Categories
Allergy friendly cafe with good nut knowledge Coffee review Coffee Roasters Observations Sustainability/environmental

Bee-ing positive at the Sugar Pot, Kennington

coffee and cake Kennington
Banana bread and coffee with a sugar pot in the background at Sugar Pot, Kennington

What is it that makes a great café? A space to slow down and think? Good coffee and cakes? A local business that forms part of its local community and gives back to that community in different ways? As I was looking around for a new café to try, I was reminded of Sugar Pot in Kennington. Their website suggested that it ticked all of these boxes and so I was eager to try it (so eager in fact that I didn’t note the opening times, they close at 3 on week-days which is a problem when you arrive at about 2.55). So a second attempt at trying Sugar Pot was arranged, this time safely before lunch. This time, in the morning, there were quite a few chairs and tables outside the café in a roped off area of the street. (We hadn’t noticed this on the first occasion we visited as they had all been piled up inside the shop by the time we arrived). Most of these tables were occupied indicating that it is clearly an attractive place for locals to meet and chat over coffee. Fortunately there were also a fair number of tables inside which suited us as a café often offers more to ponder inside than out (though outside offers a different perspective particularly for people watching).

Inside, each table has an individual character and one in particular offered several points to think about both in terms of physics and aesthetics (you will have to visit to understand). However, it was elsewhere that my attention was drawn that day. Coffee is roasted locally by Cable Bakery while the cakes are from John the Baker of the Kennington Bakery. Sugar Pot definitely gets a tick in the “allergy friendly” box because they answered confidently (and with required caveats about traces) my dreaded question “does it contain nuts?” So I was able to enjoy a lovely slice of banana bread with my coffee. Most of the usual espresso based drinks are available (but not listed on the menu) together with a French Press coffee for those who prefer a non-espresso brew.

Interior Sugar Pot, Kennington
Noticeboard, magazines and coffee counter at Sugar Pot in Kennington

The community feel of the café was immediately apparent with a notice board adjacent to the counter being packed with notices of different activities happening around the locality and within Kennington Park which is just opposite. Underneath the counter were books and magazines and an advert for volunteering with the local bee keeping and urban farming organisation Bee Urban. This is indeed another way that Sugar pot gets involved in its local community. The coffee grounds are donated to Bee Urban for use in their Kennington Park based composting facility. Bees of course have an Albert Einstein link with physics as he is alleged to have said

“If the bee disappeared off the surface of the globe, then man would have only four years of life left. No more bees, no more pollinators, no more plants, no more animals, no more man.”

I do not know if he really did say this but it is a sad reflection on our society that rather than address our environmental crimes we are researching pollinating with drones. However, it turns out the the bee has a much more exciting, almost shocking, link with physics and one that I only discovered thanks to the excellent book “Storm in a Teacup” by Helen Czerski¹. The bee is indeed a very positive creature.

ultra violet, bee, bumble bee
The world looks very different to a bee. Image © www.gardensafari.net

Whether or not they have a happy disposition, it seems that 94% of bees are, electrically speaking, positively charged². They pick up a static charge while flying through the air in a similar way to a balloon being rubbed on your hair. Flowers meanwhile have a negative charge meaning that in addition to colour, shape, scent and pattern, bees can recognise flowers by their electric fields. These fields in turn mean that pollen from the flower ‘jumps off’ and adheres to the bees fur before the bee has even landed, increasing the efficiency of the bee as a pollinator. But it turns out that there is much more to it. When the positive bee lands on the negative flower, there is a charge transfer that results in a change of the electric field around the flower for a duration of 100 seconds or so. By constructing artificial flowers held at different voltages containing either a sugar reward or a bitter centre, researchers at Bristol university found that bees could learn to recognise which ‘flowers’ contained the sugar and which were too bitter to be visited by sensing the electric field around the ‘flower’. It suggests that the changing electric field of real flowers provides a mechanism by which the bee can recognise if a flower has been recently visited by another bee and so been recently pollenated. This would mean that by ‘feeling’ the electric field of the flower, the bee may decide that it would be more rewarding to carry on to a differently charged flower. You can read more about the research in the paper here.

It seems to me that learning about how the bee senses its environment reveals even more about the amazing way that nature (and physics) works. And this offers a link back to Sugar Pot. On the shelf behind the counter back at Sugar Pot was a card that had the message “Keep safe, live to be”. What does it mean “live to be”? In the environmental encyclical Laudato Si’, Pope Francis urges everyone to slow down and notice things such as the bee commenting that “If someone has not learned to stop and admire something beautiful, we should not be surprised if he or she treats everything as an object to be used and abused without scruple.” He goes on “… when media and the digital world become omnipresent, their influence can stop people from learning how to live wisely, to think deeply and to love generously… True wisdom, as the fruit of self-examination, dialogue and generous encounter between persons, is not acquired by a mere accumulation of data...”³ Which is one reason that in order to be, we may want to come back and take a closer look at those bees. Taking time to experience our coffee in a relaxing space such as Sugar Pot and to watch and ponder as the bee uses senses of which we are barely aware can never be a waste of our time. Indeed, it is possible that our world may depend on it.

¹Storm in a Teacup, Helen Czerski, Transworld Publishers, 2016

² Clarke et al., “Detection and learning of Floral Electric Fields by Bumblebees”, Science, 340, 6128, 66 (2013).

³The passages quoted are from paragraphs 215 and 225 respectively of Laudato Si which can be read online.

Sugar Pot can be found at 248 Kennington Park Road, SE11 4DA

Categories
Coffee review Observations Science history slow

Like clockwork at Doctor Espresso, Putney Bridge

Doctor Espresso Putney Bridge
There is a lot of physics in this photo alone, but there is even more to be seen if you visit this lovely little cafe.

“Isn’t it a thing of beauty?” So wrote Brian’s coffee spot review of the 1956 Gaggia Tipo Americana espresso machine found at the Putney Station branch of Doctor Espresso. And it is only possible to answer this question in the affirmative. There is something about a mechanical piece of equipment (particularly if it is shiny and has levers) that ignites a feeling of awe. Perhaps it is the awareness of the complexity of the tasks that, when traced through the machine, are revealed to be the result of a series of simple, but ingenious steps. Perhaps it is the feeling that it is possible for someone, one individual, to know inside out how the piece of equipment works and, if necessary, to build it. Perhaps it is because it is shiny. Nonetheless, I had been itching to go and try The Caffetteria, the Doctor Espresso café opposite Putney Bridge station for ages, since I chanced upon its review in Brian’s Coffee Spot. Trundling through the hot streets of London in a bus in this recent heatwave nearly made me reconsider and yet we ploughed on, finally arriving in this shaded spot in the mid-afternoon.

There is very little seating inside but the shade outside enabled us to take a seat by the window. A perfect location to watch people coming and going to and from Putney Bridge Station: who will pick up that 5p on the floor? Will anyone notice? There are a few more chairs and tables across the pavement next to the tree. Several cakes tempted us but we resisted, instead I enjoyed a (single) espresso, Italian style, very drinkable. There is something very relaxing about enjoying an Italian espresso in an independent (or at least very small chain) café. The café aims to “provide a tranquil environment for customers to relax and converse” and it would certainly appear to do so with odd pieces of decor and posters prompting different bits of conversation. The barista was very friendly and trusted us to enjoy our coffee outside before coming back in to pay. Perhaps this seems a small thing, but trust helps to build societies and small gestures of good, repeated, have a ripple effect on our world¹. A nice touch.

espresso Doctor Espresso Putney
The result.
A single espresso ready for enjoying.

Brian’s Coffee Spot describes the process of ‘pulling’ an espresso using this lever machine (the oldest working espresso machine in London apparently). The machine combines the beauty of the mechanical with the skill of the barista to produce a great coffee. This is not human vs machine but human working with machine to create something that others appreciate. A similar respect for the machine was expressed by the clock maker John Harrison about three centuries ago. Harrison had just made a clock that was able to keep time accurately over many weeks while at sea. His task was necessary because having a clock that accurately kept the time at the departure port  would enable a ship’s navigators to calculate their geographical position based on a comparison of this port time to the local time experienced by the ship. He was trying to solve the problem of ‘longitude’. Harrison had taken 19 years to develop his H3 clock which could keep time accurately at sea despite changes in temperature, humidity or rough conditions but within a few more years he’d produced the H4 (which can now be seen in the National Maritime Museum). Significantly smaller than the H3, Harrison said of it:

“I think I may make bold to say, that there is neither any other Mechanical or Mathematical thing in the World that is more beautiful or curious in texture than this my watch or Time-keeper for the Longitude…”²

Enjoying coffee in the company of posters
A conversation piece? The physics of buoyancy or the deceptions of marketing. You could spend a long time at Doctor Espresso thinking about these things.

Harrison lived before espresso machines were invented. Self-taught, Harrison designed and built his own clocks. How many of us would be able to do that? Although we wear watches, how many contain batteries and other components that produce a simple action (showing the time) by complex means. The opposite of what we admire in the lever operated espresso machine. Each individual element may be elegant, but as a composite it can be ugly, however aesthetically satisfying. Harrison built his first clock before he was twenty years old and almost entirely out of wood. Working on the basis of a pendulum, he ensured that the cogs did not wear down as they may be expected to do by utilising the grain of the wood and by using only fast growing oak². Why would this make a difference? Trees that grow fast will have well separated growth rings. As the ring is an area of weakness in the wood, a fast growing tree would have a lot of solid wood compared to a relatively small number of rings, thus affecting the structural properties of the cogs. Moreover Harrison’s wooden clocks did not need oiling because those bits that needed oiling were carved from a tropical hardwood that exuded its own grease. In later clocks Harrison was to overcome the problem of the varying temperature experienced at sea by inventing the bimetallic strip. Two metals of different thermal expansion coefficients placed on top of each other, this simple piece of kit is essential for all sorts of modern machinery including, probably, the espresso machine sitting beautifully at Doctor Espresso.

A warm afternoon in a café of such elegant machinery offers plenty of opportunities to ponder the world of clockwork and levers. Do we understand how having a clock would allow us to calculate our geographical position? What about latitude? How many of us could do this for ourselves? And as we check the time while finishing our espresso, how many of us can appreciate the simplicity that leads to complexity and build our own?

 

¹A bit of cod-philosophy formed by combining bits from Pope Francis’ encyclical Laudato Si’ with Paddington 2.

²Quoted from “Longitude”, Dava Sobel, 1995

Doctor Espresso’s Caffetteria is at 3 Station Approach, SW6 3UH

Categories
Coffee cup science General Observations Science history slow

Drip coffee

The universe is in a cup of coffee. But how many connections to different bits of physics can you find in the time it takes you to prepare a V60? We explore some of those links below while considering brewing a pour-over, what more do you see in your brew?

1. The Coffee Grinder:

coffee at VCR Bangsar
Preparing a V60 pour over coffee. How many connections can you find?

The beans pile on top of each other in the hopper. As the beans are ground, the bean pile shrinks along slipping layers. Immediately reminiscent of avalanches and landslides, understanding how granular materials (rocks & coffee beans) flow over each other is important for geology and safety. Meanwhile, the grinding itself produces a mound of coffee of slightly varying grain size. Shaking it would produce the brazil nut effect, which you can see on you breakfast table but is also important to understand the dynamics of earthquakes.

Staying at the grinding stage, if you weigh your coffee according to a brew guide, it is interesting to note that the kilogram is the one remaining fundamental unit that is measured with reference to a physical object.

2. Rinsing the filter paper:

V60 chromatography chemistry kitchen
A few hours after brewing pour over, a dark rim of dissolved coffee can be seen at the top of the filter paper. Chromatography in action.

While rinsing the filter we see the process of chromatography starting. Now critical for analytical chemistry (such as establishing each of the components of a medicine), this technique started with watching solutes ascend a filter paper in a solvent.

Filtration also has its connections. The recent discovery of a Roman-era stone sarcophagus in the Borough area of London involved filtering the excavated soil found within the sarcophagus to ensure that nothing was lost during excavation. On the other hand, using the filtered product enabled a recent study to concentrate coffee dissolved in chloroform in order to detect small amounts of rogue robusta in coffee products sold as 100% arabica.

3. Bloom:

bloom on a v60
From coffee to the atmosphere. There’s physics in that filter coffee.

A drop falling on a granular bed (rain on sand, water on ground coffee) causes different shaped craters depending on the speed of the drop and the compactness of the granular bed. A lovely piece of physics and of relevance to impact craters and the pharmaceuticals industry. But it is the bloom that we watch for when starting to brew the coffee. That point where the grinds seem to expand and bubble with a fantastic release of aroma. It is thought that the earth’s early atmosphere (and the atmosphere around other worlds) could have been helped to form by similar processes of outgassing from rocks in the interior of the earth. The carbon cycle also involves the outgassing of carbon dioxide from mid-ocean ridges and the volcanoes on the earth.

As the water falls and the aroma rises, we’re reminded too of petrichor, the smell of rain. How we detect smell is a whole other section of physics. Petrichor is composed of aerosols released when the rain droplet hits the ground. Similar aerosols are produced when rain impacts seawater and produces a splash. These aerosols have been linked to cloud formation. Without aerosols we would have significantly fewer clouds.

4. Percolation:

A close up of some milk rings formed when dripping milk into water. Similar vortex rings will be produced every time you make a pour over coffee.

Percolation is (almost) everywhere. From the way that water filters through coffee grounds to make our coffee to the way electricity is conducted and even to how diseases are transmitted. A mathematically very interesting phenomenon with links to areas we’d never first consider such as modelling the movements of the stock exchange and understanding the beauty of a fractal such as a romanesco broccoli.

But then there’s more. The way water filters through coffee is similar to the way that rain flows through the soil or we obtain water through aquifers. Known as Darcy’s law, there are extensive links to geology.

Nor is it just geology and earth based science that is linked to this part of our coffee making. The drips falling into the pot of coffee are forming vortex rings behind them. Much like smoke rings, they can be found all around us, from volcanic eruptions, through to supernovae explosions and even in dolphin play.

5. In the mug:

Rayleigh Benard cells in clouds
Convection cells in the clouds. Found on a somewhat smaller scale in your coffee.
Image shows clouds above the Pacific. Image NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

Yet it is when it gets to the mug that we can really spend time contemplating our coffee. The turbulence produced by the hot coffee in a cool mug prompts the question: why does stirring your coffee cool it down but stirring the solar wind heats it up?

The convection cells in the cooling coffee are seen in the clouds of “mackerel” skies and in the rock structure of other planets. The steam informs us of cloud formation while the condensation on the side of the cup is suggestive of the formation of dew and therefore, through a scientific observation over 200 years ago, to the greenhouse effect. The coffee cools according to the same physics as any other cooling body, including the universe itself. Which is one reason that Lord Kelvin could not believe that the earth was old enough for Darwin’s theory of evolution to have occurred. (Kelvin was working before it was known that the Sun was heated by nuclear fusion. Working on the basis of the physics he knew, he calculated how long the Sun would take to cool down for alternative mechanisms of heating the Sun. Eventually he concluded that the Sun was too young for the millions of years required for Darwin’s theory to be correct. It was the basis of a public spat between these two prominent scientists and a major challenge to Darwin’s theory at the time).

 

Of course there is much more. Many other links that take your coffee to the fundamental physics describing our world and our universe. Which ones have you pondered while you have dwelt on your brew?

Categories
Home experiments Observations slow Tea

A coffee balancing act

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

Clouds of steam hover just above your brew, dancing on the surface in sharp, almost violent, sudden movements. You can see it almost every time you drink a long black, cup of tea or even a glass of hot water. But what on earth is going on?

Back in 2015, a paper by Umeki and others showed that these dancing white mists were levitating water droplets, a common manifestation of something that had been noticed in lab experiments a few years earlier. Hundreds of water droplets, each about 10 μm diameter (the size of the smallest grains in an espresso grind) somehow just hover above the coffee surface. You can read more about that study here. Yet there remain questions. How do the water droplets levitate? What causes those violent movements in the cloud? Can contemplating your coffee help to understand these questions?

To explore what is happening with the white mists, we need to view them in an environment that we can control so as to change one or other of the parameters in the ‘coffee’ and see what happens to the mists. And this is what Alexander Fedorets and co-workers have been doing for a few years now (even before the work of Umeki). What Fedorets has noticed is that when you heat a small area (about 1mm²) of a thin layer of liquid, it is not just possible to create these white mists, you can see the droplets levitating and they form hexagonal patterns of droplets. This is quite astonishing because whereas we are used to solids forming crystals (think of water and snowflakes for example), a formation of liquid droplets in a “self-organised” pattern is an unusual phenomenon.

floating, bouncing drops
You can stabilise much larger droplets of water (up to a couple of mm diameter) by vibrating the water surface. This is a very different phenomenon but is also an interesting effect you can create in your coffee.

Then we can ask, what is it that causes these droplets of water to levitate above the surface? According to a recent paper of Fedorets, the answer is indeed as simple (in the first approximation) as the fact that these droplets are in a delicate balance between being pulled into the coffee by gravity and pushed upwards by a stream of evaporating water molecules. This balance suggests that we can do a ‘back of the envelope’ calculation to estimate the size of the droplets and also to understand what happens when the coffee cools down. We start by thinking about the gravitational pull on the droplet, the force on that is just F↓ = mg (where g is the gravitational acceleration and m is the mass of the droplet) so, if we write this in terms of the density of water, ρ, and the radius, r, of the droplet:

F↓ = ρ (4/3)πr³.g

Similarly, we know how to calculate the upwards force on a particle created by a flow of liquid (steam). It is the same expression as Jean Perrin used to understand the layering of water colour paint in a droplet of water (which is the same as the layering of coffee in a Turkish coffee) and so proved experimentally Einstein and Langevin’s theories of Brownian Motion (which you can read about here). If the steam has a velocity U and the dynamic viscosity of the steam is given by μ, the upwards force given by the steam is:

F↑ = 6πμUr

For the droplet to ‘balance’ (or levitate) above the surface, F↓ = F↑ so with a bit of re-arrangement we get the radius of the droplet as given by:

r = √[9μU/(2ρg)]

Plugging in sensible numbers for μ (2×10^-5 kg/ms) and U (0.1 m/s), and using the density of water (10³ kg/m³) and g = 9.8 m/s² gives a radius for the droplet of 17 μm which fits very well with what is observed.

Rayleigh Benard cells in clouds
The white mists often seem to vanish as if they were sustained by Rayleigh Benard cells in the coffee. Rayleigh Benard cells can also be found in the clouds in the sky, in fact, anywhere where there is convection.
Image shows clouds above the Pacific. Image NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

But does the expression tell us anything else? Well, the radius is proportional to U; the velocity of the steam. So if you increase the temperature, you should increase the radius of the levitating droplets. This is exactly what is seen. Also, as the temperature of your coffee drops and there is less steam coming off the surface, it will become harder to stabilise these white mists; the mists will disappear as the coffee cools. This is something you can test for yourself: what is the optimum temperature at which to see the white mists (and drink your coffee)?

But the study by Fedorets showed something else. Something quite intriguing and perhaps relevant to your experience. Fedorets had stabilised the droplets on the surface by using an infra red laser and held them into a fixed area by only heating a small region of the liquid. In that sense the study is quite far from our physical experience with a coffee. But what Fedorets noticed was that these stabilised droplets grew with time. As the droplets grew, the bottom of the droplet got closer and closer to the liquid surface until, suddenly, the droplet collapsed into the liquid. This collapse caused a capillary wave on the water surface which is a small wave regulated by the surface tension of the water. And this wave then caused the surrounding droplets to collapse into the liquid interior. Because this happened very quickly (the wave travels at about 1m/s which is equivalent to a slow stroll at 3.6km/h), to us, looking at our coffee, it would appear that a violent storm has momentarily erupted over the surface of the white mists.

As the wavelength of a capillary wave is determined by the surface tension of the liquid, this suggests that if you change the surface tension of the coffee you may change the speed or perhaps the appearance of the collapse of these white mists. You can change the surface tension of your coffee by adding either soap or alcohol to your long black. Umeki did add a surfactant (to reduce the surface tension) and didn’t notice a significant difference to the speed of the wave but maybe other factors (such as temperature) were dominant in that experiment. It certainly seems a good excuse to investigate. Let me know if you experiment with your coffee and if the white mists move faster or slower in your Irish coffee compared with a morning V60, you may want to film the results if you intend to drink the coffee afterwards.

The work of Fedorets and of Umeki were both published under ‘open-access’ meaning that anyone can read them (without paying). You can read Umeki’s study here and Fedoret’s study here.

Categories
Allergy friendly cafe with good nut knowledge Coffee review Observations Science history Sustainability/environmental

Creating movement at Kahaila, Brick Lane

coffee Brick Lane, against trafficking, women's project, charity
Kahaila on Brick Lane. A small shop front concealing a large interior.

It’s always great to find an independent café selling good coffee (and cake) while giving something back to the community. It’s a reason to seek out small businesses rather than chains. Kahaila café on Brick Lane absolutely falls into this category. Although I had visited Kahaila previously, on that occasion the beigels (almost) next door were ‘calling’ and I did not give this space the time it deserved. This time however, the beigel shop had come first allowing us plenty of time to sit and ponder in this spacious café.

I had an espresso (toffee notes) together with a raspberry topped vegan chocolate cake (confidently nut free). There were a large variety of alternative cakes on offer at the counter along with cold drinks should you want them in summer. The espresso was a very enjoyable accompaniment to the cake (or should the cake be an accompaniment to the coffee?). The large room at the back of the café offered plenty of seating and was well lit by sunlight streaming through a window built into the roof.

coffee cake, Kahaila, Brick Lane
Raspberry vegan chocolate cake with espresso. The blue cup can affect the way the coffee is experienced.

One thing that immediately makes this café different from many others, is the fact that there is a donation box on the wall. Information cards on the table tops explain that Kahaila works as a charity providing education and support to women prisoners, helping women who have experienced abuse or are vulnerable in other ways to learn skills in a bakery and also offering a safe house for women who have been victim to exploitation and trafficking. All in all a café in which it would be good to spend more time (if only it were closer!). And assuming that the cakes are from the bakery, it forms a giving-circle with some great bakes on offer.

The vegan chocolate cake was a case in point. Beautifully presented, balanced in taste, in a perfectly sized portion to enjoy with a coffee. Ordinarily cakes require butter and eggs, how did the bakers manage it? Of course, a recipe was not given at the counter, nor would it necessarily have been particularly helpful to answer the question. Because the answer, if one exists, is a mix of their experimentation with flavours and textures together with an advancing knowledge of what each cake ingredient does.

sugar in a jar, Kahaila
The way these sugar cubes stacked in the jar and the sugar granules at the bottom reminded me of something. I was not able to put my finger on what it was…

Consider the egg yolk. In addition to adding mouth feel and texture to the cake or biscuit, the yolk contains emulsifying agents, such as lecithin, which act to stabilise suspensions of oil in water¹. With a hydrophobic section at one end of the molecule and a hydrophilic section elsewhere, the presence of lecithin molecules in the mixture prevents droplets of oil from grouping together and coalescing so as to separate into oil/water layers. By experimenting with non-egg based lecithin, a baker can combine different flavours and textures to produce a vegan cake.

A few years ago, a somewhat similar problem was vexing materials scientists: how to remove toxic lead from piezoelectric devices. Piezoelectric devices expand or contract when they are subjected to an electric field. This makes them useful for moving mechanisms such as watches and even as a way to open/close hot water valves in coffee machines. The problem was that one of the best piezoelectric materials we had was lead zirconate titanate (or PZT for short). In order to make the PZT material, the lead had to be sourced in quite large quantities and yet, being toxic and environmentally damaging, it was considered advantageous (even necessary) to remove the lead.

doorway in Kahaila
A painted doorway inside Kahaila in combination with flowers in front suggests a thought train about the way bees see.

However, just like the egg yolk in cookie recipes, you cannot just remove it and produce the same sort of effect in the finished product. You need to understand what role the lead was playing in order to be able to substitute it properly and even then, the effect may not be as good as the original ingredient (without some tweaking elsewhere in the recipe also). Consequently a lot of research has been undertaken in order to find new piezoelectric materials and to understand them so as to optimise the piezoelectric effect. Partly this involves adding the new ingredients slowly to understand their role. Partly it involves changing the growth conditions (somewhat equivalent to the baking temperature) in the crystals that are made. Always it involves experimenting and understanding the role that different ingredients play in our final devices.

Research is still ongoing to find a good substitute for lead in piezoelectric devices. But it goes to show that there are many connections between diverse areas of our experience. Unlike research into piezoelectric materials though, the advantage in experimenting with cakes is that the test of the result is in the eating. Now to experiment with some biscuit recipes…

Kahaila is at 135 Brick Lane, E1 6SB

¹On Food and Cooking, the science and lore of the kitchen, Harold McGee

 

 

 

Categories
Allergy friendly cafe with good nut knowledge Coffee review Coffee Roasters Observations Science history Sustainability/environmental

Paradigm shifts at The Observatory, Marchmont St

lines on a table, parallax
An espresso using coffee from Redemption Roasters and a chocolate brownie. What more could you ask?

Many years ago, there was an aquatics shop on the site of what is now The Observatory, a combined photography gallery and coffee shop. Although there is plenty to see through this glass fronted café, you do not feel that you are in a goldfish bowl so much as that this is a space created for you to slow down and contemplate your surroundings. The large rooms and comfortably spaced tables do, of course, give the opportunity for people watching: when we visited, there were people working with their laptops on some tables while others were having business meetings. Then there are the photographs, currently (though only for a few more days), an exhibition of photographs from the 60s and 70s by John Bulmer.

The coffee is supplied by Redemption Roasters and I enjoyed a dark, toffee like espresso with a very good slice of a chocolate brownie (confidently nut free). Several types of milk are on offer for milk based coffee drinks as well as a selection of cold drinks, together with a wide variety of cakes. It is definitely a place to return to when in the area.

coffee the Observatory, TLR
Cakes on the counter at The Observatory. Note the twin lens reflex “camera” on the shelf behind the counter.

While waiting for my coffee, I noticed the grain of the wood in the table. Dark, almost parallel lines on a lighter wood. You can see it in the photograph. Looking around the café, such parallel lines were everywhere. Planks of wood lined the walls, vertical, parallel lines stretching up to the ceiling. In the room towards the back of the café, the ceiling also had parallel lines on it which, given I was viewing them from a distance, appeared to converge with the effect of perspective. It is difficult to know whether these effects were deliberate in a gallery/café so dedicated to an exploration of the visual but I like to think that the small twin lens reflex camera on a shelf (which sadly turned out to be a pencil sharpener on sale) was a nod to this idea shifting lines of sight and perspective.

By definition, two parallel lines are lines that will never meet, no matter how far the lines are extended. If they were to meet at any point, they would not be parallel. This offers a way of measuring the distance to stars as well as providing food for thought on our way of seeing our place in the universe. The idea is that of parallax. If you were to measure the relative position of a star against the background of stars at midnight in June, and then go back to measure the same star relative to the same background at midnight six months later in December, you may find that the star seemed to have moved. The amount it moves, its parallax, is determined by how close the star is to the earth (have a look at the diagram).

parallax and coffee
As the point of view moves around the Sun (represented here by a V60), the closest coffee bean appears to shift relative to the background coffee beans.
The lower two diagrams are an attempt to see things from the perspective of the Lego person separated by “6 months” distance.

Take as an example the star Sirius. Located relatively close to us at a mere 8.6 light year distance, Sirius has a parallax of 0.38 arc seconds or, equivalently, about 0.0002 of the angular diameter of the moon viewed from Earth¹. Stars that are further away are going to have an even smaller parallax until the parallax becomes so small as to be difficult to measure. Even for nearby stars such as Sirius, the small size of the effect meant that it wasn’t until 1838 that it was first measured. Which may be part of the reason that the theory of Aristarchus (310-230BCE) never caught on when it was proposed.

Aristarchus was an early proponent of the idea that the Earth went around the Sun (and not the other way around). The Greek’s realised that if Aristarchus was correct, there should be a parallax effect for the stars viewed at different times of the year (every 3 months)¹. Unfortunately, the Greeks also considered that the stars belonged to a thin shell, so effectively all the stars were at the same distance from the Earth. Consequently, the parallax effect that they looked for (if Aristarchus was correct) was for two stars on that shell to move first towards then away from each other as the Earth circled the Sun¹. They never observed this effect and so considered the heliocentric theory “inconsistent with observations”¹. Although we would now say that the fact that they didn’t observe any such shift is consistent with the huge distances to the stars (and therefore small shifts) involved, for the ancient Greeks it was a problem. As Archimedes commented, if Aristarchus’ theory had been true, it would mean that the universe was much bigger than they at that time thought.

Guardini has written about the effect on the human psyche of this changing idea of the universe and our own place in it (from the Greek’s idea of finite and limited, to finite with a God outside, to infinite and back towards finite but incredibly large). Do our ideas, our models, about the universe affect not only how we interpret the experimental evidence we see, but also our way of being, our behaviour towards our fellow humans and our planet?

Viewing things from a different angle, seeing the effect of a change of line of sight, it brings us right back to the photography in the gallery and the twin lens camera on the shelf. There are certainly many things to contemplate while enjoying a coffee at The Observatory. Which means a second espresso should definitely be a possibility.

You can view some street photography, including some photographed with a twin lens Microcord TLR camera on Artemisworks gallery here.

The Observatory is at 64 Marchmont St, WC1N 1AB

¹Astronomy, the evolving universe (6th edition), Michael Zeilik, John Wiley & Sons, 1991

 

Categories
General Observations Science history Sustainability/environmental Tea

Why politicians should drink loose leaf tea

Coffee Corona
Notice the rainbow pattern around the reflected light spot?
The universe is in a cup of coffee but to understand rising sea levels, it’s helpful to look at tea.

The universe is in a glass of wine. So said Richard Feynman. It has been the focus of this website to concentrate instead on the universe in a cup of coffee, partly because it is much easier to contemplate a coffee over breakfast. However there are times when contemplating a cup of tea may be far more illuminating. Such was the case last week: if only a politician had paused for a cup of tea before commenting on rising sea levels.

There are many reasons to drink loose leaf tea rather than tea made with a bag. Some would argue that the taste is significantly improved. Others, that many tea bags contain plastic and so, if you are trying to reduce your reliance on single-use plastic, loose leaf tea is preferable. Until last week though, it had not occurred to me that brewing a cup of tea with a mesh ball tea infuser (or a similar strainer) was a great way to understand the magnitude of our problem with rising sea levels. If a stone were to enter a pond, the pond-level would rise; if a spherical tea strainer (full of loose leaf tea) were to be placed in a cup, the soon-to-be-tea level would rise.

Clearly, because we know our physics, we would not place a strainer of tea into an existing cup of hot water as we know the brewing process relies on diffusion and turbulence, not just diffusion alone. So what we more commonly observe in the cup is actually a tea-level fall as we remove the straining ball. Fortunately, we can calculate the tea level decrease, h:

A schematic of the tea brewing process

My cylindrical tea mug has a radius (d) of 3.5cm. The radius (r) of the mesh ball is 2cm. We’ll assume that the tea leaves completely expand filling the mesh ball so that the ball becomes a non-porous sphere. Clearly this bit is not completely valid and would anyway create a poor cup of tea, but it represents a worst-case scenario and so is good as a first approximation.

Volume of water displaced = volume of mesh ball

πd²h = (4/3)πr³

A bit of re-arrangement means that the height of the tea displaced is given by

h = 4r³/(3d²)

h = 0.87 cm

This answer seems quite high but we have to remember that the mesh ball is not completely filled with tea and so the volume that it occupies is not quite that of the sphere. Moreover, when I check this answer experimentally by making a cup of tea, the value is not unreasonable. Removing the mesh-ball tea strainer does indeed lead to a significant (several mm) reduction in tea level.

Earth from space, South America, coffee
Assuming we are truly interested in discovering more about our common home, we can gain a lot through contemplating our tea.
The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler

What does this have to do with politicians? Last week a congressman from Alabama suggested that the observed rising sea levels could be connected with the deposition of silt onto the sea bed from rivers and the erosion of cliffs such as the White Cliffs of Dover. If only he had first contemplated his tea. Using a “back of the envelope” calculation similar to that above, it is possible to check whether this assertion is reasonable. As the surface area of the oceans is known and you can estimate a worst-case value for the volume of the White Cliffs falling into the sea, you can calculate the approximate effect on sea levels (as a clue, in order to have a significant effect, you have to assume that the volume of the White Cliffs is roughly equal to the entire island of Great Britain).

Mr Brooks comments however do have another, slightly more tenuous, connection with coffee. His initial suggestion was that it was the silt from rivers that was responsible for the deposition of material onto the sea bed that was in turn causing the sea level to rise. About 450 years ago, a somewhat similar question was being asked about the water cycle. Could the amount of water in the rivers and springs etc, be accounted for by the amount of rain that fell on the ground? And, a related question, could the amount of rain be explained by the amount of evaporation from the sea?

The initial idea that the answer to both of those questions was “yes” and that together they formed the concept of the “water cycle” was in part due to Bernard Palissy. Palissy is now known for his pottery rather than his science but he is the author of a quote that is very appropriate for this case:

“I have had no other book than the heavens and the earth, which are known to all men, and given to all men to be known and read.”

Reflections on a cup of tea.

Attempts to quantify the problem and see if the idea of the water cycle was ‘reasonable’ were made by Pierre Perrault (1608-80) in Paris and Edmond Halley (1656-1742) in the UK. Perrault conducted a detailed experiment where he measured the rain fall over several years in order to show that the amount of rain could account for the volume of water in the Seine. Halley on the other hand, measured the amount of evaporation from a pan of heated water and used this value to estimate the evaporation rate from the Mediterranean Sea. He then estimated the volume of water flowing into that sea from a comparison to the flow of the water in the Thames at Kingston. Together (but separately) Perrault and Halley established that there was enough water that evaporated to form rain and that this rain then re-supplied the rivers. Both sets of calculations required, in the first place, back of the envelope type calculations, as we did above for the tea-levels, to establish if the hypotheses were reasonable.

If you missed the coffee connection, and it was perhaps quite easy to do so, the question that Halley studied concerned the rate of evaporation as a function of the water’s temperature. This is something that is well known to coffee drinkers. Secondly however, one of Halley’s experiments about the evaporating water was actually performed at a meeting of the Royal Society. It is known that after such meetings, the gathered scientists would frequently adjourn to a coffee house (which may have been the Grecian or, possibly more likely, Garraways). As they enjoyed their coffee would they have discussed Halley’s latest results and contemplated their brew as they did so?

What this shows is that sometimes it is productive to contemplate your coffee or think about your tea. Notice what you observe, see if you can calculate the size of the effect, consider if your ideas about the world are consistent with your observations of it. But in all of it, do pause to slow down and enjoy your tea (or coffee).

Categories
Coffee review Observations

Bright Lights at Bloomsbury Coffee House

Bloomsbury coffee house sign
A wooden sign advertising a coffee house. What makes a modern coffee house?

The coffee houses of the eighteenth century were places where ideas were debated, new innovations created and, of course, coffee consumed. What would a modern day equivalent look like?

Bloomsbury Coffee House is in a basement on Tavistock Place. It is ideally located close to a few universities and was busy but not crowded when we arrived one afternoon during the week. There are two large rooms forming the café with several tables and artwork dotted around the room. In the warmer months, there are also a couple of tables outside in the little terraced area by the steps leading down to the basement. Many people inside that day were on laptops (there is free wifi), some were involved in conversation either with each other or through the laptop. Presentations were being discussed, new ideas bounced around. It is possible that sometimes, when thinking about past coffee houses we can be tempted to focus on what has been lost (in terms of conversation and debate) rather than what has been retained in a modern manifestation (such as idea creation and discussion via Skype, from within the coffee house). At the Bloomsbury Coffee House that day I had an espresso (Allpress) and a cinnamon bun while there were also a variety of milks on offer for other espresso based drinks. These were all a significant improvement on the coffee that was served in the establishments of the past.

lattice structures ceiling bloomsbury coffee house
A 2D square lattice pattern on the ceiling. But what is the smallest repeating pattern that you can see? Is it centred on the large squares or the small squares?

Each table was individual, some reminding me of old school desks, while the ceiling was plastered with a 2D square lattice pattern. Staring at the ceiling, prompted the question, was it the large squares or the small squares that formed the repeating unit of the structure? Quickly this made me think about Polonium. When thinking about how atoms form 3D crystal structures, we sometimes naively draw a cube with an atom at each corner. In fact, this arrangement (the simple cubic structure) is quite unstable (try stacking oranges on top of each other so they form a cube) and, for elements that do form into cubic crystal structures, a more common form of base unit is a so-called face centred or body centred cubic. One element that does form a simple cubic structure though is polonium, an element that is probably more famous for being the poison used in the Litvinenko case a few years ago.

However, an alternative train of thought was suggested by the blackboard on one of the walls of the room. A colourful message announced that the Bloomsbury Coffee House had won a Time Out Love London award. The writing, in red and blue, was a little tricky to read from the back of the room. With the lighting, the red appeared slightly brighter and more visible than the blue. Perhaps coincidentally, this is the correct way round (in terms of order of brightness) for an odd optical effect that happens as the light fades towards evening (and, in a connected manner, why it is hard to find a matching pair of socks in the dark).

writing on the wall
The blackboard at Bloomsbury Coffee House

In order to ‘see’, the eye uses a series of cells called rods and cones. The rods are the more light sensitive and more plentiful (there are more than 100 million in a human eye) but they do not have any mechanism to detect colour. Instead, they show a good response over the entire visible range with a peak response rate at ~507 nm¹ which corresponds to a blue wavelength. The cones by contrast give us the ability to discern colour. We have blue, green and red sensitive cones which show responses that peak in the blue, green and red parts of the visible spectrum respectively. The problem with the cones is that they do not respond very well in low level lighting conditions. Hence, during the day, in normal lighting conditions, the cones are active and our eyes (usually) show a peak response to yellow-green light at 555 nm. As the light falls and twilight and darkness comes in, the cones cease to work leaving only the rods so our eye’s peak response shifts to light with a blue wavelength. Subsequently, a bright red rose seen during the day may appear dimmer than the green leaves in the evening. A sea of blue and red flowers may shift from appearing bright red to bright blue as night falls.

Unfortunately, Bloomsbury Coffee House closes at 6pm which, during summer, is too early for us to see whether we can see this effect ourselves. But if you are lucky enough to have access to a garden or park where there are red flowers and are able to sit and watch them as night falls, do observe and see if you can see this shift in apparent brightness for yourself.

Bloomsbury Coffee House is at 20 Tavistock Place, WC1H 9RE

¹The Feynman Lectures on Physics, Vol I

Categories
Coffee cup science General Observations

Strumming along on a coffee

coffee at Watch House
What links a coffee to a guitar amplifier?

What links a coffee to music by the likes of Eric Clapton and Jimi Hendrix?

As we sit back and enjoy the aroma from our coffee, we may rue the fact that our precious brew is evaporating away. We know from experience that hot coffee evaporates faster than cold coffee and we may dimly remember the physics that explains why this is. But have you ever stopped to consider that it is this bit of your coffee that forms a link between your drink and those famous guitarists?

The link concerns the mechanism behind the evaporation. To evaporate out of the coffee, a water molecule needs to overcome a certain energy barrier, let’s call it W, in order to escape. Given that W is constant, the more energy a water molecule has, the greater its likelihood of escape. So we could say that the probability of a water molecule escaping the coffee goes as exp{-W/kT} which means, the higher the temperature, T, the smaller the ratio W/kT and hence the greater the probability (because the exponential is raised to a negative power and hence is a dividing factor). The k is a constant known as the Boltzmann constant.

thermometer in a nun mug
Hot coffee evaporates more. Something that Halley had noticed in his experiments at the Royal Society

Now think about how the amplifiers used by many musicians work. It seems that many guitarists favour valve amplifiers owing to the type of sound they produce. Certainly Clapton and Hendrix were well known for their use of valve amps. A valve amp works by a process of thermionic emission in which electrons are ‘evaporated’ from a hot metal wire before being accelerated to a positively charged plate. This bit is the ‘valve’. In order to escape the metal wire, the electrons have to overcome a certain energy barrier, let’s call it Ω. Just as with W and the coffee, this barrier is a property of the metal that the electron evaporates from. The more energy an electron has (the higher its temperature), the greater the likelihood of it escaping the metal filament and fulfilling its role in the valve amplifier. Hence the mathematics describing thermionic emission is the same as the mathematics describing the evaporation in your coffee cup¹ and the probability of thermionic emission goes as exp{-Ω/kT}.

Now the size of the barrier is of course different in the two cases (Ω is much larger than W) which is why you have to plug in your amplifier to the electricity supply rather than just let it sit on the table top. But this is a difference of size rather than of kind. It is another of those connections between your coffee cup and the world that can be stranger than you may at first think.

If you think of a connection between your coffee and an interesting bit of physics, why not share it in the comments section below.

¹This discussion originally appeared in (and was adapted from) the Feynmann Lectures on Physics, Vol. 1

Categories
Allergy friendly Coffee review General Observations

Getting to the point at Sharps

coffee and Caffeine at Sharps
Coffee at Sharps Coffee Bar.

There will be plenty to notice at any café that shares space with a barber’s shop. And so it was the case at Sharps Coffee Bar on Windmill Street. The café is at the front of the barber’s shop which is separated from the tables by a glass wall: people watching in a type of human goldfish bowl. The counter was on the left of the shop as we walked in and it was great to see that in addition to the usual espresso based drinks there was an aeropress coffee available (as well as batch brew). Given the chemistry of pre-brewed coffee, I tend to pass on batch brews though I am aware that there are many people who enjoy speciality coffee who will disagree with me. However, given that the barista on the day was “still perfecting” his aeropress recipe, I enjoyed instead a long black prepared with The Barn roasted beans.

The sign in the window suggested that “maintenance matters” which is something that I am sure that we can all agree on, whether it is on haircuts, coffee equipment or even equipment in a science lab. A stitch in time saves nine so they say. On the board listing the prices, it was good to see that Sharps coffee bar mentioned the use of almond milk. Although personally I generally drink black coffees, cross contamination can be an issue for allergy sufferers and so it is always helpful to be alert to the use of nut-based milks when they are used (you can read more here). Edibles were supplied by Kaffeine. Behind the bar there were a couple of trough-like sinks while the contrast in the wood and the tiling on either side of the bar provided another avenue of thought.

cacti in a row
Sign, window and cacti at Sharps Coffee Bar

In the window, a row of cacti caught my attention. Cacti seem known for two things. One is that they are (generally) prickly and the other that they are extremely water efficient.  But these two facts can also apparently be linked. Some cacti use their spikes or hairs to change the local atmosphere around them so that air is trapped in the hair or that air flow is reduced. Both of these measures would help to prevent water loss from the main body of the plant. It is an example of the structure of something affecting the environment around it. Similar effects can be seen on the hairs on a spiders legs which trap air allowing the spiders to survive if they are submerged as well as to waterproof the legs in more general times. Some plants similarly use hairs (and therefore the air trapped in them) to waterproof their leaves. The benefit of this for the plant is that waterproof leaves mean that drops of water roll off of them causing the leaves to be self-cleaning. This is an effect that people are trying to mimic in order to make self-cleaning surfaces for human use.

View of St Paul's Cathedral London
There is a whispering gallery in the dome of St Paul’s Cathedral. An interplay between sound waves and the shape/size of the dome.

Structures can also be used to trap sound waves either deliberately with meta-materials or, almost accidentally such as the whispering galleries of cathedral domes. Moreover the hairs themselves can act as part of a sound detection system. Human ears for example have tiny hairs in the cochlea. As a sound comes in and these hairs vibrate, the movement of these hairs gets converted to a nerve impulse that we can eventually ‘hear’. Perhaps this could take us into a consideration of what hearing is, what sound is and, in a Berkeley-type way whether we actually experience anything outside of ourselves at all. However, more directly it takes us back to the barber’s shop and how evolution has resulted in a wide variety of structural adaptations that allow different life forms to live optimally in their environment.

And with that, it would probably be time to sit back and enjoy another coffee.

Sharps coffee bar is at 9 Windmill Street, W1T 2JF