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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!

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.

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)

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

Notes from Berlin

What a cinnamon bun! Refinery coffee, Berlin
What a cinnamon bun! Coffee and bun at Refinery Coffee, Albrecht Strasse, Berlin

Cinnamon buns, doughnuts and plenty of coffee.

There is a very vibrant speciality coffee scene in Berlin with plenty of excellent cafes offering an interesting variety of coffees and pour overs. A city break of just a couple of days is nowhere near enough to even start to scratch the surface of the city. Coupled to that, we arrived during the Berlin coffee festival so many cafes were participating in public cupping and tasting events. So much to explore. But if you are rushing around, can you really stop and notice things?

How can you experience a place when you travel? Carl Jung pondered this very point when thinking about Rome, he wrote:

“I have travelled a great deal in my life, and I should very much have liked to go to Rome, but I felt that I was not really up to the impression the city would have made upon me…. I always wonder about people who go to Rome as they might go, for example, to Paris or to London. Certainly Rome as well as these other cities can be enjoyed aesthetically but if you are affected to the depths of your being at every step by the spirit that broods there, if a remnant of a wall here and a column there gaze upon you with a face instantly recognised, then it becomes another matter entirely.”*

We may not all have the sensitivity of Jung towards visiting a place but it can nonetheless be illuminating to reflect on the sentiment. This is particularly true of a city like Berlin where the remnants of walls are an ever present reminder of the dangers of ideologies, as well as the ease with which they can seize us.

pour over, Roststatte, Berlin
Pour over at Roststatte, spoilt for choice for coffee in Berlin.

How do you visit a cafe so that you can appreciate the space beyond the aesthetic? We visited several cafes including Brammibal’s Donuts, Common Ground, Oslo Kaffeebar, the Refinery and Roststatte. We also attempted a visit to The Barn (Mitte) but it was sadly too crowded on our visit. Each cafe revealed something unique and each was memorable for its own reasons. The lovely pour-over at Roststatte, the long black with character at the Refinery, the vegan doughnuts during a heavy rain shower at Brammibals. And yet we know how many cafes we missed (as you can see in this guide here or here).

And yet, what stood out as something to stop you in your tracks? What can you sit and dwell with as you savour your coffee? In hindsight, it is interesting that the connections at Oslo Kaffeebar were both very much connected with nature. It was not the wood lining of the cafe and the plentiful wooden furniture around the cafe but the spiders web style tiles on the table and something we saw at the window.

tiled table, Oslo Kaffeebar, Nordbahnhof, Berlin
The spider-web tiled table at Oslo Kaffeebar, near the Nordbahnhof in Berlin

The tiles on the table at the Oslo Kaffeebar were a regular array of spider’s webs. Each identifiable immediately as a web and striking for its regularity. The surprising uses of spider’s silk have featured on Bean Thinking before in a cafe that sadly no longer exists, but it was the regularity of the webs that prompted thoughts about the effect of different drugs, sadly including caffeine, on the behaviour of spiders. But it was a visitor to the outside of the cafe that struck us. A bird, silhouetted against the light, was perched on the (vertical) brick wall outside the cafe. What was it doing there? After it flew off, it was back, again in the same awkward perch but then it darted into the corner that the window made with the brick wall exterior to the cafe, could there be a nest there? The decline of bird species in our world as industrial scale farming has replaced hedgerows with monotonous fields of crops is well documented. But there is more to the bird-human interaction than that. Some bird species have adapted to the way we have traditionally built our houses, the problem being that modern building methods and renovations can threaten their ability to share our space. Other bird species have evolved to adapt to the way humans want to interact with birds with Great Tits for example apparently evolving longer beaks to make it easier for them to access the food put in bird feeders. What do these considerations reveal about evolution and our place in the world?

Oslo Kaffebar, Berlin
View from inside the Oslo Kaffeebar. To what extent does our culture influence our architecture, decoration and even our science?

On the other side of the Tiergarten, the pink tiling of Brammibal’s Donuts contrasted with the teal tiling that had been ubiquitous on the U-bahn line 5. The teal tiling somehow highlighted how even strictly utilitarian architecture nonetheless evokes an emotional response. In addition to considering how this challenges our understanding of architecture as representative purely of form, it can prompt a question: is a utilitarian philosophy consistent with an environment that allows science, (and the pursuit of knowledge for curiosity’s sake) to flourish**? (a question with repercussions for our own, consumerist and atheistic society). To what extent is our scientific development dependent on the prevalent attitudes of our culture? To be somewhat hyperbolic about it, is it possible to continue to do science, as we have traditionally understood it, in a consumerist society that demands constantly new entertainment (itself a form of consumerism)? Do we not replace ‘science’ with ‘technology’ and replace those questions that ask about our place in a world of reality and truth with questions that ask how we can better manipulate our world (where truth and reality as such no longer matter)? And what, in turn, does that do to our understanding of humanity’s place in the universe and so back to our cultural outlook?

We are then left with a couple of questions for ourselves. When travelling, can we allow the space to affect us with, as Jung says, “the spirit that broods there”, or do we take ourselves, imposing our own lens on another space? Can we open ourselves to encounter and is it not urgent, lest walls arise in our minds as well as our countries? I do not have any answers to such questions, but the cafes of Berlin, of London, and of many other places around the world would be a great place to ponder them.

*C.G. Jung “Memories, Dreams, Reflections” Fontana Press, 1961 and reprint editions.

**The question really is, if we consider that the best thing for society is to maximise the happiness of the maximum number, this could tend to promote the sort of science that produces results, technology or devices quickly. This short-term investment in science is contrary to the ideal of funding science for the sake of knowledge and arguably against the idea of being able to investigate the world as it is as opposed to merely developing the technologies that we can use. Is this true? Does it matter?

Frothy physics for a coffee & science evening

A full line up of milk froth! How did each type of milk compare? And why….?

Last Tuesday saw the first of what will hopefully be an autumn-winter series of “coffee & science evenings” at Amoret Speciality Coffee in Notting Hill. These evenings are designed to be conversational; spaces where people can get together and chat about the strange things that they have observed in their coffee (or perhaps the common things that link to stranger things).

The event last Tuesday was in the latter category. We have all seen milk frothed, and noticed how it is different in different milk types (cow and plant), or seen how some foams seem to age while some seem to last forever. But why are some foams stable while others age? And what is the additive in the “Barista edition” oat milk that encourages better foaming and is connected with the foams that you can sometimes see washed up on the beach after a stormy sea?

The oat milk barista edition saw considerable ‘ripening’ of the foam structure as it aged. But does it matter?

We were joined for the evening by Prof. Jan Cilliers of the Earth Sciences department at Imperial College. Why would a professor of Earth Sciences be interested in foam? Well, part of his research involved understanding the use of foams in the froth flotation technique of mining. You can read more about that here. How does it link back to your cappuccino? You can watch some more milk foams age to investigate.

Finally we had the foam line up. Sadiq Merchant of Amoret prepared a series of 8 milk foams using homogenised full-fat milk, non-homogenised full fat and semi skimmed milk, the non-homogenised full fat milk that is used at Amoret, a lactose free milk, coconut milk, oat milk and oat milk Barista edition. The differences were fascinating. That the semi-skimmed milk produced a good stable foam was explicable with its fat-protein content, but why did the lactose-free milk foam so much? Regular oat milk performed fairly poorly: a foam that quickly aged and returned to liquid, but the barista edition oat milk did not last too long either. After 15 minutes there was considerable ‘ripening’ of the microfoam into larger bubbles (as you can see in the photo), but will most coffee drinkers be aware of this? Many of us will have finished our coffee within 15 minutes and be ordering our next one!

More events soon! Sign up to the events list or send an email to find out more.

Our next event on 22 October focuses more on the espresso part of the coffee. What makes a good crema? What are the connections between pulling an espresso and soil science, what can we learn about irrigation and soil ‘health’ by thinking about coffee? What about the grind size distribution? And can we make a connection between pulling an espresso and an old method of measuring blood pressure? (though the question here is not really can we, that answer is yes, the question is should we).

If you are in London, do come along on Tuesday 22nd October, you can sign up for that particular event here or sign up to the events list (to hear of future events) here. If you are not in London but still want to join the conversation, you are welcome to add comments here, head over to Facebook or see you on Twitter.

Hidden Coffee in Camden

coffee Camden Road station
Single origin pour over, banana bread & water at Hidden Coffee, Camden Road

Hidden Coffee is inside Camden Road station. But this is no ordinary station-cafe, because of what lies within, perhaps you could say, ‘hidden’, from the view from the street. A few tables outside barely suggest the fairly large area inside. You can choose from a variety of the usual types of coffee or enjoy a coffee on pour-over while you sit down to ponder your surroundings. We also had a vegan, gluten free, nut free banana bread, which does make you wonder what was in it, but which went very well with the single origin Guatemalan coffee I had on pour over.

The space suggests that it used to be a pub, or that it is open at night, however the signs clearly indicate that Hidden Coffee is closed by 5pm. Because looking inside, it is clear that there is a vault extending into an area screened off from the main cafe, plenty of space that must have been used by the restaurant that existed here before Hidden opened recently. Mosaics on the walls of the vault glint in the reflected light from the cafe and the roof curves intriguingly back into a large, inaccessible, space. There is currently an art exhibition at the cafe featuring pictures of local buildings.

vaults, deductive reasoning
Iron work and vaults. Inside Hidden Coffee

The vault is a consequence of the train line overhead, now part of the overground system. The vaults being a way of providing the strength needed to support the railway line above but also giving space for shops and businesses beneath. This could take you onto a consideration of how architecture assists in distributing load, or the idea and limits of deductive reasoning and its reliance on an idea of shared, knowable truths (we know there are train lines over head partly because of our familiarity with this form of architecture, partly because we walked through a door next to a train station). Or you could notice the glinting mosaics and wonder about the chemistry of the pigmentation in each of the pieces.

Looking out the window while drinking my coffee though I noticed the pine cone decoration on the railings. Several thoughts suggested themselves. How do squirrels remember where they hide their winter stocks? And related to that, how does memory work: why can I never remember the tasting notes of the coffees I enjoyed if I don’t write them down (only that I liked the coffee)? Why were the railings so obviously re-purposed? They are either not original or they have been adapted to incorporate a concrete step beneath them? And how do pine cones work?

The pine cone opens in response to dry weather to expose the pine kernels and closes in response to more humid weather so as to protect the seeds. But it was only back in 1997, that researchers used electron microscopy to see the structure of the cones and to measure the response of different types of cell to controlled humidity. They found that the response of the cells to humidity depended on the winding of cellulose structures around the cell. If the cellulose was wound with a high winding angle, the cell tended to elongate in humid conditions. Conversely, the cells having cellulose aligned more along the cell length (a low winding angle) didn’t elongate so much in response to humidity. The effect of coupling these two cell types together was to create an analogue to a bimetallic strip which bent in response to humidity rather than temperature.

exterior hidden coffee Camden Road
Pine cones and railings. And you see why it is obvious they have been repurposed?

It is reminiscent of a device I once read about, created perhaps by a member of the Lunar Society. The designer had cut a series of discs out of a small log of wood and joined them loosely together (presumably with a type of resin) so that they formed what would have appeared as a wooden caterpillar. On the front disc, he (and if it was a Lunar Society member it would have been a he) put a hook facing backwards on the bottom of the disc. A similar hook was placed on the back disc. When the humidity increased and the wood expanded, the caterpillar extended and hooked forwards. As the humidity decreased and the caterpillar shrank again, the back of the caterpillar would move towards the front forming a ‘self-propelling’ model caterpillar.

Unfortunately I can no longer find the reference to this device so if you know who invented it or where it is referenced please do let me know. In the meanwhile, enjoy the effects as the days turn humid/dry as we change seasons, and perhaps contemplate a hidden coffee while you do so.

Hidden Coffee is in Camden Road (overground) station, 33 Camden Road.

The universe in a cup of coffee

black coffee, Vagabond, Highbury
The universe in a cup of coffee, but how much can we take this literally?

When people ask, what is Bean Thinking about, they often get the reply, it’s about “the universe in a cup of coffee”*. And it is perfectly true, much of the physics of the coffee cup is mirrored by the physics of the universe: you could think about the Black body radiation and the Cosmic Microwave Background, or the steam from the cup and cloud formation, but what about General Relativity? Could it really be that physics such as that of General Relativity mirrored in a coffee cup?

It could, perhaps, initially appear a ludicrous idea. Einstein’s theory of General Relativity explains the gravitational attractions of massive objects such as stars and planets through the curvature of space-time. And although what occurs on the planetary scale must also be valid on the scale of the coffee cup, we would surely expect classical, Newtonian physics to dominate here. But that would be to neglect the equally ludicrously named “Cheerios effect” and a paper that was published in Nature Communications earlier this month.

The cheerios effect is the phenomenon that you may have noticed on your tea or coffee whereby two floating objects on the surface are attracted to each other (and named after observations of the effect in a breakfast bowl). Two bits of a dropped biscuit come together or two bubbles bounce to form a pair. The effect occurs because both objects dent the surface of the drink by bending the surface of the liquid through surface tension effects. Consequently, the two objects don’t float on a flat coffee surface but a curved one and when they get close enough together, the surface tension effects bring the objects together into one big indentation rather than two smaller ones.

You can see surface tension effects from the curvature of the coffee around the edge of a cup. It is also visible around objects that float on top of the coffee.

On the face of it, this has similarities with the ‘cartoon version’ (or schematic) of the idea of gravity in general relativity. Each massive object (ie. any object with mass) bends the space-time around it, the more massive an object, the more the space-time is bent. This has the effect of seeming to bend light and leads to gravitational attraction. And yet there are very many differences. A liquid surface is 2D, planets clearly move in at least 4D, the way the surface bends owing to surface tension is surely not the same as the way that space time bends owing to its distortion through massive objects. It could go on only it turns out that some of the maths is quite similar: the surface is distorted proportional to the mass of the object in a cup of coffee, the attraction between the objects is a product of both masses (as it is with gravity). Indeed, it has even been proposed that studying the cheerios effect could be a way of gaining insight into some of the problems of general relativity. But there was always a catch: Friction.

On the surface of a coffee, although the floating object is bending the surface proportional to its mass, it is in some sense in contact with the fluid. When the object moves, there is a frictional resistance to the movement caused by the object’s interaction with the coffee. This makes it quite different from the situation in space. And so you would have been correct in your suspicion that general relativity would not be easily found in a coffee cup, but only for reasons of friction.

Which is where the recent Nature Communications paper comes in. Rather than float objects on coffee, the researchers floated silicone oil droplets on liquid nitrogen. Being a liquid, the nitrogen is subject to surface tension effects just like coffee, but being a very cold liquid (196 C below freezing point), it shows a second effect when the (room temperature, ie. warm) oil droplets are floated onto it: the inverse Leidenfrost effect.

Coffee, Van Gogh
What do you see in your coffee cup?

Again, you may have seen the Leidenfrost effect while frying eggs (or tofu if you’re vegan). When the frying pan is very hot, drops of water sprinkled into the pan will immediately vaporise in the layer between the pan and the droplet causing the drop to dance around the pan as if it is flying. The inverse Leidenfrost effect is, perhaps unsurprisingly, the inverse of this. When the liquid is very cold and a hot object is introduced to its surface it will instantaneously vaporise meaning that the hot object on the surface will skip over the cold liquid, without friction.

The reason that this is relevant to the idea of general relativity in a coffee cup is that this bending of the surface of the liquid nitrogen, coupled with the inverse Leidenfrost effect effectively levitating the drops means that you have a warped liquid surface, like the bending of space-time, but the floating object moves with absolutely no friction, because there is no contact between it and the liquid beneath. Clever.

And so what happens when you introduce two droplets to the nitrogen surface? How do they interact? Well, they attract each other and can even orbit each other like planets until, as the friction effects start to grow even in this system, the drops cease behaving as planets and can collide. It is a fascinating observation but one with relevance to biological self-organisation rather than an immediate extension to general relativity. That will be for another study, perhaps one with super-cold brew coffee.

So, the universe in a cup of coffee? Perhaps. But sometimes not strictly literally.

You can read the paper in Nature Communications here (it’s open access), or the summary in Physics.Org here.

*With suitable acknowledgement of the Feynman anecdote that you can see here.

Lazing Under the Willow Tree, Stoke Newington

Under the Willow Tree, Stoke Newington, Coffee in Stoke Newington, Green Lanes
No name but a friendly cafe. Under the Willow Tree in Stoke Newington

We delayed our visit to Under the Willow Tree by a day because we noticed that the cafe was closed on Monday afternoons owing to “Sing and sign” sessions for the local community. What a brilliant idea and the sort of community engagement that makes a neighbourhood cafe particularly special. Definitely a cafe to visit.

Coffee is by Grumpy Mule while the tea is by Ero’s. There is a good selection of pastries on the counter and food for brunch/lunch on the menu. The only problem was that there was no sign on the frontage of the cafe to tell us that we’d arrived, we guessed based on the postcode and the fact that this was the only place serving this sort of coffee in the area.

The cafe is definitely child-friendly. With a children’s play area at the back and toys on the shelf by the water, there is plenty for kids to do while their parents enjoy some time with a coffee. Although there are also tables away from the play area if you wanted a coffee away from the kids. A table towards the back of the cafe is suspended by rope perhaps making you think of swings, or tree houses, while the rest of the cafe is fairly minimalist, focussing you on the coffee and the play.

It is no bad thing to focus on play and indeed, it could offer a first physics connection, or at least materials science, with this cafe, in the form of the English Willow needed to make cricket bats for Test cricket. The fibres within the wood provide the toughness needed to prevent the wood from splintering as the ball hits the blade.

coffee, Grumpy Mule, coffee in Stoke Newington, Willow Tree
The coffee reminded me of the picture of the Black Hole, but this halo expanded and dispersed more like a stellar dust cloud.

But keeping with the Willow tree, the remarkable thing about it is how it bends down to the water’s edge, providing shade and shelter for all manner of wildlife. There is another type of deciduous tree in a London park that hangs across a footpath, lazing in a manner similar to that of the willow at the water’s edge. And although it is perfectly possible to walk underneath it on part of the path, I find it perhaps more respectful to bow to the tree as I walk underneath. Walking the path at different times of the year, it is noticeable that the amount I need to bow increases as winter moves into spring and summer. The weight of the leaves pulls on the branches pulling them down.

As the tree has horizontal branches hanging over the path, it is not a simple case of Hooke’s law (where the amount the tree stretches down is directly proportional to the gravitational force of the leaves acting on the branches). But nonetheless, it does give you an indication of the collective mass of the leaves.

The fact that the tree dips down towards the path when it has leaves and moves up away from the path each winter, implies that the tree branches are acting within the elastic limit. That is, that the response of the branch to a load is still reversible. If the stress becomes too much, the extension of the tree will become plastic rather than elastic and the branches would not return to their original position. The elastic limit will vary from wood type to wood type and with different materials. Sometimes we would want elasticity and so we’ll choose one wood type, sometimes rigidity and so another. One reason that willow is a good wood for cricket bats is also this elasticity: the elasticity of the wood as the ball hits it being determined by small pockets of air in the bat.

Tree, bowing tree, effect of leaves on branch bending
This tree bends over the path a bit more in summer than it does in winter. How much do leaves weigh?

There is a similar balance that may occur in your coffee cup if you enjoy a cappuccino. The difference between a pourable foam and one that stands ‘peak like’ on the cup. The ability of the barista to pour and draw the latte art requires a foam that is fairly stiff but still pourable. This is quantified by measurement of the “yield stress” of the froth. The yield stress is the minimum shear stress needed for a liquid or foam to start to flow. So to make latte art, you would need a foam that is stiff enough to hold the design, that is, it has lots of little bubbles that make the foam more firm. But at the same time that the foam is not so stiff that it does not pour (so you need to ensure that you have a lot of liquid milk content within the foam). The yield stress increases as the foam drains and so a good, pourable foam can be achieved by forming lots of smaller bubbles (thinner channels between the bubbles = slower drainage) and pouring it fairly quickly after foaming. But if you wanted to make 3D art of the form in the photo, you would want foam of a different stiffness, a different type of elasticity. You would probably want a drier foam.

In a sense, it is interesting to note that much that determines the response of a substance is about the voids within it rather than purely the material it is made from. Perhaps there is an analogy back to the cafe there: much that makes a coffee shop is the atmosphere created by the cafe rather than purely the coffee and pastries that are stocked. Or maybe that’s one step too far, and we need to go back to ponder and play Under the Willow tree while we enjoy our coffee, foamy or not.

Under the Willow Tree is at 114 Green Lanes, N16 9EH

3D hot chocolate art on an iced chocolate, Mace, Mace KL, dogs in a chocolate
A key to good latte art is understanding good foam. This foam would require different properties to the swans and tulips you may also see in your cup.

The interdependence of science and (latte?) art

latte art, hot chocolate art, soya art, albedo, science and art mixing
The difference in contrast between the art on a cafe latte and a hot chocolate is revealing of a lot more than just a tulip.

In Paradiso, Canto II, Dante asks Beatrice about the Moon: “what are the dark marks on this planet’s body that there below, on earth, have made men tell the tale of Cain?”*

On Earth below, it is perhaps the brightness of the milk in the latte art that we notice in our coffee. But it is in fact precisely the contrast that we notice, both on the Moon and in our coffee.

What causes this contrast in the coffee and how does it link back to the Moon? Watching videos of, or if you are lucky to be close enough, baristas making latte art, you may be struck by the skill of the barista to form the milk into complex patterns and art. Swans, tulips and other designs appear on the surface of the drink with seemingly simple oscillations of the hand. And yet, if you’ve ever thought about attempting this art, you will appreciate how hard it is to design this contrast. How does the first pour of the milk lead to a significant uptake of the coffee (and hence a brown colouring), while the second part of the pour is dominated only by the milk and hence the shapes appear?

It must be partly a turbulence effect. The initial milk pour is from a significant height which would churn up the coffee meaning that the suspended particles in the coffee then get caught in the spaces between the bubbles in the milk’s microfoam. The second part of the pour is from a lower height which leads to a reduced mixing between the two liquids.

Brew&Bread, latte art Sun, KL latte art
Complicated patterns are revealed by the difference in colour between the coffee and the pattern.

Yet this is only part of the story. Another perspective on it could be to consider the ‘albedo’ of the drink. The albedo is a measure of how reflective a surface is, so highly reflective surfaces (milk bubbles, ice sheets) have a higher albedo and less reflective surfaces (the coffee liquid, the earth’s surface) have a lower albedo. Part of the visibility of the latte art comes from this difference in reflectivity between the pattern part and the base part of the coffee.

In Earth science this has consequences for climate change: if the ice (high albedo, highly reflective) melts and reveals earth or sea (lower reflectivity, lower albedo), more sunlight is absorbed by the Earth and consequently you get local heating and locally accelerated ice melting. This may have consequences more globally in terms of climate change.

For Dante, it explained the colouration of the Moon. As his guide Beatrice explained to him: different parts of the Moon shone differently depending on their composition**.

Another example of latte art. Science meets art meets the skill of the person producing it.

Which takes us to another connection between science and art. It is recognised that, in European science history at least, Galileo first realised that the ‘dark marks’ on the Moon’s surface indicated that there were mountains and craters on the Moon. He was able to do this because he saw the Moon through a telescope and deduced that the patches were shadows. But when we think about this, it can’t be the whole story. While a telescope magnifies a distant object we still see, effectively, a 2D surface. We see the mountains on the Moon in the shadows because we know they are there. But how did Galileo know? Indeed, another astronomer at the same time was looking at the Moon through a telescope and could deduce only “strange spottedness”. What was the difference between Galileo and Thomas Harriot that allowed the former to see what the latter could not?

It has been suggested that it was Galileo’s artistic training that meant that he recognised the shades of light and dark as shadowsª. His practise at chiaroscuro drawing meant that he knew how to render depth using light and darkness in 2D images. When he saw the Moon, he could recognise the mountains. Another scientist, not familiar with how to render depth in painting, may instead see latte art on the Moon.

There are many ways in which our different backgrounds benefit each other and in which it benefits us to work as teams rather than individuals. There remain some though where the right combination of knowledge of both art and science combined with a particular skill at rendering them, can result in brilliant coffees, or astonishing discoveries, through connecting dots that otherwise could not be seen.

*The Divine Comedy, Dante Alighieri, Paradiso, Canto II. It is interesting here that Dante uses the word “planet” for the Moon, something that we would not do now. In a way it emphasises how our descriptive language changes with time and therefore how there may still be hope for Pluto’s rehabilitation.

** It is interesting here though that Beatrice’s answer to Dante is given to him only after she has convinced him through two experiments that his own explanation for the patches of the Moon was wrong.

ª Styles of Knowing, Chunglin Kwa, Pittsburgh Press, 2011