Category: General

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Coffee cup science Coffee review General Science history

Is it a third?…. Treelogy, Paddington

Outside Treelogy on Eastbourne Terrace, Paddington. The topiary could suggest a series of strontium atoms lining up on top of each other.

Good coffee near a mainline train station? It’s often difficult to find a good spot to take time to enjoy a coffee if you only have about 30 minutes (or less) before your train. Fortunately for coffee lovers in London, both Kings Cross (/St Pancras) and Paddington have several very good speciality coffee places nearby. There’s the cafe in the Pilgrm hotel just across the road from Paddington on London St, but Treelogy is perhaps even closer, directly opposite the buildings that house the new Elizabeth Line on Eastbourne Terrace.

Treelogy appears to have opened in April 2023. There does not seem to be much information online about it apart from Trip Advisor reviews so, having approximately 50 minutes before we needed to catch a train, we decided to stop at this new cafe. The interior is very modern and open. The counter is in front of you on the left as you enter with plenty of seats in the window and along the wall, as befits a cafe that is also close to a station. The style of some of the seats in the cafe and the fact that it is going to attract people who are about to embark on journeys (or have just come off a journey) means that there are elements here that could remind you of the scene in Edward Hopper’s Nighthawks. The coffee appears to be roasted by Treelogy themselves. There was a wide selection of pastries and breakfast bagels arranged on the counter and so we ordered two coffees to stay, and a bagel for the train.

The “Real Time” clock by Maarten Baas in Paddington. How much do they pay that man to be there all day?

We intended to sit on the bench just outside the cafe with our coffees but nonetheless we were offered our coffee in ceramic cups which was a nice touch. Inside, there was plenty to notice: circular lights on the wall leading to the back of the cafe which resembled ship lighting. A coffee dictionary book (and a book by Martin Wolf) that could offer a good read or a thought train on the physics of finance and the (Brownian-motion) links to coffee. The travellers with their roller bags going in and out of the cafe, who are they and where are they going? Yet, moving outside and settling down, the oat milk flat white and long black were both a very enjoyable way to spend time with a coffee.

As we were ‘spending the time’ with the coffees, the hands of the “REAL TIME, Paddington” Maarten Baas clock were being re-drawn every minute. Installed back in 2021, this clock appears as if the time is being painted onto the clock face by a man who seems trapped inside the clock. Each minute he erases the minute hand before redrawing it into its new correct position. Literally marking the minutes before our train is due.

For a physicist waiting for a train, an immediate thought may occur: what does ‘Real time’ mean? Admittedly, this question fades into the background again as the man wanders around, points at something on the clock, adjusts his position and then gets ready to move the clock hand again. The art is distracting from the question. But the question keeps surfacing: what is a minute, what is a second, is time absolute? There is perhaps a diversion that could be made here to a more philosophical question about the nature of time and our perception of it but we only had one long black and one flat white, the physics may take longer than that anyway!

A closer view of the man in the clock as he is erasing the minute hand of the clock. The colour bands on the clock face are not really there but are the result of the projected video onto the clock face and the way that the camera images that.

The physics bit remains because you may remember hearing about Einstein’s twin paradox, a thought experiment arising out of an aspect of his theory of Special Relativity. Relativity in general in physics refers to moving ‘frames of reference’, a classic case is that of a person on a train relative to a person on a station platform. For the person on the train, they are stationary, with respect to the train carriage. If they bounce a ball on the floor of a carriage, the ball bounces straight back up at them. They do not experience themselves moving (apart from when the train is accelerating or braking) and instead to them it appears that the person standing on the station platform is moving, backwards at the speed of the train.

Ordinarily our brains will process this and recognise that it is we who are on the train that are moving and we identify the ‘rest frame’ (the frame that is not moving) with the station platform. However we may all have experienced the sensation when on a train in a station next to another train. As the guard whistle blows the train moves but we cannot immediately tell whether it is our train that moves or the train next to us. This is the essence of relativity: all reference frames move relative to each other. The frame that is genuinely at rest is the one we define so (even the station platform is moving relative to the Sun, we just don’t notice this movement of the Earth at all).

Einstein’s theory of special relativity arises out of the special case when one of the moving frames is travelling at close to the speed of light, c. As the speed of light in a vacuum is constant, what would happen if someone travelling in a car at a speed just less than c looked at themselves in the rear view mirror? Einstein’s answer was that they would see themselves as anyone would because, relative to the reference frame of the car, the speed of light is still constant, it is still c. However an observer outside the car looking at the car and the person looking at themselves in the mirror also measures the speed of light as c, not nearly 2c (the speed of light plus the speed of the car). The speed of light in a vacuum is constant!

The explanation for this apparent problem is that our perception of time (and of distance) is not the same at different speeds. A person moving at a fast speed (relative to a person defined at rest) would have a wrist watch that was slow, relative to the person at rest – moving clocks go slow. This is the origin of the twin paradox which is that if one of a pair of twins travels away from Earth at close to the speed of light and returns, they will return younger than their twin who remained ‘at rest’ on Earth (but not relative to the twin who travelled who considered themselves at rest too so their earth bound twin should, to them, be younger).

Topiary at the entrance to Treelogy. The atomic clocks used in the study described in the text used super cold strontium ions positioned just above each other.

The solution of the twin paradox comes with Einstein’s second theory of relativity: General relativity.  Special relativity only concerns the case when different frames of reference move at constant relative velocity to each other. General relativity extends the case to accelerating frames and gravity. In order to meet again, the twin in the space ship had to turn around (decelerate and accelerate again). This changes the situation from the case expected purely from special relativity. There is a lot of experimental evidence for both special and general relativity, but recently one test of general relativity tested the idea on a very small scale.

The theory of general relativity postulates that it is not just moving clocks that go slower. Clocks in strong gravitational fields will also run more slowly. The extreme example of this would be the event horizon of a black hole, but even on Earth, a clock closer to the centre of the Earth will tick more slowly than one that is further away. Remarkably this prediction has recently been verified using extremely accurate clocks by measuring time using atoms spaced just 1 mm apart. The ‘clocks’ of the atoms 1 mm lower moved slower than the clocks of the atoms 1 mm above. Absolutely astonishing! And yet absolutely expected because one remarkable and weird feature about physics is that it seems to be universally applicable: what happens at the event horizon of a black hole shares the same physics as what happens in conditions far less extreme, conditions found in a coffee cup.

The Real Time clock is 7.8m above the pavement where I was enjoying my coffee. These experiments mean that I can be confident that the clock is going very slightly faster than the time I experience sitting on the bench. However, I shouldn’t use this thought to justify enjoying my coffee much longer and thereby miss the train! It seems that our trains aren’t quite so precise as the deviations implied by the theory of General Relativity. It is still necessary to get through the barriers with several minutes to spare. Treelogy, and the clock man, will have to wait for a return visit.

Treelogy is at 48 Eastbourne Terrace, W2 6LG

More about Einstein’s theories of relativity can be found here or in a good book in a library.

Categories
Coffee review General Observations Science history slow

By Jove, it’s Ditto, Kuala Lumpur

Ditto, KL
A sign above the five-foot-way alerts you to the cafe above. “Ditto” in Bukit Damansara, KL.

“Ditto” it turns out can represent a number of meanings. No longer merely a shorthand for saying ‘the same thing’, it is now a Pokemon character and a fantastically chilled cafe on the first floor of a row of shops on Jalan Kasah in Kuala Lumpur. Ditto, the cafe, moved to the Damansara site in October 2022 having previously been a pop-up style cafe in Petaling Jaya.

A small sign hanging from the ceiling of the ‘5 foot way’ advertises that you can find the cafe up a set of unassuming looking stairs between two shops. Climbing the stairs, you do not expect the door at the top to open into such a quiet, ambient and welcoming space. Opening the door to the air conditioned cafe, the counter is diagonally left. A couple of circular tables are on your immediate left while a table full of coffee beans and coffee related books lies to your right. We first arrived very shortly after the cafe opened at 10am and so we had the place to ourselves. The coffee menu is extensive. Coffees from roasters around the world are available to try either as espresso based drinks or V60. Obviously I went for the V60.

interior cafe, Ditto, KL
Inside Ditto. Potted plants are dotted around the inside of the cafe while you could also choose to sit at a seat looking out of the window.

The first coffee I tried was a Colombian from Netherlands based roaster Manhattan Coffee Roasters. Very well made and interesting as a coffee, I was convinced that this was somewhere I could enjoy a geisha on my second visit. Almost tea-like, this geisha cup was a bit subtle for me although I could appreciate the different flavour notes coming out. Other drinks were also available (Kombucha, chocolate based drinks etc), though the focus is very much on the coffee. With such an extensive coffee menu, there are many more coffees than I would be able to sample before returning to London. It’s definitely a place that you can return to again and again while still finding something new.

The coffee arrived in a jug together with a couple of cups and a card reminding me of the tasting notes of the coffee I had chosen (though the print was too small for me to be able to read without glasses!). The jug showed evidence of condensation around the rim reminiscent of the physics of dew and the greenhouse effect. Physics was apparent too in the title of a book on display with the retail coffee beans: “The physics of filter coffee”. Flicking through the book, it was clear that this was a very comprehensive guide to the physics of how to brew good coffee. Should this go on the Christmas book wish-list? Elsewhere books and magazines offered plenty to think about on issues about the architecture of cafes or the types of coffee to be found around the world.

Table that resembles the surface of Jupiter
One of the circular marble tables in Ditto. The way the rock has formed suggests a view of the planet Jupiter. An overhead light has formed a triangle reflected from the table’s surface.

This is definitely a space in which you can sit, enjoy a well made coffee and contemplate whatever thought train your mind decides to take you on. And yet, I would defy anyone to look at the circular table and not think “Jupiter”.

The tables are made of marble, the layers that made the first set of sedimentary rock (that is the basis of the metamorphic marble) are clearly visible as horizontal lines cutting through the entire circle of the table. They are the stripes of Jupiter. The colour too is similar to the images that we have seen either from telescopes or from the satellites that have flown by Jupiter since Pioneer 10 first flew by in 1973. Looking at the coffee on the table, we could find ourselves echoing the quote from one of the scientists involved in the latest fly-by probe (called “Juno”) describing the “incredibly beautiful” planet as “…an artist’s palette… almost like a van Gogh painting.”

We have been aware of the weather patterns that form these stripes, and in particular the “Great Red Spot” for hundreds of years. Yet it turns out that we still have a lot to learn about them. For example, the clouds in the band at the equator are moving eastwards, the stripes immediately north or south of those are moving westwards and then the wind pattern changes again with the latitude, eastward and westward as each stripe is formed. Then, every 4-9 years, depending on the latitude, the colours of the stripes change, a change that can be associated with brief but disruptive changes to the weather patterns. Shape shifting rather like the Pokemon character “Ditto” that is the inspiration for the name of the cafe.

Cassini portrait of Jupiter, copyright with NASA
Not a table! A view of the planet Jupiter taken by the Cassini mission in 2000. Photograph shared according to NASA image use policy.

Recent results from the Juno mission have revealed one of the things that could be underlying this shifting weather pattern: oscillations in the planet’s magnetic field. Juno, which has been measuring the magnetic field of Jupiter since it first started orbiting it in 2016 has revealed that the magnetic field strength is oscillating on a similar time scale to the changing patterns observed in the weather. Could this somehow be driving the weather that we see? Juno has also shown clearly a new feature in the magnetic field where the field lines are particularly intense, called the “Great Blue Spot”, this feature too may be oscillating spatially over the surface of the planet rather than rotating around it as the Great Red Spot seems to do.

Juno, the satellite, was named after Juno the Roman goddess who is the female counterpart of the Roman god Jupiter. Considered in some ways to be patron of women, there seems another link here to this women-run cafe. We may be tempted to think that we have fully explored this physics connection that has looped back to the space in which we are enjoying our drink. But there is one more connection between Jupiter and this cafe. The first probe to fly by Jupiter was Pioneer 10 in 1973. It was then that we first saw images of this planet close up. The first time we saw these stripes in such detail. The satellite was launched by NASA in 1972, the same year that this area of KL was being developed. Perhaps you could say 1972 was the same year this area of KL was ‘launched’. There truly are links and connections wherever we care to find them. When we slow down with our coffee and contemplate our surroundings while open to going on a thought-journey, we never know where we may end up.

Ditto Speciality Coffee Bar is at 128A Jalan Kasah, Bukit Damansara, 50490, Kuala Lumpur, Malaysia.

Categories
General Observations Science history

Worth dying for? A glassy tale.

Pureover, pureover in packaging
The PureOver in its packaging. Glass and cardboard, no plastic in sight. The PureOver is designed to brew filter coffee but without the need for filters.

It was the middle of the afternoon and we had friends over, friends who wanted coffee but, “only a small cup”. What were our options? We could make a V60 which would be a bit of a waste or an Aeropress which, while great for a small coffee for one person, is pushing it a bit for two people (even if one only did want a “tiny” bit). It was time to dust off the PureOver. This all-glass brewing device makes approximately 2-300ml of filter coffee entirely without the need for any filters. It is my go-to brewing device for a decent sized cup of coffee for one person or a “small” and “tiny” cup for two people. The PureOver was designed by a group of glass-blowers in Portland (USA) who wanted to be able to brew drip coffee without waste filters. It is now made commercially in China and shipped around the world for people who want to brew likewise.

The PureOver works by creating a filter bed out of the coffee grounds themselves. The design of the brewer ensures that the coffee is fairly well packed at the bottom of the pot allowing the water to filter through but without (much) sediment falling into the cup underneath the brewer. I have written about the PureOver, including a “how-to” brew guide, elsewhere. The PureOver works well, brews a lovely cup of coffee and looks great. Which shows how well the hard bits have been hidden; much of life is an art where the performance hides the work behind it. In some parts of our lives this is obvious. Acting, for example needs to appear natural and not reveal the work that has gone into developing the character the actor plays. I think the same is true of teaching/tutoring* physics. Such teaching should be a seamless conversation and discussion between students and tutor, in some way hiding the work that has gone into the preparation of that conversation. The PureOver is exactly the same. There is a lot of physics that is within the filtration bed and the diffuser design, but the bit that I would like to focus on is the bit that we look straight through without noticing. It is the role of the glass.

The diffuser sitting on top of the Pour Over coffee brewer. The holes are to ensure that the water falls evenly and slowly onto the grounds below.

The PureOver is made of borosilicate glass which was first invented by Otto Schott (1851-1935) in the nineteenth century. It is made by combining silica with boron trioxide (B2O3). One of the things that makes borosilicate glass so special is that it has a really low thermal expansion coefficient. From a practical point of view, and why this matters in the PureOver, is that it means that it is not likely to shatter as you add boiling (or just off the boil) water to the glass. You can brew coffee without the brewer breaking. We just want to be able to use the coffee brewer without thinking too much about it, using borosilicate glass allows us to do this.

If we do think about it a bit more though, the thermal expansion coefficient reveals something to us of the atomic structure of the material. All atoms in a solid vibrate, as they gain more energy (in the form of heat), the amplitude of that vibration increases, so they vibrate more. But atoms within a solid structure do not vibrate symmetrically. It is much harder (it takes more energy) to push them together than it is to pull them apart. This means that as the temperature increases they can vibrate ever so slightly further away from each other than they can towards each other and the net effect is that the atoms get further away from each other and the material expands**. The thermal expansion coefficient can therefore reveal clues as to the internal energies and structure of different solids. Applying this to borosilicate glass itself gets problematic as glass is a disordered rather than a well defined crystalline structure, but the principle is there.

We often come across borosilicate glass in “Pyrex” glassware, although since the 1930s/40s “pyrex” has been made of soda-lime glass rather than the original borosilicate. Nonetheless, it is a story involving pyrex that provides the title of this post. In 1953, a chemist working at Corning Glass Works in New York State, got a surprise as he dropped a piece of experimental glass he had been working on when he removed it from the furnace. Donald Stookey had serendipitously discovered “Pyroceram” a type of glass that was not only extremely heat resistant, it had also bounced, not smashed, when he dropped it. However despite being commercialised for other specialist products, Pyroceram was not, initially, used for kitchen items because the parent company Corning, also sold Pyrex and did not want any competition with that other successful product. So more research was done on Pyroceram which did lead to new commercial opportunities, including one that we probably have with us right now. Because the toughness aspect of the Pyroceram type glasses developed into what we now know as “Gorilla Glass” which is probably the screen on your smartphone.

Perhaps not quite how the designers imagined brewing a coffee. I brew the PureOver into my V60 jug in order to avoid the few grains of coffee that get through the filter from going into the final mug of coffee.

You can read more about the story of this discovery (and how it got used in the Apple iPhones) in the June 2022 issue of Physics World. Stookey went on to be awarded the US National Medal of Technology by President Reagan and of course, Gorilla Glass is now found in many products. So you would be forgiven for thinking that this marvel of technology is a recent phenomenon as an unbreakable glass would surely have been highly valued if it had been invented earlier. The story of a Roman craftsman may provide a contrasting pause for thought. As described by Petronius (quoted in the book “The Alchemy of Glass”***):

“There was once a workman who made a glass cup that was un-breakable. So he was given an audience of the Emperor with his invention; he made Caesar give it back to him and then threw it on the floor. Caesar was as frightened as he could be. But the man picked up his cup from the ground: it was dented like a bronze bowl; then he took a little hammer out of his pocket and made the cup quite sound again without any trouble. After doing this he thought he had himself seated on the throne of Jupiter especially when Caesar said to him: ‘Does anyone else know how to blow glass like this?’ Just see what happened. He said not, and then Caesar had him beheaded. Why? Because if his invention were generally known we should treat gold as dirt.“

*I am careful to keep my comment here to tutoring as that is what I have most experience of. If you teach larger groups or in a school, please do let me know what you think, whether this applies to teaching too, in the comments.

**See for example “Thermal Physics, CJ Adkins, Hodder and Stoughton, 1976

*** “The Alchemy of Glass; counterfeit, imitation, and transmutation in Ancient Glassmaking”, Marco Beretta, Watson Publishing International, 2009

For more about glass including the question of how transparent glass is, please see this post by Bobreflected.

Categories
General Observations Science history Sustainability/environmental

Reflections, deviations…. coffee

The reflections from the surface of a cup of coffee of a building opposite a central London cafe. Towards the edges of the cup, the coffee bends upwards, revealed by the lines bending that would be expected to be straight.

A “flat white” could be ordered from many a coffee shop. A “flat black” may be a physical impossibility. We can realise this by gazing contemplatively, or perhaps even longingly, at a long black while it cools. Notice that the surface of the coffee is ever so slightly curved. Leaving aside the white mists that you may see skipping across the coffee surface, the coffee is flat in the middle of the cup but rises towards the edges. If you have noticed this, it is most probable that you did so because of the different way the light is reflected over the surface of the coffee. It is most obvious if you can arrange the reflections on the cup to reflect something supposedly straight: a window frame or a beam of strip light for example. The reflection is fairly clear and fairly straight until about 5mm from the edge of the cup where suddenly it bends. You can see an example of this in the photograph on the right.

The reason for the curvature is of course surface tension, which is the same effect that makes droplets form into shapes that are close to spheres. First investigated by Agnes Pockels and Lord Rayleigh in the nineteenth century, surface tension is caused by the fact that molecules at the surface of the water (in the coffee) will feel a net attraction to the other molecules within the water. There being no molecules of water above the surface of the cup, the surface molecules are pulled back towards the liquid in the cup. At the sides of the cup something slightly different is happening. There, the molecules in the water will be pulled back towards the liquid but will also experience the uncompensated attraction (or repulsion) from the atoms in the mug material. Exactly analogous to surface tension, but in the solid, the interaction of the surface energy of the mug with the surface tension of the liquid will pull the liquid into different shapes. It is for this reason that highly waterproof surfaces, such as fresh oak leaves, will form spherical drops of water, but wettable surfaces, such as an oak leaf in autumn, will accumulate flatter, less spherical droplets on the surface.

coffee, red wine, wet coffee stain, coffee spill, coffee ring
The interaction between the surface tension of the water and the surface energy of the solid surface it sits on determines the shape of the droplet. These drops of coffee and wine on paper were for an experiment about coffee ring formation. The droplets are: Drops of coffee (left), soapy coffee (middle) and red wine (right)

We see the effects of surface tension too when a bubble, or a small bit of dust, sits on the surface of the coffee. Again, looking at the light reflections, we see how the coffee, or tea, bends near the floating object showing how un-flat the surface really is. Bubbles are usually large enough that we can see them directly. In the photograph on this page for example, you can clearly see the reflections from the surface of the bubble together with the bent reflections of light from the surface of the liquid. However in the case of the dust, sometimes the dust is small enough that the reason that we see it is because of the change of the path of the light reflected from the surface. For a similar reason, the insects that skate the surface of a pond are visible because of the light patterns they make rather than their intrinsic visibility. Each time we are using the deviation of the light from its expected path in order to deduce the presence and shape of an object hidden to our view.

A similar deviation of the expected path of light is seen in the phenomenon of gravitational lensing which has been used to infer the presence of black holes. Such a deviation even provided experimental evidence for Einstein’s (then) recently proposed General Theory of Relativity, just over 100 years ago on May 29, 1919. The idea that light had weight and would be deflected by a gravitational field was not new, indeed, even the Newtonian model of gravity predicted that light would be deflected as it went past a massive object*. The question was how much and, as an important secondary question, how to measure it. As Arthur Eddington later described in his book “Space, Time and Gravitation”*, according to Newton, any object thrown horizontally on the Earth’s surface would fall 16 feet (in his use of units, 4.88 m in SI) in one second. The same was true for light. However with Einstein’s theory, the predicted deflection of light was 32′ (9.75m). The difficulty for the experimentalist is that in the same second, the light would have travelled nearly 300 000 km. Detecting such a small deflection over such a large distance would be difficult, harder than seeing a grain of dust on the coffee surface. Which is where the light deflection comes in. Because if you watch as the light from a distant star travels past a massive and fairly large object, such as the Sun, you should be able to discern the small, but significant deflection. And on May 29th 1919 a total solar eclipse (which thereby blocked the extra and interfering light from the Sun) offered a perfect opportunity for Eddington and an expedition sent by the Royal Society and Royal Astronomical Society (to Brazil and West Africa) to attempt to measure such a deflection.

tea reflections, bubble on tea, surface tension, light bending
The way that light reflects off a surface of a cup of tea in this case, reveals the curvature of the tea surface. In this case the curvature is clearly due to the bubble in the centre. Sometimes you can see distortions on the surface caused by bits of dust which are difficult to see on their own.

Although the deflection was significant, working with large telescopes and photographic plates, the magnitude of the deflection of the light that they were looking for was still only 1/1500 of an inch on the photographic plate. Two groups at two different locations took multiple photographs of the eclipsed Sun and the stars around it in order to measure the position of the stars as seen behind the Sun and then compare that to the position of the stars when they had been photographed earlier in the year without the Sun between them and the Earth. Eddington describes the experiment:

“There is a marvellous spectacle above, and, as the photographs afterwards revealed, a wonderful prominence-flame is poised a hundred thousand miles above the surface of the sun. We have no time to snatch a glance at it. We are conscious only of the weird half-light of the landscape and the hush of nature, broken by the calls of the observers, and beat of the metronome ticking out the 302 seconds of totality.”

Finally after developing and comparing the images back in London, the team confirmed a deflection of 1″.98 +/- 0″.12 (Brazil) and 1″.61 +/- 0″.30 (W. Africa) for the stars closest to the Sun (NB. 1″ indicates 1 second of arc). Einstein’s theory had predicted a deflection of 1″.74, Newton’s theory had predicted 0″.87. The results of the light deflection were far more in agreement with Einstein’s new theory of General Relativity than with the classical Newtonian model.

The ‘wobble’ of a few of the stars on the photographic plates had confirmed a prediction of the theory of Relativity. Which could lead to the question: What do you see, or not, as the light dances off of your coffee?

*”Space, Time and Gravitation: an outline of the General Theory of Relativity”, Sir Arthur Eddington, Cambridge University Press, first printed 1920, 1968 edition.

Categories
Coffee review General Observations Science history slow Sustainability/environmental

Me time at Hétam

Iced chocolate at Hetam. The chocolate is sourced from Indonesia. At the time of visiting, drinks were only available in take-away cups, hopefully this will change as the cafe becomes more established and the pandemic restrictions that were in place at the time of visiting are eased.

In 2021, a new cafe opened up in Bangsar, Kuala Lumpur, Malaysia. Called Hetam, it is a cafe almost designed for the post-pandemic, Instagram age that we find ourselves living in. At the time of visiting, there was no ‘inside’ to this cafe, everything was outdoors: customer seating was outdoors, even the ordering and the counter were outdoors. Umbrellas provided some protection from the downpours as well as the hot sun that you can get in Kuala Lumpur. You order at a counter which is on the right of what looks like it used to be an ordinary house on the service road parallel to Jalan Maarof (between Lorong Maarof 5 and 6). The house is now the headquarters for the online section of Hetam and is where they package up their online sales. There are a small selection of edibles to the right of the cash till but the main focus is on the coffee, tea and chocolate. The coffee is roasted by Hetam. At the time of visiting, the coffee was a choice of either an Indonesian natural or a Brazilian washed coffee and available as any of the usual espresso based drinks. I found that the Indonesian worked better in the espresso but that when brewing with an Aeropress at home, the Brazilian came out on top. Various Japanese Genmaicha and Hojicha teas were available but each time, I focussed on the coffee. The chocolate also is sourced by Hetam mostly from Indonesia and is well worth trying.

The staff at Hetam were very friendly and knowledgable. When we first arrived, they talked us through checking-in using the MySejahtera (Covid-19) app when we didn’t have data on our phones (as of 1 May 2022, hopefully MySejahtera will be something you don’t need to use any more). This led to a conversation on the origins of Hetam and their hopes for the cafe for the future. We ordered a hot long black and an iced chocolate and took a seat in the side/back garden of the house. The space seems almost made for Instagram. Infact, perhaps it was. Carefully arranged bamboo adorns the sides of the garden. White pebbles form the floor while strategically placed bits of tree are scattered throughout the space leading to a certain, specific aesthetic. The first time that we enjoyed a coffee at Hetam, another couple were already there. As we sipped our coffee, the couple split into model and photographer and, with what appeared to be a well practised routine of recognisable Instagram poses, set about photographing each other against different backdrops. In subsequent visits, we enjoyed the place to ourselves.

The counter at Hetam is helpfully under a shelter, the other seats are mostly under umbrellas. You get a glimpse here of the ‘insta-ability’ of the cafe. Random dead logs form a counterpoint feature to the white pebbles of the seating area.

The name “Instagram” is apparently a derivation of a combination of “instant camera” and “telegram”. The idea being that a message is sent through an image acquired by an instant camera. The word camera is in turn derived (from both Latin and Greek) from the word for a chamber or a vault. Presumably this was a suitable name for the camera because early photographs were taken through a pin hole into a vaulted dark chamber. Which brings us into the realm of physics as the photograph is literally that which is written by light. Film cameras and even the old Polaroid instant cameras, could still, legitimately be said to take photographs. The light would fall onto a chemically active film and change it based on the exposure levels so that the image was written directly by the light. When it was developed, the negative would be the reverse of the places on the film ‘written’ by the photons of the light (for a description of the process and a recipe for developing film with coffee click here, opens as pdf). This is not true of the sort of “instant cameras” most would now use to upload an Instagram post. In the case of digital cameras, the photons of the light still activate a light sensitive electronic chip behind the camera lens, but much of the interpretation of the image is done using computer software. For example, many of the light sensitive cells in the camera are not colour sensitive, they are only sensitive to the number of photons that fall on them (the intensity of the light). Colour images are formed by considering neighbouring cells which each have a different coloured filter covering them. The relative intensity of the electronic response within each group of cells is then interpreted by the software as a different colour. At this point can it be said that the image is written by the light? The final image is a mixture of the light falling on the photoactive cells and the interpretation of that electrical data by the software in the phone or digital camera. The light directs the electrons within the device but does it write the image?

Table, pebbles and bamboo in the seating area of Hetam, KL.

There’s also the issue of what it means to have the image and to share it. The picture on the phone, the image shared through the screens, is a collection of data points that no one can hold. A photograph printed from film or even the negative is, in that sense, more tangible. In the case of the negative, what you hold is what was written by the photons, by the light, at the point at which the subject was seen. In either case though what does it mean to have, or even to share, that image? Erich Fromm in his book “To have or to be” contrasts a poem of Tennyson with a haiku of Basho*. In the former, Tennyson ‘plucks’ a flower out of a wall in order to study it. Basho in contrast looks “carefully” at the flower; paying attention to it but not possessing it. Fromm questions our mode of being, suggesting that Tennyson could be compared “to the Western scientist who seeks the truth by means of dismembering life.” Is this fair? Does our desire to possess an image, pluck a flower or to ‘capture’ a moment and thereby ‘keep’ it necessarily imply that we would seek truth by means of dismembering life?

Which may take us to a consideration of those dead tree branches on the gleaming stones. They appear like petrified wood, wood that has been preserved for years through a process of fossilisation. We cannot own such objects, they outlast us. If we photograph it we cannot keep that moment, what does it mean to us if we don’t look carefully at the instant but rather try to pluck it for posterity?

So finally back to Hetam. While it may be ideal for Instagram, and while it will definitely be worth a few good photo ‘captures’, the space is also ideal for contemplation. For sitting with a coffee, enjoying the moment, appreciating the surroundings, both aesthetic and people, and for being rather than having. A friendly, outdoor and relaxed cafe, what more could you want?

Hetam is on Jalaan Maarof just next to the Petronas petrol station on the service road to Jalan Maarof.

*”To have or to be” by Erich Fromm, Jonathan Cape publishers, 1976 (1978)

Categories
General Home experiments Observations

A short (lived) black

coffee at Story
A black coffee with bubbles on top. The colours on a bubble are the result of light interference. But sometimes the top of the bubble could appear black. What is happening there?

The long black can be distinguished from the Americano by the order in which the espresso and the water are added to the cup. This in turn will affect the type of bubbles on the surface of the coffee. As a guess, the long black (espresso last) will have many more but smaller bubbles than the Americano (water last) which will probably have larger, but fewer bubbles. Perhaps this guess is wrong, this could be an excuse to get out and drink more coffee.

We are used to the coffee being black and the bubbles on the surface reflecting a rainbow of shimmering colours that change with the light and with time before they finally burst. We know the physics of the colours on the bubbles: they are the result of the interference of reflections from the outer and inner surface of the bubble cancelling out certain colours and adding to others dependent on the bubble skin’s thickness. But what about black bubbles? Or, if not entirely black, perhaps the cap of the bubble can, for a short while, appear black just before the bubble bursts?

It is easier to take a short break from coffee and look for this effect in soap films. Like the bubbles on coffee, soap bubbles are caused by the surfactant in the soap solution having a hydrophilic (water loving) and hydrophobic (water hating) end. The hydrophilic end of the surfactant can point into the water (coffee) leaving the hydrophobic end to form a surface. When this is agitated with air, the hydrophilic ends remain contacted with water resulting in bubbles which are thin layers of water surrounded by these surfactant molecules. In coffee the surfactant is not soap but is formed by the lipids and fatty acids. These bubbles are therefore slightly weaker than the soap based bubbles and so while they will form on a coffee, it is not easy to make a film of a coffee bubble in the same way as you can dip a wire loop into a soap solution and come out with a soap film.

However, we can use the stability of the soap film to investigate the colours in the coffee bubbles and watch the colours evolve with time. At this point, I would strongly encourage anyone reading to grab a solution of soap and a wire loop and start playing with soap films.

Soap film in a wire loop held by a crocodile clip.
A soap film in a wire loop showing reflected horizontal coloured bands that are the result of light interference.

Holding the wire loop so that the soap film is vertical with a light source shining at it, we can watch as the film changes from being uniformly transparent to having bands of colour form and move down the film. We watch as there is a red/green band and another red/green band and then on top of the bands there appears a white, or at least pale blue, almost white, band and above that a layer that doesn’t reflect the light at all. If we view the soap film against a dark background looking only at the reflected light, this top portion of the film appears black. Rotating the loop we can see that the bands effectively stay in the same position because it is gravity pulling on this soap film that is causing the film to be thicker at the bottom than at the top. And we recognise that the coloured bands are revealing that thickness change to us by the fact that they are changing throughout the film. If we are careful as we rotate the wire, we could even see vortex like motions as the layers settle into their new position relative to the frame including at the very top where there are swirls and patches of fluid that mix the black layer with the coloured bands. What is going on there?

In fact, this black layer is one of the thinnest things that they human eye can see, and it occurs because of a subtle piece of physics. All waves have a number of properties defined by the position of the peaks and troughs on the wave. The wavelength is the distance between two equivalent points on the wave. The amplitude is the height of the peak (or trough). And the phase is the position of the wave relative to the peak (or trough). When light is reflected at a surface of a material that has a refractive index greater than that which the light is travelling through (eg. air into water, soap, or glass), the reflected wave has a 180 degree phase shift relative to the incident wave. Each peak becomes a trough, each trough becomes a peak. When light is already travelling through water, soap or glass and gets reflected at the surface of the material that is effectively air, there is no phase shift and the light is reflected back with the same phase as the incident wave (a peak remains a peak and a trough a trough).

At the top of the soap film, the layer is so thin that the light reflected from the first surface (180 degree shift) overlays that reflected from the back surface (no phase shift) so that peak and trough cancel each other out and we see no light reflected whatsoever for any visible wavelength; the surface looks black.

As bubbles ‘ripen’ or age, they will become thinner at the top of the bubble. It is at this point that you may be lucky enough to see a region of the bubble from which no light is reflected, this is the black film.

Which leads to some immediate questions. When we look carefully at the soap film, the boundary between the upper white band and the black film is quite sharp, it is not gradual as we may expect if the soap film were completely wedge shaped with gravity. It suggests that the top of the film is very thin and then suddenly gets thicker at the point where we start to see the colour bands. Moreover, the black film does not appear to mix with the thicker film just beneath it. As we watch, just before the soap film bursts, we get turbulence between the black layer and the thicker film, but the turbulent patterns appear like two fluids next to each other, not the same fluid in a continuum. And then, one final question. If we can’t measure the thickness of the black film with light (because it is all reflected as black) how can we know how thick this film is? If we rely on the light interference method, all we can say is how much thinner it is than the wavelength of light.

In fact, careful experiments have revealed two types of black film, which to us experimenting at the kitchen table would be indistinguishable. There is the common black film and the Newton black film. The Newton black film is effectively two layers of surfactant molecules only and is about 5nm thick (which is 5 millionths of a millimetre). The common black film is thicker, but is still much less than 100 nm thick. Investigating how these films behave is still an active area of research.

One last observation may prompt us to play for a bit longer with the soap films. Johann Gottlob Leidenfrost (1715-94) noted that if you put a sharp object such as a needle through the region of the soap film that showed the coloured bands, the film could self-heal and wouldn’t necessarily burst. If however you pierced the black region of the film, the film always burst entirely.

It seems that we could play endlessly with soap films, perhaps while watching the bubbles in our coffee. However you enjoy your coffee, have fun experimenting.

A couple more soap films showing reflected coloured interference bands. At the top, the film has become so thin that no light is reflected (clearly seen in the image on the right, where the lamp in the top left should be a circular reflection but is not reflected in the region above the coloured bands). In the image on the left, you can see what looks like turbulence or mixing just above the uppermost band.
Categories
General Home experiments Observations Science history

Up in the air with a Pure Over Brewer

The diffuser sitting on top of the Pure Over coffee brewer. The holes are to ensure that the water falls evenly and slowly onto the grounds below.

The Pure Over is a new type of coffee brewer that is designed to brew filter coffee without the need for disposable paper filters. The brewer, which is completely made of glass, is a perfect size for brewing one cup of coffee and, as promised, makes a lovely cup without the need for wasteful paper filters. Generally, for 1-cup filter coffees, the Pure Over has become my go-to brewing method, although it does have a few idiosyncrasies to it that are helpful to be aware of while brewing.

An advantage of this brewing device is that it provides a large number of opportunities for physics-watching, including a peculiar effect that connects brewing coffee to an air balloon crash into the garden of a London Coffee House. It concerns a feature of the Pure Over that is specific to this particular brewing device: the ‘diffuser’ that sits on top of it.

The glass diffuser has five small holes at the bottom of it which are designed to reduce the flow of the water onto the coffee bed so that it is slower and more gentle. In order to avoid the paper filters, the Pure Over features a filter made of holes in the glass at its base. This filter does surprisingly well at keeping the coffee grounds out of the final brew, but it works best if the coffee bed just above it is not continuously agitated. The idea of the diffuser is that the coffee grounds are more evenly exposed to the water, with the grounds closest to the filter being least disturbed and so the coffee is extracted properly.

As water is poured from a kettle through the diffuser, the water builds up in the diffuser forming a pool that slowly trickles through the holes. Initially this process proceeds steadily, the water is poured from the kettle into the diffuser and then gently flows through and lands on the coffee. At one point however, the pressure of the steam within the main body of the brewer builds until it is enough to push the glass diffuser up a bit, the steam escapes and the diffuser ‘clunks’ back onto its base on top of the pure over. Then, this happens again, and again, until there is a continuous rattle as the steam pressure builds, escapes and builds once more.

The ideal gas laws, such as that found by Jacques Charles, relate the volume and pressure of a gas to its temperature. The application of the laws helped to improve the design of steam engines such as this Aveling and Porter Steam Roller that has been preserved in central Kuala Lumpur, Malaysia.

The pressure of the steam builds until the force exerted upwards by the rising steam is greater than the weight of gravity pulling the diffuser down. Once enough gas escapes, the pressure is reduced and so the steam no longer keeps the diffuser aloft which consequently drops with a clunk. The motion could take our thoughts to pistons, steam engines and the way that this steam movement was once exploited to drive our industrial revolution. Or you could go one stage earlier, and think about the gas laws that were being developed shortly before. There’s Boyle’s Law which relates the pressure of a gas to its volume (at constant temperature). That would perhaps partially explain the behaviour of the pure over. But then there’s also Jacques Charles and his observation that the volume of a gas is proportional to its temperature (at constant pressure). This too has relevance for the pure over because as we pour more water in from the kettle, we warm the entire pure-over body and so the temperature of the gas inside will increase. Consequently, as the amount of hot water in the pure over increases, the temperature goes up, the volume of that gas would increase but is stopped by the diffuser acting as a lid. This leads to the pressure of the gas increasing (Boyle) until the force upwards is high enough, the diffuser lid rises upwards on the steam which escapes leading the pressure to once again drop and the diffuser top to go clunk and the whole cycle begins again.

Of course, we know that Boyle’s law is appropriate for constant temperature and Charles’s law is appropriate for constant pressure and so the laws are combined together with the Gay-Lussac/Amonton law into the ideal gas laws which explain all manner of things from cooling aerosols to steam engine pistons. And yet, they have another connection, which also links back to our pure over, which is the history of hot air balloons.

Charles discovered his law in around 1787, a few years after the first non-tethered hot air balloon ascent, in Paris, in June of 1783. The hot air balloon is a good example of the physics that we can see in the pure over. Although Charles must have suspected some of the physics of the hot air balloon in June, he initially decided to invent his own, hydrogen filled balloon which he used to ascend 500 m in December of 1783. Hydrogen achieves its lift because hydrogen is less dense than air at the same temperature. However, it is the hydrogen balloon that links back to coffee and coffee in London.

hot air balloon
The ideal gas laws also contribute to our understanding of the operation of hot air balloons. We are familiar with them now, but how would such an object have been perceived by observers at the time of the first flights?

The first balloon flight in England took place using a hydrogen, not a hot-air, balloon in 1785. The balloon was piloted by Vincenzo Lunardi who was accompanied by a cat, a dog and, for a short while, a pigeon (before it decided to fly away). But it was not this successful flight that connects back to coffee, it was his maiden flight on 13 May 1785. On that day, Lunardi took off from the Honourable Artillery Company grounds in Moorgate, flew for about 20 minutes and then crashed, or as they said at the time “fell with his burst balloon, and was but slightly injured”(1) into the gardens of the Adam and Eve Coffee House on the junction of Hampstead Road and, what is now, Euston Road. In the 1780s the Adam and Eve coffee house had a large garden that was the starting point for walks in the country (in the area now known as Somers Town)(2). Imagine the scene as, quietly appreciating your tea or coffee, a large flying balloon crashes into the garden behind you.

The Adam and Eve is no longer there, in fact, its original location now seems to be the underpass at that busy junction, and the closest coffee house is a branch of Beany Green. However there is one, last coffee connection and it brings us back to the pure over. The pressure of the steam under the diffuser needs to build until the upwards force of the steam can overcome the gravitational force down of the weight of the glass diffuser. In the same way Lunardi had to have enough lift from the hydrogen balloon to compensate for the weight of the balloon and its passengers. Lunardi had wanted to be accompanied by another human on the day of his successful flight. Unfortunately, the mass of two humans in a balloon was too much for the balloon to accommodate which is why, the human was replaced by the dog, the cat and the pigeon.

Which may go some way to illustrate how far the mind can travel while brewing a cup of coffee, particularly with a brew device as full of physics as the Pure Over.

1 London Coffee Houses, Bryant Lillywhite, George Allen and Unwin publishers, 1963

2 The London Encyclopaedia (3rd edition), Weinreb, Hibbert, Keay and Keay, MacMillan, 2008

Categories
Coffee cup science General Observations Science history Sustainability/environmental

Pure Percolation

Pure over boxed
The Pure Over in its box. The glass base is designed with an inbuilt filter, avoiding the need for disposable paper filters but making the physics of percolation unavoidable.

It was entirely appropriate that the first coffee I tried in the Pure Over coffee brewer was the directly traded La Lomita Colombian from Ricardo Canal via Amoret Coffee. Ricardo was a special guest at one of the Coffee and Science evenings we held at Amoret Coffee in Notting Hill (pre-pandemic) where, among other things, he spoke about how he is using Biochar on his coffee farm. Biochar is a porous, charcoal based material that can help to provide the coffee plants with nutrients as well as water, thereby reducing the amount of fertiliser the plants need. To understand how it works, we need to understand a bit about percolation, which of course we also need to understand in order to brew better coffee in the Pure Over. Indeed, there are enough similarities, and an extension to a quirk of how espressos are brewed, that it is worth spending a little more time thinking about this process and the connections revealed as we brew our coffee.

Percolation recurs in many of the brew methods we use for making coffee. The V60, Chemex, Kalita wave, percolators and the espresso itself, all rely at some point on water flowing through a bed of ground coffee. The flavour of the resultant cup is dependent on the amount of coffee surface that the flowing water is exposed to together with the time that it is in contact with the coffee. What this means is that grain size, or the degree to which you grind your coffee, is critical.

Playing with brewing coffee, we know some things by experience. Firstly, frequently, the flow through a coarse grind of coffee will be quite fast (probably too fast to make a good cup). Secondly, we know that for any particular brew method, the more water we pour into the brewer, the faster the water initially comes through. We also know that we can affect the flow rate of water through the coffee if we increase the area of the coffee bed, or decrease its thickness. These observations were quantified into an equation by Henri Darcy in 1856. Darcy’s work had been as an engineer, designing and building public works such as the aqueduct that brought drinking water into the city of Dijon in the 1840s. Darcy received significant recognition at the time for his work including the Légion d’honneur, but it is more for a later set of experiments and particularly for his equation that we remember him today. In the 1850s Darcy was working on the problem of water purification. Passing water through a bed of sand is still used as a method of purifying the water today. Darcy used a series of cylinders filled with sand to investigate how quickly water trickled through the sand bed in order to come up with a proper quantification of those things that we too know by experience with our coffee filters. You can read about the mathematics of Darcy’s equation here.

espresso puck
An espresso puck. The compact structure nonetheless allows water to percolate through it at high pressure.

Darcy found that the flow rate of water through the sand bed increased when the porosity of the bed was higher (fine, dense sand would delay the flow of the water more than coarse, loosely packed sand). If there was a greater pressure on the water at the top of the bed (ie. more water is on top of the sand), the flow rate through the bed would increase too. Conversely the flow would get slower as the water was made more viscous. This is something we too know from experience: try to pour honey through the coffee grounds and it just won’t work.

For us to apply Darcy’s insights into making better coffee, it means that we need to think about the grind size. Too coarse and there will be lots of empty space through the bed of grounds: the porosity is high, and the water will flow straight through. Too fine and the flow rate will decrease so much that rather than just the sweet and slightly acidic solubles that first come out of any coffee extraction*, there could be too much of the bitter organic compounds that come out later, changing the character of the cup. With coffee we have an additional concern. Unlike sand, coffee grinds will swell, and splinter, as water is added to them, closing up any narrower paths and lengthening the brew time. This also means that, unless we properly wet the grounds prior to filtering our coffee, the extraction will be non-uniform and not reproducible. Another reason to bloom coffee thoroughly before brewing.

There is one more factor in brewing our coffee however that Darcy’s equation, which is valid for more stable systems, overlooks. Darcy assumed a constant flow rate of water through the sand bed, but coffee is different. In his book about espresso*, Illy showed that the flow of the water through an espresso puck was not constant over time. Something really interesting was happening when you looked carefully at an espresso puck. Ground coffee can come in a large distribution of sizes. In addition to the grind that we are aiming for, we also get a whole load of smaller particles called ‘fines’. Sometimes this is desirable, but with espresso, and by extension with our filter coffees, these fines add a twist to the physics of the percolation. As the espresso water is pushed through the coffee puck, the fines get pushed down through the puck between the ‘grains’ of the coffee grinds. This reduces the flow rate of the water until the point at which they get stuck. This will have the effect of increasing the contact time between the coffee and the water and so allowing more flavour solubles to be extracted. But crucially, these fines remain somewhat mobile. If you were to turn the whole espresso puck upside down (and Illy had a machine that allowed him to do this in-situ), the fines would again go on the move. Migrating from the new top of the puck to the new bottom. Filling the voids between the slightly too coarse grains. Complicating the simplifications in Darcy’s equation, but adding flavour to our brew.

Watch House coffee Bermondsey
There is a fountain on the wall (right hand side) of the Watch House cafe in Bermondsey. Many public fountains in London date from the 1850s emphasising just what a problem access to drinkable water once was.

Which leaves the connection between the farming method and the coffee. Biochar is formed by burning carbon containing waste (such as plant matter) in a low oxygen environment. Burying the resultant charcoal is therefore a way of storing carbon, and preventing its release into the atmosphere, for many years. But it is not just good for carbon storage. The buried charcoal is highly porous and traps nutrients within its structure so that the plants growing near it can be fertilised more efficiently. Moreover, the fact that it is porous, just like the coffee or sand beds, means that it traps water for a long time. Consider how long it takes a used filter full of coffee grounds to completely dry out! The water gets trapped within the porous structure and does not evaporate easily. This aspect of the biochar means that, as well as nutrients, the plants that grow nearby get a good source of reliable water. The ancient civilisations of the Amazon region used something similar to biochar in their farming techniques resulting in soil now known as “Terra Preta”, an extremely rich form of soil that improves plant growth. On his farm, Ricardo is going fully circular and making his biochar out of old coffee trees. The old trees thereby giving new opportunities to the fresh growth. It is a carbon capture scheme that reduces the need for fertilisers and that relies on percolation physics to work to best effect for the plants.

It seemed a moment of perfect coffee-physics poetry to use coffee grown on a farm using these techniques while initially experimenting with my own, percolation sensitive, Pure Over brewer. Percolation physics and interconnectedness all in one cup.

*Illy and Viani (Eds), “Espresso Coffee”, 2nd Edition, (2005)

Categories
Coffee cup science General Observations Science history Uncategorized

Coffee quakes

ripples on coffee at Rosslyn, the City
From ripples on the surface, to listening to the sound your coffee makes. What links a coffee to an earthquake?

What do you hear when you listen to your coffee? Or a related question, what links your coffee to earthquakes and seismology?

In recent weeks I have been making coffee with milk, not often, but enough to notice something slightly strange. While heating the milk in a small saucepan, I have accidentally tapped the side of the pan while the milk was in it. The tap, perhaps unsurprisingly, produced a ripple on the surface of the milk propagating away from the point of tapping. But what was surprising was that a very short time later, a second ripple was generated, this time from the other side of the pan propagating back towards the original wave.

The first ripple had not yet travelled across the milk surface before the second ripple had been generated and travelled back towards it. Something was causing a vibration on the other side of the pan before the first ripple had had a chance to get there. Was the pan acting like a type of bell which, as I tapped it, started to resonate all around its circumference?

Assuming that the vibration of the tap travels at the speed of sound through the metal of the pan, it would take about 50 μs for the vibration to travel half way around the circumference of the pan (diameter 14cm, with a speed of sound in steel ~ 4500 m/s). But then, if the pan were resonating, the resonance frequency would depend on the speed of sound in the milk filling the pan, which would increase as the milk was warmed. Would we see evidence for this if we video’d tapping the pan as we heated the milk?

coronal hole, Sun
Observing periodic changes to the luminosity of stars can indicate the elements within them. Image credit and copyright NASA/AIA

Rather than watching the liquid within, we could also learn about the interior of a cup of coffee by listening to it. The “hot chocolate effect” is the classic example of this. The effect occurs when hot chocolate powder is added to warm water or milk and stirred. Think about the pitch of a sound made by tapping gently on the base of your mug while you make a cup of hot chocolate. Initially, adding the powder and stirring it will introduce air bubbles into the liquid. As you stop stirring the hot chocolate but continue to tap the base of the cup the air bubbles leave the drink. The cup is acting as a resonator, so the sound that you hear (the resonance of the cup) is proportional to the speed of sound in the liquid in the cup. As the speed of sound in hot water containing lots of air bubbles is lower than the speed of sound in hot water without the air bubbles, the note that you hear increases in pitch as the bubbles leave the drink. You can read more about the hot chocolate effect in an (instant) coffee here.

It is here that we find the first connection between coffee and earthquakes. Seismologists have been listening to the vibrations of the Earth for years in order to learn more about its interior. By observing how, and how fast, waves travel through the earth, we can start to understand not only whether the inside is solid or liquid, but also what the earth is made from. This is similar to learning about the air bubbles in our hot chocolate by listening to the sound of the mug. More recently, the seismologists have shown the effect of the Covid-19 related “lockdowns” on reducing seismic noise. Something that does not have an obvious coffee cup analogy.

But seismology is not just confined to the Earth. Vibrations of a different kind have also been used recently to learn more about the interior of stars, although here it is a mix of seeing and ‘listening’. Generally, when the surface of an object vibrates, it leads to compressions and expansions of the medium within the object. This is the essence of what sound is. But in a star, these compressions and expansions also result in changes to the luminosity of the star. So, by looking carefully at the frequency of the variation in brightness of different stars, it should be possible to work out what is going on inside them. It is a branch of physics now known as “Astroseismology”. Recent astroseismology results from NASA’s Kepler satellite have been used to challenge theories about how stars form and evolve. It had been thought that as a star develops, the outer layers expand while the core gets smaller. The theories proposed that this would result in a certain change to the rotation speed of the core of the star. The astroseismology observations have revealed that, while the gist of the theory seems right, the core rotates between 10 and 100 times slower than the theories would predict. As one astroseismologist said “We hadn’t anticipated that our theory could be so wrong…. For me, finding that problem was the biggest achievement of the field in the last ten years.”.

We now use strain gauges in electronic measuring scales. They were originally invented for an entirely different purpose.

Seismology and astroseismology offer clear links between listening to your coffee cup and earthquakes (or star quakes). But there is one more earthquake related connection to the coffee cup and it could be noticed by any of us who want to improve our home brewing technique.

To brew better coffee, we need to measure the mass of the coffee beans that we are using. Typically we will use a set of electric scales for this. Inside the scales is a device, called a strain gauge, that shows a change in its electrical resistance as a result of the pressure on it (from a mass of coffee for example). The scales translate this change in the electrical resistance to a mass that is shown on the display. One of the inventors of the strain gauge however was not thinking about measuring the mass of coffee at all. His interest was in earthquakes and specifically, how to measure the effect of the stresses induced by earthquakes on elevated water tanks. In order to do that he needed a strain gauge which led to the devices that you can now find in your measuring scales.

Two links between your coffee cup and earthquakes or seismology. Are there more? Do let me know of the connections that you find, either in the comments below or on Twitter or Facebook.

Categories
General Home experiments

Filtering

When you prepare a filter coffee with a paper filter, you typically rinse the filter before starting the brewing process. As you do so the paper swells and can absorb several ml of water.

The other morning while preparing a V60, I noticed that the filter paper absorbed between 3-6g of water (3-6ml) each time I rinsed the filter before making a new coffee. My mind wandered to re-hydrating space food and the importance of water in the texture of the food we eat (and coffee we drink). And then I was reminded of a question I had been asked during these Covid-19 times: would a face mask that is damp work better, or worse, than a dry one for reducing the transmission of SARS-CoV-2, the virus that causes Covid-19?

The answer did not seem obvious. On the one hand, when we wet the paper filter while brewing coffee, the fibres within the paper swell and reduce the pore size of the filter. It seems likely that cotton fibres in a mask would behave similarly. This would have the effect of slowing and reducing the transmission of particulates through the mask. But on the other hand, we’re not thinking about particulates but about small amounts of viral material hosted in water droplets that are somehow exhaled. I decided on the “no idea” response at the time and put the question aside. Until the other morning while preparing coffee.

Unsurprisingly this question, and many like it are now the subject of intense research. I say unsurprisingly because a few years ago a new family of superconductors was discovered with (relatively) very high transition temperatures*. I was on holiday at the time but when I returned, it was to a large number of emails and ideas for experiments on these new materials that became known as the iron based superconductors. We had our first paper on these materials within a couple of months which, like all papers on this at the time, was uploaded, without peer review, to a pre-print server. Eventually most of the papers on the pre-print server got published in peer-reviewed journals, but this process was slow because it relied (and still does) on other scientists reading and taking the time to carefully respond to the points in your manuscript, then for you to address these points, for them to read it again and then, hopefully, ok the paper for publication. If you wanted to get the paper out and for a discussion to start, it had to be uploaded to the pre-print server.

canali Curators Coffee
Iron is a magnetic element. It was puzzling how a magnetic element could exist in a superconducting material and, moreover, seemed to make these materials even better superconductors than their non-magnetic counterparts.

Clearly, in order to keep up with scientists worldwide, we were looking at the pre-print server every morning looking for new ideas and new observations (and if anyone had done the same as we were trying to do at that precise moment but ‘beaten’ us to it). We had to be careful while assessing the claims in the pre-print papers. Some of the pre-prints were eventually withdrawn as they had made overblown claims (admittedly very few). Many were revised and had their claims either subtly altered or brought down a bit from hyperbole before being published in the journals. But none of this mattered to the world outside the lab because while exciting to us, and while the temperature of the transition was, from a physics perspective, very high, for the general public it would have been hard to get excited about materials that went superconducting below about 50 K or, in more common units, -223 C.

This side-story matters because, like our superconductors, the pandemic is the subject of intense research with much of it being uploaded to pre-print servers first so that scientists world wide can get into a conversation about the latest results. However, unlike our superconductors, the general public cares a great deal about a pandemic that is affecting us all and about the scientific rationale for measures such as mask-wearing, social distancing etc. While it is tempting to read the pre-prints, as I am not working in the field, it is not possible for me to read the papers on pre-print servers and be able to have a good guess as to whether the claims are reasonable, over blown or under-evidenced. So, I try to rely only on papers that are past the point of peer review and published in scientific journals. There is something very disheartening about reading an interesting newspaper report that near the end says “the study, which has not yet been peer-reviewed…”. Will the interesting study hold up? It is difficult, from outside the research area, to tell.

However, we need to get back to the masks and the filters. Was there a study, in the peer-reviewed and published literature, that looked at whether moistened masks performed better than non-moistened masks?

Masks: can we set up an experiment to see how effective ours are relative to the fitted N95s that are not available to most of us?
Masks: can we set up an experiment to see how effective ours are relative to the fitted N95s that are not available to most of us?

In fact, there is a lot of research on the effectiveness of masks. The research includes computer modelling, imaging of real people breathing/talking/coughing with and without masks and more reproducible tests where the mask material is tested using the conditions of a simulated sneeze. This last study also tested whether that simulated sneeze is contained better by a cloth mask (with filtration down to PM 2.5) or a damp cloth mask (with the same nominal filtration).

The different types of research are needed because they answer different types of question. How effective each type of mask is will depend on the type of material (tested with the simulated sneeze) and the way that people wear them (tested by the imaging of people wearing masks). While the computer modelling suggests what may happen in more ‘real life’ environments such as being outdoors with a gentle wind blowing.

In terms of the initial question about the damp masks, it turns out that the fact that the fibres in the mask swell with the water does indeed help reduce the droplet transmission through the mask material. But the authors caution that if the mask is worn for a longer period of time, the damp mask may get saturated with virus loaded droplets and so the mask would need to be changed (and refreshed with fresh water) frequently in order for it to be effective against transmission of the virus loaded droplets. (It’s also noteworthy that the effect of the damp mask was only tested for one mask type that may not be typical of what the general public wears). However, for most of us it would not be practical anyway to wear a damp mask. Moreover, if we were having to change the mask frequently, it may not be helpful for us at all. But the good news is that the imaging studies show that we don’t have to do either.

A fantastic report in Scientific Advances showed two things. First, that most masks that we wear properly give a significant benefit for the people around us. And secondly, they provided an experimental set up that can easily and relatively cheaply be replicated by people with a little technical knowledge and a mobile phone. However, given that ‘relatively cheaply’ still means about $200, I’ll take their results instead, if you don’t mind spending the money on a laser and some lenses (or happen to have some lying around), please do let me know how you get on.

Press Room coffee Twickenham
Another paper filter, this time at the Press Room, Twickenham. When we add water to a (dry) paper filter, the fibres within it swell and expand making it a better filter. Would the same happen with masks?

The authors took several of the types of face mask being worn by the public and imaged the droplets coming from a person speaking through each of them. The masks tested included surgical masks, N95 masks, and hand-made masks with 2-layers of cotton or 2-layers of cotton with an extra polypropylene layer in the middle. All of these masks reduced the droplets transmitted through the mask significantly. Indeed, relative to no-mask, some home-made multiple cotton layer masks cut the droplets by nearly a factor of 10. The exceptions were bandanas and neck gaiters. The bandanas that were tested only cut the droplets getting through by a factor of 2, but the gaiters were worse. Speaking through the neck gaiter that they tested, the authors observed that the number of droplets getting through the gaiter actually increased relative to speaking wearing no mask. While this seems counter-intuitive, they suggested that this was likely because the gaiter was breaking up the larger droplets into multiple smaller droplets and so their equipment, which just measured the number of droplets, measured an increase relative to someone wearing no mask.

The problem here of course is, as the computer simulations showed, smaller droplets stay in the air for longer, larger droplets tend to fall with gravity. Something else that we know by thinking about our coffee.

So the final conclusion? Yes, it is possible that a damp mask may be better than a dry one though there are caveats on that result. But in actual fact, most masks that we wear in an indoor environment will help to protect other people (though maybe be careful with the gaiter materials). And a second conclusion? Perhaps preparing a coffee should be a time of escape from the concerns of coronavirus and really, next time, I should just enjoy the moment and think about re-hydrating space food.

*Actually, the iron-based superconductors had been discovered a couple of years previous to the excitement. But at that point, the reported transition temperatures were low enough that even the superconducting field was curious but not excited.