Coffee review Coffee Roasters Observations Science history slow

Wonders of the World at Espresso Base, Bloomsbury

Hasten coffee, long black, black coffee, espresso base
‘Has Bean’ coffee at Espresso Base

Espresso Base is exactly the sort of café that you want to make sure that you know about, but part of you is selfishly quite happy if not too many others do. It is not that the the place is small, far from it. There is plenty of space in the courtyard at Espresso Base, beside St George’s Church, to sit and enjoy your coffee. The thing is, it is great to have the place almost entirely to yourself. With few others around, the oasis-like quality of the place is emphasised, astonishing as it is so close to the busy Bloomsbury Way. Only this oasis serves great coffee. Their coffee is roasted by Has Bean, which I admit is the reason that I first dropped into Espresso Base a few weeks ago. The black coffee that I had was certainly very good and the environment in which to enjoy the coffee was thought provoking which, for me, is an important aspect of any café. Cafés need to be places that you can go, slow down and notice things and Espresso Base certainly falls into that group of cafés that I would highly recommend both for the coffee and the café.

stone recycling, slate, slate waterfall, geology
The purple slate waterfall feature in the courtyard area at Espresso Base. You can just see the stone with the rectangular holes carved into it at the bottom of the wall.

On the day that we arrived, it had been raining. For a café with seating outside this may have posed a problem but the chairs had been thoughtfully folded so that they remained dry. The rain had however seeped into some of the paving slabs around the chairs and so that was the first thing to notice, the fact that many objects when wet appear darker, why? Opposite our seating was a rock feature that to me looked like a waterfall made out of slate, the slate had a purple tinge which again, had been made slightly more purple by the rain. Below the slate ‘waterfall’ and forming a wall, were a series of stones that had clearly been taken here from somewhere else. I say ‘clearly’, because the stone at the bottom had two holes that had been carved out of it, one square, one slightly more rectangular. Presumably the stone had been used as part of a gate post in the past and yet there is no evidence of the remains of a gate on the other side of the courtyard (I think that a gate post would have to be deeper than the square indent in the paving slab that is at the other side of the courtyard). It is therefore more likely that the stone had been used somewhere else beforehand and ‘recycled’ for use in this wall. This juxtaposition of slate above and recycled stone below reminded me of the early geologists and how they identified the Great Glen fault that runs through Loch Ness in Scotland. Slate is a metamorphic rock, meaning that it has undergone changes due to the high pressure and temperatures within the Earth. Slate is however quite a low-grade metamorphic rock so, compared with higher grade metamorphic rocks, it has not been subjected to that much pressure or that much temperature. By mapping the lower grade and higher grade metamorphic rocks along the Great Glen, the early geologists noticed a line that sharply separated the metamorphic rock types. This fault would have, in the past, caused earthquakes as the ground slipped along the fault.

Replica of Mausoleum of Halicarnassus
The steeple of St George’s church, Bloomsbury Way. The statue on top is of King George I rather than King Mausolus in  his chariot. The statue of Mausolus, his wife/sister Artemisia and a horse from his chariot can be seen in the British Museum.

On leaving Espresso Base I turned and looked up at the church. If you get a chance, take a look at the steeple. Particularly ornate, the stepped steeple is apparently built to the description of the Mausoleum of Halicarnassus by Pliny the Elder. This monument was one of the seven wonders of the Ancient World and was built to be the burial chamber of King Mausolus of Karia. Described as standing approximately 40 m in height, this massive stepped, marble pyramid stood on top of 36 columns surrounded by statues. Topping the pyramid was a statue of King Mausolus himself, in a chariot. This ancient wonder is thought to have been destroyed by an earthquake in the fourteenth century after which the stones were ‘recycled’ by the Knights of Malta to build a fortress. A history that is aptly mirrored in the geology and stone recycling evident in the courtyard of Espresso Base.


Espresso Base can be found in the courtyard of St George’s church, Bloomsbury Way, WC1A 2SE

Artefacts from the Mausoleum of Halicarnassus can be seen in room 21 of the British Museum (conveniently just around the corner from Espresso Base).

Geology help from: “Geology Today, Understanding our planet”, Murck/Skinner, John Wiley & Sons, 1999

Coffee cup science Observations slow

Coffee & Contrails (I)

contrail, sunset
A set of criss-crossing contrails taken in the evening.

If you gaze up at the sky on a clear day, you will often see a few contrails tracing their way across the blue. Formed as a result of water in the atmosphere condensing onto exhaust particles from aeroplanes, contrails are a regular feature of the skies in our modern life. There are at least two ways that I can think of, in which the physics of the contrail is connected to the physics of the coffee cup, so, there will be two Daily Grind articles about them. This first one, about the physics of how we see them, and a second post (scheduled for 10th June) about interesting effects that we can see in them.

Perhaps now would be a good point to go and make a cup of coffee before coming back to this post. Make sure that you notice how the steam clouds form above the kettle spout as the water boils. Do you see the steam at the spout itself, or just a few centimetres above it? With the cup next to you, notice the steam rising above it. Does the steam seem more obvious on some days than others? For example, the coffee always seems to me to steam more on cold damp days in winter than on warm-ish days in late spring. Both of these observations (about where and when we see the steam clouds) are mirrored in the contrails, it’s time to take a closer look at the coffee.

V60 from Leyas
The clouds above a coffee cup are a rough indicator of the relative humidity.

The difference in the day to day visibility of the steam above the coffee cup is an indicator of the relative humidity of the atmosphere. If we prepare our cup of coffee on a day when the relative humidity is already high, adding that extra bit of water vapour from the cup leads to clouds of steam above the mug, as the water condenses into droplets of liquid water and forms clouds. If our coffee was instead prepared on a day with low relative humidity, the water vapour above the coffee cup is less likely to condense into clouds. Contrails are formed high in the atmosphere when the relative humidity is quite high. Exhaust particles from the engines of the plane offer a surface onto which the water in the surrounding (humid) atmosphere can condense to form clouds. We know that it is mostly the atmospheric moisture that is forming the contrails (rather than water from the exhaust itself) because of research done by NASA. In research flights, the amount of water vapour leaving the aeroplane engine was 1.7 grammes per metre of travel while the mass of water in the contrail was estimated to be between 20.7 and 41.2 kilograms per metre. This means that contrails can give a clue as to the weather: on dry days, contrails will not form because the water in the atmosphere is likely to remain a gas and therefore invisible to us, it is only when the air is already quite humid that contrails are likely to form and persist.

glass of milk, sky, Mie scattering
A glass of (diluted) milk can provide clues as to the colours of the clouds in the sky as well as the sky itself

Then there is the question of why we see them at all. Contrails appear as white clouds trailing behind the plane. We see them as white because of an optical effect caused by the size of the condensed droplets of water (actually ice) in the contrail. Objects appear as having different colours either as a result of light absorption by chemicals in the object (leaves are green because of chlorophyll) or as a result of light scattering from the object. A water droplet is colourless and so the colour we see coming from the droplet must be purely a consequence of light scattering rather than a light absorption effect. Clouds appear white because the water droplets within the cloud are as large, or larger than, the wavelength of visible light (0.7 μm). Droplets this size will scatter all wavelengths of visible light and so appear white. If the droplets were much smaller than the wavelength of light they would scatter different wavelengths by different amounts. It is because the atmosphere is full of such tiny particles (and molecules) that blue light is scattered more than red light in the atmosphere and so the sky appears blue to us from our vantage point on the Earth’s surface. Milk is composed of large fat droplets (which will scatter a white light) and smaller molecules which will preferentially scatter blue light, just as the sky. This is why you can mimic the colours of the sky in a glass of milk. It is because the water droplets have formed a few cm above the kettle spout that you can see them scattering the light. For exactly the same reason, the contrails in the sky appear as white clouds.

A hot air balloon in a sky full of contrails

Contrails can persist in the sky for anything from a few minutes to a few days. Just like clouds, contrails affect the way that light (and heat) is reflected from the Sun or back towards the Earth. However, unlike normal clouds they are entirely man-made, another factor that could have an unknown effect on our climate. A few years ago, a volcano eruption in Iceland caused the closure of UK airspace (as well as the airspace of much of Europe). I remember being in the queue to buy a cup of coffee in the physics department and hearing the excited conversation of two atmospheric physicists behind me. For the first time they were able to study some particular atmospheric effects without the influence of any contrails. In effect they could start to understand the influence of contrails by this unique opportunity of taking measurements during their absence. What was a major pain in the neck for so many travellers in 2010 meant a lot of extra (but presumably very interesting) work for them.

Coffee & Contrails (II) is about the structures you can sometimes see within the contrail. If you can think of any other connections between coffee and contrails (or coffee and clouds) why not let us know in the comments section below.

Home experiments Observations slow

Patterns in a tea cup

light patterns on the bottom of a tea cup
Looking into my peppermint tea. Dancing filaments of light are just visible

Have I been unfair to tea drinkers? It has been pointed out to me on more than one occasion recently that tea is also a good source of science in a cup. So, last week, I drank a large amount of tea and started gazing into my (peppermint) tea cup. I watched as dancing lines of light played on the bottom of the cup. Never staying in one position for long, the filaments moved around, snaking across the tea cup. You can possibly see them in the picture on the right, although you would get a better view of them if you watched them dance yourself in a cup of freshly made tea. Similar lines can often be seen at the bottom of the swimming pool. Such lines of light must be caused by something in the water (or tea) bending the light from the surface into concentrated patches on the bottom. But are the two effects, though visually similar, caused by the same thing? And, what can this possibly have to do with forensic science and drug dealers?

straw, water, glass
When light travels from one medium to another (e.g. air to water) it gets bent by refraction

When light passes from air into a transparent medium (eg. into tea) it gets ‘bent’, in a process called refraction. This is why a spoon (or straw) put into a glass of water looks bent when viewed from the side (see picture). The amount that the light bends is dependent on the angle at which it hits the tea surface and by the density of the tea. The fact that you have to be able to see the bottom of the cup to see this effect, makes tea ideal for viewing it. (If your coffee is transparent enough to view these dancing lines of light, you may well want to check that you are brewing it correctly).

I’m not an optics person but it strikes me that there are at least two easy ways for these light patterns to form. Firstly, small waves on the surface of the water/tea will cause the light hitting the waves to be refracted by different angles as they go through the water. The patterns that form on the bottom of the pool/cup will therefore move with the waves. It is easy to see how such waves could form in a swimming pool, it is not so easy to imagine them in a tea cup. A second way to form these patterns is if the light is refracted through regions of different density, such as slightly hotter and slightly cooler tea. Such regions will occur in a tea cup because the tea is being cooled at the surface by contact with cool air and so there will be a continuous convection process in the cup. Warm water is less dense than cold water* and so will refract light slightly less than cold water will. Consequently, as the slightly cooler and slightly warmer regions of tea bend the light by slightly different amounts you should see patterns forming on the bottom of the cup as different amounts of light get to the bottom at each point.

So we have two possible causes for the light patterns on the bottom of a tea cup. How could we distinguish between them? Perhaps it would be an idea to get two identical cups, one filled with cold water, one with hot water (or a clear tea such as peppermint). Which shows the dancing filaments? Both of them, neither of them? Another experiment could be to observe the filaments in a cup of hot tea and then wait for the tea to cool. Do the light patterns fade as the tea cools?

tea pot science
Not always coffee. Tea can be interesting too.

The link to forensic science comes from the fact that light passing through transparent substances of different density will be ‘bent’ by different amounts. Imagine a drug dealer has been caught with some illegal substance wrapped in cling film. Although it looks to us like any other piece of cling film, that piece of film has been made in a specific factory at a specific time. This means that the roll of cling film that this piece was taken from will share variations in thickness and density with the cling film wrap. A type of cling film ‘finger print’. The density variation in the cling film can be photographed with a technique called the Schlieren photograph which exploits the fact that the light is refracted by varying amounts as it passes through these varying densities. If the police can get hold of the cling film in the suspected drug dealers home, this too can be imaged. If the ‘finger prints’ (changes in density etc.) of the two samples of cling film match, the suspect may be in significant trouble. The motto of this: Ensure that you have a decoy roll of cling film to hand before wrapping anything or, what is probably much better, spend time contemplating your tea in a café instead.

What do you think causes these patterns? What do your experiments reveal? Comments always welcome, please leave them in the box below.


* Between 0-4ºC the density of water decreases with decreasing temperature. For the purposes of this blog article it is assumed that you are drinking normal tea at around 60ºC rather than ice tea.

cafe with good nut knowledge Coffee review Science history slow

Spinning a yarn at E&J’s Pantry, Endell St.

E&J's Pantry on Endell St
E&J’s Pantry on Endell St

There are still a few areas of central London which seem a little short on good cafés. One such area lies just east of Covent Garden. So it was very fortunate that, on arranging to meet a friend nearby, I came across E&J’s Pantry on Endell St. The coffee is from Nude roastery and the interior, while not exactly spacious is large enough that we were able to sit undisturbed for quite some time. Along with good coffee, they serve lovely cakes which (according to their website) are made in their own kitchen. This is presumably why they could tell me confidently which cakes were nut free. (Those who follow @thinking_bean on Twitter may know that this is a bit of a hot topic for me.) I enjoyed a very good Long Black and a cake, before sitting back and taking in the surroundings.

On one of the walls inside E&J’s Pantry are a series of photographs. Each photograph is suspended by a thin thread from a rail near the ceiling. The observation reminded me of spiders webs and the (often heard) claim that spider silk is a natural material that is “stronger than steel”.

photographs, spiders web, nylon
Photographs inside E&J’s pantry. Can you see the thin threads holding up the pictures?

Unfortunately, the claim that “spider silk” is stronger than steel is a little disingenuous. For a start, there are many forms of spider silk. A ‘typical’ orb spider for example, will combine at least four types of silk to make a web. Secondly, even for the main type of structural silk (Major ampullate), the statement that it is stronger than steel is sadly pushing it a bit. The issue is that it depends on exactly how you define ‘stronger’ and the species of spider that makes the silk. Spider silk can be comparable to steel in terms of its tensile stress (how much it takes to break it), but it is when it is compared to steel based additionally on the weight of the material that spider silk can be considered ‘stronger‘. When you combine this with the fact that spider silk is more environmentally friendly (and biodegradable) than man-made comparable fibres such as Kevlar, it is clear why research is being done into understanding, and synthesising, spider silk.

A question arises. If it is so strong and so lightweight, why don’t we farm the spiders to harvest the silk? Wouldn’t this be quicker than trying to synthesise it? Clearly we weren’t the first to think this and a farmer in North Carolina, USA, tried in the 1930s. Unsurprisingly, there were issues. Firstly, it took 57000 spiders to produce 0.45 Kg (1 lb) of spider silk. Secondly, if they weren’t kept in (expensive) solitary confinement, they ate each other. It seems that the N. Carolina spider farm was not a commercial success. However, as described in the New Yorker (8th Feb, 1941), a certain Miss Mary Pfeifer did harvest spider silk in the first half of the twentieth century, for use as cross hairs in targets for surveyors and, more sinisterly, bombers. Glass engraving at the time was not fine enough for making the cross hairs. The thinnest line that could be made by a diamond cutter into glass was about double the diameter of the silk from spiders webs and so spider silk had an obvious ‘niche’ market.

HM Ng, spider on web
It takes several types of silk to spin a web. Image © HM Ng

In 1941, Pfeifer would pay “small boys” from the neighbourhood 15 cents for each useable spider that they caught and brought to her. She would then harvest the silk and wind it onto spools ready for use in target sights. Since then we have developed nanofabrication techniques which mean that very thin strands of metal (such as platinum) can be positioned onto the lenses. Continuous strips of metal of around 10 nm thickness (this is one thousandth of the width of a spider silk) can be routinely deposited. Through the development of these and similar manufacturing techniques we no longer need spider silk for use in cross hairs. It is probable that the market cornered by Mary Pfeifer no longer exists.

Spider silk however remains one of many areas where, by studying nature we get clues as to how to overcome various technological challenges. Sometimes devices possibilities are obvious, such as with the opportunity of synthesising material with the strength to mass ratio of spider silk. Sometimes however devices are a long way off. It would be a shame if we prioritised research into devices at the expense of appreciating the ingenuity of nature’s own solutions to its problems. As the story of Mary Pfeifer shows, sometimes today’s obvious devices are not those of tomorrow, who knows where research done purely out of curiosity would lead us.


E&J’s Pantry is at 61 Endell Street, WC2H 9AJ

More information about spiders webs can be found in “Spider Silk”, L Brunetta and CL Craig, Yale University Press, 2010


General Science history slow

Of worms and grind

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

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

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

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

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

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

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

Coffee cup science Coffee review General Observations slow

Rain drops at Notes, Covent Garden

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

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

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

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

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

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

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

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