General

Semi skimmed at Full Fat, Balham

exterior of Full Fat Balham

The shopfront almost seemed to skinny for the name of this cafe.

Just around the corner from Balham tube station, on Chestnut Grove is a new (old) café, Full Fat. Although it has only been in its current location since September 2018, it was previously known as the Balham Kitchen and was apparently quite popular, not just because it was a friendly local café, but also because of the coffee and the chapatis.

We had chanced upon Full Fat while in Balham and took the opportunity for a chapati brunch. During our coffee break several customers came in and had a chat with the two people behind the counter. With coffee roasted by Workshop and an excellent range of homemade chapatis, along with friendly people, what is not to like? We enjoyed an Americano and an oat milk hot chocolate together with two chapatis. My egg chapati was perfectly done, just the right amount of pepper-to-egg balance. And the coffee was also very well made with plenty to think about just by gazing into it.

Although the café itself is quite small, there are three tables and several seats, enough to be able to ensure that you can probably perch somewhere to enjoy your coffee and chapati. There are even entertaining drawings on the walls of the café that make me wonder whether these are previous customers, immortalised on the walls enjoying a cup of coffee with their morning paper? Certainly they are a good reason to put down your smart phone and just soak in the atmosphere here.

pencil drawings in Full Fat

Pencil drawings at Full Fat Balham

Apart from the drawings, the other decoration in the café that caught my attention was behind another table: a striped piece of woodwork that was reminiscent of a type of cake served in Malaysia and Singapore, kueh lapis. It is a layered cake, the idea being that you peel each layer off to eat it, extending the enjoyment that you can get out of a cake. Although the layers peel easily, ordinarily the cake holds together as a cake, the layers do not glide over each other as if they are wholly separate, perhaps like chapatis stacked on top of each other. No, whether the cake works or not, as a kueh lapis, is down not just to the flavour, but also to the texture and to the way that each layer peels from the next, the subtle tug of one layer held, but not quite, by the last.

These interlayer or interface effects are often, ultimately, an atomic phenomenon. Just as when you drop a drip of coffee on the table, the thing that ultimately determines the shape of the droplet is the attraction between the molecules in the water and the atoms on the table surface*, so the stickiness of the cake has to be occurring, ultimately, at the atomic level.

Interface effects can be crucial in other solids too, not just coffee and cake. Consider sapphire. Sapphire has the molecular formula Al2O3. Ordinarily it is colourless and transparent, it becomes blue when impurities are added to it. But sapphire has another property which is that it is electrically insulating: a sapphire would not conduct any electricity if you tried to use it to connect to your light bulbs. This insulating behaviour is shared with another oxide, strontium titanate, SrTiO3, which is also a colourless and transparent material. Nothing of any interest there then. But, and this is the key thing, if you took a piece of strontium titanate and grew the sapphire on top of it, under certain growth conditions, this bilayer becomes extraordinarily electrically conducting, far better than many metals that you can think of. And it is because of the atomic effects that occur at the interface between the strontium titanate and the Al2O3.

Layering of wood at Full Fat

Can you see the layering on the wooden panel behind the table? Thought not, you’ll just have to visit Full Fat and see for yourself.

But then another example, a new finding that is perhaps more closely associated with coffee. When you take the semiconductor molybdenum ditelluride (MoTe2) and sandwich a thin layer of it between two sheets of graphene, some atomic-level interactions occur. In the case of MoTe2, the “band gap” of the semiconductor (which determines how it conducts electricity when light is shone on it) is altered by the van der Waals forces associated with the graphene layers: the interface effects are changing the way that the semiconductor reacts to light. Ordinarily if you shine a pulsed laser at such a semiconductor, the electrons† that get excited across the band gap are few enough that they behave as a gas within the semiconductor. This means that if you add more electrons (by pulsing the light on the semiconductor again), the density of the electron ‘gas’ will increase. What researchers have just shown is that for this 2D layer, if you shine very high powered lasers at the MoTe2 layer for a short length of time, so many electrons get excited that the semiconductor no longer behaves as if it contains an electron gas, but an electron ‘liquid’. A sort of droplet of electrons in the locality of the laser beam. And because of the way that the band structure had been affected by the interface layers, they managed to obtain this behaviour at room temperature. Although such liquids had been created before, the new thing about this result was that previously these experiments were usually done at very low (-269C) temperatures. Quite a temperature increase on previous results!

Droplets of an electron-hole excitation may seem a far step from the droplets of coffee that you could be enjoying at Full Fat. However, it is just a short hop for the imagination if you stopped to give it time to think. What will you notice next time you are in a café?

Full Fat is on Chestnut Grove, literally just around the corner from Balham tube station.

*Assuming that the table is flat. If the table is nanostructured, the structure itself can influence the ‘wettability’ of the table.

†Yes, and holes.

Coffee and science: a problem shared?

coffee and Caffeine at Sharps

What is the future of coffee? Science? Our society? Are these things held together more closely than we imagine?

There is a lot of science in coffee (and a lot of coffee in science). And there are also many scientists who are keen coffee drinkers and vice versa. But is there more in common between these two fields than even this? Could a shared problem be hiding a different (shared) problem?

One issue for coffee drinkers is reliability and reproducibility. How can we ensure that we get a good cup each time we visit a café or brew our own? In a similar way, how do we ensure that our experimental results in science are correct and reproducible? It is a fairly fundamental tenet of science that an experiment should be able to be reproduced in another lab with similar equipment. The suggestion is that this is not always happening, we have a ‘reliability’ problem in science (and sometimes in coffee).

A possible solution, in both fields, is some form of automation. In the world of coffee this is quite obviously just by making coffee via a machine. There have been several attempts to make reproducibly good coffee using an automated pour over machine. In the world of experimental science, it is not quite so clearly an automation process but is described instead as “data sharing”. The results of all experiments, or at least those that are published, should be shared (uploaded with the published paper) so that others can examine the data in more detail and form their own conclusions†.

For both coffee and science, it is suggested that this opening up of our process so that it is more transparent or reliable, will increase the reproducibility of good results and, crucially, mean that we get those results faster. We will get reproducibly good coffee without having to queue so long in the morning; we will make discoveries more quickly and have faster progress in science.

It seems that the problem that we thought we had, reproducibility, is perhaps not the one that we are actually aiming to solve. The problem we seem to be interested in is ensuring faster progress.

coffee under the microscope

We can look at coffee under the microscope (here are two different coffees ground to the same degree). But do we need to look more closely at the process of making good coffee or of doing science?

But an emphasis on faster progress can undermine our initial ideal of a reproducibly good result. For scientific research the emphasis on getting results quickly (at least within the time frame of the science funding cycle) has led to predictable problems. There are cases that I know about where results that were contrary to those that were wanted were suppressed. Not permanently. No, that would be demonstrably scientific fraud. No, suppressed just long enough for the first ‘ground breaking’ paper to be published. Then, after a suitable length of time, the second paper showing the problems with the first can follow up. Those involved get two papers (at least), and rapid progress is shown to be happening in the field. Would data transparency help here? Clearly not, because the initial set of data would still be suppressed until it was wanted those few months later.

What we need is a change in the structure of how science is done. We need to value scientific integrity and so trust that other scientists do too. We know that the current situation whereby promotions, funding etc are determined by the number of papers in ‘good’ journals, can act to undermine scientific integrity. This needs to change if the reliability issue is to be addressed. In the type of case described above, there would be no consequences for the people who kept their names on the paper(s) published. The only consequences would be if anyone refused to have their name on the paper as they knew it was misleading. And even then, the consequences would be to that person/those people in terms of their CV, and publication list, not those who published the paper and of course, shared the data.

coffee at Watch House

A good pour over takes time.
What are we looking for in coffee, in science? Is progress an aim of itself?

For the coffee, there are already discussions about whether the increase in throughput offered by automated coffee brewing techniques really contributes to the coffee experience that the cafés are trying to encourage. Can we really expect someone to slow down, take in the aroma, the mouthfeel, the taste and flavour if we rush the cup through to them on a production line? Isn’t part of the enjoyment of something to have to wait for it (hence lent before Easter; fasting before a feast)?

It is not that automation necessarily is bad. We can get a genuinely all round good coffee in a café that utilises a machine based pour over (perhaps). We can also get genuinely reproducible data in a situation where data is routinely shared. It’s just that data sharing does not solve the reproducibility problem, nor does automation give us continually good coffee. What makes the difference is a café that cares about the product that they are serving; scientists that care about the integrity of the research that they are doing. Automation processes give us faster results, they do not, automatically, give us better science (coffee).

Moreover, our desire for faster progress obscures questions that we should be asking if we slowed down a little. What is a good coffee experience? Who (if anyone) should own the scientific data shared? Is our desire for good coffee, quickly and (relatively) cheaply obtained, an aspect of that consumerism that is damaging for the planet’s ecological health? How much do we need to trust each other (and take responsibility for our own integrity) for our society, including our scientific society, to function? Is faster progress in and of itself, a “good” to aim for?

And perhaps, there is a final, more fundamental question. Have we become so accustomed to seeing ourselves and our work as merely a cog in a machine that we have become inured to the dehumanisation of society which seems to us almost natural and itself progress? Is this what we want for society?

The process of making a good cup of coffee indeed shares many things with the process of doing science. Perhaps this should not be surprising, both are practises embedded in our society. Certainly our view of the society that we live in can be informed by slowing down with our coffee as we enjoy a little science (or should that be the other way round)?

 

†It is not quite an automation process in the sense that the data is taken by a machine and then uploaded. However, it is still a dehumanisation process. At the root of the concept is the idea that the human experimenter can be taken out of the process. I would be happy to expand on this in the comments but for the sake of readability haven’t done so here.

To stay or to go at Cafe from Crisis

coffee commercial St volcano

Cafe from Crisis on Commercial Street, E1. Notice the arches…

It was not what I had expected. Entering the door of the Cafe from Crisis, you go up a ramp with a bench running alongside it before the counter looms in front of you with a large café space opening up to your right (previously partially obscured from your view by the wall for the ramp). Perhaps it is fitting that my expectations were wrong. Many of us have ideas about the homeless (why they are homeless, what homelessness is etc) that may not match fully with the reality. And this café is, after all, in the head office of Crisis, a UK national charity working with the homeless and homelessness.

The coffee is roasted by Volcano and there are a large number of food options (including vegan and veggie) and cakes at the counter. A selection of keep cups are also arranged in a rack on the left of the counter, should you not have one yet. We ordered an Americano and tea (to stay) and took our numbered wooden spoon to the table so that they could find us. Although it was late lunchtime and busy, the drinks arrived fairly quickly with the coffee in a (Crisis themed?) red cup. Apparently serving coffee in red cups make us perceive the coffee as warmer than if it is served in a blue cup. Whether this is true or not, the warm brew was very welcome on this cold January day. The café is situated on a street corner which means that it has many windows, each topped with a shallow arch. The building looks fairly modern from the outside, but the arches were reminiscent of the way that older buildings can be dated by the window style, along with other features. The Cure played in the background which entertained my tea drinking companion but made me wonder about the ideas of Pythagoras on the psychological impacts of different sorts of music (and whether it affected the ability to find thought connections in a café).

plant in a coffee cup

It turns out there are many things to notice in this photo. From the bricks to the self-defence tactics of plants. But what about the nature of the home of the plant?

As we sat, enjoyed our drinks and looked around, we noticed that some plants had found a home in coffee cups placed on the tables around. Small plants in plastic pots (a nod to the anthropocene as pointed out by @lifelearner47 on twitter) were dotted around the café. Did they move from an espresso to a long black cup as they grew larger? Perhaps it was the spiky plant in one of the pots, but my mind immediately jumped to hermit crabs and their search for a new shell each time they grew a bit bigger. Marine hermit crabs  have been shown to be happy in any old discarded shell. Normally these are the ex-homes of gastropods that have, well, “moved on” would be a euphemism, but marine based hermit crabs have been known to make their shells out of all sorts of things including our plastic litter. Land based hermit crabs however are far more demanding and only move into shells that have been specially remodelled by earlier generations of hermit crabs for their own use. This means that land based hermit crabs have to develop a social awareness of other hermit crabs when they want to swap shells.

Apparently the interaction goes something like this: A group of hermit crabs come together in a small-ish area and begin to scope each other out. The loose collection becomes a cluster as the crabs explore whether one of the larger crabs can be evicted from its shell. As the process of eviction is about to occur, the remaining crabs (which can number quite a few, 10 or more) literally ‘line up’ in order of shell size so that, when the largest is evicted, each crab can move up to the next sized shell leaving the smallest, most undesirable shell on the seashore and the poor evicted crab, shell-less.

Several questions arise but one is, do the crabs make decisions, “to stay or to go” based on how advanced the eviction process is? So, say a crab wanders into an area with an unusually large number of crabs in it (perhaps 4) but the crabs are all lined up in a queue ready to swap into each others shells. Do the crabs coming into the area stick around for a long time or do they head off somewhere else? Or, conversely, what if they enter an area where there are more than the usual number of ‘colleagues’, but they are all scattered about, not yet ready to evict the largest crab. What would our incoming crab do then?

coffee red cup Crisis

What would you learn if you noticed the connections your mind was forming while enjoying a coffee?

These questions were addressed by a group working with the terrestrial hermit crabs of Costa Rica. By defining five cells on the beach, each with a different arrangement of (empty but inaccessible) shells that the incoming hermit crab may want, the researchers found that the incoming hermits were making some strikingly sensible decisions. When the crab came into a region of scattered shells (that the incomer mistook for fellow crabs owing to a trick with a combination of loctite glue and partially burying the empty shells that the researchers used to fool the incomers), the incomer tended to stick around, waiting for an opportunity to swap a shell. If the incomer came but saw that the queue of shells had already formed, it still stayed a bit longer in the region relative to a control area devoid of shells, but it did tend to leave it after some time, perhaps to look for new shells elsewhere. The researchers concluded that when the crab came into an area and thought it had a pretty good chance of inserting itself into a good queue position, it would stay in the area waiting for the eviction to occur and the shell swapping process to start. However when the crab came into an area where the queue had already formed, it was unlikely to be able to get a good position in the queue and so would investigate the situation for a bit before wandering off elsewhere in the search of a new shell in a different area.

Does this have any relevance to a café trying to do a bit to address the problems of homelessness and the homeless in our city and country? I will leave that to each reader to ponder. However, it was a great opportunity to learn something new about our world, which only happened because I stopped to notice something in a café and then wondered how hermit crabs get their homes. It’s always good to slow down and notice things. What will you see next?

Cafe from Crisis (London) is at 64 Commercial Street, E1 6LT.

Telling the time with an Aeropress?

Aeropress bloom, coffee in an Aeropress

The first stage of making coffee with an Aeropress is to immerse the coffee grind in the water. Here, the plunger is at the bottom of the coffee.

On occasion, it takes a change in our routine for us to re-see our world in a slightly different way. And so it was that when there was an opportunity to borrow an Aeropress together with a hand grinder, I jumped at it. Each morning presented a meditative time for grinding the beans before the ritual of preparing the coffee by a different brew method. Each day became an opportunity to think about something new.

Perhaps it is not as immediately eye catching as the method of a slow pour of water from a swan necked kettle of a V60, and yet making coffee using the Aeropress offers a tremendously rich set of connections that we could ponder and contemplate if we would but notice them. And it starts with the seal. For those who may not be familiar with the Aeropress, a cylindrical ‘plunger’ with a seal tightly fits into a plastic cylinder (brew guide here). The first stage of making a coffee with the Aeropress is to use the cylinder to brew an ‘immersion’ type coffee, exactly as with the French Press (but here, the plunger is on the floor of the coffee maker). Then, after screwing a filter paper and plastic colander to the top of the cylinder and leaving the coffee to brew for a certain amount of time, the whole system is ‘inverted’ onto a mug where some coffee drips through the filter before the rest is forced out using the plunger to push the liquid through the coffee grind.

clepsydra creative commons license British Museum

A 4th century BC Ptolemaic clepsydra in the British Museum collection. Image © Trustees of the British Museum

Immediately perhaps your mind could jump to water clocks where water was allowed to drip out of two holes at the bottom of a device at a rate that allowed people to time certain intervals. It is even suggested that Galileo used such a “clepsydra” to time falling bodies (though I prefer the idea that he sang in order to time his pendulums). With many holes in the bottom of the device and an uneven coffee grind through which the water (coffee) flows, the Aeropress is perhaps not the best clock available to us now. However there is another connection between the Aeropress and the clepsydra that would take us to a whole new area of physics and speculation.

When the medieval thinker Adelard of Bath was considering the issue of whether nature could sustain a vacuum, he thought about the issue of the clepsydra¹. With two holes at the bottom and holes at the top for air, the clepsydra would drip the water through the clock at an even rate. Unless of course the holes at the top were blocked, in which case the water stopped dripping, (a similar thing can be observed when sealing the top of a straw). What kept the water in the jar when the top hole was blocked? What kept it from following its natural path of flowing downwards? (gravity was not understood at that point either). Adelard argued that it was not ‘magic’ that kept the water in when no air could go through, something else was at work.

What could be the explanation? Adelard argued that the universe was full of the four elements (air, water, fire, earth) which are “so closely bound together by natural affection, that just as none of them would exist without the other, so no place is empty of them. Hence it happens, that as soon as one of them leaves its position, another immediately takes its place… When, therefore, the entrance is closed to that which is to come in, it will be all in vain that you open an exit for the water, unless you give an entrance to the air….”²

inverted Aeropress and coffee stain

The Aeropress inverted onto a coffee cup before the plunger is pushed down. Complete with coffee stain behind the cup where the inversion process went awry.

Now, we would argue that whether the water flows down and out of the Aeropress, or not, depends on the balance of forces pushing the water down and those pushing it up. The forces pushing the water down and out of the clepsydra, or Aeropress, are gravity and the air pressure above the water in the cylinder. Pushing it up, it is only the air pressure from below. Ordinarily, the air pressure above and that below the water in the Aeropress are quite similar, gravity wins the tug of war and the water flows out. In an enclosed system however (if the holes at the top are blocked), were the water to flow out of the bottom, the air pressure above the coffee space would reduce. This makes sense because, if no new air gets in, the same amount of air that we had before now occupies a larger volume as the water has left it, the pressure exerted by that air will have to be less than before. A reduced air pressure means a reduced force on the water pushing it down through the filter and so the force pushing the water down can now be perfectly balanced by the force (from the surrounding air) pushing the water up: the water remains in the Aeropress. The only way we get the coffee out is to change the balance of forces on the water which means pushing down the plunger.

But perhaps it is worth stepping back and imagining what the consequences could be of having the idea that the universe was just full of something that had to be continuous. You may find it quite reasonable for example to consider that vortices would form behind and around the planets as they travelled in their circular orbits through this ‘something’*. Such vortices could explain some of the effects of gravity that we observe and so there would perhaps be no urgency to develop a gravitational theory such as the one we have. There would be other consequences, the world of vacuum physics and consequently of electronics would be significantly set back. In his lecture for the Carl Sagan Prize for Excellence in Public Communication in Planetary Science, The Director of the Vatican Observatory, Br Guy Consolmagno SJ explored previous scientific ideas that were almost right, which “is to say wrong” (You can see his lecture “Discarded Worlds: Astronomical Worlds that were almost correct” here) If it is true that so many scientific theories lasted so long (because they were almost correct) but were in fact wrong, how many of our scientific ideas today are ‘almost correct’ too?

It makes you wonder how our preconceptions of the world affect our ability to investigate it. And for that matter, how our ability to contemplate the world is affected by our practise of doing so. They say that beauty is in the eye of the beholder. For that to be true, the beholder has to open their eyes, look, contemplate and be prepared to be shown wrong in their preconceptions.

What connections do you make to your coffee brew each morning? I’d love to know, here in the comments, on Twitter or over on Facebook.

 

* Does a connection between this and stirring your freshly brewed Aeropress coffee with a teaspoon trailing vortices stretch the connectivity a bit too far?

¹ “Much Ado about Nothing: Theories of space and vacuum from the Middle Ages to the Scientific Revolution”, Edward Grant, Cambridge University Press, (1981)

² Quoted from Adelard of Bath’s “Quaestiones Naturales” taken from Much Ado about nothing, page 67.

Corona gazing in cafes

interference patterns on coffee

There are many ways in which rainbows of colour are produced as light interacts with our coffee or in a cafe. Looking around yourself now, how many do you see? What physics underlies each?

As the nights grow longer and the days colder, we notice that windows steam up as the water vapour in the café condenses onto the cooler glass. Perhaps we see a similar thing on our glasses while we are drinking tea or on the windows of a bus. Initially we perhaps become frustrated at our inability to see what is going on outside but then we notice the colourful patterns around the lights of passing cars and of street lights. Haloes of coloured light around a central bright spot. What does this tell us and where else can we see it, either in a café or in life generally?

On a window pane, a large number of small droplets of water have condensed into what appears to us as a fog on the glass. As the light shines through from the car headlights, each droplet acts as an obstacle to the light and so bends it. You could see a similar effect with the waves on the sea going around stones or perhaps if you brew a large cup of coffee with the surface waves going around a spoon (let me know if you manage to see this bending in a coffee cup). The amount that the light bends is dependent on the wavelength of the light (look carefully at the waves going around obstacles in ponds to see this) and so different wavelengths (different colours) get bent by different amounts and interfere with each other at different points – a spectrum is produced. It is a phenomenon known as diffraction.

Not all beans are equal! How could you quickly distinguish between arabica and robusta beans?

This phenomenon means that we have a way of separating the frequencies (or wavelengths) of light. And so this means that we have a way of measuring the chemical composition of some substances as different chemicals absorb different frequencies and so have ‘fingerprints’ in the light they scatter. By passing the light scattered from a substance (such as arabica coffee beans compared to robusta) through a diffraction grating (which is an obstacle with a pattern of fixed size), we can separate the frequencies being scattered and see if any of them are ‘missing’ (ie. they have been absorbed by the material we’re studying). It would be  a bit like looking at that rainbow pattern in the café window and not seeing blue, its absence tells you something. This is one of the ways that robusta beans can be quickly found if they have been substituted for arabica beans in coffee trading.

Coffee Corona

Look carefully: Sometimes you can infer the existence of a thin (white) mist over your coffee by the corona pattern around reflected light fittings.

But it is not just its technological aspect that has interest for us surely? When gazing at the moon on a misty evening, the halo around the moon suggests the clouds between us and it. It is something that poets have remarked upon to evoke atmosphere, it is something that we can gaze at as we imagine the giant café window of our atmosphere. But the size, and distinctness of the lunar corona actually give us clues about the droplets making up the cloud. And then we look closer to home and to our own coffee and we see the same diffraction pattern again looking back at us from our coffee’s surface. Occasionally it is possible to see haloes on the coffee surface around the reflection of overhead lights in the café. A coffee corona! This reveals to us the fact that there are droplets of water above the surface of our coffee; an extra layer of hovering droplets. Something that we can sometimes see more directly in the dancing white mists.

Diffraction is a beautiful phenomenon that allows us to gaze and to contemplate how much we are able to deduce and how much we have yet to understand. How atmospheric our coffees and cafés are and the journey of understanding that we have taken to get to this point. Coffee gazing is a hobby that should be taken up by far more of us.

Bean Thinking noticing afternoons are going to start in London in early 2019. To find out more information, sign up to the Bean Thinking events list here:

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

 

Noticing at Artisan, Ealing

coffee Artisan Ealing

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

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

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

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

Lampshades at Artisan Ealing

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

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

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

menus and lampshades in Artisan

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

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

 

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

 

Air raising

Small waves seen from Lindisfarne

How do clouds form? How does temperature vary with altitude, and what does coffee have to do with any of it?

You put a drop of alcohol on your hand and feel your hand get cooler as the alcohol evaporates, but what has this to do with coffee, climate and physics?

Erasmus Darwin (1731-1802) was the grandfather of Charles of “Origin of the Species” fame. As a member of the Lunar Society (so-called because the members used to meet on evenings on which there was a full moon so that they could continue their discussions into the night and still see their way home) he would conduct all sorts of scientific experiments and propose various imaginative inventions. Other members of the Lunar Society included Matthew Boulton, Josiah Wedgwood and Joseph Priestley. The society was a great example of what can happen when a group of people who are interested in how things work get together and investigate things, partly just for the sake of it.

One of the things that Darwin had noticed was that when ether* evaporates from your hand, it cools it down, just as alcohol does. Darwin considered that in order to evaporate, the ether (or alcohol or even water) needed the heat that was provided by his hand, hence his hand started to feel cooler. But then he considered the corollary, if water (ether or alcohol) were to condense, would it not give off heat? He started to form an explanation of how clouds form: As moist air rises, it cools and expands until the moisture in the air starts to condense into droplets, clouds.

hole in water alcohol

There are several cool things you can notice with evaporating alcohol. Here a hole has been created in a thin layer of coffee by evaporating some gin. You can see the video of the effect here.

As with many such ideas, we can do a ‘back of the envelope’ calculation to see if Darwin could be correct, which is where we could also bring in coffee. The arabica growing regions are in the “bean belt” between 25 °N and 30 °S. In the sub-tropical region of that belt, between about 16-24°, the arabica is best grown at an altitude between 550-1100 m (1800-3600 ft). In the more equatorial regions (< 10º), the arabica is grown between 1100-1920m (3600-6300 ft). It makes sense that in the hotter, equatorial regions, the arabica needs to be grown at higher altitude so that the air is cooler, but can we calculate how much cooler it should be and then compare to how much cooler it is?

We do this by assuming that we can define a parcel of air that we will allow to rise (in our rough calculation of what is going on)¹. We assume that the parcel stays intact as it rises but that its temperature and pressure can vary as they would for an ideal gas. Assuming that the air parcel does not encounter friction as it rises (so we have a reversible process), what we are left with is that the rate of change of temperature with height (dT/dz) is given by the ratio of the gravitational acceleration (g) to the specific heat of the air at constant pressure (Cp) or, to express it mathematically:

dT/dz = -g/Cp = Γa

Γa is known as the adiabatic lapse rate and because it only depends on the gravitational acceleration and the specific heat of the gas at constant pressure (which we know/can measure), we can calculate it exactly. For dry air, the rate of change of temperature with height for an air parcel is -9.8 Kelvin/Km.

contrail, sunset

Contrails are caused by condensing water droplets behind aeroplanes.

So, a difference in mountain height of 1000 m would lead to a temperature drop of 9.8 ºC. Does this explain why coffee grows in the hills of Mexico at around 1000 m but the mountains of Columbia at around 1900 m? Not really. If you take the mountains of Columbia as an example, the average temperature at 1000 m is about 24ºC all year, but climb to 2000 m and the temperature only drops to 17-22ºC. How can we reconcile this with our calculation?

Firstly of course we have not considered microclimate and the heating effects of the sides or plateaus of the mountains together with the local weather patterns that will form in different regions of the world. But we have also missed something slightly more fundamental in our calculation, and something that will take us back to Erasmus Darwin: the air is not dry.

Specific heat is the amount of energy that is required to increase the temperature of a substance by one degree. Dry air has a different specific heat to that of air containing water vapour and so the adiabatic lapse rate (g/Cp) will be different. Additionally however we have Erasmus Darwin’s deduction from his ether: water vapour that condenses into water droplets will release heat. Condensing water vapour out of moist air will therefore affect the adiabatic lapse rate and, because there are now droplets of water in our air parcel, there will be clouds. When we calculate the temperature variation with height for water-saturated air, it is as low as 0.5 ºC/100 m (or 5 K/Km), more in keeping with the variations that we observe in the coffee growing regions†.

We have gone from having our head in the clouds and arrived back at our observations of evaporating liquids. It is fascinating what Erasmus Darwin was able to deduce about the way the world worked from what he noticed in his every-day life. Ideas that he could then either calculate, or experiment with to test. We have very varied lives and very varied approaches to coffee brewing. What will you notice? What will you deduce? How can you test it?

 

*ether could refer to a number of chemicals but given that Erasmus Darwin was a medical doctor, is it possible that the ether he refers to was the ether that is used as an anaesthetic?

†Though actually we still haven’t accounted for microclimate/weather patterns and so it is still very much a ‘rough’ calculation. The calculation would be far better tested by using weather balloons etc. as indeed it has been.

¹The calculation can be found in “Introduction to Atmospheric Physics”, David Andrews, Cambridge University Press

 

 

Feeling the Earth move at Pritchard and Ure, Camden

Egg no pales, coffee, garden centre

Fried egg on cactus leaves. Cactus festival at Pritchard and Ure, Camden

Good coffee in a garden centre, in (nearly) central London, with some physics thrown in? Today’s cafe-physics review seems unlikely on several levels. And then it becomes even more unlikely as you realise that this garden centre and café are also a social enterprise where people “disadvantaged in the labour market” are helped back to employment through working here. All in all, Pritchard and Ure represent a great café to have come by.

Pritchard and Ure can be found in the gallery space of a warehouse type shop that houses the Camden Garden Centre. They serve Workshop coffee together with an extensive selection of alternative drinks and food. As it was lunchtime we enjoyed a spot to eat which gave me an opportunity to try cactus (it was cactus festival at the garden centre). Cactus leaves with re-fried beans and a cactus-water mocktail which came together with a reusable metal straw. The straws were being sold (together with brush straw cleaners) at the counter. After lunch there was a very well made long black (interestingly I was given the choice to have it either as a 6oz or an 8oz, ie. more or less water depending on whether I wanted more or less coffee taste) and resisted (somehow) one of the tempting cakes before having a wander in the garden centre.

equations art work coffee Camden

But are they real?
The equations are the writing on the wall at this cafe.

There are of course many things that you can notice and connect with/to in a garden centre. Plants, biosphere, windows and greenhouse effect, the carbon cycle, the nature of colour, the list could go on. In addition to all of these, to the left of the counter was an art piece on the wall with a list of various equations and comments. Were all these equations real? One thing in particular though in this café/garden centre was particularly mesmeric: the disco ball suspended as a pendulum from a beam across the ceiling. Initially we watched as the ball just glinted reflected light as it slowly swayed to and fro in its oscillation. It took 22 seconds to cover 5 oscillations while I estimated it was 7m in length. Knowing that there is a formula for calculating the period of oscillation I wondered, was my estimation any good?*

During the hour it took us to enjoy lunch, the position of the Sun moved in the sky so that the disco ball started to reflect an array of polka dots of light onto the walls surrounding us (you can see these in the photo). Owing to the combined rotation and oscillation of the ball it wasn’t too easy to measure the time period from these oscillations but about 4 seconds per swing (as I had obtained by merely watching the ball) seemed comfortingly correct. The sun slowly moved round and these dots danced until at some point the sun had moved far enough that the glitter ball was no longer in direct light. But had the Sun moved or the Earth rotated underneath it? We all know the answer (or at least we think we do), but we could use the pendulum to prove it (and to calculate our latitude).

discoball cafe

Disco ball pendulum together with polka dot reflected sunlight. The view from the gallery at Pritchard and Ure.

In various science museums around the world, different Foucault pendulums swing to and fro all day above circular patterns on the floor. The pendulums appear to rotate clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere thereby illustrating the rotating earth underneath the pendulum. The idea is of course that the pendulum continues to swing in the same plane as it was when it was started off but as it is swinging the earth is rotating underneath it giving an apparent rotation of the pendulum swing over the course of a day. If we were at the north (or south) pole, the period of one complete rotation of the pendulum through a circle on the floor would take 24h. As most of us are not at the pole (and Pritchard and Ure certainly is not), the period of complete rotation is lengthened by a corrective factor proportional to the sine of the latitude. Consequently, it is perfectly feasible for us to calculate our latitude by observing a pendulum swinging for long enough in the absence of any breeze.

It is a great piece of evidence for the rotation of the earth (and by implication the fact that the earth is not flat and that the sun is not going round the earth each day). It’s also a very simple (hiding some complicated maths) demonstration that anyone could set up if they wished to carefully do so. So next time you see a disco ball suspended as a pendulum in a café, you would have another reason to start singing “I feel the Earth, move, under my feet…”

Pritchard and Ure is in the gallery of Camden Garden Centre at 2 Barker Drive, St Pancras Way, NW1 0JW

*7 m is an over estimate of the length of the pendulum based on the period of the oscillation. A length of 7m would give a time period of 5.3 seconds, whereas 22 seconds for 5 oscillations is about 4.4 seconds for one giving a calculated length of just under 5m. More details about how to calculate this are here.

Exploring the sound of coffee

coffee at Watch House

We’re used to thinking about the aroma of coffee and how it looks, tastes, even how it feels, but what about how it sounds?

How much attention do you pay to your brewing coffee? You know the aroma, how the coffee blooms, you anticipate the taste and feel the warmth of the steam rising off the brew. But what about the sound? Admittedly this depends on your brew method, but what about the sounds as you filled the kettle or prepared a pour over brew? It turns out that the sound of dripping water was the subject of a recent paper in Scientific Reports.

Perhaps take time to watch a tap dripping into a bowl of water. Or maybe use this as an excuse to make another coffee by drip brewing. Each drop falling onto the water (or coffee) below first deforms the water’s surface then, as far as we can see, rebounds up with a splash of a returning drop or droplets. The phenomenon of what causes the characteristic sound of the drip has been investigated for over 100 years but in 1959 it was established using high speed photography that there were four key phases to any drip sound. First, the drop fell on the liquid, then a cavity formed just under the water surface and an air bubble formed just under that. Finally the water surface recoiled leading to a jet of droplets returning from the surface. It has been thought that the sound, that ‘plink’ of the dripping tap, was caused by that trapped air bubble expanding and contracting as it moved through the water under the water’s surface¹. But this has now been confirmed, along with some other interesting, coffee related, observations using ultrafast video recording (30 000 fps for most of the work, 75 000 fps for some of the extra details).

lilies on water, rain on a pond, droplets

Like the sound of falling rain? What causes the dripping sound of a tap?

The authors of this recent paper describe what must have been a fun experiment to do, dripping water into a tank below. You can see some of the videos of the droplet entering the water by scrolling down to the “supplementary information” in the paper. Two microphones (one above, one below the water surface) recorded the sound waves coming from the dripping ‘tap’ simultaneously with the video recording so as to match the timing of the sound with what was happening in the video. The microphone above the water surface largely recorded the same sound waveform as the microphone under the water with one crucial exception. When the authors lined the tank with MDF wood, the underwater sound was ‘damped’ quite quickly, in comparison the bare tank amplified the sound and so the sound wave took much longer to decay. Above the surface however, it didn’t matter whether the tank was lined or not, the sound signal remained the same. This may sound somewhat insignificant, but it means that it cannot be the sound created by the wobbly bubble itself merely propagating through the surface of the water. If this were the case, the microphone above the water surface should show the same signal as the microphone under the water’s surface. Instead the authors suggest that the oscillating bubble causes the surface of the water immediately above it to vibrate (in the bit that is depressed owing to the droplet having fallen into it) and it is this that we hear above the water surface.

science in a V60

Droplets on the surface of a brewing V60 may also form owing to a temperature difference between the dripping drops of coffee and the coffee ‘bath’ underneath.

It is a beautiful set of experiments but how can it link to coffee (apart from with the dripping)? It is in the way that it gives us the chance to experience our coffee with experiments involving more of our senses than just smell, touch and taste. Firstly, the study emphasises the connection between the drop’s diameter and speed to the sound of the drip (the best sounds are for drops between 1mm and 5mm diameter). This suggests that by changing the brewing parameters (whether you prepare your V60 in a jug or a mug or change the filter paper to a metal kone for example), you may hear a change in the sound of the drips. Do you? Secondly, it has been suggested that the sound that is formed is dependent on the temperature difference between the dripping drop and the water bath underneath. A temperature difference between drop and bath would also explain an odd phenomenon I noticed in the V60 a while back. Do you notice a difference in the sound of the brewing coffee when you prepare cold brew pour over as opposed to a standard breakfast brew? Lastly, the authors of this study found that they could suppress the sound of the plink by reducing the surface tension of the water bath that they were dripping water into. In their case they added washing up detergent to the bath. This seems an awful waste of coffee but is it possible that something intrinsic to our coffee brew could do the same thing? Oil will also change the effective surface tension of the water and different coffees (and different roast strengths) change the oil content of the brewed coffee. Have you noticed any change in the sound of the drips of the coffee depending on how dark a roast coffee you use?

It may not make ground-breaking science but it does offer us an opportunity to pay even more attention to our coffee. Does the sound of your coffee reveal the beauty of the physics at work just under its surface?

¹ Some history of the investigation into the dripping sound as well as the experiments can be found in: Phillips et al., “The sound produced by a dripping tap is driven by resonant oscillation of an entrapped air bubble”, Scientific Reports, 8, 9515 (2018)

(Im)perfect reflections on coffee

science in a V60

Have you noticed droplets like these dancing on your drip-brewed coffee?

With the recent coffees from Hundred House and Quarter Horse, there have been many opportunities to observe the coffee brewing in the V60 in the mornings. The steam rising from the filter paper, the different ways different coffees bloom and out-gas, the droplets that skim the surface of the coffee and bounce off the walls of the jug and then, of course, the many different effects with light. Watching the dancing droplets (an explanation of why they may dance is here), it is perhaps not immediately obvious that you could form a connection between these, the light reflections and an insight into something you may have noticed while passing through customs. And yet the connection is definitely there.

The connection is formed through a technique called Raman spectroscopy. Named after Chandrasekhara Venkata Raman (1888-1970) who discovered the Raman effect in 1928. As the ‘spectroscopy’ part of the name suggests, it is a technique that offers a way to identify different chemicals, or components, in a substance. For coffee it has been used both as a non-destructive technique to determine the kahweol content of coffee beans and hence help as a test for identifying rogue robusta in arabica beans and as a way of analysing the brewed coffee. But what is it, how does watching a brewing V60 help to understand it and why would you want to know about Raman spectroscopy while travelling through an airport?

beauty in a coffee, coffee beauty

A collection of bubbles on the side of the coffee. What happens when one of the dancing droplets collides with a group of bubbles?

Generally, it helps to begin with coffee and the link is the way in which the droplets bounce off the side of the jug. Brew a coffee and watch them (if you are a non-coffee drinker, you could try dripping hot water through a filter paper into a jug). When one of these droplets hits the wall of the V60 container, it generally bounces back with a trajectory expected for an elastic collision. Given the relative masses of the droplet and the jug, the speed of the reflected droplet is essentially unchanged (even if its direction is reversed). This is similar to what we would normally expect for light. We are used to considering light as waves but because of the wave-particle duality of quantum mechanics it is equally valid to consider light as a stream of particles called photons. As the photons hit a surface and are reflected off, they recoil with the same energy that they initially had, just like the droplets in the coffee. But now look more closely at the dancing droplets. Normally they hit the walls and not each other but just occasionally, they can hit either another droplet or a group of bubbles that have formed on the coffee surface. In these cases, rather than get reflected as before, the droplets transfer some of their energy to the collection of bubbles causing them to move and to wobble. And when the droplet is reflected back, it has a noticeably slower speed (and so we could say a lower kinetic energy) than when it initially danced into its collision. Where is the analogue with light?

When we think about a coffee bean, we probably think about something that is about 1cm oval, brown and quite solid. But if we zoom in, we find that it is made up of a collection of atoms bound together in molecules or, if we are thinking about a solid like salt, in a crystal structure. These atoms act as if they are balls connected by springs and so they wobble as would any structure of masses connected by springs. This is true whether the crystal is diamond or the molecule is caffeine, kahweol, cocaine or semtex (do you see where the customs part is going to come in yet?). Different crystal structures have different atomic arrangements meaning that they are effectively connected by springs of differing strength. If you build a mental model of masses connected with springs, you can see that changing the spring strength will change the vibration energy of the structure. So if now we think about the photons hitting such a structure, while most will bounce off as we saw with the droplet hitting the V60 wall, some photons will trigger a wobble in the crystal structure and bounce off with lower energy. It is a process analogous to the droplet hitting and bouncing off the collection of bubbles on the coffee surface.

Sun-dog, Sun dog

Sun dogs are caused by a different interaction between light and crystals. Rather than the inelastic scattering of Raman spectroscopy, Sun dogs are caused by the refraction of light by hexagonal platelets of ice crystals.

When a photon of light loses energy, it is equivalent to saying that the frequency of the light has changed (which is very closely related to what Albert Einstein got his Nobel prize for in 1921). So a photon that creates a crystal vibration and is scattered off with lower energy has a lower frequency (or longer wavelength) than it had when it first hit the crystal. Importantly, the energy lost by the photon is identical to the energy gained by the vibrating crystal and so by measuring the frequency change of the scattered light we have a way of determining the energy of the crystal (or molecule) vibration. As this energy depends on the way that the atoms are arranged in the crystal or molecule, measuring the frequency shift offers us a way of identifying the chemical under the laser light: kahweol or cocaine.

It is not an easy technique as you can guess from the V60 analogy. Only around one in a million photons incident on a solid will be Raman scattered. You need some pretty decent optics to detect it. Nonetheless, it is a powerful technique because no two chemical structures are the same and so it can be used to identify tiny amounts of smuggled material completely non-destructively. It becomes easier to understand how this elegant technique has become useful for many areas of our lives from customs, through to pharmaceutical development and even into understanding how fuel cells work.

Although it is stretching the analogy too far to say that you can see Raman scattering by watching the droplets on your V60, it is certainly fair to say that watching them allows you the space to think about what is happening on a more microscopic level as your bag is hand-scanned at customs. What do you see when you look closely at your brewing coffee?