Category: General

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Allergy friendly cafe with good nut knowledge Coffee review General Observations Science history slow

Feeling the Earth move at Pritchard and Ure, Camden

Egg no pales, coffee, garden centre
Fried egg on cactus leaves. Cactus festival at Pritchard and Ure, Camden

Good coffee in a garden centre, in (nearly) central London, with some physics thrown in? Today’s cafe-physics review seems unlikely on several levels. And then it becomes even more unlikely as you realise that this garden centre and café are also a social enterprise where people “disadvantaged in the labour market” are helped back to employment through working here. All in all, Pritchard and Ure represent a great café to have come by.

Pritchard and Ure can be found in the gallery space of a warehouse type shop that houses the Camden Garden Centre. They serve Workshop coffee together with an extensive selection of alternative drinks and food. As it was lunchtime we enjoyed a spot to eat which gave me an opportunity to try cactus (it was cactus festival at the garden centre). Cactus leaves with re-fried beans and a cactus-water mocktail which came together with a reusable metal straw. The straws were being sold (together with brush straw cleaners) at the counter. After lunch there was a very well made long black (interestingly I was given the choice to have it either as a 6oz or an 8oz, ie. more or less water depending on whether I wanted more or less coffee taste) and resisted (somehow) one of the tempting cakes before having a wander in the garden centre.

equations art work coffee Camden
But are they real?
The equations are the writing on the wall at this cafe.

There are of course many things that you can notice and connect with/to in a garden centre. Plants, biosphere, windows and greenhouse effect, the carbon cycle, the nature of colour, the list could go on. In addition to all of these, to the left of the counter was an art piece on the wall with a list of various equations and comments. Were all these equations real? One thing in particular though in this café/garden centre was particularly mesmeric: the disco ball suspended as a pendulum from a beam across the ceiling. Initially we watched as the ball just glinted reflected light as it slowly swayed to and fro in its oscillation. It took 22 seconds to cover 5 oscillations while I estimated it was 7m in length. Knowing that there is a formula for calculating the period of oscillation I wondered, was my estimation any good?*

During the hour it took us to enjoy lunch, the position of the Sun moved in the sky so that the disco ball started to reflect an array of polka dots of light onto the walls surrounding us (you can see these in the photo). Owing to the combined rotation and oscillation of the ball it wasn’t too easy to measure the time period from these oscillations but about 4 seconds per swing (as I had obtained by merely watching the ball) seemed comfortingly correct. The sun slowly moved round and these dots danced until at some point the sun had moved far enough that the glitter ball was no longer in direct light. But had the Sun moved or the Earth rotated underneath it? We all know the answer (or at least we think we do), but we could use the pendulum to prove it (and to calculate our latitude).

discoball cafe
Disco ball pendulum together with polka dot reflected sunlight. The view from the gallery at Pritchard and Ure.

In various science museums around the world, different Foucault pendulums swing to and fro all day above circular patterns on the floor. The pendulums appear to rotate clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere thereby illustrating the rotating earth underneath the pendulum. The idea is of course that the pendulum continues to swing in the same plane as it was when it was started off but as it is swinging the earth is rotating underneath it giving an apparent rotation of the pendulum swing over the course of a day. If we were at the north (or south) pole, the period of one complete rotation of the pendulum through a circle on the floor would take 24h. As most of us are not at the pole (and Pritchard and Ure certainly is not), the period of complete rotation is lengthened by a corrective factor proportional to the sine of the latitude. Consequently, it is perfectly feasible for us to calculate our latitude by observing a pendulum swinging for long enough in the absence of any breeze.

It is a great piece of evidence for the rotation of the earth (and by implication the fact that the earth is not flat and that the sun is not going round the earth each day). It’s also a very simple (hiding some complicated maths) demonstration that anyone could set up if they wished to carefully do so. So next time you see a disco ball suspended as a pendulum in a café, you would have another reason to start singing “I feel the Earth, move, under my feet…”

Pritchard and Ure is in the gallery of Camden Garden Centre at 2 Barker Drive, St Pancras Way, NW1 0JW

*7 m is an over estimate of the length of the pendulum based on the period of the oscillation. A length of 7m would give a time period of 5.3 seconds, whereas 22 seconds for 5 oscillations is about 4.4 seconds for one giving a calculated length of just under 5m. More details about how to calculate this are here.

Categories
General Home experiments Observations Uncategorized

Exploring the sound of coffee

coffee at Watch House
We’re used to thinking about the aroma of coffee and how it looks, tastes, even how it feels, but what about how it sounds?

How much attention do you pay to your brewing coffee? You know the aroma, how the coffee blooms, you anticipate the taste and feel the warmth of the steam rising off the brew. But what about the sound? Admittedly this depends on your brew method, but what about the sounds as you filled the kettle or prepared a pour over brew? It turns out that the sound of dripping water was the subject of a recent paper in Scientific Reports.

Perhaps take time to watch a tap dripping into a bowl of water. Or maybe use this as an excuse to make another coffee by drip brewing. Each drop falling onto the water (or coffee) below first deforms the water’s surface then, as far as we can see, rebounds up with a splash of a returning drop or droplets. The phenomenon of what causes the characteristic sound of the drip has been investigated for over 100 years but in 1959 it was established using high speed photography that there were four key phases to any drip sound. First, the drop fell on the liquid, then a cavity formed just under the water surface and an air bubble formed just under that. Finally the water surface recoiled leading to a jet of droplets returning from the surface. It has been thought that the sound, that ‘plink’ of the dripping tap, was caused by that trapped air bubble expanding and contracting as it moved through the water under the water’s surface¹. But this has now been confirmed, along with some other interesting, coffee related, observations using ultrafast video recording (30 000 fps for most of the work, 75 000 fps for some of the extra details).

lilies on water, rain on a pond, droplets
Like the sound of falling rain? What causes the dripping sound of a tap?

The authors of this recent paper describe what must have been a fun experiment to do, dripping water into a tank below. You can see some of the videos of the droplet entering the water by scrolling down to the “supplementary information” in the paper. Two microphones (one above, one below the water surface) recorded the sound waves coming from the dripping ‘tap’ simultaneously with the video recording so as to match the timing of the sound with what was happening in the video. The microphone above the water surface largely recorded the same sound waveform as the microphone under the water with one crucial exception. When the authors lined the tank with MDF wood, the underwater sound was ‘damped’ quite quickly, in comparison the bare tank amplified the sound and so the sound wave took much longer to decay. Above the surface however, it didn’t matter whether the tank was lined or not, the sound signal remained the same. This may sound somewhat insignificant, but it means that it cannot be the sound created by the wobbly bubble itself merely propagating through the surface of the water. If this were the case, the microphone above the water surface should show the same signal as the microphone under the water’s surface. Instead the authors suggest that the oscillating bubble causes the surface of the water immediately above it to vibrate (in the bit that is depressed owing to the droplet having fallen into it) and it is this that we hear above the water surface.

science in a V60
Droplets on the surface of a brewing V60 may also form owing to a temperature difference between the dripping drops of coffee and the coffee ‘bath’ underneath.

It is a beautiful set of experiments but how can it link to coffee (apart from with the dripping)? It is in the way that it gives us the chance to experience our coffee with experiments involving more of our senses than just smell, touch and taste. Firstly, the study emphasises the connection between the drop’s diameter and speed to the sound of the drip (the best sounds are for drops between 1mm and 5mm diameter). This suggests that by changing the brewing parameters (whether you prepare your V60 in a jug or a mug or change the filter paper to a metal kone for example), you may hear a change in the sound of the drips. Do you? Secondly, it has been suggested that the sound that is formed is dependent on the temperature difference between the dripping drop and the water bath underneath. A temperature difference between drop and bath would also explain an odd phenomenon I noticed in the V60 a while back. Do you notice a difference in the sound of the brewing coffee when you prepare cold brew pour over as opposed to a standard breakfast brew? Lastly, the authors of this study found that they could suppress the sound of the plink by reducing the surface tension of the water bath that they were dripping water into. In their case they added washing up detergent to the bath. This seems an awful waste of coffee but is it possible that something intrinsic to our coffee brew could do the same thing? Oil will also change the effective surface tension of the water and different coffees (and different roast strengths) change the oil content of the brewed coffee. Have you noticed any change in the sound of the drips of the coffee depending on how dark a roast coffee you use?

It may not make ground-breaking science but it does offer us an opportunity to pay even more attention to our coffee. Does the sound of your coffee reveal the beauty of the physics at work just under its surface?

¹ Some history of the investigation into the dripping sound as well as the experiments can be found in: Phillips et al., “The sound produced by a dripping tap is driven by resonant oscillation of an entrapped air bubble”, Scientific Reports, 8, 9515 (2018)

Categories
General Observations Science history slow

(Im)perfect reflections on coffee

science in a V60
Have you noticed droplets like these dancing on your drip-brewed coffee?

With the recent coffees from Hundred House and Quarter Horse, there have been many opportunities to observe the coffee brewing in the V60 in the mornings. The steam rising from the filter paper, the different ways different coffees bloom and out-gas, the droplets that skim the surface of the coffee and bounce off the walls of the jug and then, of course, the many different effects with light. Watching the dancing droplets (an explanation of why they may dance is here), it is perhaps not immediately obvious that you could form a connection between these, the light reflections and an insight into something you may have noticed while passing through customs. And yet the connection is definitely there.

The connection is formed through a technique called Raman spectroscopy. Named after Chandrasekhara Venkata Raman (1888-1970) who discovered the Raman effect in 1928. As the ‘spectroscopy’ part of the name suggests, it is a technique that offers a way to identify different chemicals, or components, in a substance. For coffee it has been used both as a non-destructive technique to determine the kahweol content of coffee beans and hence help as a test for identifying rogue robusta in arabica beans and as a way of analysing the brewed coffee. But what is it, how does watching a brewing V60 help to understand it and why would you want to know about Raman spectroscopy while travelling through an airport?

beauty in a coffee, coffee beauty
A collection of bubbles on the side of the coffee. What happens when one of the dancing droplets collides with a group of bubbles?

Generally, it helps to begin with coffee and the link is the way in which the droplets bounce off the side of the jug. Brew a coffee and watch them (if you are a non-coffee drinker, you could try dripping hot water through a filter paper into a jug). When one of these droplets hits the wall of the V60 container, it generally bounces back with a trajectory expected for an elastic collision. Given the relative masses of the droplet and the jug, the speed of the reflected droplet is essentially unchanged (even if its direction is reversed). This is similar to what we would normally expect for light. We are used to considering light as waves but because of the wave-particle duality of quantum mechanics it is equally valid to consider light as a stream of particles called photons. As the photons hit a surface and are reflected off, they recoil with the same energy that they initially had, just like the droplets in the coffee. But now look more closely at the dancing droplets. Normally they hit the walls and not each other but just occasionally, they can hit either another droplet or a group of bubbles that have formed on the coffee surface. In these cases, rather than get reflected as before, the droplets transfer some of their energy to the collection of bubbles causing them to move and to wobble. And when the droplet is reflected back, it has a noticeably slower speed (and so we could say a lower kinetic energy) than when it initially danced into its collision. Where is the analogue with light?

When we think about a coffee bean, we probably think about something that is about 1cm oval, brown and quite solid. But if we zoom in, we find that it is made up of a collection of atoms bound together in molecules or, if we are thinking about a solid like salt, in a crystal structure. These atoms act as if they are balls connected by springs and so they wobble as would any structure of masses connected by springs. This is true whether the crystal is diamond or the molecule is caffeine, kahweol, cocaine or semtex (do you see where the customs part is going to come in yet?). Different crystal structures have different atomic arrangements meaning that they are effectively connected by springs of differing strength. If you build a mental model of masses connected with springs, you can see that changing the spring strength will change the vibration energy of the structure. So if now we think about the photons hitting such a structure, while most will bounce off as we saw with the droplet hitting the V60 wall, some photons will trigger a wobble in the crystal structure and bounce off with lower energy. It is a process analogous to the droplet hitting and bouncing off the collection of bubbles on the coffee surface.

Sun-dog, Sun dog
Sun dogs are caused by a different interaction between light and crystals. Rather than the inelastic scattering of Raman spectroscopy, Sun dogs are caused by the refraction of light by hexagonal platelets of ice crystals.

When a photon of light loses energy, it is equivalent to saying that the frequency of the light has changed (which is very closely related to what Albert Einstein got his Nobel prize for in 1921). So a photon that creates a crystal vibration and is scattered off with lower energy has a lower frequency (or longer wavelength) than it had when it first hit the crystal. Importantly, the energy lost by the photon is identical to the energy gained by the vibrating crystal and so by measuring the frequency change of the scattered light we have a way of determining the energy of the crystal (or molecule) vibration. As this energy depends on the way that the atoms are arranged in the crystal or molecule, measuring the frequency shift offers us a way of identifying the chemical under the laser light: kahweol or cocaine.

It is not an easy technique as you can guess from the V60 analogy. Only around one in a million photons incident on a solid will be Raman scattered. You need some pretty decent optics to detect it. Nonetheless, it is a powerful technique because no two chemical structures are the same and so it can be used to identify tiny amounts of smuggled material completely non-destructively. It becomes easier to understand how this elegant technique has become useful for many areas of our lives from customs, through to pharmaceutical development and even into understanding how fuel cells work.

Although it is stretching the analogy too far to say that you can see Raman scattering by watching the droplets on your V60, it is certainly fair to say that watching them allows you the space to think about what is happening on a more microscopic level as your bag is hand-scanned at customs. What do you see when you look closely at your brewing coffee?

 

Categories
Coffee Roasters General Observations

As quick as (a) Quarter Horse

Dog and Hat, Dog & Hat, Hundred House, Quarterhouse coffee
The package from Dog & Hat with Hundred House and Quarter Horse. Is it a particularly contemplative dog with the monocle?

Links with science can be found everywhere, from the café to the coffee roaster. A couple of weeks ago a delivery from Dog and Hat coffee gave me an opportunity to explore the random thought paths that may occur if you stop to ponder your coffee at home rather than in a café. The first coffee, an Ethiopian from Hundred House prompted thoughts on star gazing. But the second coffee, a Mexican from Quarter Horse coffee was equally thought provoking.

Finding time to prepare a V60 and sit with the SCAA “flavor wheel” as a guide, I was rewarded with a sweet, well rounded and perfectly enjoyable brew. I found fruity notes of blueberry and cherry/pineapple though the tasting notes on the packaging say “green grape, toffee and cocoa”. Sadly I missed the cocoa but this offers a good excuse for another slow brew with the coffee wheel at hand.

Thinking about the name of the coffee, I started to consider how you could quarter a horse. Perhaps not a literal horse given the ethical considerations but rather an irregularly shaped volume. How would you divide, into equal portions, an irregularly shaped object such as a horse? It seemed related to the question of finding the shortest route between two locations, how would you calculate the best route to take from A to B? In the 1950s a computer scientist called Edsger Dijkstra (1930-2002) came up with an algorithm to calculate precisely this problem. Originally designed to show the shortest routes between 64 cities in the Netherlands, Dijkstra’s algorithm is now ubiquitous in our lives.

Quarter Horse but how would you
A close up of the Quarter Horse Coffee Bag.

One of the ways in which we have started to rely on such algorithms is in car GPS devices or even on our phones trying to navigate to our destinations. Or at least, many of us do. London taxi drivers however have been shown to have developed a different brain structure from the general population that means that, for them, Dijkstra’s algorithm may be unnecessary. A few years ago, a study compared brain scans of people who had been driving London’s “black cabs” for a number of years to those of us in the general population. A follow-up study followed three sets of people over several years. A control group of people in the general population and a second group of people who studied the “Knowledge”, the navigational test that London taxi drivers have to pass in order to become cabbies. The Knowledge tests the driver’s ability to recall tens of thousands of London’s streets and the prospective cabbie can be asked to navigate between two points anywhere within a 6 mile radius of Charing Cross. Typically it takes years to acquire the Knowledge and not everyone who starts on the Knowledge will pass (the pass rate is only about 50%). This means that this second group of people splits into two groups; those who studied and passed the Knowledge and those who studied but did not pass.

The studies proved illuminating. One particular part of the brain, the posterior hippocampus had a greater volume of “grey matter” (the brain processing cells) in taxi drivers who had studied, and passed, the Knowledge compared with the general population. Moreover, those that had been taxi drivers for longer, showed larger posterior hippocampi. The changes in the brain seemed to lead to the cabbies having not only better navigational ability than the general population but better memory for London based information. The study of the trainees moreover confirmed that these brain changes occurred as a result of learning the Knowledge, showing that our brains are adaptable and still able to develop well into adulthood. While the brains of all the study participants started off similarly, those that went on to pass the Knowledge had a larger posterior hippocampus than those who either didn’t study or studied but hadn’t passed. However it was not all good news for the cabbies. The growth of the posterior hippocampus seemed to occur at the expense of the anterior hippocampus in long serving taxi drivers (but not newly qualified ones). The improved memory for London based information shown by the taxi driving group was also accompanied by a poorer ability to learn other visual information/memory related tasks in those that passed the Knowledge compared to the general population.

taxi and motorcycle, London
London black cab drivers have been shown to have a larger volume of grey matter in the posterior hippocampus area of their brains, demonstrating that our brains remain adaptable well into adulthood.

Perhaps the ability of the cabbies to navigate quickly around London’s streets suggests a second connection with Quarter Horse. A Quarter Horse is a breed of horse that can sprint very quickly over short (less than a quarter of a mile) distances. Which goes faster, the cabbie with the Knowledge or us with our smartphones once we have plugged in our destination? We are reminded of the tale of the hare and the tortoise. But I think a different tale is more appropriate. A tale that in reality was only ever a snippet of an ancient saying but has been developed into tales by thinkers such as Isaiah Berlin and Ronald Dworkin.

“The fox knows many things but the hedgehog one important thing”.

What does this mean? It seems there is a connection here between coffee roasting and taxi drivers, between algorithms and personal development, between coffee science and writing about coffee science. Is this connection really there or is it a meaningless statement that leads us into blind alleys of coffee consideration? It may be time to stretch our brains, grow our grey matter a bit and contemplate. Am I a fox or a hedgehog and where do London cabbies and coffee roasters fit in?

Quarter Horse coffee is online at https://quarterhorsecoffee.com

You can find out more about the coffee subscription site Dog and Hat on their website https://dogandhat.co.uk

You can read more about the taxi driver study on the Wellcome Trust’s press release about it here.

Enjoy your coffee, have fun thinking, grow your grey matter.

 

 

Categories
General Observations slow Sustainability/environmental

Time out

Perhaps an unusual post but there is so much opportunity to stop, think and notice at the moment. Whether it is relaxing in a café with a cold brew or sipping a take-away in a park. There is time to slow down and ponder. Here are three points that have been puzzling recently. What do you think? Perhaps you have other things that you ponder while sitting in a café? Let me know either in the comments section below, on twitter or on Facebook.

oat milk, kone, filtering
Oat milk filtering through the Kone filter – but what does oat milk tell us about Brownian motion, molecular ‘reality’ and the nature of a scientific theory?

Molecules, the atmosphere and oat milk.

On pouring home-made oat milk into a cup of black tea, it is noticeable that a large part of the oat milk is dense and falls to the bottom of the cup (before being stirred by the turbulence in the tea). A similar phenomenon is found in the rarefaction of gases through the height of the atmosphere and in the distribution of dye in water paint. This latter effect was used to establish the existence of molecules back in 1910. The idea that Brownian motion was caused by molecules had been problematic because there was no way to see molecules in a liquid producing the Brownian motion. The theory linking the two was only developed properly in the early twentieth century. What makes a scientific theory? Is it legitimate to postulate something that cannot currently be observed experimentally?

Packing value

Why does roasted coffee often come in plastic packaging that is unrecyclable and not very reusable? What could prompt a move to a more circular economy. Would it be possible to recycle plastic bottles into coffee ‘boxes’ with an air valve at the bottle top (see pictures). This would increase the recyclability without seeming to affect the taste of the coffee?

bottle, coffee bottle, coffee box, coffee packaging
An idea for a circular economy suitable coffee packaging? Recycled plastic bottles as airtight coffee containers.

Related to that, what are your coffee values? Do you favour taste and aroma, traceability, sustainability? Does the packaging that your coffee arrives in feature? Which of these is more important to you? Does the way you drink coffee reflect this?

Footfall past a café

How many people are walking past the café you are sitting in each minute? How many does that translate to per day (accounting for differences in day/night footfall)? Assuming the paving stones remain the same, how long would it be until the successive footprints of all these people caused erosion of the pavement surface? What are the implications of this for the geological features near you?

Whatever you think about in a café or while drinking a coffee, enjoy your time taken out to think. Perhaps you will notice something (or realise something) very interesting or noteworthy and if you have any thoughts on any of the above do let me know either in the comments, on Twitter or on Facebook.

 

Categories
Coffee cup science General Observations Science history slow

Drip coffee

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

1. The Coffee Grinder:

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

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

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

2. Rinsing the filter paper:

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

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

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

3. Bloom:

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

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

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

4. Percolation:

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

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

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

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

5. In the mug:

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

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

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

 

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

Categories
General

New findings in arabica…

coffee and Caffeine at Sharps
Things are not always as they seem. Speciality coffee helped scientists to develop a method for detecting fraud in coffee sold as 100% arabica. But how?

…or why adding chloroform to coffee can be a good idea.

Perhaps you remember a story from a few weeks ago that up to one in ten bags of “100% arabica ground coffee” on sale contained “substantial” amounts of robusta coffee?

The story suggested that, perhaps unsurprisingly, fraud is quite common in the coffee industry with cheaper robusta being substituted for the more coveted arabica in a substantial number of packs of pre-ground coffee. But how did the authors of the paper measure this and why did speciality coffee play an important role in the study?

The study used ¹H NMR (nuclear magnetic resonance) spectroscopy to measure the concentration of a particular “finger print” chemical known as 16-O-methylcafestol or 16OMC for short. This aspect of the study was not new. The compound 16OMC was known to be found in robusta (Coffea canephora) while it had not been previously found in arabica (Coffea arabica) beans. It had therefore been considered an excellent marker chemical as to whether a sample of arabica beans had been contaminated with a cheaper robusta.

Previous studies had also used NMR to check for 16OMC but in those studies, they had used a conventional NMR machine and the data collection and analysis had taken a long time. It was also expensive, which meant that it had shortcomings as a technique for quickly investigating fraud within the industry.

The difference in this new report was that firstly, the scientific team investigating the coffees used an NMR machine that fits on a lab table-top: portable, commercially available, and so a possible tool to quickly detect fraud. But secondly, the authors ‘double brewed’ the coffee using chloroform. They first dissolved the ground coffee in chloroform which was filtered using filter paper and then dried and re-dissolved in fresh chloroform to produce a super-concentrated coffee-chloroform brew. This super-concentrated chloroform coffee enabled the authors to obtain a much better signal to noise ratio on the data and so improve the reliability of the detection of any rogue robusta.

neon sign, light emission
NMR uses the light emitted/absorbed from energy levels in atomic nuclei. An analogous effect causes light to be emitted/absorbed by energy levels in electrons. An effect you will have seen on many a high street in these neon signs.

But why could this group use a portable NMR machine whereas previous studies required far more expensive and bulky pieces of kit? NMR works because, just like electrons, atomic nuclei (protons, neutrons) have a property called spin. This spin gives rise to a magnetic moment which means that when you apply an external magnetic field to the sample, some nuclear magnetic moments are parallel, some perpendicular and some antiparallel to the applied field. Consequently, the different moments have different energies which, being on the atomic scale, are quantised meaning that they form discrete levels. This difference in discrete energy levels means that the nuclei will emit/absorb energy (i.e. light) at specific frequencies, which we can calculate. Moreover, the frequency is directly proportional to the applied magnetic field (because the larger the field, the bigger the energy difference between the levels): increase the field applied and you increase the resonance frequency of the nuclei.

But there is one more detail. The nuclei do not exist in isolation, they are affected by the chemical environment that they are in. So a proton in 16OMC will respond slightly differently to an applied magnetic field than a proton in say, water. Rather than be at the resonance frequency we have calculated, the frequency will shift as a consequence of the chemical environment surrounding the proton. As you may expect, this shift is small, but it is significant. It is partly because of this effect that NMR is such a fantastic tool for chemical analysis¹. Typically, the shift is of the order of parts-per-million from the non-shifted resonance frequency. So, in the coffee study discussed here, the interesting “fingerprint” peak is at 3.16ppm. Given that the machine was operating at 60MHz, this means that the scientists were looking at shifts of 189.6 Hz to the non-shifted resonance signal.

It seems sensible that the bigger the shift, the easier it would be to resolve these chemical fingerprints. To get the larger shift requires using a higher operating frequency which is exactly what more traditional NMR spectrometers used. However, given what we know about nuclear energy levels (above), a large energy level split (i.e. high operating frequency) requires a large magnetic field, and large magnetic fields require expensive and bulky pieces of kit. To put this all in perspective, the magnetic field of the Earth at its surface is (variable but around) 0.00005T. A fridge magnet has a field about 0.01T. Commercially available, small rare earth magnets can have fields about 0.3T. A 60 MHz NMR spectrometer looking at ¹H nuclei would need 1.5 T, higher frequency NMR spectroscopy would require still higher fields. The sort of magnetic fields that would be needed for the more traditional NMR technique therefore require large superconducting magnets which are bulky and require expensive cooling. Being able to use a lower frequency for such sensitive measurements is a significant engineering, as well as scientific, achievement.

Look carefully next time you add milk to your coffee. The ‘milk rings’ that can form offer an historical connection to understanding energy transitions in atoms as you can read about here.

So where does the speciality coffee come in? Well, it turns out that by measuring speciality coffee the team uncovered a surprising result: 16OMC was present in arabica beans too.

In order to calibrate the technique, the study had obtained traceable coffees known to be purely arabica or purely robusta. Some of these coffees were sourced from Ethiopia and were grown far away from any possible robusta hybridisation. They were speciality coffee. When the team measured these samples with their concentrated coffee extraction technique, they found that these too contained a small peak at 3.16ppm. Previous studies had missed this because it is such a small quantity. So, as well as determining a technique to quickly establish whether a given coffee on sale is fraudulently being marketed as 100% arabica, this new technique enabled the scientific community to learn something new about arabica. The coffee is more chemically rich than was realised.

If you would like to read more about the study, the authors have summarised it here as well as publishing the paper as open access (so you can download it for free) here. A summary of the results by the company that made the spectrometer can be found here. You can learn more about NMR spectroscopy online, or by obtaining a book from the library such as:

¹ Nuclear Magnetic Resonance Spectroscopy, Robin K Harris, Longman, (1983,1986)

Categories
General Observations Science history Sustainability/environmental Tea

Why politicians should drink loose leaf tea

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

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

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

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

A schematic of the tea brewing process

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

Volume of water displaced = volume of mesh ball

πd²h = (4/3)πr³

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

h = 4r³/(3d²)

h = 0.87 cm

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

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

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

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

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

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

Reflections on a cup of tea.

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

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

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

Categories
Coffee cup science General Observations

Strumming along on a coffee

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

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

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

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

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

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

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

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

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

Categories
Allergy friendly Coffee review General Observations

Getting to the point at Sharps

coffee and Caffeine at Sharps
Coffee at Sharps Coffee Bar.

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

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

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

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

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

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

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

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