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Carbon Kopi

Carbon Kopi, coffee Hammersmith, coffee Fulham
Carbon Kopi, the sign in the window above giving a clue to the name without being a direct reference.

The name of this relatively new cafe in Hammersmith/Fulham was intriguing on several levels. Kopi means coffee in both Malay and Indonesian and, having recently travelled back from SE Asia, it was interesting to see what the link to this cafe may be. Then there was the pun in the name. The website explains it as representative of a desire to make a consistently good coffee, each being a carbon copy of the other. So both the name, and the cafe’s symbol have appeals for a coffee-science website. And so it was that we wandered down Fulham Palace Road to finally arrive at Carbon Kopi a few Saturdays ago.

The cafe occupies a corner building and is much larger than you may expect it to be. It is also friendly, airy and light with large windows giving plenty of illumination to the space. Allergen information was clearly labelled on the cakes and edibles (with extra information in a folder), which is always great to see.

Coffee was by Square Mile with guest roasters on batch brew and so we had a long black and oat milk hot chocolate which came served in huskee cups. Huskee cups are produced by re-using the husks otherwise discarded during the coffee milling stage. A re-usable cup that reduces waste certainly, but does it reduce the carbon footprint? An answer that depends on how many times you use it. Continuing the environmental theme, near the door, there was a separate bin for compostable cups. This was excellent to see because if compostable cups do not get to an industrial composting facility, they can take an absolute age to break down in a conventional compost heap.

Hat and huskee
Coffee in a huskee cup at Carbon Kopi. A protrusion on the saucer fits into the base of the huskee cup and stops it slipping across the saucer. Unlike graphite where the regular hexagons of carbon form layers that slip over each other to form a solid lubricant.

Across the road, the St Alban’s Church was made of brick. One row upon another, the set of bricks formed a layered structure. Where they met at corners or against the pavement they formed abrupt discontinuities, a sort of dislocation. Together with the small protrusion on the middle of the huskee cup saucer (to stop the cup slipping?), and the speaker above the door entertaining us with 80s music, the natural connection here was graphene.

Graphene is a form of carbon that is a single atomic layer thick. Each carbon atom is arranged into a flat hexagonal structure exactly like graphite but, unlike graphite, there is only one layer of these atoms in graphene. The strength and strange electrical properties of this material, together with its lightweight form, have made this material an intense subject of research for the past 15 years or so. A recent Physics World podcast tested a set of headphones with the vibrating membrane made of graphene. The idea being that the strength of the material combined with its relatively low mass, would enhance the way that we heard the sound coming through the speakers. You can listen to the review (though not the speakers) here.

coffee Hammersmith
Each layer of bricks forms a regular set of layers. But where they come up against each other discontinuities are formed. These can cause special problems in sheets of graphene.

But are there aspects of graphene that may be more applicable to the cafe and coffee industry? Various teams around the world have been working to make membranes of graphene work as single molecule detectors. The idea is that molecules adsorbed onto the surface of a graphene membrane change the electrical properties of the membrane to an extent that can be measured even in the case of single molecule adsorption. The sensitivity of the electrical properties of the graphene to different molecules could mean that graphene based devices would make very sensitive contamination detectors, including allergen detectors. Such sensors are the subject of a research collaboration at the National Physical Laboratory in Teddington and could mean that, rather than be in any doubt as to whether a substance contains an allergen, it could be quickly tested by passing it through a graphene sensor.

All this is quite far from the coffee and cakes at Carbon Kopi. But if you are in the area, it is a lovely place to stop, enjoy a coffee and contemplate the bricks of the church opposite.

Carbon Kopi is at 11 Margravine Road, W6 8LS

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A little fog

canali Curators Coffee
Clouds viewed from a London cafe. How do clouds form?

Clouds form because water droplets condense. But there is a hidden difficulty in this seemingly simple statement because, while true, it is not, at first sight, clear how they condense.

To see the problem imagine spilling coffee on two consecutive days, a really damp one and then a really dry one. We know from our experience that when the weather is dry the coffee will evaporate and dry more quickly (leaving a coffee-ring). On damp days the drop is more stable against evaporation, that is, it stays as a droplet. We can continue our thought experiment by thinking what happens when we have a large coffee spillage versus a drop. The drop will dry quickly whereas the large spill will take ages to dry out (unless we mop it up).

Where does this leave clouds? Consider two water molecules coming together and condensing into a very small drop. It is quite clear that, just like our small coffee drop spill, this droplet will be unstable against evaporation, meaning that it evaporates almost as soon as it has formed. Perhaps this seems an extreme example, we do not often consider a water droplet as being formed of two molecules (nor is it clear that the term ‘evaporation’ is strictly appropriate in this case). So how many water molecules would have to, spontaneously, come together to form a droplet that does not evaporate almost as soon as it is formed? Take a guess. What seems reasonable?

coffee bowl pour over
Frequently water droplets will condense onto something as opposed to merely forming on their own. Consequently it is useful that our planet is fairly dusty.

At a relative humidity of 101%, a stable droplet has to be larger than about 0.1 µm diameter* (larger than about 1/50000 of a coffee bean). Which means that to form a stable droplet, about 140 million water molecules would all have to combine in the same spot and condense together simultaneously. It seems not terribly likely and yet this is what our statement at the start of this post implied “clouds form because water droplets condense”.

Which aspect of our understanding is wrong, or incomplete?

It is in our assumption about how the water molecules are condensing. Rather than spontaneously combine, each molecule condenses onto something, just as a dew forms on the ground, so these droplets start to condense onto dust particles and other, smaller, aerosols in the atmosphere. This means that at the heart of most cloud droplets is a bit of dust and that dusty places may be expected to be, all else being equal, more cloudy. Or at least that last part was my understanding of the situation: would a take-away coffee taken away in a polluted London street appear to steam more than in the by-ways of a village?

Unable to determine how to design an experiment to test this idea (while keeping all other things equal), it was interesting to come across an almost flippantly made statement in a book while I was preparing for the next evening of Coffee & Science at Amoret.

“Urban emissions of sulphate aerosols from fossil fuel burning and dust production caused by industrial activity and human occupation result in poorer visibility and increased frequency of fogs [in dense urban areas such as cities]”.

Does our coffee steam more in the cities? The answer to this may well be ‘yes’!

And there was more, apparently the increasing use of clean air legislation has resulted in fewer foggy days and more days of sunshine in urban areas**. Is it possible therefore that you could start to use your take-away coffee cup as some form of pollution detector? Watching for the steam to appear as you wander from street to street.

Sadly for the coffee cup pollution detector, whether the water condenses onto the dust droplet or not is also a function of the temperature and humidity, parameters that will make it tricky to develop the pollution detecting re-usable coffee cup. But, the physics is sound and if you do one day come across such a device, please remember where you read it first!

*”Introduction to Atmospheric Physics”, DG Andrews, (2008)

**”The ice chronicles: the quest to understand global climate change”, PA Mayewski & F White, University Press of New England (2002)

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Which direction? At Jacob the Angel, Neal’s Yard

Jacob the Angel, coffee Covent Garden
It is easy to miss Jacob the Angel as you enter Neal’s Yard, but an angel above the hoarding gives it away.

Jacob the Angel is tucked into Neal’s Yard in London’s Covent Garden. Named after Thomas Neale (1641-1699), Neal’s Yard is part of his development which is now known as Seven Dials. And rather like the larger 17th century development, this cafe-physics review of Jacob the Angel has a similar dilemma: so many avenues to explore, each wrestling for attention, which one to pursue?

But first the coffee. Roasted by Square Mile, coffee is available as the usual espresso based drinks or on V60 pour over. I had a Rwandan V60 that was full bodied and full of treacle like flavours. Owing to the geometry of the cafe, I didn’t get to check my ‘flavour notes’ against what the tasting notes thought I should perceive. The cafe space itself is fairly small but with a surprising amount of seating. Given this, it can feel a bit close as you squeeze past some of the people sitting down in order to place your order, (hence not double checking the tasting notes) however that is quickly set aside as you can gaze at the large selection of cakes (all with allergens clearly marked) arrayed on the counter.

On the walls of the cafe were paragraphs about the history of coffee and how a man named Jacob opened Britain’s first Coffee House in 1651 at the Angel Inn (in Oxford). The coffee itself came presented in a manner that was reminiscent of solar eclipses, while the sink next to our table was strikingly similar to those in my A-level chemistry lab. Unable to dissociate my memories of the sink with the reality of the environment at Jacob the Angel, it was a bit shocking when someone came to fill their glass of tap water there – don’t they realise what could have been in that sink?! Each thought train surfacing as a potential direction for the review, but then, above me, something moved. Looking up it was clear that a plant that was hooked to the ceiling was moving in a draught, but where was the breeze coming from? A small air-conditioning/heater unit was on the other side of the coffee house, circulating the air that was moving the plants.

plants, Jacob the Angel, Coffee Covent Garden
Plants above the tables at Jacob the Angel. How do they move in the breeze?

The moving plant had appeared to my peripheral vision as if it was floating in the breeze or perhaps flying. Now clearly there cannot be a flying plant, but in some ways the swaying leaves do illustrate the fluidity of air, which is a necessity for flight. The moving air demonstrates how the air imparts a force to the leaves (and the pot) causing them to sway. For things that genuinely fly this would be experienced as ‘drag’ – something that we have probably all experienced, even when not flying. Drag is increased if the object moving through the fluid (air) has a larger surface area perpendicular to the direction of movement: all being equal, bigger objects experience more drag. Imagine moving a spoon through coffee, it is easier to move a stirring stick rather than a tablespoon. But then, drag also depends in a non-trivial way on the shape of the object and how that changes the vortex wake behind it (look again at the spoon and how the vortices form behind it as it is dragged through coffee, you do not see those so easily with a stirring stick).

It is partly this sort of shape effect that seems to be behind Orsted’s recent restatement of the calculation of the amount of energy that their off shore wind farms can generate. By actually going out and measuring the air flow around the off shore wind farms, Orsted discovered that the air flow (which would be used to generate power) is affected not just by the individual windmill (as had been known and calculated), but its neighbours and the way these combine into the shape of the wind farm. There is still a lot we don’t understand about exactly how spoons move through coffee.

vortices in coffee
Vortices behind a spoon dragged through coffee.

But there is also a connection to a different type of “flying machine” if only through the name of the coffee house. For it was from the Angel Inn in (what is now) Aldwych that, more than 250 years ago, that an unusual ‘flight’ took place*. It was described in an advertisement in the paper:

“On Monday, the 5th of April 1762, will set out from the Angel Inn behind St Clements Church in the Strand…. a neat flying machine, carrying four passengers, on steel springs and sets out at four o’clock in the morning, and goes to Salisbury the same evening, and returns from Salisbury the next morning at the same hour… Each passenger to pay 23 shillings for their fare, and to be allowed 14lb weight baggage”.

How many more avenues could be followed while enjoying a slow coffee at this small but fascinating little cafe? Do let me know what you ‘see’ next time you visit.

Jacob the Angel is in Neal’s Yard, Seven Dials, London.

*”London Coffee Houses” by Bryant Lillywhite, pub. 1963

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Goodbye to the take-away cup

Back in April 2017 I was given a “completely compostable” disposable cup in order to try some batch brew. But how “compostable” is “completely compostable” really? It needed to be tested! And so, once it was empty, the cup was placed into a worm composting bin and left to see how long it took to compost.

Each week I took a photograph of the cup to see how it was composting, the results of which were made into the film below. How long did it take? You can watch the film or scroll past to find out more:

Did it compost?

110 weeks! That is more than two years in the worm bin. Is that how long you thought it would take? When things are marked “compostable”, even when they are marked with a regulatory compostable mark like EN13432 or ASTM6400, this usually means the item is compostable only in an industrial setting. Industrial composting facilities are kept at 58C, very far from the conditions found in a London based worm bin (more details here) or indeed from most people’s idea of a compost bin.

The OK Vincotte label is for items that are supposed to be genuinely “home” compostable. Will this bag from Amoret coffee compost in the worm bin? It is in there now but as we are in winter, the worms have slowed down to such an extent that it would not be fair to start a new #willitcompost just yet.

What about defining labels for a genuine “home” composting environment? The problem here is that a worm composting bin in London will be very different from a more conventional compost heap in a tropical country. How can you define one set of conditions that are universally applicable? One label that tries is “OK Vincotte” but it seems quite rare and indeed I have only seen this once ‘in the wild’: on bags of Amoret roasted coffee (see picture). Have you spotted them anywhere else?

The conclusion from all this? We all need to think about how we each can live more simply and sustainably. Perhaps a re-usable cup will be part of the way that you do this. (Some of them are reviewed by Brian’s coffeespot linked here). Or maybe you’ll opt to drink your coffee to-stay. Whatever else it involves though, it can’t be by putting each “compostable” take-away coffee cup we consume in a worm composting bin in London or imagining that they will somehow compost in a landfill!

Do let me know what you are doing to address the issues of your own coffee waste either in the comments below, on Twitter or over on Facebook. I look forward to continuing the discussion there.

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Ringing in the New Decade

Happy New Year!

Nicaragua, direct trade, Amoret, Java beans,
Sometime this week I’ll brew this with a V60 and adapt an ‘examen’ to help me review 2019. I was thrilled to be able to meet the farmers, Dania and Desiree, at Amoret coffee earlier this year. One of the things I’m sure will feature in my ‘gratitude’ examen.

Each New Year is an opportunity to look back at the previous year, anticipate the future year and perhaps make resolutions to improve our lives, or even of those of people around us. Maybe this is even more true this year which is not just the start of a year, but of a decade.

This year I have been lucky to meet, or to continue friendship with, many people who have taught me all sorts of things about life, physics and coffee. There have also been some great finds of some fantastic cafes, trying to make a difference to their local community while serving excellent coffee.

And yet, as the year or the decade turns and we resolve to get fitter, pay more attention to sustainability or whatever seems important to us right now, we will inevitably take our existing selves into the new day and our resolutions will meet the reality of who we are: a bell rings at certain frequencies owing to the resonances of the vibration on the surface of the bell. The resonances of the bell depend on its exact shape and size, it is not easy to change the sound of the bell unless you change its temperature or even the interior to a different gas or muffle. (You can see images of how a violin vibrates at resonance here). The surface of a coffee resonates similarly, if we put it on a vibrating surface with a frequency that matches the fundamental vibrations of the surface. Nonetheless, thinking about these resonances can take us in surprising directions. The mathematics that describes them was developed by Friedrich Bessel (1784-1846) but, Bessel was not thinking about resonances when he formulated what is now known as Bessel functions. And it is possible, his life may have taken a very different direction were it not what happened from 1799.

Resonating coffee.

In the new year of January 1799, when he was just 14, Bessel was apprenticed to an imports and exports company with the hope that he would become an accountant. And maybe we would have heard no more about him had he not got interested in the problem of longitude and solving the navigational issues of the time, important for the company for which he was working. This issue got him thinking about astronomy and he caught the attention of the authorities of an observatory who gave him a job there and encouraged his observations and interest. But it was while thinking about “many body problems” or how multiple massive objects interact with each other via gravity that he came up with the mathematical description that we now know as Bessel functions. It is these Bessel functions that also describe the resonances on a bell and in a coffee cup.

Sun, heat, nuclear fusion
What links coffee to the Sun? So many things! But for the purpose of this post, we can find clues as to the interior of stars by watching the way they vibrate, analogously to a bell. What would Bessel think? Image © NSO/AURA/NSF

What does this leave us with in our thoughts for 2020? That what we are interested by may lead us to discoveries in various tangential and scarcely believable connections? That what we plan for our lives may not be how they have to end up? That it benefits us to stop for 5, 10 minutes, even half an hour and just contemplate our world in our coffee? (ok, that last one did not come from Bessel). Where-ever your paths lead and your interests lie, happy new year! May the 2020s be a decade where we can all slow down, notice, contemplate and appreciate the beauty of this strangely connected world which is our home.

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A Weight-y issue

Waves on the surface of of a coffee. But what do we know about gravity driven waves rather than surface tension driven ones?

Ever swung a bucket of coffee round in circles swooping down towards the floor and then over your head? Why would you, you may well ask? Well, the answer may surprise you. It’s all about turbulence.

We have probably all come across turbulence, perhaps by watching how milk is added to a black coffee or seeing the steam interact with the air as it evaporates off a hot mug of tea. But it turns out that there is a lot that we do not yet understand about turbulence and this is where the bucket of coffee comes in.

Waves on the surface of a coffee can be dominated by gravity or capillary effects. Capillary waves are short wavelength (higher frequency) waves that are forced into oscillation by the effects of the surface tension of the liquid pulling the surface of the coffee back into shape once its been distorted. Gravity waves are longer wavelength (lower frequency) waves where the disturbed surface of the coffee is pulled back into shape by gravitational effects rather than surface tension effects.

Benjamin Franklin famously stilled the (capillary) waves on one of Clapham Common’s ponds by adding just a teaspoon of oil to it.

The frequency at which there is a crossover from gravity dominated waves to capillary dominated waves is dependent on both the density and surface tension of the liquid as well as the strength of the gravitational acceleration experienced by the mug of coffee. (We’re getting to the bucket). On Earth, the gravitational acceleration is 9.8m/s, the ratio of a liquid’s density to surface tension is quite similar for many liquids and so the transition frequency between these two regimes is generally in the region of 10Hz.

What this means is that if you wanted to study the turbulence affecting one type of wave only you could measure at higher frequency (and so measure capillary waves) or measure the turbulence in a liquid in lower gravity eg. on the International Space Station (so that capillary waves dominate at lower frequencies too). But both of these types of measurement don’t give any insight into what’s happening to turbulent waves sustained by gravity, such as Rossby waves which travel the whole circumference of planets with atmospheres and affect the weather in different parts of the globe.

So how could you study turbulence in the gravity dominated surface waves of water? It goes back to the bucket mentioned earlier. By putting a freely moving bucket (the authors called it a ‘gondola’) at the end of the arm of a centrifuge of 8 m diameter, the authors of a recent paper created an effective gravitational force on a liquid of up to 20x the value of the Earth’s gravitational acceleration. It’s sort of like the bucket of coffee being whirled around in a circle apart from a lot bigger and capable of moving at up to 67 rpm! This meant that they could measure the effects of turbulence on gravity driven waves up to about 100Hz allowing them a large frequency range over which to compare their results to theoretical predictions.

Coffee, Van Gogh
Turbulence comes in many forms: What do you see in your coffee cup?

And when they did so, they proved one nagging problem for theoreticians studying turbulence: the size of the ‘container’ becomes important, something that models had previously neglected. For the 23cm wide bucket of distilled water used by the authors, this may be something that we can easily visualise but the research has consequences for how we understand the Rossby waves that circle our planet as well as the large wavelength waves in oceans. Slightly more connected with coffee (or at least doughnuts), the results are also important for understanding turbulence in plasma waves in tokamaks.

You may have better things to do over the holidays than swirl a bucket of coffee round and round while watching for the waves on top of it, but if you are stuck for something to do…

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Coffee inside Kopiku, Sri Hartamas, KL

The gate advertising Kopiku. It leads to somebody’s garden

Kopiku means “my coffee”, a very apt name for coffee sold direct from the coffee farmer through their own cafe. Many cafes will be able to share with you their ‘directly traded’ coffee where the cafe has a one to one relation with the coffee farmer. But Kopiku takes this one stage further because Kopiku is run by the farming family themselves.

Kopiku is along a residential street in Sri Hartamas in Kuala Lumpur. We came across it because of the not-so-subtle painting on the (open) gate leading up to somebody’s backyard: “Coffee inside”. Driving past this one day prompted a curiosity, would this be good coffee? What sort of cafe operates from somebody’s garden? As it turns out it is a very good coffee from a small farm in Indonesia. The cafe opened back in August when the son of the family came over to study in Malaysia. When we first visited, there was only one other table there, the second time we visited it was packed. It seems that word is spreading and Kopiku is (deservedly) getting popular.

There are a few chairs and tables scattered around the small garden where you can sit and enjoy your freshly brewed coffee. Although the coffee is currently prepared as standard espresso based drinks, the beans are available for retail at an astonishingly reasonable price. I enjoyed a good conversation with the owner/barista talking about how best to bring out the fruity notes of the coffee (a pour over on a cold day apparently), something I plan to test when the beans come with me back to London. And how best to roast the coffee for different effects. The coffee is roasted on the farm and then sent over to Malaysia every couple of weeks so it is guaranteed to be fresh.

coffee beans from Kopiku Sri Hartamas
The coffee bean bag from Kopiku. Some of these beans are coming back with me to London to test the suggestion of the cafe owner that it’s best enjoyed as a pour over during colder weather.

Inside the garden, there is a bookshelf with an interesting selection of titles. I have sometimes wondered, when faced with similar bookshelves, whether you could make a story from the titles of the books at the end of each row. But then the fish in the tank near the shaded seats (where we sat on our first occasion in the cafe) and the waterfall feature on the wall (near where we sat on our second visit) offered different things to think about.

For a start, there is the fact that the water, falling down the 2m high granite wall, seems to stick to it. There was no splatter from the surface, it was as if a film of water was slipping down the rocks into the pool below. Initially this prompted thoughts on waterproof vs hydrophilic surfaces and their connection with coffee rings/stains and printing technology. And yet, something in the water fall was a bit more mesmerising. Watching the sheet of water flow into the small pond below, considering the energy taken to pump it up to the top of the wall again so that it could cascade down.

Which brings us up against a problem, along with part of a solution: how best to transition towards renewable electricity energy sources? Wind power is very good while it is windy, and solar while it is sunny, but how do we store the electricity generated then so that it can be released when we need it on calm, dark nights (or at other times of low generation)?

One of the older solutions for this problem turns out to look somewhat similar to the water feature at Kopiku: pumped hydro storage. The idea is frighteningly simple. When electricity is needed, water cascading down from a high level reservoir to a lower level reservoir can drive turbines and thereby generate electricity. But when a lot of electricity is being generated but demand is low, the water from the lower level reservoir can be pumped up back to the top (using the surplus electricity) ready to be allowed to cascade down and regenerate electricity as and when it is needed.

Various dewars of nitrogen
Nitrogen flasks at Chin Chin (London). A solution for energy storage as well as for ice cream?

A similar solution uses liquid nitrogen: during windy or sunny times when a lot of electricity is being generated, the surplus electricity is used to compress nitrogen and turn it into a liquid (which is very cold at -196C). Storing the nitrogen is quite easy, effectively it is stored in giant thermos flasks and, when these are well maintained, doesn’t result in that much loss of liquid over many days. When the electricity is needed on the grid, the nitrogen liquid is allowed to return to room temperature and so expands rapidly to form nitrogen gas. This expansion can be used to drive turbines which generates electricity and returns it to the network as and when it is needed.

Incidentally, that rapid expansion of liquid nitrogen into a gas can be a problem in labs like the one in which I run experiments. If 1L of liquid nitrogen is allowed to suddenly heat and become a gas, it forms, roughly 700L of nitrogen gas. In a closed space this could result in oxygen displacement and so the people in the lab could suffocate. Generally each nitrogen ‘flask’ in our lab contains 200L. You do the maths but we ensure we have good procedures in place (including oxygen sensors) to ensure that we can experiment with liquid nitrogen safely, and have fun.

The space for coffee at Kopiku however is very open and, even were nitrogen present, could not ever cause a problem! A lovely environment in which to enjoy some lovely coffee. Do sit back and let me know what you notice when you ponder your surroundings.

Kopiku is at Jalan Sri Hartamas 1. Look for the gate!

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Searching for the light at Alchemist, Singapore

Alchemist, Singapore, Raffles Quay coffee
Almost a hole in the wall. Alchemist in the Hong Leong building was a welcome break from the heat of Singapore.

Is coffee a diuretic? Perhaps it seems strange to start a review of a fantastic little cafe with such a question, but all will become clear. Or will it?

Alchemist coffee in Singapore’s Raffles Quay district was a serendipitous find. A small outlet, almost a deep hole in the wall (with bench seating) in the middle of a walkway through a building. The shady walkway is the sort of space in Singapore that you duck into in order to avoid the glare of the Sun and take brief advantage of the air-conditioning in the otherwise powerful heat. And yet, escaping into this passageway, I was immediately struck by the aroma of the coffee indicating that a speciality coffee store was nearby. On noticing the queue of customers coming out of the door, this was definitely marked as a cafe to return to at a quieter time.

Returning a bit later we noticed that, at these quieter times, it was possible to have a pour over of some locally roasted coffee. I tried the Kenyan with currant and hawthorn tasting notes as, although I forage for hawthorn in the autumn in the UK in order to make brown sauces, it is unusual to find it as a tasting note there. We watched as great care was taken to prepare the pour over (Kalita wave) and the barista took a small glass of the coffee to try before serving it to me in the pre-warmed cup. Which marked another point of interest in this small cafe, although you may expect such a small outlet to serve only take-away coffee, even for customers who want to sit on the two bench seats that line the sides of the shop, the coffee is in fact served in a proper cup, an excellent point to see. Alchemist is actually three cafes, the one that I tried in Raffles Quay and two others, with the larger branch at the International Plaza being where they also roast the coffee.

Alchemist inside coffee rack
Inside there is a rack of items for sale that include freshly roasted coffee and filters for the Kalita wave

A rack of items for sale featured filters for the Kalita wave as well as bags of the coffee roasted by Alchemist. And while initially this prompted thoughts of the differences in fluid dynamics between the Kalita wave (flat bottomed, ridged filters) and the Hario V60 (conical, flat walled filters), the reflections of the lights above in the coffee below turned this thought train in quite a different direction.

Like the cafe Alchemist, in some senses the discovery of the element phosphorus was an accidental affair. Accidental in the sense that Hennig Brand (~1630-92) who discovered it, was looking for something quite different: gold. Brand was an alchemist in the original sense of the word and, for whatever reason, thought that he may find a source of production of gold in urine.

Who knows how much urine he had to store and had to boil before he noticed its glow in the dark properties that were caused by the element phosphorus? Brand’s discovery occurred after the introduction of coffee into European coffee house culture, could its reputation as a diuretic have helped in the discovery of phosphorus? While entirely speculative, what is clear is that the name ‘phosphorus’ comes from the Greek and means the bringer of light (phos). The element phosphorus is used in many fertilisers as well as in matches.

Alchemist roasted coffee
Turning coffee into gold. This bag of Guatemalan beans has proved to be great in the Aeropress.

The name of the element “phosphorus” conjures up terms such as phosphorescence, fluorescence and luminescence. While we sometimes use the term phosphorescence to describe substances that glow in the dark. This is because phosphorescent materials absorb higher energy light (such as UV) and then re-emit it some time later (which can even be hours after being ‘excited’ by the higher energy light such as sunlight). Fluorescent materials on the other hand also emit lower energy light as a result of the substance absorbing higher energy light, but they do so fairly immediately. Strictly speaking however the ‘glow in the dark’ properties of phosphorus do not come from phosphorescence but chemiluminescence: it glows in the dark because it emits light as a result of a chemical reaction, in this case oxidation.

The lights on the ceiling in the Alchemist were of the fluorescent type and so we may think that our connections with Hennig Brand and the alchemists of old are limited to the speculations on the name. But we’d miss one detail were we to do so. Fluorescent lights can use a voltage to excite mercury vapour to emit light in the (high energy) ultra violet region. This UV then interacts with a coating on the inside of the glass tube of the light which then fluoresces to give the light that we see reflected on our coffee. The substance that provides the coating? What else but phosphorus.

From Germany to Singapore, alchemy to Alchemist, and even urine to coffee, the reflections, metaphorical and actual, between the chemists of old and the baristas of now, consist of more than just the name.

Alchemist (Singapore) is in the Hong Leong building (Raffles Quay that was tried here) as well as the International Plaza (where they roast the coffee) and the Khong Guan building.

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Espressos in the evening

Where it all happens. Amoret Coffee in Notting Hill.

Two weeks ago saw the latest in the series of “coffee and science” evenings at Amoret Coffee in Notting Hill. Designed to be informal (and hopefully conversational), each evening explores a different aspect of the interaction and connections between coffee and science (or more specifically, physics). This time, we were also very fortunate to be joined by Ricardo of La Lomita coffee farm in Columbia.

Last time we had investigated foam and so this time we looked more at the base of the cappuccino: espressos. We started off with Sadiq of Amoret preparing a pour over (this time of an Ethiopian) in order for us to feel coffee focussed before leaping into a discussion of the extraction of espressos. And an experiment! How does the extraction of the espresso vary with the strength? We were exploring the extraction-strength relation described on Barista Hustle. Three espressos were prepared by Sadiq: one that was spot on, one that was under extracted and one that was left for too long to percolate through the puck. How did they taste and compare? While various participants took to the very important, but ultimately subjective, taste tests, Sadiq used the Total Dissolved Solids meter to explore how ‘strong’ the coffee was in terms of the percentage of dissolved solids. The extraction on the other hand is a function of the time of the brew and as more water goes through the espresso puck and the shot pull time gets longer, the strength of the coffee (as measured by the percentage total dissolved solids) can get relatively lower as the espresso yield (the size of the drink) gets larger.

straw, water, glass, refraction
The total dissolved solids meter uses the different refractive indexes of coffee and water to measure the amount of coffee dissolved in the beverage. The refractive index is what causes a straw to appear to bend when it is put in a glass of water.

A note on the physics here: the total dissolved solids meter uses the refractive index of the coffee to evaluate the ‘strength’. According to Illy*, the refractive index of a strong espresso is 1.341 at 20C. In comparison water has a refractive index (at 20C) of 1.333. Assuming light enters the coffee at an angle of 20 degrees, this means that the difference in the refraction of the light between coffee and ordinary water is 14.78 – 14.87 = -0.09 degrees. A pretty sensitive meter.

We followed this up with an exploration of crema. What, if anything, does crema tell you about a coffee? Does it even matter? I was impressed by the fact that some members of the group could recognise the Nicaraguan from the Ethiopian espresso just from the way it looked; the Nicaraguan had a different crema effect and coloration than the Ethiopian. Among other factors, the colour of the crema will be influenced by the number of suspended small particles in the coffee. A detail that brought us back to a link with Prof Jan Cilliers who had come along last month. A review paper on the science of cremas included a reference to Jan’s work on froth flotation. A connection between coffee cremas and the froth flotation technique used in mining, an excellent point for an evening of interconnectedness!

The ancient Greeks considered the circle to be the perfect shape. I'd suggest they were nearly right. The perfect shape has to be a cylinder.
The ancient Greeks considered the circle to be the perfect shape. I’d suggest they were nearly right. The perfect shape has to be a cylinder.

By this time we had moved upstairs at Amoret and the discussion continued about extraction techniques and percolation. Which linked very nicely to the work that Ricardo of La Lomita is doing at his coffee farm in Columbia. Ricardo uses biochar around his younger plants. Biochar is charcoal, formed by burning old plant matter (in Ricardo’s case, old coffee trees) in a low oxygen environment. This leaves the carbon of the trees intact and so acts as a way of sinking carbon (for many years) into the soil and avoiding its escape as CO2 into the atmosphere. In addition to this, the percolative structure of the charcoal traps nutrients within the structure giving the coffee plants every chance of success in their growth. As a last point, the way that the biochar holds and stores water (think about how an espresso puck remains damp or a V60 filter keeps the water for an age), means that the coffee plants are more resistant to drought, which is an increasing problem for coffee farms in a time of climate change.

More evenings are planned for early in 2020, do join us if you can. There were some excellent suggestions for topics for future events, so together with a few that we were thinking about already, there is plenty to think about for next year! However, if you have a question about the physics of coffee, have noticed something in coffee that you would like to explore or just generally want to think more about one or another aspect of coffee, do tweet, FB or email me your suggestions. Looking forward to 2020 already.

*Illy and Viani (Eds), “Espresso Coffee”, 2nd Ed (2005)

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Clouds, condensation and coffee

Clouds in my coffee. There is, perhaps unsurprisingly, plenty of atmospheric physics you can encounter in your cup.

As we approach the end of the year, it is a good time to notice the changes in the weather. If you are in the northern hemisphere, the nights grow longer as the days grow colder. If you are in the southern hemisphere it is the opposite. And yet around the world, we have things in common. There may be days when it is more cloudy and days when there is a heavy dew (or even in some places a frost) on the grass. But what has this to do with coffee?

It’s to do with some experiments that you can do at home or on your way to work. And, in particular, with two effects you can see in your coffee cup.

To start with the dew, perhaps you’ve noticed the condensation around the rim of the cup or the coffee pot when you brew the coffee and the hot steam condenses onto the cold mug around it. Condensation happens because the temperature of the mug is lower than the ‘dew point’ of water at that humidity and pressure. Below the temperature of the dew point, the water vapour will condense into the liquid droplets that we then see dotted around the mug.

coffee bowl pour over
You can see the condensation on the V60 brewer here. Looking at the dew formed in the mornings, what does it tell you about the temperature of space?

It is a similar effect on the grass: the temperature there is lower than the point at which the water vapour in the air starts to condense out of the air and so you get dew. William Charles Wells published his “Essay on Dew” in 1814. The result of more than two years of careful observation, Wells found that dew formed only under certain weather conditions and only on certain space (sky) facing surfaces. Wells’ results can be used to show that the space around the earth is much colder than the surface of our planet. His results (together with some back of the envelope calculations) can therefore also be used to show that the Earth is in a delicate balance and has a natural greenhouse effect. As the weather changes this year and you notice the dew, can you see how Well’s could come to this conclusion?

The second coffee experiment we could do at this time of year is to see whether pollution affects our steaming take-away coffee. While generally it’s always a better idea to sit in a cafe and take the time to enjoy your coffee, there are occasions when a take-away is necessary. Just as with the dew, clouds start to form when the air temperature drops below the dew point. However, water droplets in the air are unstable to evaporation and so as soon as a pure water droplet is formed, it will evaporate unless it has a diameter larger than about 0.1 µmª. This may seem small and yet to spontaneously form a droplet with this diameter would take the accumulation of several million water molecules (I will leave it to you to do the estimate!). This represents a very improbable occurrence and yet we can see that clouds are everywhere, how can this be?

contrail, sunset
Contrails are caused by condensing water droplets behind aeroplanes. But why are they white and what does that tell you about the water droplets within them?

The answer comes from the dust. Fortunately we are a dusty planet and these bits of dust in the atmosphere act as ‘nucleation’ points for water to condense onto. This makes the condensation of water into droplets much more likely and so clouds – which are an accumulation of droplets – can form.

Which brings us back to the coffee. If clouds require dust in order to form droplets, and the steam above your coffee is a grouping of water droplets, does it not make sense that your coffee should be steamier next to a polluted road than in the middle of a park (for the same temperature coffee)?

It’s an idea that I’ve never been able to test but the shift to colder weather here offers a(nother) perfect opportunity.

Does your coffee steam more when you take it away from a city cafe?

I look forward to hearing about the results of your experiments, in the comments here, on Twitter or on Facebook.

ª Introduction to Atmospheric Physics, Andrews, Cambridge University Press, 2008