2 years in

3D hot chocolate art on an iced chocolate, Mace, Mace KL, dogs in a chocolate

Happy birthday to me

Last weekend, Bean Thinking turned 2. So I’ve been looking back at the cafés I’ve visited over the past two years. Bean Thinking started as a way to slow down and to try to see things in a (slightly) different way, to really enjoy the coffee but also to take time to explore the stories, and the science, that can be found in different cafés. I’ve enjoyed the coffee in each café that I have visited but, as always happens, some stick in the memory a little more than others.

So I decided to pull together five cafés which, for me, had an interesting story to tell or prompted an unexpected chain of thoughts. I have sadly had to leave out some great cafés and some really fun stories (for me to think about at least). However, these five stood out. Each café introduced an unexpected bit of science to me, or had something about them that meant that slowing down and enjoying the coffee provided a really special moment. Consequently, each café features for slightly different reasons, and so rather than create a top 5 (which would be impossible anyway), I have listed them alphabetically. I hope you’ll excuse this trip down memory lane.

Amoret, Hammersmith

Kettle drum at Amoret

Coffee on a drum at Amoret

It is not every day that a well made V60 can transport you to another planet. Yet that is what happened for me at Amoret in Hammersmith. The cylindrical design of the table reminded me of a drum but the question is, why do drums make the sounds that they do? The answer to this question took me on a journey into sounds. Just how different would Bach’s famous fugue sound if played on Venus rather than Earth? And then a surreal moment as a Dutch TV station decided to take Bananarama to Venus courtesy of research conducted at Southampton University. This was all accompanied by great coffee in a very pleasant cafe, the review can be found here.

Coffee Affair, Queenstown Road,

Contemplating the floor at Coffee Affair

Contemplating the floor at Coffee Affair

Where better to slow down and appreciate the moment than a place reminiscent of the geology of the South Downs that helped Charles Darwin to argue the case for his theory of evolution. Coffee Affair occupies the old ticket office at Queenstown Road station. The fixings and the floor of the café reveal evidence of the people who inhabited this space in times past. Watching the V60 being prepared, slowly, carefully, exactly, emphasises this sense of time. The result is great coffee in a place that almost forces you to step out of the speed of modern life and stop, put down the smart phone and take time to just notice. Coffee Affair was reviewed here.

Lumberjack, Camberwell,

Lumberjack coffee Camberwell

Exploring local connections at Lumberjack

There’s a strong emphasis on keeping it local at Lumberjack in Camberwell, as well as a preoccupation with all things wooden (this being an enterprise set up with London Reclaimed). So it was interesting to discover that there was a fairly local connection between Camberwell and the ultimate ‘local’ London tree, the London Plane. Not only that, but research that had been published a few weeks before I went to review Lumberjack had shown that, surprisingly, the wind speed needed to fell a tree was fairly constant at around 56 m/s, irrespective of the size or type of tree. This surprising finding was the cherry on the cake for this ultimate in local reviews (here).

Red Door, Greenwich,

vortices, turbulence, coffee cup physics, coffee cup science

Beautiful physics at Red Door

Just what would happen if you put a cup of coffee on a record player? A turntable in a corner at Red Door in Greenwich meant that not only did I start to think about this question, I decided to start some experiments to find out. The resulting physics was physically as well as scientifically beautiful. The experiments can be done by anybody with equipment that you can probably find at home (though I would recommend not using an actual turntable). It turned out to be an elegant experiment involving vortices, but as Helmholtz noticed, similar vortices form in organ pipes, the atmosphere and even in electromagnetism. Truly a beautiful piece of connected physics that I would have missed had I enjoyed my coffee ‘takeaway’. More here.

The Turkish Deli, Borough Market,

Turkish coffee

The universe in a cup of coffee at The Turkish Deli

“The universe is in a glass of wine” so said a Greek poet according to Richard Feynman, but at the Turkish Deli it is more obvious in a cup of coffee. When made properly, Turkish coffee requires at least four minutes of ‘settling time’ before it can be enjoyed. You could use this time to think about how the concentration of coffee particles changes as a function of the depth. Similar considerations led Jean Perrin to conduct experiments back in 1910 that he declared showed that “… it becomes very difficult to deny the objective reality of molecules” (which before that point had indeed been very much denied). Now that The Turkish Deli also roast and grind their own coffee on-site, there is even more reason to visit and ponder the connectedness of our coffee and our planet. The Turkish Deli was reviewed here.

With so many more cafés to explore, and things to discover, who knows what the next year or two will bring. And if you’ve got a recommendation or found a great café where you have stopped and noticed something intriguing, no matter how lateral, why not drop me an e-mail, I’d love to hear your experiences of slowing down and appreciating our coffees.


Seeing things at a kopitiam (coffee shop)

Rocky, Bangsar, KL, Malaysia, koptiam

A kopitiam in Bangsar, Kuala Lumpur, Malaysia

One of the great things about travelling is exploring the different cafe and coffee cultures in different countries. Is it the coffee that is important? Or food, alcohol or maybe just the opportunity for socialising? In Singapore and Malaysia, the “kopitiam” (or coffee shop) is a familiar part of each neighbourhood. Each kopitiam serves local coffee (kopi) and a variety of foods which are usually prepared while you wait, from stalls around the edge of the kopitiam. The kopitiam provides a space for socialisation and meeting people over a bowl of steaming noodles. Inside electric fans are blowing continuously in an effort to lessen the heat. Frankly, the local coffee is not to my taste but there are plenty of other things to eat and drink in each kopitiam. A breakfast of “kueh” and black tea for example is a welcome change from toast at home! In many areas of Singapore, and to a lesser extent Malaysia, local kopitiams are closing to make way for the new style cafés which serve a range of freshly roasted, pour over or espresso based coffee. Not being Malaysian or Singaporean I do not want to comment too much on that, I guess it is similar to the decline of the “caffs” in the UK. Mourned by many in the community but welcomed by others for the improved quality of the coffee.

straw, water, glass

An everyday example of refraction. The water refracts the light to make the straw appear ‘broken’.

However, with so much going on in a kopitiam, the temptation to look at a kopitiam-physics review was too great, especially when I started to “see things” at the edge of the shop. Am I going mad? No, it was not that my imagination was playing with my mind; I saw the ingredients for a mirage. You see, at the edge of the kopitiam the hawkers will cook noodles, or rice dishes etc. and this creates heat. Above some stalls there will be clouds of steam rising as the noodles boil in a pan. The clouds appear white because of the scattering of light by reasonably sized water droplets (more info here and here). Above other stalls, there is no steam but the heat created by the cooking makes the air immediately above the stove warmer (and therefore less dense). This less dense air refracts light less than air at room temperature. It is refraction that causes that straw in your iced coffee to look as if it is broken as you look at it (see picture). In the kopitiam, it means that as you look through this region of warm air you see a wobbly or wavy type pattern as the light from outside is refracted by different amounts depending on the temperature of the air that it goes through. It is this that is the primary ingredient for seeing a mirage.

The fact that air at different temperatures refracts light by different amounts is the reason for mirages in the desert. Frequently, warm air is trapped at ground level by a layer of cold air above it. The light is bent as it travels through these layers (see diagram here) and so it may appear as if they sky is on the ground (which the brain will interpret as a pool of water on the ground). Conversely, if there is a layer of cold air trapped beneath a layer of warm air, the light is bent downwards and so objects that are usually below the horizon due to the curvature of the earth can be seen (illustrated by the diagram here).

Edmond Halley, Canary Wharf, Isle of Dogs, view from Greenwich

The view towards the Isle of Dogs (and Canary Wharf) from Greenwich. Things have changed a little since Halley’s time.

Back in 1694 Edmond Halley (who drank coffee with Isaac Newton at the Grecian) was investigating the evaporation of water as a function of temperature. He wanted to see if evaporation alone could explain the rainfall and the quantity of water in the river system. As he did so he noticed that, in still air, there was a layer of water vapour that formed above the bowl of evaporating water. He noticed this because it refracted the light in an unusual manner. At the time, there was reported to be an unusual phenomenon that occurred at high tide near Greenwich. It seems that cows used to graze on the Isle of Dogs in London. Ordinarily the cows could not be seen from Greenwich because they were too far away, but occasionally, at high tide, the cows would be visible. Putting together what he knew about the evaporating water Halley wrote “This fleece of vapour in still weather… may give a tolerable Account of what I have heard of seeing the Cattle at High-water-time in the Isle of Dogs from Greenwich, when none are to be seen at low-water (which some have endeavoured to explain by supposing the Isle of Dogs to have been lifted by the Tide coming under it.) But the evaporous effluvia of water, having a greater degree of refraction than the Common Air, may suffice to bring these Beams down to the Eye, which when the Water is retired, and the vapours subsided with it, pass above, and consequently the Objects seen at the one time, may be conceived to disappear at the other”*. I think that although he had the mechanism correct (in terms of refraction), the cause of this odd refraction was temperature inversion and a layer of cold air immediately above the Thames rather than water vapour but what do you think? Let me know in the comments section below.


* Punctuation and capitalisation kept as in original. Taken from Edmond Halley, “An Account of the Evaporation of Water, as It Was Experimented in Gresham Colledge [sic] in the Year 1693. With Some Observations Thereon” Phil. Trans. 18, 183-190, 1694″

Red Door, Greenwich

Red Door Greenwich, Red Door

Interior of Red Door cafe, Greenwich

Red Door in Greenwich is a great escape from the bustle of the busy streets surrounding it. Although it was crowded when we visited, it was still possible to find a table and have a conversation without too much background noise. I had heard good things about Red Door and wasn’t disappointed. Good coffee (from Monmouth), nice cake and warm surroundings. Definitely a place to go to when in Greenwich. The music that was playing was coming from a record player in the corner. A proper turn-table playing vinyl records. Suddenly, there were so many possibilities for stories for a Daily Grind article. There was the fact that records are analogue based (as opposed to the digital CDs), or perhaps I could write about the physics of a valve amplifier and how it relates to the evaporation of water from coffee (some of the physics is very similar). However what I started to get obsessed with is: what would happen if you put a coffee on a record player?

Now, I am an experimentalist and I do have a record player at home but before I could say “what would happen if…” my plans for experimentation with the record player were blasted out of the water. So I had to make a model record player out of a rotating spice rack. This probably worked better as I could control the speed of rotation, though it did make taking photographs tricky.

record player, turntable

The record player at Red Door

So, what would happen if we put a coffee at the centre of a turntable? The movement of fluids in cups and on record players is extraordinarily complex and is indeed very far from my ‘area of expertise’. However, we can start to understand what might be happening in the cup by making some approximations. Our first approximation is that the coffee in the mug rotates as a ‘rigid body’, meaning that it rotates as a whole. As the coffee cup rotates about its central axis on the “record player” the coffee inside the cup will (eventually) also rotate at the same angular velocity (speed of rotation). The fact that there is a rotation means that there is a force acting on the particles in the coffee liquid. This force produces an acceleration that increases with increasing distance from the axis of rotation. Each coffee particle is of course also subject to the vertical action of gravity. The combined acceleration means that each particle is simultaneously being pulled downwards and inwards. As the acceleration due to rotation increases with increasing radius, the horizontal acceleration becomes increasingly dominant away from the centre of the cup. This leads to the familiar curved surface (a dip at the centre of the mug) that we see with rotating fluids.

vortices, turbulence, coffee cup physics, coffee cup science

This polystyrene cup was rotated about its axis before being stopped. The water inside continues to rotate causing turbulent layers at the edges. These have been visualised with a small amount of blue ink.

Yet we know that this cannot be the full story. If we suddenly stop rotating the mug, the coffee in the mug continues to rotate for a while but does not do so indefinitely; it slows down. We can understand this by refining our approximation that the coffee inside the mug rotates as a rigid body. In fact, the coffee is a viscous liquid and the viscosity means that the layer of coffee immediately adjacent to the mug walls will move at the same speed as those walls: Stationary wall, stationary coffee. The coffee towards the centre of the cup meanwhile continues to rotate for a while. Imagine suddenly stopping the record player so that the mug is now still but the coffee inside continues to spin around the central axis. Stress is being produced between the stationary ‘layers’ of coffee next to the mug wall and neighbouring ‘layers’ of rotating coffee. This stress leads to turbulence. We can make this turbulence visible if, instead of coffee we use a mug of water. Rotate the mug of water as before and then suddenly stop the mug rotating. As with the coffee, the water continues to rotate. Now drop a tiny amount of water soluble ink or food colouring into the very edge of the water (I used a cocktail stick dipped in ink and held against the mug wall so that a small amount dripped into the water). As the water continues to spin, the ink is caught up in the turbulence and the vortices it produces can be seen. These concepts of boundary layers and turbulence are important for many applications including weather systems and car design. We need to understand how liquids (or gases) flow past each other in order to predict the weather and we need to know how they flow past solid objects in order to make cars more aerodynamic. In the coffee however I think that this turbulence is one of those things that is worth just creating and appreciating. A great demonstration of beauty, art and science in a mug of coffee.

Please do share your pictures of these coffee cup vortices if you manage to create them, particularly if you are able to see the effect with cream in coffee. You could either write about your results in the comments section below or email me photographs of your coffee and I will include them on this page. As always, enjoy your coffee.

My thanks to Kate & Edward of Red Door for sending me the photos of Red Door.

Extra photos of vortices in a rotating coffee:

Rotating coffee

An attempt at visualising the vortices using cream in coffee. Not so successful though you can see at least 2 well defined vortices in the top left of the image. Introducing the second liquid right at the edge of the mug seems critical, not so easy with cream as it is with ink!