Month: October 2017

Categories
Coffee review Observations Tea

Light and gravity at Tab x Tab, Westbourne Grove

drinks in ceramic mugs, Westbourne Grove
A soya hot chocolate and my black coffee at Tab x Tab

Earlier this summer, a new café opening on Westbourne Grove attracted a lot of attention. “Tab x Tab” quickly received reviews from Brian’s Coffee Spot (who noted the unusual espresso machine), Bean There at and Doubleskinnymacchiato. Bean There at also suggested that there should be plenty to ponder at Tab x Tab when I finally got the chance to get there. And so, a trip to this café had been on the agenda for a fair while.

Wandering into the café, it seemed exactly as described by the reviews: clean, sharp interiors in a modern building. It was fairly crowded when we arrived just after lunch and so we ordered before taking a seat at the bar (two of the few seats left). I had a long black while my fellow imbiber had a soya hot chocolate. The drinks arrived in those distinctive mugs mentioned by doubleskinnymacchiato (and pictured above). As we had just had lunch, on this occasion we didn’t check the edibles on offer but with plenty of other reviews of the coffee and the cake, I’m sure that you’ll find recommendations there (I understand the avocado on toast with cashew nut is well worth trying).

Graphite, double layer graphene, stacked hexagons
Plant on two slates at Tab x Tab, Westbourne Grove

Sitting down to enjoy our drinks, the first thing to notice was that Bean There at was absolutely right. Despite the slightly minimal and elegant decoration, there were plenty of things dotted around that were slightly quirky. Firstly there was the plant that had been placed on two hexagons of slate that had been ever so slightly displaced from each other, presumably for aesthetic effect. Could this link to graphene and graphite with their strong intra-layer bonding and weak interlayer bonding (so the hexagons of carbon in graphite slide over each other)?

Then there was the selection of items for sale that also provided food for thought. Books and other items from the School of Life, something to think about as you stop with your coffee perhaps. In the other direction, on the counter top, a couple of Venus Fly Traps were waiting for their lunch. There is so much we have yet to learn about the symbiotic relationships between plants and animals and especially between plants and fungi. As we looked further around the café, there was something else a little odd. Just as the name “Tab” was written both the correct way and upside down in the window, so the plants in the hanging baskets were hanging upside down.

which will win, gravity or light
Plants hanging upside down in the window at Tab x Tab

This seemed a bit strange in itself. Plants have a tendency to move upwards towards the light. This behaviour of plants (and trees in particular) provides one way to identify which way is south when walking in the country without a compass¹. It is odd to see a plant growing downwards and suggests that the plants in the window are regularly rotated so that they don’t try to reach up. As Simone Weil wrote “Two forces rule the universe: light and gravity”². Which would win in the end? To be fair, Weil was not referring to the light that streamed through the windows in Tab x Tab giving the plants the force they need to move upwards. Nonetheless, whether one is thinking literally or analogously, it is an interesting question what pulls us down, what brings us up?

There is a story that Newton arrived upon his idea of universal gravitation by contemplating a falling apple. Considering that the plants were approximately 2m above the floor level, and using the fact that the acceleration due to gravity, g,  is 10 m/s², if the plants were to fall from their hanging position, they would take:

s = ½gt²

t = 0.6 seconds

to fall and smash to the ground*. While this brings to mind Newton’s experiments dropping pigs bladders filled with liquid mercury from the dome of St Paul’s Cathedral, it is worth instead thinking more about the universal nature of the gravitational force. This is of course what made Newton’s idea of gravity different from the theories that had preceded it. People had known that if an apple fell from a tree (or a plant fell from its hanging basket) it would fall to Earth. What was key to Newton’s idea was that what applied to the apple, applied to all other masses too. The same maths that could be used to calculate how fast a plant dropped, could be applied to the Moon. So, if this was the case, could we calculate the orbital distance of the Moon in the time it took us to enjoy a coffee at Tab x Tab? We know that the Moon’s orbital period is τ = 27.3 days (2.36 x 10^6 seconds) so assuming that the gravitational force acting on the Moon is balanced by the centripetal force, we can equate the two:

Gravity: F = GMm/r²

Centripetal: F = mv²/r

Where, G is the gravitational constant (6.67 x 10^11 Nm²/kg²), M is the mass of the Earth (5.97 x 10^24 Kg), m is the mass of the Moon and r the moon’s orbital distance (which is what we want to calculate). If we assume that the Moon travels in a circular orbit (not quite true but not a bad first approximation), then we know the speed, v, of the moon in terms of the orbit period, it is just:

v = 2πr/τ

A bit of re-arrangement and some plugging in of values leads to a back-of-the-envelope value for the Moon’s orbital distance of 383 000 Km. A value that does not compare badly at all with the average distance of the Moon given by NASA as 384 400 Km.

Perhaps if we’d stayed for an additional flat white we could have refined the calculation somewhat and so obtained a value closer to reality. Nevertheless, the fact that the force that is pulling the plant down at Tab x Tab is the same as is pulling the Moon around the Earth, and that we can quickly check this (and get an approximately correct answer to our calculation), is one of those ‘wow’ moments in physics. Realising the universality, and elegance, of certain mathematical relations. So perhaps it is entirely appropriate that this thought train of mathematical elegance was prompted by the quirky but aesthetic elegance you will find at Tab x Tab.

Tab Tab can be found at 14-16 Westbourne Grove, W2 5RH

¹ The Walker’s Guide to Outdoor Clues & Signs, Tristan Gooley, Hodder & Stoughton, 2014

² Gravity and Grace, Simone Weil, Routledge (1995 vsn)

*Although you could use a more accurate value for g, the error on the estimate of the height of the plants makes such precision potentially misleading. The value 0.6 seconds is absolutely a back-of-the-envelope, calculation.

Categories
Coffee Roasters General Home experiments Observations

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.

Categories
Coffee review Observations Science history

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)