Category: Tea

Categories
General Home experiments Observations Tea

Freezing point

coffee and ice in New Cross on a wooden table
Isn’t it a fact that water boils at 100C and freezes at 0C?

Water boils at 100ºC and the ice in your iced latte is at 0ºC. These are facts that we think we know about water: it boils at 100ºC and it melts at 0ºC. A sharp observer may point out that these are pressure dependent and that if we were at the top of a mountain, the water would boil at a slightly lower temperature (I once had a student argue that this was a good reason to only ever drink green tea at high altitude). But if we are at ground level and it is a normal day, we will be fairly certain that the water for our coffees would boil at 100ºC and ice would form at 0ºC.

Yet these ‘facts’ hide some complicated physics and some oddities about our planet. Pure water, that is, water without any impurities in a clean vessel (such as a clean, scratch free glass) does not boil at 100ºC but at temperatures significantly higher than that. Nor does pure water freeze at 0ºC but at temperatures significantly below that. These are phenomena known as superheating and supercooling respectively and, if you are observant, you could see them occasionally in your coffee cup. To see why, and how, we need to think a bit more about how water freezes.

blue tits, mint water, mint infusion, mint leaves in water
If you put pure water into the freezer, you may find that it freezes at a temperature considerably lower than 0C

If you fill an ice cube tray with water and put it in your freezer, you would expect ice cubes to start forming at about 0ºC. We expect the freezing temperature to be the same as the melting temperature, that is the temperature at which the ice cubes would melt. And yet, if you make the water very pure (even distilled water would be a start) and put that in a clean, defect free container (such as a clean glass jar) in the freezer, the freezing process will not begin until much lower temperatures. It’s because the water has to crystallise and change state from a liquid to a solid and to start this process, there needs to be a seed, a surface on which the ice can form. Called a “nucleation site”, this seed could be a piece of dust, a small impurity in the water, a scratch on the surface of the container holding the water, or in fact anything that allows the bonds of ice to start to form. The same is true at the other end of the temperature scale. When the liquid water turns into steam, nucleation sites are needed so that the gas bubbles can start to form at those sites. In the absence of impurities in the water, the water will not boil until temperatures high above 100ºC.

Fortunately in tap water, or in your super-filtered water that you make your coffee with, there are plenty of such nucleation sites so the water boils and freezes at roughly the temperatures you’d expect them to. The same is not true however for clouds in the sky where some (high altitude) clouds have been shown to contain water droplets that are at -35ºC, well below the “freezing temperature”. Exactly why this occurs is still puzzling and a topic of research, but when you stop and think about it, how would you actually measure this temperature? If you supercooled a cup of water and then put a thermometer into it, the thermometer would provide a nucleation site and the water would immediately freeze. How can you measure the water’s temperature without a thermometer?

kettle, V60, spout, pourover, v60 preparation
You are unlikely to see superheating when you boil the water for your coffee in a kettle like this.

Recently a study reported in Physical Review Letters used a laser to measure the diameter of a series of supercooled liquid droplets by determining the energy of a resonance that depended on the droplet’s size. To calculate the temperature of the droplet, the authors then used the principle that as water evaporates, the droplet from which it is evaporating will become colder at the same time that it shrinks in size. Measuring the size of the droplet allowed them to calculate the evaporative loss and therefore the temperature of the drop. They double checked this new technique by measuring (with the same laser) the energy of a particular atomic bond in water that has a known temperature dependence (at higher temperatures). The temperature determined from the drop’s size corresponded with the extrapolation of the energy of this atomic bond and so the team were fairly confident that they had measured liquid water to very cold temperatures indeed. In fact, the authors suggested that it was still possible to have liquid water at 230.6±0.6 K which, in more every-day units corresponds to -42.55ºC, well below the nominal ‘freezing point’.

So pure, liquid, water can get very cold indeed. But could you ever see this in your coffee cup? Although you may like to try some experiments with freezing ultra-pure water, it is easier to see the phenomenon of superheating in your coffee. However, given the possibility of an accident, it may be safer to watch the effect on the video below. The idea is that if you put very pure water in a clean cup into a microwave, it is possible to superheat it well above 100ºC without it boiling, because there are no nucleation sites in the cup or the water on which the steam bubbles could start to form. When you take the cup out and put a nucleation site in (perhaps a spoon or maybe even instant coffee granules), the water will boil suddenly as a result of those new nucleation sites and can even explode. Obviously if you were anywhere near the water when this happened you could get seriously burnt and so it is probably safer to watch the Mythbusters do it with their robotic arm. Enjoy the video, enjoy your coffee, preferably far from superheated:

 

 

 

Categories
General Home experiments Observations Science history slow Sustainability/environmental Tea

Coffee and the world

Welcome to the first post of 2018, Happy New Year! But before embracing 2018, perhaps let’s take a moment to remember those things that we discovered in 2017 that connect your coffee cup (or brewing device) with the physics of what occurs in the wider universe. Here are some of the highlights for me this year, if you want to share your highlight, please comment in the section below.

latte art, flat white art
A properly made latte. But what if you add hot espresso to the milk instead of the other way around?

1) Latte layering

In mid-December a study was published in Nature Communications that explored the complex, but elegant, physics involved in making lattes (ok, not quite by the technique that you would hopefully find in your neighbourhood café but keep with this…). When a hot, low density, liquid (espresso) was poured into a hot higher density liquid (milk) contained within a cold mug, the competition between the density gradients of the liquid (vertical) and the temperature gradient from the cup wall to the liquids (horizontal) produced multiple layers of varying coffee/milk concentration in the cup. Too late for a 2017 Daily Grind article, this looks to be too good an experiment to pass by, hopefully it will appear on the Daily Grind in early 2018.

 

science in a V60
Could this V60 mystery now be solved?

2) Bouncing drops

November 2017 saw research published about what happens when a cold droplet falls onto a hot liquid (think milk and coffee). The temperature difference causes currents to be established within the droplet (and in the main liquid) that in turn create air flows between the droplet and the liquid bath that prevent the droplet from merging with the bath. The research can explain why it is that you can sometimes see raindrops staying as spheres of water on the top of puddles. It may also explain a puzzling phenomenon that I have seen while brewing coffee in a V60.

 

Vortex rings get everywhere.

3) Vortex rings in coffee

June 2017 and it is again about adding milk to coffee (why do I drink coffee black?). When one liquid (such as milk) is dripped into another (such as coffee), it is very likely that you will observe the milk to form “vortex rings”. These rings are related to smoke rings and have, in the past, been proposed as an atomic model. This year however it was suggested that these vortex rings could form as a type of magnetic nanostructure. Mathematically impressive, beautiful, perhaps quite useful and mathematically similar to something you can find in your coffee.

 

bloom on a v60
How do craters form?

4) Crater shapes

April 2017. What happens while brewing a pour over? As you drip water onto a granular bed (or, in coffee terms, ground coffee in a V60 filter), each drop will create a crater. The size and shape of the crater will depend on the density of the granular bed (espresso puck or loose grounds in a filter) and the velocity of the falling drop. Fast frame photography revealed how the shape of the crater changed with time for different scenarios.

 

Coffee bag genuinely home compostable
How it started.
The Roasting House bag before it went into the worm composter.

5) A home experiment

Perhaps not quite in the theme of the other four stories but this is an experiment that you can do at home. Some have proposed compostable coffee cups as a more environmentally conscious alternative to ordinary, disposable, coffee cups. But how “compostable” are compostable cups and compostable packaging? Between May and September 2017, #howlongtocompost looked at how long it took the Natureflex packaging (used by the coffee roasting company Roasting House for their ground coffee) to compost in a worm composting bin. This one worked quite well. Within 17 weeks, it had been eaten by the worms. In comparison, the “completely compostable” take away coffee cup is still in the worm bin (although considerably degraded) 37 weeks after the start of the experiment. If you are interested, you can follow #willitcompost on twitter. Will it finally compost? I’ll leave you to place your bets but you may decide that a link to Brian’s coffee spot guide to re-usable cups will be helpful.

 

What will 2018 bring? Certainly there will be more composting experiments as I have a coffee bean bag from Amoret coffee, 3 different compostable cups and a compostable “glass” to try with the worms. But in terms of the science? We’ll have to wait. Meanwhile, if you have a coffee-science highlight from 2017, please do share it either here in the comments section, on Twitter or on Facebook. Happy New Year to you all.

 

 

 

 

 

Categories
General Home experiments Observations slow Tea

Coffee and cream baubles – not just for Christmas

floating, bouncing drops
Drops of water can be stable on the water’s surface for many minutes if you put the water on a loudspeaker, more info on how to create these at home here.

You may have noticed them before: balls of liquid dancing on the surface of your coffee (or tea) that seem to last for ages before being absorbed into the drink? Perhaps you have added milk to your coffee and noticed that it took some time before the milk entered into the brew?

It turns out, there’s some very interesting physics that is happening whenever you add milk to your tea or when you are preparing a pour-over. It can link coffee to wine and to quantum mechanics. It is worth taking a closer look at these drops.

You may remember that you could use a loud speaker to make droplets of coffee bounce on a cup of the same. The vibrations in the cup meant that the air between the droplet and the drink never got squeezed out of the space between them. So, rather than coalesce, the drop jumped up and down on the coffee surface before finally disappearing under. This type of bouncing bauble has been shown to behave in similar ways to quantum particles in wave-particle duality. An analogue of quantum physics in the macroscopic droplets on the surface of your drink.

But that type of bauble required the use of a loud speaker (or some similar way of generating vibrations on the surface of the coffee). What if you could ‘bounce’ a drop of coffee on a cup of coffee without any external props like speakers? Well, it turns out that you can. In November 2017 a group of researchers showed how a temperature difference between a drop falling into a drink and the drink itself could result in the drop appearing to float on the surface of the drink for many seconds. The obvious example was cold milk into a cup of coffee (or tea). But I think that it may also happen in a V60 when you prepare a pour over, more on that below.

science in a V60
Bubbles of liquid dancing on the surface of a brewing coffee.

The idea is quite simple. If there is a temperature difference between the drop and the coffee, when the drop approaches the coffee, there will be thermal gradients across the drop/cup system. Surface tension is temperature dependent: the higher the temperature, the weaker the surface tension. Differences in surface tension across the surface of a liquid result in compensating liquid flows (one of the best places to see this is in a glass of wine, but there’s also a great party-trick experiment you can do to demonstrate it which is here). So, because there is a temperature difference across the surface area of the droplet (owing to the difference between the droplet and the cup), there will be liquid flows set up within the drop. These flows are like circulating vortices which draw the surrounding air into the gap between the drop and the cup and so prevent the existing air between the drop and the cup from escaping. If the air has nowhere to escape to, the drop can’t merge with the drink, in fact it ‘levitates’ for a number of seconds.

The authors suggest that this is a reason that you can often see rain drops staying on the top of puddles or ponds before being subsumed into the water, or why you can see the cream (or milk) stay as globules on the surface of your coffee (or tea). And so I wonder, could this also be the explanation for an odd phenomenon that I sometimes notice while brewing coffee in my V60. Perhaps you have seen this too? After some time, the new drops of filtered coffee impacting on the surface skit along to the edge of the jug. They stay as balls of coffee on the coffee’s surface for quite some time before becoming part of the brew. You can see a photo of some of these droplets above. Initially I thought that this was because the surface of the coffee had started to vibrate with the impacting droplets. But it is also possible that it could be this temperature effect. As the (brewed) coffee in the jug would be cooler than the water dripping into it from the filter, there would be a temperature difference between the droplet and the coffee but the reverse of the milk-coffee situation. The drop would be warmer than the coffee it’s dripping into. The authors of the study suggested that it was the magnitude of the temperature difference that was the key, not the sign of the temperature difference. So that would fit with the V60 observations seen previously. However how would you show which effect (vibration or temperature difference) is responsible for the behaviour?

Enjoy playing with your tea, coffee and V60s. Do let me know the results of your experiments. Is it a vibration thing or does the temperature difference have to be there to begin with? Let me know what you think is going on.

I am also grateful to Amoret Coffee for alerting me to this story in the first place through Twitter. If you come across some interesting coffee-science, please let me know, either here in the comments section (moderated, please be patient), or on Twitter or Facebook.

 

 

 

Categories
Coffee review General slow Tea

Data overload at The Gentlemen Baristas

coffee Borough
The Gentlemen Baristas in Borough.

Borough is always such a great place to wander. Walking around the backstreets with their bits of hidden history. The other day, we had visited the market, wandered down Redcross Way past the old Crossbones graveyard and hit upon The Gentlemen Baristas on Union Street. It is difficult not to have heard about these Gentlemen and my visit there was long overdue and so, we wandered in to try this famous venue.

The shop front advertised itself as a “Coffee House”. A very accurate description and a nod to the Coffee Houses of the past. As it was shortly after lunchtime, it was very crowded with a diverse bunch of people and felt a little cramped at the counter. Nonetheless, the queue was quick and friendly baristas soon took our order allowing us to retire inside to try to find a table (no chance) or a stool next to a bar (successful). Around us, people were either chatting over their coffees or working on laptops.

While waiting for my long black (intriguingly described on their website as a “well mannered coffee”), I noted the various posters describing different types of screw head or parts of the human skeleton. Enough detail to be a phone distraction but surely there was more physics waiting to be seen in this convivial back room of a coffee house? A blackboard at the end of the bar, offered details of the wifi as well as a quote (slightly adapted) from PG Wodehouse about the benefits to friendship of a shared taste in coffee. On a shelf opposite the blackboard were a number of books including a thick book detailing coffee trading in years gone by. From the fact that the books were stacked horizontally, it would appear that they are not consulted often.

shelf books hats Borough
The lighting made photography difficult but you can see the books (and the hats) on this shelf at The Gentlemen Baristas

Sitting between this juxtaposition of wifi information and old books, caused me to pause. I have heard it said that we “know” more now than we have ever known in the past. That we have access to an enormous amount of knowledge merely through our phones. Is this correct?

On one level it is certainly un-arguable. Ninety percent of the world’s data in 2013 had been generated in the previous two years. If you need to find anything out, a quick duckduckgo (or if you have to, a google) will often lead to websites detailing all sorts of quirky bits of information. If we want to know the radius of the Earth or the size of an espresso grind, we no longer have to remember the answer, nor even really to have a feel for the answer, instead we can almost immediately find webpages that tell us (here and here).

And yet, this answer seems unsatisfactory. While there is an awful lot of information available to us at the tap of a phone, it is questionable whether that information translates to our own knowledge. Although collectively we can understand amazing things such as gravitational waves, individually we may struggle to explain how a toilet works. We need the plumber’s knowledge as much as we need that of the cosmologists. Does it matter who knows? What level of knowledge does someone need to have to say that they ‘know’ something?

coffee long black gentlemen baristas
Taking time to stop and think about what it’s all about. My coffee at The Gentlemen Baristas

Perhaps this appears a very strange cafe-physics review, where is the physics? But part of the rationale behind Bean Thinking is also to slow down and contemplate and it seems that The Gentlemen Baristas offers the perfect environment in which to do so. A café that mixes the new with the old, a space in which the practices of one can inform the other.

So to return the thought train to the area local to the Gentlemen: Writing in the second century AD, the Stoic philosopher Marcus Aurelius wrote

“In death, Alexander of Macedon’s end differed no whit from his stable-boy’s. Either both were received into the same generative principle of the universe, or both alike were dispersed into atoms.“

It is a quote you will probably find very easily via a search engine, or slightly less easily if you read his “Meditations”. But it is perhaps worth pondering, in what sense we ‘know’ what he was meaning. Strolling past the ribbons and messages memorialising the (estimated) 15,000 people who lay buried in the ‘outcast’ graveyard of Crossbones, what about our own attitudes to our modern outcasts? And perhaps more tellingly, our attitudes to those in positions of power or influence?

Perhaps it will take a lifetime of understanding our personal reactions to the poor, the prostitutes, the homeless and the powerful to really know what Aurelius meant. It certainly requires of us that we stop, pause and reflect on the knowledge that we come by. So it is far from obvious that it benefits us to use the wifi password rather than sit, slow down and contemplate. And where better to do so than in a friendly café with good coffee and seats to ponder the moment?

The Gentlemen Baristas can be found at 63 Union St, SE1 1SG

 

 

Categories
General Observations slow Tea

Back of the envelope calculations with coffee

coffee at Watch House
Coffee is generally a great help for reading, but to properly see the clouds in your coffee, it may help if you prepared yourself a brew now.

To read this post it will help if you have a cup of lovely, hot, freshly prepared coffee or tea with you.

Got it? Ok, let’s begin.

A few weeks ago, there was a talk given by Prof. Paul Williams of the University of Reading about the Mathematics of turbulence and climate change. An entertaining talk about the importance of, and the effort of comprehension required to, use mathematics in order to understand climate change. There were several thought provoking comments through the talk that demanded further reflection. But one, almost throw-away comment has been bugging me since. Although I’ve forgotten the exact words, they went along the lines of

Of course mostly we think about the impact of climate change on the weather, after all, we live in the bottom few metres of the atmosphere and so that is what mostly affects us. What I would like to talk about is the effect of climate change on airplane turbulence…

The bottom few metres of the atmosphere? It’s true. The bit we’re most experienced with is just a tiny portion of it. It’s about perspective. To us, it seems the atmosphere is very big, we pump all sorts of exhaust fumes into it and they disappear. We have expressions such as “the sky is the limit” that suggests that the atmosphere is a huge volume of gas. We all know it is not really limitless, but day to day, on our human scale, it seems enormous.

Now the mathematics that Prof Williams uses to calculate the effect of changing temperature and carbon dioxide levels on the jet stream (and consequently the turbulence felt by planes) is way beyond the sort of back of the envelope calculation that we can do with a cup of tea (or coffee). Understandably, to even start to comprehend these mathematical models requires years of training in maths and physics. However, assuming that we are not ourselves atmospheric physicists, there are things that we can do to help us to see our atmosphere in a more realistic way. And this is where your coffee comes in.

Earth from space, South America, coffee
Clouds swirling above our common home. But if the atmosphere is represented by the white mists on the surface of a cup of coffee, what size coffee are we drinking?
The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler

Take a close look at that coffee. Assuming it is not cold brew, hopefully your coffee or tea is still fairly warm. Watch the surface of the coffee. You may start to see movement such as convection in the mug, perhaps you can see a film of oil on the surface. But do you see something else? In very hot tea or coffee, you should be able to see what appear as white mists hovering over the surface of the cup*. It is easy to miss them, but as you watch, cracks suddenly appear in the mists and then there is a re-organisation of them which allows you to start to see them dancing over the surface of your drink*.

These mists are the result of the levitation of many thousands of droplets of water just above the surface of the coffee. I have written about them elsewhere. No one knows quite how they levitate above the surface, but what is known is that they are at a distance of up to 100 μm (0.1mm) from the surface of the coffee.

Let’s construct a scale model of our coffee as the Earth and its atmosphere. These mists can then do a fairly good job of representing the atmosphere with its drifting clouds. So, assuming that the mists are the atmosphere and the coffee is the Earth (on the same scale), what size of coffee would you have to have? Would you be drinking:

a) an espresso

b) a long black

c) a venti

d) a ristretto

Think you know the answer? Let’s work it out with a “back of the envelope” calculation. The easy bit is deciding the radius of the Earth, it’s just under 6400 km, our first problem comes with the estimate of the thickness of the atmosphere. There are several layers in the atmosphere. The one that we are most familiar with, the one closest to us is the troposphere. This extends for the first 16 km above the surface of the Earth (though this varies with latitude, it is only 8 km at the poles). Most of our weather happens in this region and it is also the layer of the atmosphere that planes fly in. Above the troposphere is the stratosphere which extends until about 50 km. Beyond that, things get very rarified indeed though the boundary between our atmosphere and “space” does not happen for several hundred km (indeed, the orbit of the International Space Station is in this bit of our extended atmosphere).

Coffee Corona
Look carefully around the central (reflected) white light. Can you see a rainbow like spreading of the colours? Another manifestation of the white mists on the coffee surface.

As we are mostly concerned with the weather (and airplane flight etc) though, it seems sensible to define the atmosphere height to be the top of the troposphere. After all, most of us will tend to think that the Space Station is in, well, space. This definition is further justified by the fact that about 75% of the mass of the atmosphere is found within this region (the atmosphere gets thinner as you go higher).

What size coffee would we be drinking if the white mists (0.1 mm above the coffee surface) represent the 16 km of the Earth’s atmosphere? We’ll call the coffee height, hc. Our first step is quite easy, we can just use the ratios of the heights to calculate the coffee size:

(height of troposphere)/(radius of Earth) = (white mist height)/(height of coffee)

A bit of rearrangement:

height of coffee = (white mist height)*(radius of Earth)/(height of troposphere)

hc = (0.1) * (6400)/16

hc = 40 mm (4cm)

So for the mists to represent the atmosphere in your coffee, you would need to be drinking a 4cm tall coffee which is probably a smallish long black. I would leave it to you to calculate the coffee size for the atmosphere defined as outer space (beyond the orbit of the International Space Station). But perhaps this perspective gives us another way of looking at our atmosphere. Vast indeed, but fragile too.

*As I was writing this, I had a warm, very drinkable, cup of coffee but it wasn’t steaming and so showed no white mists over the surface. The mists are best seen in freshly made, very hot drinks.

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
General slow Sustainability/environmental Tea

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.

Categories
Coffee review Observations Sustainability/environmental Tea

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.

AMM, LP, NC
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

Categories
Coffee review Observations Science history Sustainability/environmental Tea

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:

 

 

Categories
Coffee review Coffee Roasters Observations slow Sustainability/environmental Tea

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