slow science

Cobwebs, Crows & Coleman Coffee, Lower Marsh

filter, Brazilian or Guatemalan, V60, rainbow, glass, Coleman Coffee, Lower Marsh, Waterloo

There’s a lot of physics in this glass cup of coffee, enjoyed at Coleman Coffee, Lower Marsh.

Coleman Coffee on Lower Marsh, Waterloo, is a surprisingly relaxing place. Surprising because the frontage gives little away. A door with windows on either side revealing a small wooden bench on the right and a larger table on the left. A food menu is on the left, the coffee menu in front of you (above the counter) and a note about how the coffee is roasted on a black board on your right. The space feels open and welcoming but it is the garden at the back that I think shifts Coleman Coffee from being a lovely little café to a great spot at which to just spend time and notice things.

My first visit was on an incredibly hot day in early July. For some reason I didn’t see the filter coffee option on the menu and so chose a long black to enjoy outside. The shade of the trees was a welcome respite to the hot Sun and the contrast created by the light provided much to dwell on with the inadequacies of my phone’s camera. Berries had formed on the tree growing up the wall of the café. After my visit I read the review of the café on Brian’s Coffee Spot and realised that these berries were mulberries. The other trees providing the shade were a Jasmine and a Pomegranate. I also found that I had missed the filter option and so a return visit was obligatory! How easy it is not to notice things.

ditch the plastic straw, enjoy a paper one

Chocolate milk and a paper straw.

A second visit sadly revealed the restricted opening hours of Coleman Coffee. Arriving at about 2.58pm, we were told it was take-away only as they were closing at 3pm. However the third visit was worth the wait. By this time the weather had turned and it had been raining, but the garden was still calling. The filter coffee on offer (V60) was either a Brazilian or a Guatemalan. Opting for the nuttier of the two (an allergy to actual tree nuts does not prevent my enjoying nuttiness in coffee!), we took a couple of glasses of water through to the back and awaited our drinks. When they arrived, it was interesting to find that the nutty coffee was truly nutty. A lovely flavour and mouthfeel to enjoy. It was also great to notice that the straw in the chocolate milk seemed to be an old-fashioned paper straw (rather than the environmentally problematic plastic straws). As it had rained, the stools outside were a little wet, even though they had been largely sheltered by the same trees above the garden. This time, the mulberry tree seemed mulberry-less, apart from the one berry lying sorrowfully on the floor. The red of the berry being squished (accidentally) underfoot leaving it lying and injured in the style of Pyramus and Thisbe. Across the other (wetter) side of the garden, three spiders were busy weaving new webs, ready to catch whatever flies came their way. It would have been easy to watch those spiders for hours but I think a good café can linger in the memory long after your visit has ended and so the spiders are still spinning their webs in my mind now.

garden spider at Coleman Coffee Waterloo

Spider on the table. What could be better than time spent contemplating their webs?

Photos of spiders webs glittering with dew drops are common place but somehow strangely attractive. Beads of dew gather at various points on the web leading to descriptions of cobwebs as being laden with jewels. A few years ago, a scientist contemplating spider’s webs asked why it was that water collected like jewels on the webs? Why didn’t it collect similarly on your hair? (You can read more about his story here). The team looked at the webs of one particular spider with an electron microscope. Electron microscopes can magnify things far more than optical microscopes (for images of coffee under an electron microscope click here) and so the scientists were able to observe how the hydrophilic (wet-able) fibres in the web turned from ‘puffs’ to ‘knots’ as they got wet. Water falling on the web was then attracted to these knots, partly due to an effect caused by the knot shape and partly due to the surface tension gradient of the water along the fibres. The results of the study can be found here.

Although it took five years of investigation after the initial contemplation, this study of spider’s webs could lead to tools that could be used for water collection or in devices to aid chemical reactions. Which brings us to the other ‘C’ of the title: crows. Sadly there were no crows in the garden on either of my visits to Coleman Coffee. Nonetheless there is a link. My first visit had been cut a little short as I was headed to the Royal Society Summer Science Exhibition. Apart from the fact that it was baking hot inside the Royal Society, this science outreach event had a good mix of science/experiments for adults and for kids, it was great to wander around and learn a large number of new things. So many exhibits caught my eye but the one that connects with Coleman’s and cobwebs was the exhibit on tool making crows.

Spider and web, Coleman

Spider building a web at Coleman Coffee

Crows have been shown to be great tool users. Particularly the New Caledonian Crow which has been shown to even make hooks out of twigs in order to fish out insects from their hiding places. While thinking about what it was that led to this species of crow becoming adept at tool use (and therefore perhaps an explanation of human tool use), it became apparent that the two particularly good tool using crow species lived on remote islands without predators. Not only did they have the physical ability to create tools (a straight beak for crows, a thumb for humans), they lived in a place where they could have time to explore and to create, to develop tools to enable them to get the most tasty bug.

Just as the scientists had needed time to watch, to investigate and to think about spiders webs in order to create new tools, so crows may have needed that time to explore their tool use. Perhaps it’s worth pushing the analogy to inner-city London (or indeed wherever you are). The more we spend time out, contemplating and enjoying nature, the more productive we can be. But to develop, we need to slow down, to think, to contemplate, and to enjoy great coffee in surroundings as special as at Coleman Coffee.

Coleman Coffee is at 20 Lower Marsh, SE1 7RJ

Reflections at Knockbox, Lamb’s Conduit Street

Knockbox, Knock box, coffeeKnockbox coffee is on the corner of Lamb’s Conduit Street and Dombey Street. It is a small place and we had to go twice in order to get a seat, though the compensation is that there are views all around the cafe (it being on a corner). I enjoyed a very good americano, made using Workshop coffee. Complementary jugs of mint infused water were dotted around the cafe which is always a nice touch. Sadly, I tried Knockbox just after lunch and so didn’t try any of the edibles on offer. This does mean however that I will just have to go back to try them at some point (and of course, to enjoy another coffee).

There were a lot of things to notice around Knockbox that day. There were the air bubbles in the water that had become stuck around the mint leaves. There were the light bulbs (that you can see through the windows in the picture). And there was the espresso machine: A gleaming piece of machinery that sat majestically on the counter. Looking at the espresso machine it was impossible not to be struck by the reflections from the surface. The reflections are not only testament to how much the staff at Knockbox must polish the machine; how reflections work is the subject of today’s Daily Grind.

espresso machine, metal, reflection

The gleaming espresso machine at Knock box

The interaction of materials with light is one of those fascinating areas that reveal physics at its most fundamental. I’ve often taught undergraduate physics students who are looking forward to learning about quantum mechanics because it is “weird”. This is true, quantum mechanics can be quirky, but electromagnetism (which is about light) can be just as odd. To get such elegant and surprising physics out of what is essentially all classical, nineteenth century theory, is one of those joys about learning about (and teaching, using and experiencing) this subject.

However, to return to the espresso machine and light.  How light interacts with objects reveals how the electrons are distributed in the material which in turn tells you something about the atoms that make up the espresso machine. (For how to experience electrons in your coffee, see Bending Coffee, Daily Grind, 26 Nov. 2014). As the electrons are electrically charged, they respond to light which is, ultimately, an oscillation of electric (and magnetic) field. Electrons in a metal are shared in an “electron sea” between all the atoms in the metal. Consequently, when light falls on a metal surface, the electrons can respond to the electric field oscillation of the light and they re-emit the light backwards as a reflection.

ImpFringe, #ImpFringe, Fox's Glacier Mints, linearly polarised light

Sugar rotates linearly polarised light. The ‘device’ above is made from layers of Fox’s Glacier Mints and 2 linear polarisers (eg. a pair of polarised sunglasses). Photographed at ‘Lit Up’, an Imperial Fringe event held at Imperial College London, that was free to the public.

On the other hand the electrons in the atoms of the plastic of the grinder (or the glasses on the top of the espresso machine) are held firmly to each atom. Therefore most of the light that we see will go straight through these substances with each atom acting to propagate the light forward but not able to completely block it for a reflection. Coffee beans too contain electrons that are held in place by the atoms in the molecules that make up the bean. Unlike the glass though, the electrons in coffee beans are held in atomic bonds that happen to have an “excitation energy” that is at a visible light frequency. Rather than let the light through, they absorb certain colours of light (more info in the Daily Grind here). The result is the opaque, deep brown of the coffee bean.

This year is the international year of light, a year which is intended to celebrate our understanding of light. There are so many light based processes occurring all around us at every moment. Why not stop in a cafe and see how many you can spot in your coffee cup?

Levitating water

V60 from Leyas

Time to look more closely at the surface of your black coffee.

Have you ever sat watching the steam that forms above a hot Americano? Beneath the swirling steam clouds you can occasionally see patterns of a white mist that seem to hover just above the dark brew. Bean Thinking is about taking time to notice what occurs in a coffee cup and yet I admit, I had seen these mists and thought that it was something that was just associated with the evaporation of the water and that “someone”, “somewhere” had probably explained it. So it was entirely right that I was recently taken to task (collectively with others who have observed this phenomenon and taken the same attitude) for this assumption by the authors of this paper who wrote “The phenomenon that we studied here can be observed everyday and should have been noticed by many scientists, yet very few people appear to have imagined such fascinating phenomena happening in a teacup., espresso grind

The water particles in the white mist are a similar size to the smallest particles in an espresso grind. Photo courtesy of, (CC Attribution, No Derivs). The coin shown is a US nickel of diameter 21.21 mm

The authors of the study show that the white mists (these “fascinating phenomena”) are, in fact, layers of water drops that have a typical diameter of around 10 μm (which is roughly the size of the smallest particles in an espresso grind). Although the white mists exist above tea and even hot water as well as coffee, they are probably easiest to see against the black surface of the Americano.

More surprising than the fairly uniform distribution of water droplet size though is the fact that the authors of this study showed that the droplets were levitating above the coffee. Each water droplet was somehow literally hovering above the surface of the coffee at a height of between 10 – 100 μm (which is, coincidentally, roughly the particle size distribution in an espresso grind).

white mists, slow science

You can (just about) see the white mists over the surface of this cup of tea (which is a still from the video below)

One of the questions that the authors of the paper have not yet managed to answer is what is causing this levitation? Could it be the pressure of the hot coffee evaporating that keeps these particles held aloft? This would explain the observation that the mists form patterns similar to those caused by (heat) convection currents. Alternatively perhaps the droplets are charged and are kept away from the coffee by electrostatic repulsion, an explanation that is suggested by the behaviour of the droplets when near a statically charged object (eg. hair comb, balloon, try it). Perhaps the levitation is caused by the droplets spinning and inducing an air cushion under them? Why not design some experiments and try to find out. It would be great if we can drink hot black coffee in the name of science. Let me know the results of your observations in the comments section below. In the meanwhile, here is a video of the white mists in tea, enjoy your coffee:

You can read the study at: Umeki et al., Scientific Reports, 5, 8046, (2015)