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Coffee under the microscope

Inside Coffee Affair

There are many great cafés in London serving excellent coffee but inevitably a few stand out. One such café is Coffee Affair in Queenstown Road railway station which ‘inhabits’ a space that really encourages you to slow down and enjoy your coffee while just noticing the environment. An ex-ticket office that whispers its history through subtle signs on the parquet floor and in the fixings. The sort of place where you have to stop, look around and listen in order to fully appreciate it. And with a variety of great coffees on hand to sample, this is a café that is a pleasure to return to whenever I get the opportunity.

So it was that a few weeks ago, I happened to wander into Queenstown Road station and into Coffee Affair. That day, two coffees were on offer for V60s. One, an Ethiopian with hints of mango, peach and honey, the other, a Kenyan with tasting notes of blackcurrant and cassis. But there was an issue with them when they were prepared for V60s. The Ethiopian, “Gelana Abaya”, caused a considerable bloom but then tended to clog the filter cone if due care was not taken during the pour. The other, the Kenyan “Kamwangi AA”, did not degas so much in the initial bloom but instead was easier to prepare in the V60; there was not such a tendency to clog.

What could be going on?

So we had a look under the microscope at these two coffees. Each coffee was ground as if it was to be prepared in a V60 and then examined under the microscope. Was there any difference between the appearance of the Gelana compared to the Kamwangi? A first look didn’t reveal much. Magnifying both coffees at 5x, it could be said that the Kamwangi had more ‘irregular protrusions’ on the ground coffee compared to the smoother Gelana, but it was hard to see much more:

coffee under the microscope

The samples of ground coffee imaged under an optical microscope at 5x magnification. Kamwangi is on the left, Gelana on the right. “500 um” means 500 micrometers which is 0.5 mm.

So, the microscope was swapped to image the coffee in fluorescence mode. It was then that the cell structure of the coffee became clear. Here are the two coffees magnified 10x:

Fluorescence microscopy 10x, Ethiopian, Kenyan, Kamwangi, Gelana

Fluorescence microscope image of the two coffees at 10x magnification. Note the open structure in the Kamwangi and the more closed structure in the Gelana.

and at 20x

Kamwangi and Gelana coffee under the microscope

A fluorescence microscope image magnified 20x – not ‘um’ means micrometers (1/1000 of a mm), so the scale bar represents 1/10 mm.

So there is perhaps a clue in the cell structure. It seems as if the Kamwangi structure is more open, that somehow the cells in the Kamwangi break open as they are ground but the Gelana somehow keeps its cells more intact. Could this be why the Gelana blooms so much more?

Which naturally leads to a second experiment. What happens when you look at these two coffees in water under the microscope? Here the fluorescence images didn’t help as all you could see were the bubbles of gas in each coffee but the optical microscope images were of more interest.

optical microscope image in water

The two coffees compared under the microscope while in (cold) water. Magnfied 5x

‘Bits’ broke off the Kamwangi as soon as water was added but in comparison, there were far fewer bits of coffee breaking off the Gelana grains.

So what do you think has happened? If you remember our question was: when these two coffees were prepared with a V60, the Gelana bloomed a lot but then clogged in the filter (without extreme care while pouring the filter). Meanwhile the Kamwangi did not bloom so much but also did not clog the filter, what could be happening?

From the microscope images, it appears that

  1. Before adding any water, the cell structure in the Kamwangi is more open, the Gelana appears ‘closed’.
  2. When water is added, there are many more ‘bits’ that come off the Kamwangi whereas the Gelana does not show so much disintegration on the addition of water.

If pushed for a hypothesis, I wonder whether these two observations are linked. What is happening is that the cell structure in the Kamwangi is, for whatever reason, fairly fragile. So as soon as it is ground, the cells break up and a lot of the carbon dioxide is released. Consequently when water is added to it, the bits of broken cell quickly disperse through the water and it doesn’t seem to ‘bubble’ that much. In comparison, the Gelana cell structure is tougher and the cells only open up when water is added. I wonder if this means that the ground Gelana coffee will swell rather than break up and so ‘jam together’ as each grain tries to expand rather like trying to inflate many balloons in a bucket. They will push against each other and prevent water from easily percolating through the ground coffee.

Sadly, many more experiments would be required before we could see if there’s any truth in this hypothesis however that does provide a great excuse, were one needed, for many return trips to Coffee Affair. Meanwhile, what do you think? Do any of the images stand out to you and why? What do you think could be the cause of our V60 coffee mystery? I’d love to hear your thoughts so please let me know either here in the comments section (moderated and experiencing a lot of spam at the moment so please be patient), on Facebook or on Twitter.

Phlogiston in the Watch House

Watch House coffee Bermondsey

The Watch House in Bermondsey

At the end of Bermondsey St, tucked away in an odd looking building on the corner, is a café known as the Watch House. Stepping inside you are met with a very strange impression: this is far from your normal rectangular room. Instead an octagonal space, complete with Victorian style tiling and wood burning stove greets you. There are about five small tables inside, which were all occupied (some shared) when we arrived late in the lunch hour. So we sat at a table outside, although there was also bench seating on the other side of the door and a lovely park just next door, the old St Mary Magdalen graveyard.

The building itself dates from the time when the “watch house” was the base for a makeshift local constabulary that would monitor the local area ensuring that no body-snatchers were operating in the graveyard next door. The body snatchers used to ‘acquire’ recently buried bodies for use in anatomy classes at the capital’s teaching hospitals. Nowadays, as with many other disused burial grounds in London, the graveyard next door has been transformed into a park. On the other side of the café, a drinking fountain (the gift of a Henry Sterry Esq.) is embedded into the wall. An interesting feature reminding us of the drive to provide drinking water to London’s population both then and now with the newly installed fountains at the nearby Borough Market.

coffee at Watch House

What fantastic colour in this filter.

As I placed my V60 on the table outside, the light shone through it making the coffee appear to glow with a deep red tinge. Temporarily ignoring my normal idea that such transient beauty can’t be captured, I tried to photograph it, an endeavour that predictably failed to capture the full radiance of the cup. Nonetheless, the clear red coffee did not have significant sediment at the bottom of the cup. Perhaps this is not surprising, it was a V60. But nevertheless this lack of sediment has a connection with the water fountains both at the Watch House and at Borough Market and the wood burning stove. You could even make a macabre link to the graveyard next door. But without pursuing that last one too much, the link is Antoine Lavoisier (1743-1794) and the transmutation, or not, of water into earth.

The problem was this: In the early seventeenth century Jon Baptist Van Helmont had planted a 5lb (2.3 kg) willow tree into a pot of soil of mass 200 lb (91 kg)¹. He covered the pot of soil and only allowed rainwater into the tree/pot system for 5 years. At the end of his experiment, the mass of soil was unchanged but the willow tree was now 169 lb 3 oz (76.8 kg). Clearly, the “element” water had transmuted into the “element” earth* and so added to the mass of the tree. A few years later and scientists boiling distilled water (which had of course been purified by previous boiling) noticed that there was always a solid residue left after the water had boiled away². Another piece of evidence for the transmutation of water into earth.

Lavoisier, who became known as the father of modern chemistry, thought differently. He had been interested in obtaining clean, safe drinking water for the inhabitants of Paris and had noticed that when rainwater was repeatedly distilled, the amount of solid residue left after boiling decreased with each distillation. How was this reconcilable with the idea that each time you boiled water part of it became the element earth? But if water wasn’t ‘transmuting’ into earth, what could explain the solid residues observed by the other scientists of his day?

Lavoisier suspected the potash or soda used in making the glass vessels used in the experiments. He thought that this could be dissolving out of the vessels when the water was boiled, leaving what looked like a solid residue at the bottom of the cup². To demonstrate that this could be the case, Lavoisier took a sealed container of water called a ‘Pelican’ (which has two arms to allow the water vapour to cool and drip back down to the base of the unit). He first weighed the water and the vessel, separately and together and then boiled the water in the sealed pelican for 100 days. After 100 days he weighed the container-water system again. The total mass had not changed. However, when they were weighed separately, something odd had happened. The glass vessel (the pelican) had lost some mass while solid salts had appeared in the vessel. Although these salts weighed slightly more than the mass lost by the pelican container, Lavoisier considered the discrepancy within error thereby showing that the ‘transmutation’ observed by other scientists was actually salt dissolving out of the glass vessel.

Lavoisier’s experiments were an important contribution to the development of experimental method as well as a refutation of the old idea of the transmutation of the elements earth-air-fire-water.

Lavoisier, drinking fountain, Bermondsey

The fountain on the side of the Watch House. How had a need for supplying the public with drinking water shaped our scientific thinking?

Which leaves one last connection: the wood stove. Since the dawn of humanity, there has been the question “what is fire?”. By the time of Lavoisier, fire was explained by the idea that matter contained more or less “phlogiston”. Something could catch fire if it contained a large amount of phlogiston, it would not ignite were it to have too little phlogiston³. One observation clearly explained by the phlogiston theory was the observation that a burning candle, covered by a glass bell jar, would extinguish itself. The idea was that the candle (which contained phlogiston) released that phlogiston into the air. If the candle burned within a jar, the air surrounding the candle would became saturated with phlogiston. Once saturated, the air could ‘hold’ no more phlogiston so none could escape the candle wick. This would mean that the flame would go out.

Lavoisier, now recognised as one of the three independent co-discoverers of oxygen, showed that oxygen, not phlogiston, was needed for burning to occur. The question is how did he do it? And a question for you, when you are enjoying your sediment free delicious coffee next to a warming wood fire: how would you?


*to be fair to Van Helmont, it is hard to blame him for arriving at this conclusion. It was still a few centuries before photosynthesis was discovered and the idea of the four elements of fire, earth, water and air was still active in his time.

The Watch House is at 199 Bermondsey St, SE1 3UW

¹”Lavoisier in the year one”, Madison Smartt Bell, Atlas Books (2005)

²”Lavoisier”, Jean-Pierre Poirier, University of Pennsylvania Press, (1996)

³”From phlogiston to oxygen”, John Cartwright, Hatfield (2000)


Coffee cup recycling

a take away cup

It is recyclable, but not easily so.

That old subject again, the recyclability of take-away coffee cups. But before you groan about our disposable culture, there has recently been some great news, at least as far as the university sector is concerned. Regular readers may know of the Bean Thinking list of Top UK Universities for Coffee Cup Recycling. You may also be aware of just how short that list has been. Now though, there are signs of change. Perhaps because it is the start of the academic year, several universities including Oxford Brookes and the University of Bedfordshire have announced new schemes for recycling their cups with Simply Cups.

Owing to the way the cups are made it is extremely difficult to recycle them; although they are technically recyclable, very few companies have the capabilities. Consequently, the majority of the cups that we use for our take-away are just thrown-away, taking many decades to break down.

compostable, coffee cup, disposable culture

Using compostables can be a step in the right direction.

It is often our universities that do the research showing just how environmentally damaging our disposable culture can be. Nonetheless many university catering departments continue to serve coffee in “disposable” cups without putting in place any scheme to recycle them. Over a year ago I started a list of the UK’s top universities for coffee cup recycling. It would be thought that it should be extremely easy to be listed here. To be listed, all a university has to do is take a responsible attitude to it’s take away coffee cup use. Preferably, they would discourage take-away coffee cup use altogether. As Loughborough University recognises, slowing down, talking with colleagues over a stay-in (washable cup) coffee can be far more productive than scurrying away with your non-degradable cup.

However, often we feel that we don’t have time to sit down for a coffee and need to take-away. At this point, to be listed on the guide, all that a university would have to do is either invest in compostable cups (despite the caveats*, this is at least a step in the right direction) or institute a scheme to collect and recycle their coffee cups (as has been done at the University of Bath, Bedfordshire, Kent, Loughborough, Manchester Metropoliton and  Oxford Brookes University).

As may be apparent from the fact that the universities can be listed within this short article, the current list is woefully short. Even after the recent good news from Oxford Brookes and the University of Bedfordshire. Most universities, including my own are sadly still not on it. So, what can you do if your university is not listed here?

  1. If you think it should be listed but hasn’t been it is very highly likely that I just don’t know about it yet, please let me know by contacting me through email, Twitter or Facebook.
  2. If your university is doing very little to discourage disposable cup use: Write to the catering department and waste management department of your university to let them know your concerns. When writing, be aware of the fact that they have probably considered this problem before and are aware of the issues but have concerns/limitations that have prevented them from implementing a policy. Consumer pressure can help to change their minds but there may be (what appear to them to be) valid reasons that they have not yet done so.
  3. Use a re-usable cup. Even if your university does not charge extra for using a disposable cup/give a discount for using a re-usable (thereby encouraging the use of re-usables), systemic change starts with individuals. Be the start of the change you want to see. You can find a review of various re-usable coffee cups here.
  4. Refuse to buy your stay-in coffee if you are served it in a take-away cup. Good coffee deserves to be enjoyed in appropriate cups and poor coffee should be avoided anyway.

You can find the list of the UK’s top universities for responsible take-away coffee cup use here.


*The word ‘compostable’ does not necessarily mean that it will compost in a home-composting environment. For this situation to be preferable to the ordinary disposable cup, it would be necessary to have some form of industrial composting facility in place.

Constructive interference at Frequency, Kings Cross

exterior of Frequency Kings Cross

Note the tiles. Frequency, Kings Cross on a rainy day.

It was a rainy afternoon when we ventured to Kings Cross and into Frequency. Suggested by the London’s Best Coffee App as the closest café to our then location, we made our way through puddles and rain onto Kings Cross Road. At that point, a brain-freeze meant that we couldn’t see where Frequency should be. The map on the app was implying that we were extremely close but there didn’t seem to be a café around. Then we saw it in front of us! The striking black and white tiling on the floor somehow hiding this shop-front from view.

The tables inside matched the tiling outside. Black and white triangles meeting at a point. My long black (from Workshop) was placed close to the intersection of these triangles. The coffee arrived in a mug, more cylindrical than standard coffee cups and so closer to mathematical models of coffee cups that are used in explanations of convection and rotation in the cups. An interesting change of aesthetic that also changes the internal dynamics of the coffee. A nice touch was that the mugs were also coordinated with the tiling, though to be fair I hadn’t noticed that at the time.

The coffee itself was extremely fruity, a lovely warming brew to enjoy while watching the rain outside. The interior of the café meanwhile was decorated with a lot of wood around together with a couple of music stands. Perhaps the music stands make sense in a café named Frequency. Indeed, according to the review on London’s Best Coffee (or as it is now known, Best Coffee), there are plans to build a music recording studio here as well as having live musical performances. However, also mentioned in that review was the fact that this café had been designed and built from scratch with the help only of online tutorials. Which makes a particularly resonant connection with something I noticed here.

mug of coffee at Frequency

Coffee at Frequency.

What caught my eye as I contemplated this café was the one bit of bright colour on the ceiling. It was also something that hints at problems that can crop up when you design and build your own electrical circuits: Parallel wires (in this case leading to the lightbulbs). Perhaps in the café, these were intended to represent music staves, certainly that would fit in the theme. However to an experimental physicist who dabbles in designing pieces of kit for electrical measurements, these parallel lines leading to a light mean something entirely different.

They mean noise.

When you are designing a piece of electrical equipment to be used for measuring voltages across an unknown material, there often ends up being a lot of wiring in the probe as well as the bit at the end of the instrument that you are actually interested in. Some of this has a practical purpose. Often we want to measure something when it is very cold so it has to be on the end of a metal rod that is inserted into a vat of liquid nitrogen or helium or that is held in a strong magnetic field. When designing the probe, the bits of wire leading to the interesting bit at the end of the rod can be almost as important to consider as the measuring bit itself.

To see why, perhaps you remember putting compasses around a wire carrying an electric current? As the electric current is switched on, the compass needles move indicating that the electrical current generates a magnetic field. The basis of electric motors and dynamos, the idea is that an electrical current will generate a magnetic field and a moving magnetic field would generate an electrical current.

transmission lines, electrical noise

The wires to the light bulbs in Frequency Kings Cross. Memories of transmission line lab experiments.

Now, imagine two parallel wires each carrying an electrical current. Both of them will produce a magnetic field, but if there is a varying current in one or other of the wires, the magnetic field will also be varying. And if there’s a varying magnetic field, it can induce a current in the neighbouring wire. In this way, electrical noise on one of the wires can be transmitted to the other.

Such electrical noise can be inconvenient if we are trying to speak on the phone and just hear a ‘hiss’, or if we are trying to listen to the radio and just can’t tune in. It could also be more problematic, imagine if there was a lot of electric noise on a machine measuring the electrical activity of your heart, an ECG. Consequently, there are whole books written on how to reduce electrical noise pick up. However one simple way to reduce a lot of the noise is to get rid of those parallel lines the like of which are on the ceiling at Frequency by twisting them together. The ‘twisted pair’ is a great way of making more sensitive electrical measurements. And if you wanted to reduce the noise further, you can shield the twisted pair with another conductor and ground (or earth) it.

The twisted pair works by reducing the magnetic coupling between the two wires. Of course, it may not be quite as immediately aesthetically pleasing as parallel wires on a ceiling but there is something quite elegant about a well made and shielded twisted pair properly grounded in an electrical circuit. And when you put everything together, ground it properly and see the noise from the electrical mains (at 50Hz) disappear, there is a certain pleasing effect from that too.

Café design as a clue to electrical design. Frequency can be found at 121 Kings Cross Road, WC1X


How compostable is compostable?

the cup before the worm bin

“Completely compostable”
But how compostable is it?

So we’re trying to do our bit for the environment and ensure that we always get a compostable cup for our take-away coffee. But have you ever stopped to wonder, just how compostable is compostable?

It is a sad fact that most items that are described as ‘compostable’ do not compost as you or I may expect. Throw a ‘compostable’ cup in a compost bin (or wormery) and you may be surprised at how long it takes to disappear. The reason is that the legal definition of compostable generally refers to industrial composting conditions. In contrast to the worm bin, or the home-compost heap, an industrial composting facility is kept at (58±2)ºC. In these conditions, something defined as ‘compostable’ by the EU regulation EN 13432 or the US based ASTM D6400 needs to have completely disappeared within 6 months but have 90% disintegrated to fragments smaller than 2mm by 12 weeks.

Perhaps it is not hard to see why the legal criteria are defined this way. How would you define common criteria for home composting? Although there is a (Belgian led) certification called “OK compost” by Vinçotte, there are as yet no widely agreed definitions for home composting. However, some companies do try to seek out truly home-compostable packaging. In the case of coffee specifically, one coffee roaster trying to keep their environmental impact to a minimum is the Nottingham based Roasting House. Although most of their packaging is paper, (recycled and recyclable), they needed something less permeable for transporting pre-ground coffee by post. Apparently this took quite a search as many bags that said they were home-compostable turned out not to be. Eventually however they chose Natureflex, a packaging that provided a good moisture and air barrier to protect the coffee but that also broke down in a home composting environment.

But how quickly would it disappear in a worm-composter? On the 6th May 2017 my coffee from Roasting House arrived double packed. First in a Natureflex compostable bag and then in the standard (recyclable) paper bag/envelope. It was ready to be placed in the worm bin on the 8th of May 2017.

See the video below for how long it took to be eaten by the worms:

Seventeen weeks later, on 4th September, it was time to declare the bag composted. After 17 weeks, the bag had started to become indistinguishable from other items in the worm bin (such as garlic skin) and when I picked up what bits seemed to remain, they quickly disintegrated in my hand. It seemed time to declare it over for the bag. A truly home-compostable bag, but how does it compare to the ‘OK Compost’ label of Vinçotte.

Coffee bag genuinely home compostable

How it started.
The Roasting House bag before it went into the worm composter.

The definition used by Vinçotte is not for a worm-composting bin but a standard home-compost heap. Ignoring this fact for the time being, the certification requires that a compostable item disintegrates to pieces less than 2mm within 26 weeks and has fully gone within 365 days when held (in a compost bin) between 20-30ºC. Within these criteria, the packaging from Roasting House is certainly “home compostable” as determined by the worms. Although there were bits of greater than 2mm after 17 weeks, just handling them reduced their size to bits in the mm range. And that was only after 17 weeks, well within the 26 specified by the criteria used by Vinçotte.

So now we’re just waiting for the coffee cup. That went into the worm bin on the 20th April 2017 and is still going, 21 weeks later. Will it be home-compostable? Will the lining that’s needed to keep the coffee from leaking out prevent the worms from breaking it down? You’ll find out here! Make sure you sign up to the BeanThinking newsletter or follow @thinking_bean on Twitter or Facebook to be one of the first to find out when the coffee cup has finally gone.

In the meanwhile, if you’re looking for an environmental solution to your take-away coffee cup habit, it is worth investing in a re-usable cup. Most councils at the moment do not provide industrial composting facilities. Moreover, it is not safe to assume that compostable items will eventually compost in a landfill as modern landfills are water-tight and air-tight. As they say here, the modern land fill is not designed to mulch as much as to mummify. So,if you want to avoid green-washing, you may want to invest in a re-usable cup, for a review of these see Brian’s coffee spot here.



A need for religion at Continental Stores, Russell Square

exterior of Continental Stores

Ghosts of shops past! Continental Stores on Tavistock Place

Many years ago Tavistock Place, now home to Continental Stores, was on my cycle route home. I can no longer remember whether the sign “Continental Stores” was visible then or whether it had a second sign over it. However, the faded red backdrop, the vintage font and the whole feel of the frontage does make “Continental Stores” (the café) stand out a bit from the crowd. Continental Stores is run by the same people who run Store St Espresso on Store St. but much of the original decoration of the café has been kept from the old shop that previously occupied this space. And although this ‘new’ branch is now more than three years old, for various reasons I’ve never quite got to visit until a couple of weeks ago.

We arrived fairly late, just half an hour before closing, and managed to get a long black before the espresso machine (which was apparently having a bad day) finally packed up. Although filter coffee was available, this is not the case when you arrive so close to closing. The coffee was however very drinkable and the window seat provided a great place to watch people pass by. Bubbles formed around the edge of the coffee, reflecting the light streaming through the window in this airy café. White mists skitted over the surface of the drink. There was plenty to consider in the café too, from the oil paintings on the wall to the subtle green colour of the glass separating the interior of the café from the bar area (for more on glass colours click here). A large amount of science in a cosy place. However today’s train of thought took a somewhat different direction. That day, sitting in the café, prompted a thought train to develop in a more introspective direction: what does climate change denial have to do with personal integrity and the need for a continuing dialogue between science and religion? And what does that have to do with coffee drinkers?

Incredibly, it started with a map.

glass and map interior Continental Stores

So much to contemplate! From glass to the map.

On the wall in the main area of the café, behind the counter, is a map depicting the world. Although there is a photo on this page, there is a far better one in Brian’s Coffee Spot review of Continental Stores which can be found here (scroll through the gallery to find it). Also on the map are two circular depictions of the Polar regions. That fact, that the poles are illustrated separately and that the map is a rectangular impression of our spherical home impressed on me the knowledge that it is extremely difficult to truly represent our globe on a flat piece of paper. All maps are projections and the one at Continental Stores is the familiar cylindrical projection where you imagine a cylinder of paper wrapped around the equator of the Earth and then project the profile of the countries around onto it.

A few years ago a Malaysian-Chinese lady, now in her 70s told me a story about growing up in Malaysia (then Malaya) under British colonial rule. At school it was always impressed upon her how much larger Britain was than Malaysia, you could see it just from looking at the maps (which were always of the cylindrical projection as displayed at Continental Stores). It was only later that she realised the importance of map projections. Although Malaysia, at the equator, was fairly well represented by the cylindrical representation, Britain, being relatively closer to the poles, was stretched and so appeared much larger. Britain is in fact larger than the Western Malaysia peninsular but not to the extent that it appeared from the map. Had the map projection been used as a subtle political tool justifying Britain’s rule over Malaya*?

Similar thoughts occurred to me recently with some of the comments that have followed hurricane Harvey in the US (and the floods in south Asia that have killed more than 1200 people but have sadly been far less reported here in the UK). Was the intensity of the hurricane, and the fact that we are experiencing similarly intense storms more frequently, a consequence of climate change?

message inside Continental Stores

From the table to our planet. A message with resonances.

Although that’s an interesting question, it’s not the one that I would like to consider today. Instead, it’s the response on social media generated by data about the frequency of the hurricanes and their strength. “Why are you only showing weather information for the past X years, if you look back further/look more recently…” etc. It is the same with graphs showing global temperatures as a function of time. People ask “Why are they plotted that way, if we looked back further/zoomed in a bit more….” It seems that there is an accusation behind many of the questions; there is doubt about the integrity of the scientist who circulated the graph. What is at the root of this?

When writing a scientific paper (even on a relatively uncontroversial topic like magnetism), there is frequently a lot of discussion about exactly how to present the data. The graphs need to be clear enough and on a scale that the ‘message’ of the paper is delivered quickly. But equally in a way that does not misrepresent the data. Then, different authors have different ideas on aesthetics. The final graph is a balance between these. So why is there such distrust of similar graphs presented on subjects such as climate change? Are we so used to being sold messages in adverts that we immediately suspect the scientists of an evil motive, trying to persuade us to ‘buy’ an ideology?

Clearly there are occasions on which data is presented in a manner to impress rather than to reveal, as was the case with the map. Though even with the map, there is some ambiguity. Some cylindrical projections can be helpful for navigators as lines of latitude and longitude cross perpendicularly. There are times when such a representation would be useful. So when we generate, share or read such  graphs, we need to ask ourselves questions about our reaction to them. Are we representing the data truthfully? Are we trying to make the data fit into opinions that we already hold? These questions apply equally whether we are creating the graph or if we are seeing it on social media and reacting to it.

black coffee Continental Stores

Bringing it back to the coffee. The bubbles reflect the light from the windows. Taking time to contemplate the drink gives us space to reflect.

These considerations generate questions of their own. What do we think science is? Do we believe in the existence of truth? What is truth anyway? What are my motives in sharing/reading this piece of information; am I trying to understand the world or manipulate it to my advantage?

Which is just one reason (of many) that a respectful dialogue between science and the humanities, between scientists and theologians is desperately needed. Religions and philosophies have been asking questions about the nature of being, questions of truth and motive for millennia. Tools such as the examination of conscience have been developed by religious traditions to allow us to interrogate our own motives and to start to understand our own behaviour. In a week when it was revealed that more than 50% of people in the UK describe themselves as having ‘no religion’ it seems to me that, whether we believe in a religion or not, many of us would benefit from such an examination of conscience before we hit ‘retweet’, ‘like’ or ‘share’. Questioning our motives before creating, sharing or commenting. But such tools require space and the time taken to slow down, perhaps in a café, to deliberate on our own attitudes. Time that is needed to help us to see if it is our behaviour that needs amending before we question the integrity of others.

Such deliberations often don’t have conclusions but instead open up more questions. The fortunate consequence of which is that it becomes imperative that we spend more time contemplating our coffee in quiet, welcoming and thought provoking environments such as that found at Continental Stores.

Continental Stores can be found at 54 Tavistock Place, WC1H 9RG.

*I have kept the name of the country Malaysia as it is now known apart from when referring to the time when Britain had colonised it and called it “Malaya”.


Coffee Rings: Cultivating a healthy respect for bacteria

coffee ring, ink jet printing, organic electronics

Why does it form a ring?

It is twenty years since Sidney Nagel and colleagues at the University of Chicago started to work on the “Coffee Ring” problem. When spilled coffee dries, it forms rings rather than blobs of dried coffee. Why does it do that? Why doesn’t it just form into a homogeneous mass of brown dried coffee? Surely someone knew the answer to these questions?

Well, it turns out that until 1997 no one had asked these questions. Did we all assume that someone somewhere knew? A bit like those ubiquitous white mists that form on hot drinks, surely someone knew what they were? (They didn’t, the paper looking at those only came out two years ago and is here). Unlike the white mists though, coffee rings are of enormous technological importance. Many of our electronic devices are now printed with electrically conducting ink. As anyone who still writes with a fountain pen may be aware, it is not just coffee that forms ‘coffee rings’. Ink too can form rings as it dries. This is true whether the ink is from a pen or a specially made electrically conducting ink. We need to know how coffee rings form so that we can know how to stop them forming when we print our latest gadgets. This probably helps to explain why Nagel’s paper suggesting a mechanism for coffee ring formation has been cited thousands (>2000) of times since it was published.

More information on the formation of coffee rings (and some experiments that you can do with them on your work top) can be found here. Instead, for today’s Daily Grind, I’d like to focus on how to avoid the coffee ring effect and the fact that bacteria beat us to it. By many years.

There is a bacteria called Pseudomonas aeruginosa (P. aeruginosa for short) that has been subverting the coffee ring effect in order to survive. Although P. aeruginosa is fairly harmless for healthy individuals, it can affect people with compromised immune systems (such as some patients in hospitals). Often water borne, if P. aeruginosa had not found a way around the coffee ring effect, as the water hosting it dried, it would, like the coffee, be forced into a ring on the edge of the drop. Instead, drying water droplets that contain P. aeruginosa deposit the bacteria uniformly across the drop’s footprint, maximising the bacteria’s survival and, unfortunately for us, infection potential.

The bacteria can do this because they produce a surfactant that they inject into the water surrounding them. A surfactant is any substance that reduces the surface tension of a liquid. Soap is a surfactant and can be used to illustrate what the bacteria are doing (but with coffee). At the core of the bacteria’s survival mechanism is something called the Marangoni effect. This is the liquid flow that is caused by a gradient in surface tension; there is a flow of water from a region of lower surface tension to a region of higher surface tension. If we float a coffee bean on a dish of water and then drop some soap behind it, the bean accelerates away from the dripped drop (see video). The soap lowers the surface tension in the area around it causing a flow of water (that carries the bean) away from the soap drop.

If now you can imagine thousands of bacteria in a liquid drop ejecting tiny amounts of surfactant into the drop, you can hopefully see in your mind’s eye that the water flow in the drying droplet is going to get quite turbulent. Lots of little eddies will form as the water flows from areas of high surface tension to areas of low surface tension. These eddies will carry the bacteria with them counteracting the more linear flow from the top of the droplet to the edges (caused by the evaporation of the droplet) that drives the normal coffee ring formation. Consequently, rather than get carried to the edge of the drop, the bacteria are constantly moved around it and so when the drop finally dries, they will be more uniformly spread over the circle of the drop’s footprint.

Incidentally, the addition of a surfactant is one way that electronics can now be printed so as to avoid coffee ring staining effects. However, it is amusing and somewhat thought provoking to consider that the experimentalist bacteria had discovered this long before us.

Breathing underwater at the London Particular

table and inside of the LP

Inside the London Particular

Tucked out of the way in New Cross, the London Particular has always been just that little bit far away to travel to, but always so tempting, a siren calling towards New Cross. The reviews of the food and the place were intriguing, while the coffee is roasted by HR Higgins, a roaster with a café that always seems closed when I get the opportunity to pass by (which is usually Sundays). So it was with some relief that I finally managed to get to the “LP” a couple of weeks ago. Towards the end of a row of shops, the space outside the café has plenty of seats where you can enjoy a spot of lunch and/or a coffee on a warm day. Inside feels more cosy. A bar on the left of the entrance forms a corridor with the wall that you walk through to get to a room with communal table at the back. In addition to the communal table, there are a series of individual high chairs along the wall. At the back of the café is a window with an old device sitting on it. “An old digital multi-meter” I said before being corrected by my sometime companion in these reviews, it has a dial, it must be an “analogue multi-meter” then! It did seem to be able to measure current and resistance and it did have a dial to indicate the value measured. Quite why it was sitting, unconnected, on the windowsill is anyone’s guess.


An Analogue multi-meter. But why was this sitting on the windowsill at the back of the cafe?

The lunch menu is good. Enough items there to provide choice, few enough that each can be done well. Significantly, the true London Particular, the pea soup, was not on the menu on the day we were there. We had a light bite of lunch, a black coffee and shared the jug of mint infused tap water that was placed on our section of the table. At the other end of the table, another customer was enjoying her lunch. So although communal, the table gave us enough room to be private and have our own conversation. A mirror along the wall above the table reflected the blackboard menu between the table and the bar. Thinking about mirror writing reminded me of Dr Florence Hensey and his letters of lemon juice ink. Back in the eighteenth century he had operated as a spy out of coffee houses on the Strand and in St Martin’s Lane¹. Spying on England for France, his letters, written in lemon juice (invisible ink) passed without detection before the frequency of correspondence drew suspicions. Times move on. Spies would surely no longer write in lemon juice or even mirror writing to avoid detection.

Lunch on a week day was a very good time to experience this café. It must get quite crowded at weekends or brunch times. So it was good to be able to sit back and contemplate our surroundings from the back of the café. In the foreground of our view though was the water jug. With fresh mint leaves stacked inside, it was evident that air had become trapped under some of the leaves forming tiny bubbles. How had the air got stuck there? Was it merely that the leaf was blocking the air bubble from rising through the water? Could there be slightly more to it?

Coffee and mint water in New Cross

Coffee and mint water at the LP

There is a popular expression “like water off a duck’s back”. Perhaps it arose because the duck’s back is often thought one of the most waterproof surfaces we know. But what makes the duck so waterproof? Why does water just form drops and then fall off the back of the duck? It is not because the feathers are oily. We sometimes ‘wax’ our waterproofs with a grease to make them resistant to getting wet and so perhaps we have thought that the duck’s back was just a bit greasy? And yet a study done back in 1944 showed that mere oil could not account for the waterproofing of the duck’s back.

Before delving into why the duck’s back is such a waterproof surface, it’s helpful to know how to quantify ‘waterproof-ness’ in the first place. To measure how waterproof something is, we use what is known as the contact angle, which is the angle that the drop makes with the surface on which it is sitting. Surfaces that are not waterproof (technically we call them “wettable” or hydrophilic), have very low contact angles, the ‘droplets’ of water on the surface are flattened. Waterproof surfaces on the other hand (imaginatively called hydrophobic), have contact angles which are much greater than 90º (it may be helpful here to have a look at the cartoon illustrating this point). Droplets that formed on a duck’s back had contact angles much greater than 90º, indeed, they formed almost spherical drops of water. What could be going on?

artemisdraws cartoon, contact angle, wettability

How ‘wettable’ a surface is can be defined by the contact angle that the drop makes with the surface. Image thanks to artemisworks.

The answer is in the details of the feather. The feather is not a flat surface but a material that has irregular protrusions and structure at the micro and nano-scale (one thousand and one million times smaller than mm scale respectively). These protrusions trap air within the feather and so effectively suspend the drop above the feather surface. The droplet does not have a flat surface on which to spread out. The structure means that the contact angles of the drops of water on a feather can be even higher than 150º; the droplets are held up almost as if they are spheres of water.

mint infused water at the LP New Cross

A breath of fresh air under water. Air bubbles trapped under mint leaves.

Another creature that uses the irregular protrusions on the hairs on its legs for waterproofing is the spider. The hairs on the legs of a spider mean that, just as the duck’s back, the spider’s legs are extremely waterproof. But it also means that air is trapped under the droplets. Consequently, if a spider finds itself submerged under water, the air under the droplets forms little bubbles similar to those under the mint leaf in the London Particular. And this allows a drowning spider the air it needs to breathe. Nanostructure helping the duck to dive and the spider to survive. And the mint water to be particularly refreshing on a warm day in a very pleasant place for a spot of lunch and a coffee.




The London Particular can be found at 399 New Cross Road, SE14 6LA

¹London Coffee Houses, Bryant Lillywhite, Pub 1963

On rings, knots, myths and coffee

vortices in coffee

Vortices behind a spoon dragged through coffee.

Dragging a spoon through coffee (or tea) has got to remain one of the easiest ways to see, and play with, vortices. Changing the way that you pull the spoon through the coffee, you can make the vortices travel at different speeds and watch as they bounce off the sides of the cup. This type of vortex can be seen whenever one object (such as the spoon) pulls through a fluid (such as the coffee). Examples could be the whirlwinds behind buses (and trains), the whirlpools around the pillars of bridges in rivers and the high winds around chimneys that has led some chimneys to collapse.

Yet there is another type of vortex that you can make, and play with, in coffee. A type of vortex that has been associated with the legends of sailors, supernovae and atomic theory. If you add milk to your coffee, you may have been making these vortices each time you prepare your brew and yet, perhaps you’ve never noticed them. They are the vortex rings. Unlike the vortices behind a spoon, to see these vortex rings we do not pull one object through another one. Instead we push one fluid (such as milk) through another fluid (the coffee).

It is said that there used to be a sailor’s legend: If it was slightly choppy out at sea, the waves could be calmed by a rain shower. One person who heard this legend and decided to investigate whether there was any substance to it was Osborne Reynolds (1842-1912). Loading a tank with water and then floating a layer of dyed water on top of that, he dripped water into the tank and watched as the coloured fluid curled up in on itself forming doughnut shapes that then sank through the tank. The dripping water was creating vortex rings as it entered the tank. You can replicate his experiment in your cup of coffee, though it is easier to see it in a glass of water, (see the video below for a how-to).

Reynolds reasoned that the vortices took energy out of the waves on the surface of the water and so in that way calmed the choppy waves. As with Benjamin Franklin’s oil on water experiment, it’s another instance where a sailor’s myth led to an experimental discovery.

chimney, coffeecupscience, everydayphysics, coffee cup science, vortex

In high winds, vortices around chimneys can cause them to collapse. The spiral around the chimney helps to reduce these problem vortices.

Another physicist was interested in these vortex rings for an entirely different reason. William Thomson, better known as Lord Kelvin, proposed an early model of atoms that explained certain aspects of the developing field of atomic spectroscopy. Different elements were known to absorb (or emit) light at different frequencies (or equivalently energies). These energies acted as a ‘fingerprint’ that could be used to identify the elements. Indeed, helium, which was until that point unknown on Earth, was discovered by measuring the light emission from the Sun (Helios) and noting an unusual set of emission frequencies. Kelvin proposed that the elements behaved this way as each element was formed of atoms which were actually vortex rings in the ether. Different elements were made by different arrangements of vortex ring, perhaps two tied together or even three interlocking rings. The simplest atom may be merely a ring, a different element may have atoms made of figure of eights or of linked vortex rings. For more about Kelvin’s vortex atom theory click here.

Kelvin’s atomic theory fell by the way side but not before it contributed to ideas on the mathematics (and physics) of knots. And lest it be thought that this is just an interesting bit of physics history, the idea has had a bit of a resurgence recently. It has been proposed that peculiar magnetic structures that can be found in some materials (and which show potential as data storage devices), may work through being knotted in the same sort of vortex rings that Kelvin proposed and that Reynolds saw.

And that you can find in a cup of coffee, if you just add milk.


Looking under the surface at Mughead coffee

Mughead Coffee, Coffee in New Cross

Set back from the busy A2, Mughead Coffee offers a space to unwind.

A new café has just opened in New Cross. Mughead Coffee opened in July 2017 and sits fronting the A2, part of an old Roman road connecting London to Dover. The large pedestrianised space outside the café provides plenty of room for a few tables together with some further chairs arranged along the café window. It also means that the cafe is set-back far enough from the road that it is possible to sit outside and enjoy the surroundings. Inside, there were plentiful seats but, sadly equally plentiful numbers of occupants relaxing in this new cafe. Clearly this new coffee place in New Cross is proving popular. And why not! Just down the road from the London Particular, Mughead Coffee serves Square Mile in a friendly atmosphere. It is easy to see this becoming a popular local haunt. The usual array of coffees were on offer together with a filter option but as we arrived shortly after lunch, the cake/edible option appeared a little depleted. The interior of the café is quite light and airy with comfortable chairs at the back and more regular seating towards the front. We ordered a long black and a ginger beer and then adjourned to a table outside to await our drinks.

The tables outside are arranged on a sloping pavement. This is not really a big deal, but did remind me of a comment made by the lecturer who was trying to instil experimental design into us as undergraduates: The only stable table is a three legged one. However there was not much time to reflect on that as very soon both coffee and ginger beer arrived with a glass of ice. The natural light revealed the oils on the surface of the coffee as they moved with convection. Different convection zones moving in the coffee just as air parcels do in the sky to form mackerel skies or hot lava moves to form different rock formations, both on Earth and elsewhere.

coffee and ice in New Cross on a wooden table

Coffee and ice at Mughead Coffee. Note the reflections on the coffee surface.

Once the ginger beer was poured into the glass, the ice cubes floated upwards with just a fraction of them bobbing above the surface, the majority of the ice cube beneath. A glance around our surroundings revealed other hints of sub-surface structures. A drain cover nearby indicated, together with some tiling along the pedestrianised zone, the line of the rain sewer running along the road. A public telephone box had no wires obviously leading from it meaning that all the wiring for the communication had to be subterranean. And a raised flower bed, full of thriving plants, had a little drainage hole right at the bottom in order that heavy rain storms did not drown the plants.

This last feature reminded me of a documentary I’d recently seen concerning climate change. Often we tend to think of climate change as involving things that we can see: the melting of glaciers or the disappearance of sea-ice, or freaky rain storms that cause local flooding. However there is another aspect, a sub-surface aspect, that has perhaps been far more visually alarming than even the break-off of the Larson A, B and C ice shelves. If only we could see it. The problem is that, as it happens below the surface of the sea, few of us see it, it is hidden from view and therefore easily hidden from our conscience. It is the drastic effect that rising sea water temperatures are having on a particularly unusual plant-animal combination, the coral reefs. Coral reefs such as the Great Barrier Reef just off Australia, are animals that exist in a symbiotic relationship with a particular type of algae called zooxanthellae. Although the ‘mouths’ of the coral eat passing zoo plankton at night, during the day, they get other nutrients from the photosynthesis products produced by the zooxanthellae that live within their skeletons. These plants give the corals those amazing colours (as well as food). In return, the coral provides the plant life with shelter (they live within the coral itself) and extra carbon dioxide.

Outside Mughead Coffee New Cross

Indications of a hidden architecture. Can you see the drainage hole at the bottom of the planter at the back of the photo?

As the sea temperature rises, the zooxanthellae become less efficient at photosynthesising and so of less use to the coral. If the temperature stays high, the coral ejects the plant life from its body causing the coral to lose all its colour, it has bleached. What sort of high temperatures are needed? It seems that if the temperature of the water is about 1-2°C above the usual seasonal maximum, the coral are ok for a few weeks. But if the temperature rise is 3-4°C (or higher) above the usual seasonal maximum, the damage can occur in just 2 days¹. Coral bleaching does not necessarily lead to coral death but if the bleaching is sustained vast areas of coral reefs can die and get destroyed, with significant impact to the local ecosystem. As corals host “nearly one-third of the world’s marine fish species…”² this impact will be far reaching and affect the livelihoods of millions of people³.

Although small scale coral bleaching has been documented since 1979¹, the first global scale coral bleaching occurred in 1998. It was 12 years until the next global bleaching event occurred in 2010. Following that, we have just had the third global bleaching event in 2015-16. In the latest episode, it is estimated that 29% of the Great Barrier Reef’s coral died (as in actually died, not just bleached). These temperature increases can be associated with global warming caused by increased greenhouse gases in the atmosphere (for more info click here (opens as pdf) or refer to [4]).

The frequency of these events, together with the fact that there were no global bleaching events prior to 1998 should be a dramatic warning siren calling on us to do something to arrest climate change. But what can be done and is it already too late? Well, it is not yet too late to do something. The plants, thriving in the box in front of Mughead can emphasise to us the importance of maintaining our local environment and by extension our global one. Taking time to slow down and take stock of what is beautiful in our environment, and the habits we need to develop to keep this for future generations, these are things that we can do. If you eat fish, was it caught sustainably? Some fishing methods can kill the coral reefs, check before you eat. This is not going to be hard to do. After all, we already do this with coffee. Many coffee drinkers (and roasters) will check how the coffee is grown and processed for both environmental cost and the conditions experienced by the farmers. Many such small actions can cumulatively build to an effort to stop climate change.

Which brings us, in a sense, back to the surroundings at Mughead Coffee. Sitting down and taking time to enjoy that coffee while appreciating our surroundings, the visible and the hidden, the busy road and the mini-oasis of plants in the planter, may help us to see that connectedness that pushes us to accept our responsibility to our common home. Contemplating the history of the road in front of us, will our planet still be beautiful in another 2000 years? With an offer of “gourmet sandwiches” on the menu (if only we’d got there early enough), there’s plenty of reason to head along to the old road in New Cross and sample the coffee while pondering our own impact on this interesting location.


¹ Life and Death of Coral Reefs, Charles Birkeland (Ed), Chapman & Hall, 1997

² Coral Reef Conservation, Ed Isabelle M Côté and John D Reynolds, Cambridge University Press, 2006

³ Chasing Coral, Netflix Documentary, 2017 (see trailer below)

4 Climate and the Oceans, Geoffrey K Vallis, Princeton University Press, 2012

Chasing Coral Trailer: