus window, I saw the scaffolding seating arrangements and wooden surfaces that can be a type of design found in many new cafés. So I worried. Was it going to be hard to ‘see the connections’ in MacIntyre? Would I end up with a great coffee but a challenge to my assumptions about the ubiquity of connectivity?

Fortunately, I needn’t have worried. The two lovely coffees that I have enjoyed at MacIntyre gave me plenty of time to really savour both the coffee and my surroundings and I was wrong in my assumptions from the bus window, connections really are everywhere. The café itself was a delightful find. Watching other customers while drinking my long black, it seemed that everyone was greeted by a cheery “hello”. Many people were clearly regulars, which is perhaps unsurprising for a friendly café with good coffee in a busy area. The scaffolding and wooden seating also works in the space at MacIntyre, giving a strangely relaxing feel to the café. The café itself is rather narrow, with the seating on one side and pastries/ordering queue on the other. Tap water was delivered with the coffee, without my needing to have asked for it.

Plant, light, scaffolding at McIntyre's Angel
Good scaffolding also has good connections.
Plant and light at MacIntyre.

MacIntyre may also be a great spot if you are into people watching. Amidst the general busy-ness, I could eavesdrop on conversations about the latest coffee news and the rise of artificial intelligence (these were two separate conversations!). Perhaps the conversations were particularly noticeable owing to the acoustics of the wooden walls and the narrow, small space of the café. At various points around the café, plants hung from the scaffolding. Some of the plants were spot-lit, which caused me to wonder whether the light that the plants were receiving was optimal for photosynthesis. The menu was projected onto the rear wall of the café, which was also decorated with hexagons, an immediate connection to graphene.

But then, in my coffee cup, the significant crema on the coffee showed evidence of amazing thermal convective motion together with turbulence. The coffee itself was very sweet with nutty overtones but the movements of the crema reminded me of cloud formation in thunderstorms. Although thunderstorms didn’t make it to the thought train of MacIntyre, another form of surface motion suggested a connection to another, unusual, feature of this café. You see, MacIntyre is a cashless business, no cash is accepted even if you’re only buying a long black. Most customers on my visit paid with their contactless cards.

The idea of a cashless society is one that has obvious advantages for both the business and the government/economy (whether it has such obvious advantages for the consumer I will leave as a point to be debated). While some countries are attempting to move to a more cashless economy, for a business to be entirely cashless is somewhat innovative. Even though MacIntyre is not the only café to go cashless (Browns of Brockley is similarly cash free), it has to be one of the first cafés to do so.

Coffee at MacIntyre Angel
Coffee and water on wood at MacIntyre Coffee. Could you increase the returns on your investments by understanding the movements on the surface of a cup of coffee?

What is the connection between this and the surface movement on my coffee? Well, it is not just at MacIntyre that a café has supported an innovation that has (or may) change our economy. Just over three hundred years ago, Jonathan’s Coffee House in Exchange Alley was a place of similar innovation, though there it was a customer rather than the coffee house itself that gave the change.

It was at Jonathan’s in 1698 that John Castaing published a paper twice a week detailing the latest stock prices titled “The course of the exchange and other things”. Recognised now as the origin of the London Stock Exchange, how stocks are priced and how their prices vary with time are subject to intense mathematical modelling. Although now, these models can be extraordinarily complex, the base of many of them share a mathematical model with the movements on the surface of your coffee cup, Brownian Motion.

Jonathan's coffee house plaque
The site of Jonathan’s in Exchange Alley. Seen while on a Coffee House tour last year.

Brownian motion is the phenomenon in which small particles of dust, or coffee grains on the surface of your coffee move in a random way as a result of collisions between the particles and the molecules in the liquid. First described in detail by a botanist, Robert Brown in 1827, the experimental evidence in favour of the molecular-collision explanation of Brownian motion came in 1910 with Jean Perrin’s careful experiments (that have featured in The Daily Grind previously). The maths behind the explanation relies on the idea of the ‘random walk‘ in which each dust particle is ‘kicked’ in a random direction by the molecules in the coffee, the consequent motion being frequently described with reference to a drunkard attempting to get home after leaving the pub. However, as this concept of the ‘random walk’ was being developed for molecules in a liquid, it was simultaneously being developed to model the movements of stock prices by the mathematician Louis Bachelier. Bachelier’s model of stock prices turned out to be the same as the model of Brownian motion, but both developed independently.

As yet, it is unclear (to me at least) whether there is a link between cashless payments and some of the maths in your coffee cup but, MacIntyre would be a great place to contemplate this as you sip your brew. Never succumb to prejudices, on which note please do let me know what you think of cashless payments, a great convenience or an invasion of privacy?

MacIntyre can be found at 428 St John St, EC1V 4NJ.

Categories
Coffee cup science Home experiments Tea

Scratching the surface in coffee week

reflections, surface tension
The effects of surface tension can be seen in the light reflected from a coffee

UK Coffee week is once again upon us meaning that all week we can be justified in thinking about, drinking, appreciating and celebrating coffee. And of course, as soon as we start to do this, we realise we have to drink, appreciate and celebrate water which is, ultimately, what really makes most of the cup of coffee. So UK Coffee Week raises money for Project Waterfall which is a charity that brings clean water to coffee growing communities. Giving something back by enjoying something good.

In keeping with the water theme, this week The Daily Grind is all about water, including an experiment that enables you to make a hole in it. As this is also the week between Palm Sunday and Easter, perhaps we could call the post “Holey water for Holy Week”.

But moving quickly to the experiment. While drinking your coffee, you may have noticed how around the edge of the cup, the coffee appears lighter, not quite so dark, as in the interior. The coffee is being bent upwards at the edge of the cup by the surface tension of the water in the coffee. Now, what happens if you add alcohol to the coffee? If you do this in your coffee cup you may well end up with an Irish coffee which may provide even more of an excuse to celebrate your coffee drinking, but if you were to put your coffee on a plate first (I know, why? but bear with me) you will get a quite different result. You will be able to make a hole in the middle of your coffee. The reason is that the surface tension of alcohol is much weaker than that of water. Consequently, if you try to mix a very thin layer of coffee with a small amount of alcohol, something slightly unexpected happens as this video shows:

The addition of a small amount of alcohol into the middle of a thin layer of water (or coffee) causes the water to recede. As the alcohol evaporates off, you are left with a dry ‘hole’ in the coffee. Why is this? It is effectively a liquid-tug-of-war on your plate. The higher surface tension in the coffee (or water) pulls against the weaker surface tension of the alcohol which eventually means that the water breaks away, leaving the hole. As the water molecules are continually moving, eventually they start to meet again over the dry spot and close the hole.

You can’t see this in your mug of course because the mixing occurs throughout the liquid while the plate ensures that this is only a surface effect.

You will need a strong alcohol, perhaps gin or vodka but please do try this experiment, let me know how you get on and enjoy the coffee, water (and alcohol) in UK Coffee week. And if you want to donate to Project Waterfall, you could either find a participating café here or donate online here.

 

Categories
Coffee review Coffee Roasters Observations Science history Tea

Good vibrations at Vagabond, Highbury

black coffee, Vagabond, Highbury
A good start to the day. Coffee at Vagabond.

A long black, flat white (with soya milk) and a tea. Yes, you could say we spent a fair while at Vagabond in Highbury the other week. It was a lovely space to catch up with an old friend again. There were plenty of comfortable seats and the staff were definitely friendly, supplying us with coffee and space to chat for a while. The coffee was good (Vagabond are roasters as well as a café) with batch brew and Aeropress/drip on offer together with the usual selection of coffees and other drinks. Tasting notes were on a black board behind the counter while on the wall, also behind the counter, was a drawing of a tongue taste map. While the science of this has been disputed, it does serve as a reminder for us to sit back and properly appreciate – and taste – what we are drinking.

Above the espresso machine was a long rectangular sign that said “coffee in progress”, suspended by four cables, one at each corner. Coffee orders were placed onto this sign allowing the baristas to keep track of who ordered which drink. Given how busy this café occasionally got (and we weren’t even there for lunch), it seems that this is a very handy system. Each time an order was placed on the sign, the whole sign oscillated, rather like a rigid trampoline. Even if you had not seen the note placed on the sign by the barista, you would get a clue, a piece of evidence, that something had just happened by the vibrations long afterwards. Perhaps you may say that the sign was some sort of “order-detector”.

order detector oscillation espresso machine
The “order-detector”: sign at Vagabond in Highbury

Or at least, that is what you may say if you were thinking about the LIGO (Laser Interferometer Gravitational waves Observatory) detectors that, back in 2015, detected the gravitational waves produced by two merging black holes between 700 million and 1.6 billion light years away. Not only do these detectors have similarities to the order-detector sign at Vagabond, the beauty of the LIGO detector is that you can start to understand how it works by staring into your coffee. The LIGO experiment consists of two detectors. Each LIGO detector is an L shaped vacuum tube (4km long) with a mirror at each ‘end’. A laser beam is split between the two legs and reflected back by mirrors at the end of each L. When the reflected laser beams return back to the detector at the corner of the ‘L’, how they interact with each other is dependent on the exact distance that each laser beam has travelled between the mirror and the detector. Think about the bubbles on the surface of your coffee. These colourful bubbles appear as different colours depending on the thickness of the bubble ‘skin’. You may remember being taught that, exactly as with oil slicks on water, it was about the constructive and destructive interference of the light waves. As each ‘colour’ has a different wavelength, the colours that destructively interfere change with the thickness of the bubble skin. You can determine the thickness of the bubble by the colour it appears.

LIGO photo
An aerial photo of the LIGO detector at Hanford. The mirrors are at the ends of the tubes going away from the main building. Image courtesy of Caltech/MIT/LIGO Laboratory

In the LIGO experiment, there is only one wavelength because the light is coming from a laser. So whether the detector registers an intense laser beam or the absence of one, depends on whether those two beams coming back from the mirrors interfere constructively, or destructively. (A deeper description of the technique of “interferometry” can be found here). As the gravitational waves emanating from the collision of the black holes encountered the mirrors at the ends of the L’s in LIGO, so each mirror wobbled a little. This small wobble was enough to change the intensity of the laser light received by the detector and so reveal that the mirrors had moved just that little bit. In fact, the detectors are so sensitive that they can detect if the mirrors move by less than the diameter of a single proton. Given that this is a sub-atomic distance, I don’t think I can even start to relate it to the size of an espresso grind, even a Turkish coffee grind is millions (billions) of times larger than the amount that these mirrors moved. Yet this is what was detected a couple of years ago in the now famous announcement that gravitational waves had been detected and that Einstein’s predictions had been shown to be true.

Watching the “coffee in progress” sign oscillate at Vagabond, it is clear how much engineering has gone into isolating the mirrors at LIGO enough that they do not move as people walk by. Yet perhaps it is interesting that, nonetheless, one of the final refinements of isolating the mirrors from the vibrations of the earth involved changing the material for the cables that suspended them, just as with the sign at Vagabond. You can learn more about the engineering behind this incredible feat of detection in the video here, or you can go to Vagabond, enjoy a lovely coffee and think about the physics of detection there.

Vagabond (Highbury) can be found at 105 Holloway Road, N7 8LT

If you would like to hear what the collision sounded like, follow the link here.

 

Categories
Coffee cup science Observations Sustainability/environmental

Stirring up some climate science

Everything is connected. At least, that is part of the premise of Bean Thinking, where the physics of a coffee cup is used to explore the physics of the wider world. So it was great to stumble upon a new connection that I had not previously appreciated¹.

vortices in coffee
Like the vortices behind a spoon dragged through coffee….

The connection is between climate science and that wonderful pastime of pulling a spoon through coffee and watching the vortices form behind it. Yet the research that revealed this connection was not looking for links between coffee and the atmosphere. Instead the researchers were interested in something seemingly (and hopefully) very far from a coffee cup: rogue waves.

Rogue waves are rare and extremely large waves that have been the subject of mariners tales for many years. Nonetheless, it is only relatively recently that they have become the subject of scientific research, partly because they are so rare and so outside our usual experience that they were thought to be the stuff of myth rather than of science. So it is only now that we are developing an understanding of how it can be that, in amongst a number of smaller waves, a massive wave of 20m height can suddenly appear, apparently out of nowhere. One of the groups looking at this problem investigated the effect of a particular sort of (known) instability on a series of waves in water. However, unlike other research groups, this particular study included the effect of the air above the water as well as the waves themselves.

Small waves seen from Lindisfarne
Rogue waves seem to come out of nowhere. A rogue wave can be 2 or 3 times the height of the other waves in the water at the time. How and why do they form?

Although this sounds a simple idea, modelling water waves in air is actually extremely complex. To do so, the authors of the study had to use a computer simulation of the air-water interface. It is not the sort of problem that can be solved analytically, instead the computer has to crunch through the numerical solutions. In order to start to see what was going on with the rogue waves, the authors had to simulate multiple waves of different amplitudes. Each simulation took weeks to perform. Given that this was only a few years ago (the study was published in 2013), you can start to see why people had previously been approximating water waves as waves in water (without worrying too much about the air interface).

Now here is where the link with coffee comes in. The group modelled waves as a function of steepness and found that, above a critical steepness, the wave breaking caused significant interaction between the air and the water layers. In addition to the bubbles that form when waves break, the movement of the air over the breaking wave formed into a vortex which, when it interacted with the back of the wave created an opposite vortex: a vortex dipole “much like the vortices that form behind a spoon dragged through a cup of coffee“.

Rayleigh Benard cells in clouds
The water droplets that form clouds are often ‘seeded’ by particles of salt or dust, such as the aerosols distributed by the vortices in this wave study. Image shows clouds above the Pacific. Image NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

Just as with the vortices in the coffee cup, vortices were forming in the air behind the wave crest (which acted as the spoon) and travelled upwards through the atmosphere and away from the waves. As each wave broke, a train of vortex dipoles were produced that twirled off into the sky. Imagine a coffee bath and multiple spoons rather than a coffee cup. The authors suggested that these vortices could carry aerosols from the sea (salt, water droplets etc) into the atmosphere. Travelling within the vortices, these tiny particles could travel far further and far higher than we may have expected otherwise. Such aerosols can be critical for cloud formation and so the effect of these breaking waves could be important for climate modelling.

While an undergraduate, I had an opportunity to study a course in atmospheric physics. I remember the lecturer lamenting that while we (as a community, but not really as the students sitting in the lecture theatre at that time) understood atmospheric modelling quite well and that we understood how to model the oceans fairly well, we got problems when we tried to put the two sets of models together. It was clear that something wasn’t quite right. Years later, it seems that at least past of the reason for that is linked to those vortices that you see as you pull your spoon through your coffee cup.

Everything is connected indeed.

A summary of the study can be found here. The abstract (and link to the pdf) of the published paper can be found here. If you do not have access to the journal through a library, an early, but free, version of the paper is here – note though that this version may not include the amendments included after peer review.

 

¹A quote attributed to Jean-Baptiste Biot (1774-1862), is perhaps relevant here “Nothing is so easy to see than what has been found yesterday, and nothing more difficult than what will be found tomorrow.”

Categories
Coffee review General Observations Science history

Some perspective at Over Under, Earls Court

Over Under Coffee Earls Court
Follow the arrow! Over Under Coffee in Earls Court.

Whenever I’m heading somewhere that I haven’t been to for a while, I check the London’s Best Coffee app to see if any new cafés have popped up in the area since my last visit. So when I was in Earls Court recently, I was very happy to be alerted to a new café on the map with a review by Beanthereat.

Over Under Coffee is at 181A Earls Court Road but is tucked around the corner from the main road and so thank goodness for the helpful arrow (and the map which told me I should be on top of it). Once found, we ordered coffee and banana bread and took a table to sit down. The friendly staff behind the counter were quite confident of the ingredients in the banana bread as it is made locally by a lady in Fulham (whose name I have sadly forgotten). The coffee and banana bread formed a great combination for a mid-morning snack. Coffee is roasted by Assembly roasters over in Brixton and came with lovely interference patterns in the bubbles on the surface together with dancing white mists, which never fail to fascinate me.

On the table next to ours was a small Kilner jar for sugar and two succulent plants. The Kilner reminded me of the use of air valves in coffee packaging (which are non-recyclable plastic) and the interesting experiment by Roasting House coffee roasters to investigate whether they are actually needed for freshly roasted coffee (which you can read about here). However it was a picture above the table that prompted the thought-train for today’s Daily Grind. A charcoal sketch, the picture featured a tree in the foreground with a fence behind it. From a very early age we are taught how to represent 3D objects on a 2D sheet of paper, the idea of perspective seems ingrained on our minds. But how intuitive is it really?

perspective in coffee
A picture at Over Under. Note the smaller reflections of the (more distant) light fittings.

Although the ancient Greek artists could convey an idea of depth in their art, the development of a mathematical understanding of perspective only came with Filippo Brunelleschi (1377-1446), although a written account of the mathematics of perspective did not arrive until Leon Battista Alberti (1404-1472). Alberti’s method for drawing in perspective used not just a vanishing point, but an additional diagonal vanishing point in order to construct a sense of depth and an accurate depiction of perspective (a description of Alberti’s method is here). The development of the understanding of perspective during the Renaissance meant that for some paintings, the ‘viewing depth’ can actually be calculated, while other artworks managed to create optical illusions whereby objects would jump out at the viewer as if they are in 3D. Works such as Andrea Pozzo’s ceiling in the chiesa di Sant’Ignazio in which a flat ceiling appears magnificently domed. Or, closer to home,  Samuel van Hoogstraten’s work in the National Gallery in London in which the viewer looks through a peep hole to see the interior of a house complete with a dog that appears to be sitting up inside the painting. Such paintings required a knowledge of the mathematical rules behind the depiction of perspective. Isn’t it surprising that the understanding of these rules is so recent?

Over Under Earls Court
Coffee with bubbles showing interference patterns at Over Under Coffee

Another art work with an interesting use of perspective that will bring us, in some way, back to Over Under Coffee is Raphael’s fresco “School of Athens“. The two figures of Plato and Aristotle stand at the centre of a diverse group of philosophers including Socrates, Zoroaster, Euclid, Diogenes the Cynic and, possibly, an image of Hypatia of Alexandria. Although the use of perspective for the architecture draws your eye towards the centre of the picture, two spheres (held by Zoroaster and Ptolemy) on the right hand side of the picture are drawn as circles rather than ellipses. Spheres viewed from an angle should be represented as ellipses if drawn correctly according to the rules of perspective. Did Raphael make an error in perspective (that may work better for our eyes?) or is the degree to which these two spheres are distorted within the limits of the fresco brush and so not visible in the picture? An episode of Radio 4’s In Our Time discusses this picture at length including a deep conversation about the significance of Plato pointing upwards towards the heavens and Aristotle indicating towards the Earth. Plato’s wisdom and Aristotle’s knowledge, above and below, much like the weave logo that brings us back to Over Under Coffee.

Over Under Coffee can be found at 181A Earls Court Road, SW5 9RB.

 

 

Categories
Coffee cup science Home experiments Observations

Biscuit Crystals

biscuits gone wrong, crystals in the oven
Expanding biscuits are a 2D example of a close packed crystal lattice.

Blaise Pascal once wrote of the benefits of contemplating the vast, “infinite sphere”, of Nature before considering the opposite infinity, that of the minute¹. And although the subject of today’s Daily Grind involves neither infinitesimally small nor infinitely large, a consideration of biscuits and coffee can, I think lead to what Pascal described as “wonder” at the science of the very small and the fairly large.

The problem was that my biscuits went wrong. Fiddling about with the recipe had resulted in the biscuit dough expanding along the tray as the biscuits cooked. Each dough ball collapsed into a squashed mass of biscuit, each expanding until it was stopped by the tray-wall or the other biscuits in the tray. When the biscuits came out of the oven they were no longer biscuits in the plural but one big biscuit stretched across the tray. However looking at them more closely, it was clear that each biscuit had retained some of its identity and the super-biscuit was not really just one big biscuit but instead a 2D crystal of biscuits. The biscuits had formed a hexagonal lattice. For roughly circular elements (such as biscuits), this is the most efficient way to fill a space, as you may notice if you try to efficiently cut pie-circles out of pastry.

salt crystals
Salt crystals. Note the shape and the edges seem cuboid.

Of course, what we see in 2D has analogues in 3D (how do oranges stack in a box?) and what happens on the length scale of biscuits and oranges happens on smaller length scales too from coffee beans to atoms. Each atom stacking up like oranges in a box (or indeed coffee beans), to form regular, repeating structures known as crystal structures. To be described as a crystal, there has to be an atomic arrangement that repeats in a regular pattern. For oranges in a box, this could be what is known as “body centred cubic”, where the repeating unit is made up of 8 oranges that occupy the corners of a cube with one in the centre. Other repeating units could be hexagonal or tetragonal. It turns out that, in 3D, there are 14 possible such repeating units. Each of the crystals that you find in nature, from salt to sugar to chocolate and diamond can be described by one of these 14 basic crystal types. The type of crystal then determines the shape of the macroscopic object. Salt flakes that we sprinkle on our lunch for example are often cubic because of the underlying cubic structure on the atomic scale. Snowflakes have 6-fold symmetry because of the underlying hexagonal structure of ice.

It is possible to grow your own salt and sugar crystals. My initial experiments have not yet worked out well, but, if and when they do, expect a video (sped up of course!). In the meantime, perhaps we could take Pascal’s advice and wonder at the very (though not infinitesimally) small and biscuits. And if you’re wondering about where coffee comes into this? How better to contemplate your biscuit crystals than with a steaming mug of freshly brewed coffee?

¹Blaise Pascal, Pensées, XV 199

Categories
Allergy friendly Coffee review General Observations Science history

Thinking space at Le Peche Mignon

Coffee in Le Peche Mignon, Highbury, Islington
Le Peche Mignon in Highbury, hidden down a side street.

It was a balmy February morning when I met an old friend at Le Péché Mignon on Ronalds Road near Highbury and Islington. I had first come across Le Péché Mignon a few months ago when I had had a lovely coffee (and a great cake, I remember the staff being very helpful to check the ingredients for my nut allergy) but too little time to properly think about the space. So, when the opportunity arose to meet a friend (who I have known since we were both 5 but haven’t seen for many years) near Islington, I jumped at the opportunity to meet there.

This small but delightful café seems to be very popular. Both the bench seat in the window (where I had sat last time) and the long, sharing-table in the middle of the café were practically full by the time we arrived in the mid-morning. Fortunately, there was plenty of space in the quiet garden at the back for us to catch up for a couple of hours (and a couple of coffees!). The coffee is roasted by Monmouth, the Americano was very well done and there were quite a selection of pastries and salads on offer. One wall of the café was lined with bottles of wine while Carambars were available to purchase next to the counter.

brick wall at Le Peche Mignon
A join between two brick walls at Le Peche Mignon. How exactly are bricks made and why are they made that way?

The garden behind the café had plenty of tables and, even though it was February, it was warm enough for us to sit comfortably outside. One of the walls of the garden was formed by two sets of brick walls that had a join between them. The appearance of a separation between the walls, together with the weather, reminded me of the crack and the imminent demise of the Larson C ice shelf. However as this was probably too close to recent posts about climate change, I started thinking about defect structures in crystals instead. While pondering this though, my thoughts turned to an entirely different subject matter, the unusual toilet at Le Péché Mignon.

Just as the toilets in our old primary school, the toilet at Le Péché Mignon is outside, in the garden. This got us reminiscing about our old primary school which, during winter, regularly closed when the outside toilets froze (hopefully not a problem for the toilets at Le Péché Mignon!). And while the school has undergone significant renovation since then, it does get you thinking about the history (and engineering/science) of toilets. While this may seem an unpleasant subject for, what is after all a café review, please do bear with me because thinking about toilets can lead to surprising connections. For example, a recent New Yorker article about confirmation bias featured quite a discussion on toilets. How? It seems that while people generally tend to think that they understand how a toilet flush works, when asked to explain it step by step, they suddenly become far less confident. Our knowledge is not so great as we tend to think it is.

cup of coffee in Le Peche Mignon
From coffee cups to aeroplanes, the hardness and porosity of materials depends on the temperature that the starting materials were ‘baked’ at.

Which brings me back to Le Péché Mignon. The issue of flushing toilets became a problem for London in the mid-nineteenth century when the introduction of the “water closet” increased the volume of water flowing into the rather inadequate sewage system (if you are interested in the history of the toilet you can click here). The great engineer Joseph Bazalgette (1819-91) was commissioned to design and build London’s sewer system in which a network of tunnels were built across the capital. Bazalgette’s northern branch lies about 5 minutes walk north of Le Péché Mignon and runs from Hampstead Heath to Old Ford in Stratford. A distance of just 9 miles (14.4 Km), this particular tunnel has a remarkably steep gradient dropping at least 4feet (1.2m) every mile (1.6 Km). Imagine water flowing down a plug hole. The turbulence and speed of the water (ahem) flowing down this ‘drain’ means that Bazalgette had to think very carefully about how he lined this particular tunnel. If he had used ordinary bricks, such as those that make up the wall around the café’s garden, they would have eroded quickly with the turbulent motion of the water. Consequently, Bazalgette specified Staffordshire Blue bricks¹ to line this tunnel. During the manufacturing process, Staffordshire Blue bricks are baked at very high temperature (and in a low oxygen atmosphere) making them particularly resistant to erosion and to water absorption. It should not surprise us that the hardness, brittleness and texture of materials should be affected by the temperature at which they are formed after all, great care is taken about the temperatures at which chocolate is melted and allowed to re-solidify. Indeed, a vast amount of research is done to understand how different materials (from ceramics to metals) respond under different heat treatments. This research is important for applications as diverse as the walls of sewer tunnels to the design of aeroplanes. And, of course, to the design of better coffee cups, a thought with which we can return to thinking about this great little café.

Le Péché Mignon can be found at 6 Roland’s Road, N5 1XH

¹”The Great Stink of London…” Stephen Halliday, Sutton, 1999

 

 

http://www.plumbing-geek.com/howdoesatoiletwork.html

http://www.baus.org.uk/museum/164/the_flush_toilet