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.

Coffee review Coffee Roasters Observations Science history slow Tea

HR Higgins, Duke Street

Interior of HR Higgins cafe
The view of H.R. Higgins (Coffee-man) from Duke Street. The Royal Warrant can be seen on the side of the wall.

Established over 80 years ago, HR Higgins in Mayfair’s Duke Street is somewhat of an institution. From the pavement, you can look into the cafe space in the basement below while the shop upstairs offers coffee beans and tea for retail. During the (earlier) mornings, coffee is also prepared for take-away at the entrance to the shop on the ground floor while the cafe downstairs is closed.

The first time I came here, it was only to buy beans. That time I tried the Rwandan Women’s cooperative coffee and was impressed by the scales used to weigh out my 250g: a proper mechanical scale set complete with weights. The second time I tried it, again I only had time to purchase beans but I determined that the next time I would definitely try the cafe downstairs because if there was so much physics to appreciate upstairs with the scales and the decor, how much more would there be downstairs. And so, I arrived one morning at 8.30am having checked the opening hours and the cafe downstairs was… closed. It turns out that although the shop is open, and although take-away coffee is served from the front of the shop, the cafe only opens much later at 10am (on weekdays).

Inside an empty cafe.
Inside an empty cafe, downstairs at Higgins. The clock on the wall is a throw back to the ’70s while the mosaic tiling on the floor is particularly mesmerising. What strikes you?

However, what was an initial disappointment turned into a great opportunity as I was able to have a proper look around, completely on my own, while the man upstairs prepared my V60. Having no intention of actually ‘taking-away’ the take-away, when I came back upstairs (and had another look at the scales and tins of coffee at the back of the store) I went outside to the “H.R.Higgins” bench to sit and enjoy my coffee and the surroundings. There were a few pastries that were also available for take-away but this time I just took my coffee and sat down.

The coffee was really good. I had been given a choice of two coffees for the V60 and went for the Honduran as it was recommended as being particularly good for the V60 brew method. It was packed with flavour notes and character as it cooled while I sat on the bench. The bench offered a view of city life. The busy cafe next-door to my left; the old sign “Duke Street, W”* on the wall opposite; the imposing “Brown Hart Gardens” which is above an early 2oth century electrical substation just to my right and of course, the cafe itself in the basement visible behind me. The bench was also a good spot for people watching. Many people, with many characters, walked past (or got their coffee in Higgins and then walked past). I thought perhaps that I even saw George Osborne** wandering by but decided to let my mind wander to think about the physics instead.

Of course there was a lot to ponder. The nature of scales and the definition of the kilogram had been an obvious starting point but the reflection of the cafe name in the window opposite me provided further directions of thought. The patterns of the tiling in the cafe could provide several avenues of thinking while the history involved with the establishment of this establishment would have prompted a significant diversion. Finally, the antique bike standing next to the bench took me on the thought-journey that occupied the rest of the time I spent on the bench and enabled me to keep my phone left solely for taking photographs.

An old bike with flowers where a delivery box used to be.
The H.R. Higgins bike. Complete with Brookes saddle and flowers for luggage, this bike gave plenty to ponder while enjoying a coffee.

Now used as a flower pot holder, this old bike looked as if it had been adapted from a delivery bicycle of a fair few years ago. The brakes were immediately attention grabbing. We have become used to the wires used to operate the brakes on modern bikes but these used firm metal rods to transfer the action on the brake levers on the handle bars down to the wheels. And then the wheels themselves had rubber tyres. Again, this is somewhat obvious and very familiar except the first bikes had iron wheels because rubber tyres had to be invented.

There is a potential diversion here to the story of rubber, which could almost be a cafe-chemistry review but we won’t go that way today. Nonetheless, it is worth pondering that rubber tyres are, just like coffee, a product with a varied history of globalisation, trade and colonisation. What enabled the bicycle wheel to evolve from cast iron to pneumatic tyres was the chemistry involved in the ‘vulcanization’ process invented by Goodyear that meant that the rubber no longer suffered from getting too soft at higher temperatures and too hard at lower temperatures. Anyway, that’s a digression.

Returning to the bicycle, a lot of physics is involved in cycling. Is it actually clear how any of us can balance on a bicycle? A short answer, and the one that is often off-handedly given, is that we can cycle because of “conservation of angular momentum”, but it turns out that it is a little more tricky than just that. A few years ago, a chemist decided to test the ideas put forward to explain how we balanced on a bicycle by building so-called “un-ridable” bicycles and found that he could actually ride some of them, thereby showing that some of our ideas on bicycle riding needed a little ‘tweaking’. The basic ideas of conservation of angular momentum were correct, but like many things, if you actually want to understand it, you need to go a bit deeper (and do a couple of experiments!).

As we move beyond the basic physics so we move to the technology of cycling and the improvements that are being made to competitive cycles (and their riders) to make them more aerodynamic. We have moved a long way from brakes using rods and delivery cycles. And yet, sometimes there are advantages to the old ways. Just as the scales at H.R. Higgins still work perfectly well with the balance and weights system, so new delivery bicycles are re-appearing in London, swapping polluting vans for cleaner-greener delivery vehicles. Just these ones no longer have metal rods for brakes and they perhaps have a pedal-assist electric motor.

Have you enjoyed a coffee at H.R. Higgins (or somewhere similar)? What did you notice that enabled you to put your mobile phone down and really think about your surroundings? Do let me know in the comments section here or via social media.

H. R. Higgins is at 79 Duke Street, Mayfair, W1K 5AS

*The single “W” on the sign (rather than the post code of the area “W1”) shows that the sign has been there since before the first World War when the London post code system was refined from the merely “W” to the W1, W2 etc. that we use now.

**George Osborne was the Chancellor of the Exchequer (finance minister for the UK government) from 2010 to 2016.

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.


What is Project 68? Kings Cross, London

Project 68 on Tavistock Place. Most of the seating is inside with four benches outside.

Opposite a post box that is more than a century old, there is a cafe on Tavistock Place with the unusual name “Project 68”. Located along a well-used cycle route, when the cafe appeared last year, an obvious question kept springing to mind: what is Project 68? The opportunity to find out and try the coffee came the other weekend on a cycle up to Highbury. Jumping off the cycles at the junction, we had to walk past a couple of black board signs advertising the cafe. “Come this way for really, really good coffee” the signs said. Should we believe it?

The coffee is roasted and supplied by SEND which stands for “Special Educational Needs and Disabilities”. This coffee roasting company works to help people with special educational needs and/or disabilities gain employment as baristas within the coffee industry. As well as working with a few London cafes to train and mentor prospective baristas, the company also sells its coffee to other cafes, such as Project 68. The counter at Project 68 had a large supply of pastries on that Saturday morning which were tempting but we were on our way for lunch. Along with the usual suspects of coffee ‘types’, hot chocolate was available as three varieties, ‘white’, and two differing cocoa percentages. The chocolate was supplied as large buttons, so one hot chocolate was two buttons. Presumably this would allow you to mix the chocolate types should you feel the need.

Inside felt very wooden, in a good way. Light shades of wooden seating complemented the wide windows onto the street. The fact that we had our bikes meant that we went back to sit outside to observe what was happening in this cafe. It seemed appropriate to start by pondering the name. What would “Project 68” refer to? A quick (pre-visit) look on duckduckgo suggested that project 68 referred to a set of Soviet era battle cruisers. This seemed very far from the feel of the cafe. An alternative could be the social riots that occurred in Paris in ’68. And although Project 68 is fairly close to some major London universities again, this didn’t seem to be the feel of the cafe. Looking around, and at the door of the cafe a more mundane explanation suggested itself. The cafe is located at 68 Tavistock Place. Was the name merely a reference to the address?

A board on Hunter St advertising Project 68 just around the corner. Could there be physics connections here with font types or stripy bollards?

Returning to the coffee. We sat outside with our bikes and then the barista brought out our long black and oat milk hot chocolate. Perfectly enjoyable, we sat back and continued to notice what we could observe. The aforementioned postbox almost jumped out at us. The cypher on the front suggesting it dated from the short reign of Edward VII (reigned 1901-10). Among other things, Edward VII had been known to run the clocks at his residence in Sandringham, 30 minutes fast. Much like daylight saving time, this extra half hour meant that there was even more daylight for hunting for him. In the UK, the clocks are brought forward and put back by one hour in March and October respectively each year. It is a desire for our own convenience set against the unchanging regularity of the Sun being directly overhead at mid-day. We could pause to think on that or get distracted by a musical connection to Edward VII as he opened the Royal College of Music in 1883. For while we are considering the music, we may start to notice the connection between this cafe, music, and the stars, and we noticed it just beneath our feet.

Many of London’s older houses and shops have an under-pavement cellar. In the past this would have been used as a coal storage area, now they find many diverse uses. A grate beneath our feet indicated that we were above such a cellar. Suddenly, just after a sip of coffee, there was a whir from beneath the pavement. A rhythmic motor-like noise below where we were drinking our coffee. A stray leaf on the mudguard of my bike indicted a draft coming from the grate too. What was this machine that had sprung into action? It is telling that we can discern many things from how something sounds. We know if our coffee grinder is working correctly by the characteristic hum of the rotation of the burrs. A problem with a vacuum cleaner is often indicated by the regular sound of the motor being disturbed by the clatter of a coin going up the vacuum pipe. Sounds can reveal what is happening in much the same way that we use our eyes to see. But fundamentally a sound is a vibration. Something is vibrating that causes the air adjacent to it to oscillate sending forth a sound wave of a varying note. The mechanism is the same whether we are considering the rotation of the drum of a motor or the subtle vibration of the internal cavity of a violin. Sometimes we can see the cause of the sound as when we notice the fast vibration of a guitar string after it has been plucked. Sound can be ‘heard’ through at least three of our senses (hearing, seeing, feeling).

Finally, it is all about the coffee. A long black balanced on one of the benches. You can see the grate on the pavement to the left of the photo.

On Earth we use sound to detect earthquakes around the world, listening for the vibrations through the ground. Often these vibrations are amplified by detectors changing the subtle oscillations of the Earth into wild wobbles of a pen drawn on paper (or now, into a more digital form). In this case, the sound is transferred to what we see. Recently, there has been the opposite case. Astronomers have noticed, by looking at different stars how each star can vibrate with different sorts of ‘note’. Just like a violin, the internal vibrations in the star will cause the surface of the star to wobble and oscillate according to different types of vibrational sound. And, just as with the Earth, how those vibrations travel around the star and persist with time reveals the composition of the interior of the oscillating sphere. Astronomy provides a further connection to Tavistock Place, if not quite Project 68. The site of Francis Baily’s home is just down the road from Project 68, at number 37. Although he does not seem to be commemorated with a blue plaque (yet?), there are plaques nearby to Lenin and Jerome K Jerome. Clearly this street has quite a history. Baily was an astronomer mostly commemorated now by “Baily’s beads” a phenomenon visible during total or annular solar eclipses. Observed by Baily in 1836, the beads are bright spots of light around the rim of the dark circle of the Moon blocking the Sun. Caused by the mountains and craters on the Moon’s surface, it’s a visual, rather than audible clue as to something slightly off-tone, or irregular, on the Moon’s surface.

Back at the cafe, the sound continued under our feet. Fairly uniform, it seemed like a machine running regularly. We guessed at what could be producing the noise. Nothing was conclusive. Perhaps it is more intriguing if the cause of the sound remains a mystery, just as the name of the cafe.

We returned our coffee cups to the counter inside the cafe and wandered off across the road to Judd Street, ready to cycle off to Highbury. As we were just about to peddle off, a couple of people were walking towards us. “What is Project 68?” one of them asked the other. There can be no such thing as a stupid question and if you would like to find the answer to this one with a lovely cup of coffee with a story, it is worth a diversion to 68 Tavistock Place.

Project 68 is at 68 Tavistock Place, WC1H 9RW


If you are tired of London

Jonathan's coffee house plaque
Jonathan’s Coffee House was the site of the first London Stock Exchange. A link between coffee and the financial markets can be made via the maths describing Brownian Motion.

London has a long history for tea and coffee drinkers. The first London coffee house opened in around 1652 in St Michael’s Alley*, followed quickly by a large number of coffee houses all over London. Isaac Newton, Edmond Halley and Abraham de Moivre were all known to drink coffee in the various establishments dotted around the city (de Moivre even charged a small fee for mathematical advice at Old Slaughters on St Martin’s Lane). Famous institutions such as the London Stock Exchange and even the RSPCA were first formed at London Coffee Houses. On the engineering front, Thomas Telford established the Institute of Civil Engineers at the Salopian Coffee House just off Trafalgar Square. Yet the story in this post comes not through the coffee houses but from historic tea drinkers and, in particular via a “prodigious drinker of tea”, Dr Samuel Johnson**.

The story is detailed in Boswell’s “Life of Samuel Johnson” and concerns a friend of Johnson: Mrs. Anna Williams (1706-83). Williams had gone blind in the 1740s and, in the later part of her life lived with Johnson in his various dwellings around Fleet Street. You can now visit the Samuel Johnson museum in one of those properties at Gough Square, just off Fleet St. Between 1759 and 1765 Williams was living a short distance from Johnson but Johnson regularly popped around for tea in the evening. It was on one such occasion that Boswell joined them. Williams would pour the tea for all the guests but Boswell wondered how she knew when to stop pouring given that she couldn’t see. Boswell thought it was possible that she had subtly dipped her finger into the tea to feel when it was about to flow over the edge of the cup. As he later found out, this was not true. Apparently she had “acquired such a niceness of touch as to know by the feeling on the outside of the cup how near it was to being full.”

The question then arises, how could she have known this just by touch?

a heat sensitive coffee mug
This coffee mug changes colour as it gets warm. The constellations slowly appear as the heat is transferred from the hot coffee inside to the outside of the mug.

A first solution would be that she was feeling the heat of the tea through the porcelain of the cup. Is this possible? It is certainly true that, once a cup is full, it feels warmer to the touch than an empty cup, but heat does not travel through a substance, such as a cup, instantaneously. Would Williams have had enough time between feeling that the cup had become warm to stopping pouring to prevent the cup from overflowing? A quick experiment with my colour changing cup (pictured) suggests that this may be unlikely. Even if she had the sensitivity in her fingertips to quickly discern a change in temperature, it took 20 seconds between boiling water being introduced to the cup before the top started to change colour. Although porcelain is thinner than my mug, and the change is probably quicker to feel than to see with the cup, it is likely that she would have carried on pouring the tea beyond the rim of the cup before realising that the cup was becoming full. Although it is possible that she could compensate for this, for example by touching the cup further towards the base, perhaps there are other ways that you can discern a cup is almost full without seeing it?

A second solution could be that her discernment occurred through a mix of touch and sound. There are a few ways in which audio signals will suggest that a cup is almost full. Coupled with the feeling of increasing warmth on the side of the cup, this may give the tea pourer increased confidence that the cup is comfortably full. One such clue is familiar to those of us who fill water bottles up from the tap, the change in pitch as the tea is poured. Similar to a Helmholtz resonator, a pourer would know when to stop as the musical note from the pouring tea changed. But the tea cup is open at the top so this effect is weak. Perhaps the sound clue instead comes from the sound that the poured tea makes as it impacts the surface of the cup of tea. When we hear a dripping tap, what we are actually hearing is the bursting of an air bubble just below the water surface. We would expect the sound of that to depend, for shallow containers such as the cup, on the depth of the tea. Consequently, if we poured the tea slowly and heard the drops of tea as they entered the cup, we may expect to gain an idea as to how full the cup is. As Boswell assumed a slight of hand (and of hygiene) on the part of Mrs Williams, it is probable that she did not pour the tea slowly enough for this to have been her primary route for knowing that the tea cup was nearly full. Perhaps Mrs Williams did not use sound after all, but relied on something else?

Bubble tea? There is a lot of physics to be found in tea as well as coffee. Take time out with your brew. What do you see, hear, feel?

There is one more clue that you could get about the relative fullness of a cup of tea using touch. If you very gently push against the cup with your finger, you can feel the resistance of the cup to movement. As the cup became heavier with tea, the resistance to its being pushed would increase (Newton’s second law). After pushing at the top of a few mugs with my finger, this seems to be possible. Unless the person watching the tea being poured was very observant, it is not clear that they would notice this. Can we gather anything of Boswell’s skills in observation? Throughout his book he describes people and social situations well and yet, he was unsure whether Williams had dipped her finger into the tea cup to know when it was full enough. I think we can probably gather that on this particular point, Boswell may well not have noticed had Williams been pushing gently at the tops of the cup to see how easily they moved. Although there is a risk of pushing the cup over, this does seem to be a very feasible way of filling a cup without using your sight.

There is however one last, maybe more boring possibility. Generally the speed at which liquid comes out of a tea pot is quite reproducible. Through the fact that she was pouring tea every evening for Johnson and his guests, it is quite possible that she knew how long to pour for each fixed angle of pour before the tea cup was properly filled. We’d still have to ask how she measured the time given that she wouldn’t have looked at her watch, but perhaps here we would have a clue from Galileo. He is said to have sung songs with a known rhythm in order to measure time (the use of the pendulum to measure time came later, partly as the result of Galileo’s work). The idea was that the rhythm is a surprisingly reproducible method for comparing time intervals. Maybe Mrs Williams sang to herself while pouring the tea for the guests.

What do you think? Perhaps you can think of another effect that could be used to determine when your tea cup is full, without any visual clues. Or maybe you just disagree with my deductions. Whatever your thoughts, do let me know in the comments below or on the various social media sites (FB, Twitter, Mastodon), I look forward to learning more and maybe, being able to pour my coffee with my eyes closed.

*Information on the London Coffee Houses can be found in the excellent “London Coffee Houses” by Bryant Lillywhite published in 1963

**The story of Mrs Williams, Dr Johnson, his tea drinking and the notes of Boswell is described in “Life of Samuel Johnson” by James Boswell


A Need for Roots, Hermanos Coffee, Portobello Road

Hermanos Colombian Coffee Roasters on Portobello Road. There was a fair amount of graffiti, which could offer further avenues of thought but is probably owing to the Notting Hill carnival which had happened just before my visit.

There is nothing quite like wandering through a market street in the hour or so before the market opens. It feels as if you are there as part of the city is waking up, things moving into place, ready to start the hustle and bustle of the day. It is one of the things I like to do when exploring a new city: wake up earlier in order to walk around and try to find breakfast, listening for the character of the place. Sometimes though, it is good to try this in your own city, it is a chance to see your home, your space, in a new light; a different aspect of its essence. So it was that I ended up wandering along Portobello Road shortly after 8am one week day morning. Market stalls were being moved into place, office workers were cycling or scooting on their way to work and a small little coffee shop with an open door seemed to invite customers in to sample their coffee.

Hermanos Colombian Coffee Roasters cafe can be found at 127 Portobello Road. Actually, it can also be found at 7 other locations including Kings Cross and Victoria Stations. Does this qualify as a coffee chain? Regardless of the number of cafes, Hermanos Coffee on Portobello Road is somehow clearly integrated into that community, so much so that this initially appeared to be a small scale single shop embedded within Portobello. When you sit to drink a coffee while the street around you ‘wakes up’, it seems as if people around drop their guard a bit, you see glimpses into relationships that later in the day will be hidden by the rush of people. Perhaps it was the time of day that made this cafe seem particularly friendly, I stepped inside to order my coffee.

Perhaps unsurprisingly, the coffee is roasted by Hermanos Colombian Coffee Roasters and they have a large selection of their coffee (and coffee making equipment) for sale on your left as you walk into this small cafe. The counter is just ahead of you (also on your left) with the menu behind the counter showing the usual selection of coffees available. I am fairly confident that they also offered a pour over coffee on the menu, but it being the start of the morning rush, I didn’t want to preoccupy the barista with making a filter for me and so I ordered a long black. Beyond the counter, there were a few seats with people already inside enjoying coffee and conversation before the start of the day. As I indicated that I wanted to sit outside, the person behind the counter asked me if I would prefer “china or a take-away cup”. It’s a small detail but it was nice to be asked. I picked up my cup of coffee from the end of the counter, wandered outside and took a seat waiting to watch what went on for the next half hour or so.

Coffee on a wooden table. Looking at the lines formed by the wooden panels, you can see which one was wonky.

I listened as the barista spoke to each new customer, some of whom were clearly regulars. “Back to hot coffees as the weather turns colder then?” I heard, as a customer walked in off the street. I then watched as the barista came outside, took a short breather during a lull in customers and greeted the person who was opening the hat store next door. Another person walked into the cafe to pick up his bag that he had left there briefly as he knew it would be ‘safe’. This is (unfortunately) not something that you would normally assume of Portobello Road. It was not just the community aspect that jumped out at the interested observer of this cafe. The science started to appear everywhere. This is of course in one sense always true. The mere fact of seeing something involves multiple elements of physics and biology without thinking about anything deeper. However, some cafes produce something in the physicist akin to writer’s block, it can be hard to link to what is around you. This is very far from the case at Hermanos.

The recent rain on the wooden table top suggested the phenomenon of coffee rings and what makes a surface wettable, while the table itself with one wonky wooden slat immediately prompted considerations on defects in crystal lattices. One of the many people who rushed by was talking to someone on a mobile phone set to speaker. This meant that the entire conversation was audible to the nearby coffee drinker. You could ponder what they were talking about or you may start to think about why it is that someone through a phone line sounds different to that same person speaking in front of you. Every sound is made up of several frequencies of sound wave. The more complex the sound, the greater the number of frequencies used to convey it. When you speak to someone face to face, all of those frequencies will be transmitted from the speaker to the listener. When a sound is transmitted through a phone line, it is necessary to limit the frequencies that the phone line can carry. For some sounds, some of the higher frequencies that contribute to that sound’s ‘sound’, will get blocked off by this bandwidth limitation. Consequently certain sounds, like “s” and “t”, will sound slightly different over a phone line than when speaking face to face. The conversation will be perfectly intelligible, but we pick up on subtleties in people’s voice and know that they sound slightly different through the phone network.

The Hermanos signboard photographed with the hat store in the background.

Elsewhere, the sign of the cafe puts a square around the “H” of “Hermanos” which prompts recollections of the element hydrogen which has that symbol on the periodic table. It was an appropriate connection because the raindrops on the signboard were reflecting the Sun which is mostly made of hydrogen being formed into helium through nuclear fusion. Looking again at the sign, the reflections and the table, it was clear how our eyes interpret lines and angles into information about distance. These are observations that scientist-artists of the past have used to formulate the rules of perspective. It caused me to look again at the wonky wooden slat and think about how I knew it was wonky (without putting my coffee on top of it). Perspective then surfaced again as the worker in the hat stall next door brought out the days collection of hats and goods. As he was standing behind a hat stand arranging a viewing table, it appeared that he was wearing one of the hats on the stands. Only the fact that he moved and the hat didn’t showed that actually my eyes had been deceived. A parallel meaning of perspective was evident around as the street changed while I was there: by the end of my coffee, the shops were open, parents were rushing children to the school around the corner, the street was alive. What would I think of this cafe if, rather than enjoying my coffee at around 8.30am, I was trying to drink it in the middle of the Saturday tourist rush?

The coffee was good. A very drinkable cup with which to enjoy my time on Portobello Road. The cafe was equally good, showcasing many different aspects of what being a cafe is about. Hermanos Coffee is definitely worth a visit and I hope to go again next time I have the urge to explore Portobello Road before the crowds arrive. It seems appropriate however to conclude this cafe-physics review with a quote from the Hermanos brothers themselves about their cafes and coffee. They say “We understand that our journey at Hermanos is also the collective journey of so many, who each in their own way contribute to and benefit from the world of coffee.” A journey that is so much easier to appreciate if you pause to sit and people watch at this lovely little cafe.

Hermanos Coffee is at 127 Portobello Road, W11 2DY and at multiple locations around London.

Coffee review

Drawing a Blank?

Blank Street Coffee on the corner of Charlotte Street and Goodge Street.

In the summer of 2020, a new neighbourhood cafe started up in New York. Now, at the end of summer 2022, Blank Street coffee has over forty locations in the US with two in the UK and the ambition of 24 in the UK by the end of 2022. This is not your usual small coffee shop. Nor is its financing. After initially raising $7m from venture capitalist firms, a recent fundraising round raised a further $25m. It is worth asking: why? What is it about this chain of cafes that makes financiers value it at more than $98m?

I came across Blank St Coffee at 44 Charlotte St on the junction of Googe St by accident. After a good Penang Assam Laksa down the road at Laksa Mania, we were after a coffee and this cafe looked, at first sight, like a small neighbourhood cafe. Judging from headlines in the New York Times, this post is going to date very quickly and conceivably, in just a couple of months we are going to wonder how it was that we had never heard of Blank St. As we got closer, the merchandise visible through the window, and other aspects of the coffee shop which are harder to pin point, suggested that this was a coffee shop backed by quite a lot of finance. There are a few such cafes around and it is not always easy to discern what it is, exactly, that indicates that they are far from my usual focus on neighbourhood cafes. However, on this occasion, we were after a coffee and thought we’d give it a try.

We ordered an Americano and an oat milk hot chocolate. The coffee is roasted by Origin Roasters and all the coffee is served in disposable cups. As we were drinking ‘in’ (on the benches outside), I refused a lid for the cup which was a mistake as the Americano had been filled to the brim of the cup. Shortly after taking the coffee from the counter and stepping outside I found, experimentally, how easy it is to spill a black coffee (as opposed to say, an oat milk hot chocolate). The over-filled Americano turned out to be an interesting feature because I had naively attributed it to human error. As with much else at Blank Street, such impressions can be deceptive.

Over-filled Americano and oat milk hot chocolate with a lid. You can see which one spilled by the liquid around the bottom of the cup.

I’ll declare a bias here. I think society works best with human interactions and community. It is why I have focussed on reviewing small, locally run, community cafes in the past. Blank Street Coffee has a different ethos which is to make good coffee affordable. While this is not necessarily a bad aim (click here for a discussion on the pressures and ethics involved in coffee pricing in cafes), Blank Street has a particular approach to cost cutting. Firstly it rents smaller spaces for its cafes. It also automates much of the coffee preparation. The baristas no longer have to make the coffee, they just push a button and the coffee comes out of the machine. This makes the over-filled Americano odd because it is an automated, not a human process, have they really designed the Americano to fill to the brim?

Blank Street Coffee explains that the fact that the baristas just have to ‘push a button’ for the coffee means that they have more time available to chat with customers. This does not make sense to me. I like knowing that the barista knows coffee and knows (and cares) how to make a good coffee. I like the fact that the barista knows more about coffee than I do and so can talk to me about different coffees and issues within the coffee chain. I do not see that the baristas can have the same in depth understanding of coffee if they are only required to push a button to make it. Nor do I think that this will reliably produce a good coffee as the coffee dosing needs to be adjusted throughout the day by experienced baristas in order to keep the espresso flavour consistent. There is a similar problem in experimental physics. In order to get more results in a given time frame (such as overnight), many pieces of equipment are now automated. This starts off as a great idea but has the result that the experimenters lose familiarity with the electronics behind the computer interface. It is hard to troubleshoot when something goes wrong if you don’t have the feeling for what different bits of the equipment do to begin with. On a practical point with the cafes, baristas are needed now because they are expected. If the aim is to provide good coffee cheaply, what is to stop getting rid of the barista entirely and allowing the customer to press the button?

Opposite Blank Street a properly blank sign. What used to be written on this sign?

The coffee itself was ok. It was nice to get a drinkable cup of coffee in a space in central London where you could sit on a bench and people watch. And in terms of the physics aspect of a cafe-physics review, there was also an appropriate point to consider. Just opposite the cafe there was a space on the wall of the shops for a shop sign. It was a type of nineteenth century panel built into the shop fronts which would in the past have been painted with the name of the shop below. Only this one was, fittingly, blank. Not really a ghost sign, it was so ghostly as to have disappeared altogether, it was a blank space. The presence of the sign was announced by its absence. A similar absence is revealing in space; “in space, no one can hear you scream.” Does this suggest that space is a vacuum? For sound waves to propagate, and so for your scream to be audible, the sound needs to create a pressure wave within a substance, whether that substance is a solid or a gas. If a sound wave cannot propagate and we take the movie-tagline literally, it would mean there is no substance in space, it is a vacuum. Depending on where you measure it, this is nearly true. In interstellar space, there is approximately 1 atom per cubic centimetre compared with 3×10^19 atoms per cubic centimetre on Earth’s surface. In intergalactic space there are even fewer atoms in a given volume. Even in interstellar space though, there are small fluctuations in the density of atoms with some regions having what appears to be a bunching up of the atoms present into waves as the shock fronts of things like distant supernovae come through. The spacecraft Voyager 1, launched in 1977, crossed the boundary into interstellar space in 2012. Voyager continues to take measurements of what it encounters and is now being used to understand the density of interstellar space, partly by measuring these bunched up bits as they flow over the spacecraft.

Voyager measures the density of space, partly by revealing the very absence of measurements for the most part. Which brings us poetically back to the name: “Blank” Street coffee. It is announcing something by its very anonymity. This anonymity is continued even inside the cafe. Painted a shade of green which is fairly instagrammable but somehow generic, a copy of other Blank Streets elsewhere. The space offers plenty to think about: what does it mean to be empty? Do we value something purely by its economic cost? And what does it mean to be anonymous, or even a unique individual, if you order coffee using an App on your phone?

Coffee at Blank Street was an experience. It can prompt many reflections on society and on physics. Yet, there are issues in its apparent anonymity and generic layout. Two weeks after visiting Blank Street, I visited a small, local cafe where the community and the physics jumped out at me. Offered the choice of many generic ‘blanks’ or a few memorable cafes, which would you choose?

Blank Street Cafe can probably, by now, be found all over London but was reviewed at 44 Charlotte Street.

Coffee cup science Home experiments Observations

Cracking Magnets

Rare earth magnets are very strong despite their size. These magnets are several times stronger than an ordinary fridge magnet.

Can you hear it? The first, second and then third and fourth cracks as a magnet is brought near a magnetic (but not magnetised) material, such as a piece of cutlery? Unlike the first and second cracks during coffee roasting, which are clearly audible, it is unlikely that you would have actually heard the cracks of a magnet. To hear them you would need to amplify the effect and connect it to a loudspeaker (there’s a link to how you can do this experiment here). Nonetheless, if you were to do so, you would hear the cutlery cracking. And while these sounds are not connected to the first and second cracks in coffee roasting, they are connected, via physics, to coffee. To see why we need to think a bit more about what is causing these magnetic creaking noises.

The effect is known as the Barkhausen effect after Heinrich Barkhausen who discovered it in 1919. It turns out the the effect reveals quite a lot about how magnets work because it reveals what is going on at an atomic level in the kitchen fork. Some metals are attracted to magnets but not others. So a fridge magnet would stick onto materials containing iron but would not stick to a sheet of aluminium; we can pick up pins, paper clips and some cutlery with a strong magnet but we could not pick up a piece of kitchen foil. These iron containing metals are magnetic but not magnetised, they will be attracted to a magnet but they will not ordinarily attract other items to themselves. We may remember from school that we can make them magnetised by continuously stroking a strong magnet along the length of the pin (or fork, or paper clip) until the pin itself is able to attract other pins to it. We may even remember the explanation for this which was that for something to be magnetised, it had to have a clear magnetic orientation of North-South throughout its structure. Within the pin (or fork or paper clip) there are many small regions, called domains, which within themselves have a north-south orientation but they do not all point in the same way throughout the fork. Each little region points in a different direction to the others and so the net effect is that there is no overall North-South magnetism in the fork as a whole. As the strong magnet is used to stroke the fork, so the small regions move to align to the direction of the stroke of the magnet. The regions stop cancelling each other out and align so that the fork itself becomes a magnet with its own North-South.

inverted Aeropress and coffee stain
The link between coffee and the Barkhausen effect in magnets can be seen in this photo: a coffee spillage. It is the way that coffee evaporates and that coffee stains form that forms this physics connection between coffee and magnetism.

To return to our un-magnetised fork, you can imagine that where all these domains meet, there will be an area of confusion where the direction changes from one orientation to that of the neighbouring domain. This is called a ‘domain wall’ and it is these domain walls that are responsible for the Barkhausen effect. You can feel the effects of domains and domain walls in this experiment taken from the Institute of Physics Spark series: take two flat fridge magnets and turn them over so that the magnetic side of each faces the other. Move one of the magnets along the length of the other one. Think about how it feels to move it. Now move the same magnet perpendicular to the direction that you initially moved it in. Try it again. You will find that in one direction the movement feels smooth whereas in the other the magnets judder against each other, the movement is not smooth at all. You are feeling the effects of moving across a series of domains and domain walls, you can read more about the experiment here.

What actually happens as you bring a strong magnet towards an object such as a fork is that those domains in the fork that are aligned in the same direction as the magnet will tend to grow slightly at the expense of the ones that are not aligned with the magnet. The initial growth happens as the aligned domains get a bit bigger, a bit rounder and fatter. The domain walls bend a bit and the domains of the non-aligned regions get a bit thinner, a bit more squished. As the magnet is brought closer still, the aligned domains will actually start to grow at the expense of the non-aligned: the domain walls of the aligned domains will start to move outwards ‘eating’ into the neighbouring regions. It is at this point that you can pick up the Barkhausen effect because as the domain walls move, they can get stuck on defects in the metal rather like an elastic band would get stuck on an obstacle. The defect could be just one or two atoms that are out of place but the effect is that, just like the elastic band, the wall around the obstacle continues growing and the domain wall stretches more like an elastic band until pop – crack – the wall moves releasing a bit of energy that you pick up on the loudspeakers. This is what you hear as the Barkhausen effect. As the walls continue to grow so they will repeatedly get snagged on different defects in the metal and repeatedly ping – crack – into growth. Eventually, as the fork itself becomes magnetic* the last few non-aligned domains also start to align with the approaching strong magnet and the whole fork acts as if it is one magnet.

coffee ring, ink jet printing, organic electronics
A coffee stain. There are many experiments you can do at home with these.

The pinging domain walls have a direct link with an effect you can see in coffee, or more specifically spilled coffee. When you spill a few drops of coffee on a movable surface, you may have noticed that you can angle the surface a surprising amount before the drop starts to run down the side. You could try it now on a coaster if you have one available to you. The drop does not move because the edge is stuck, ‘pinned’, on defects on the surface of the coaster. These defects could be a crack in the material or a bit of dust or even a slight irregularity on the surface. Whatever it is, this defect acts to keep the edges of the drop in place. The first effect you would notice is that you can move the drop to a near vertical without it moving, the drop shape gets distorted but the drop itself does not move. The second effect is more subtle and is what happens if you leave the coffee drop there to dry.

Once spilled, the water in the droplet starts evaporating and eventually the droplet will dry leaving a coffee stain. The consequence of the pinning that you have just noticed is that the edges of the drop are quite stuck: the drop can’t just shrink. Instead, as the water evaporates, the drop will get flatter and because the water evaporates more quickly from the droplet edge (to see why click here), there will be a flow of water inside the drop from the centre to the edges. As the water flows outwards so it takes the coffee sediment with it which means that the dried coffee becomes a ring of sediment at the edge of the dried droplet.

Although it is on a different scale, it is the same sort of pinning that is happening in the coffee ring and in the Barkhausen effect. There are connections between physics and coffee to be found in many surprising places. Where will you find one today?

*This is an instance in which scientific English is not the same as English-English. In scientific-English, the fork is always a magnetic material it is just not fully magnetised. In English-English we tend to use the word ‘magnetic’ only for those materials that attract iron etc. to them. For ease of reading I have kept with the English-English usage here but if you are interested, you can read more in these links about magnetism and magnetic materials.


Coffee: emissions or waste?

Plastic free coffee? Is it possible? Is it desirable?

Plastic free July is nearly with us once again, prompting us to look again at the sustainability (or not) of the coffee we enjoy each day. Whether we drink our coffee at home or in a cafe, it is easy to see plastic items associated with the coffee. In a cafe there are the take-away, disposable, cups, together with the cartons of milk and perhaps, plastic cutlery. Even at home, we see the plastic packaging in the coffee bags that we buy or receive through the post and perhaps with the milk (or mylk) cartons that we ourselves are using. Some have argued that given that we are in a climate emergency, at this point we need to focus on the most urgent problem of all, the reduction of greenhouse gases. These are valid concerns and it is certainly true that the emissions costs associated with packaging and transporting items using low mass containers like plastic are lower than if the same product were transported in heavier, but more obviously sustainable, materials such as glass. Should this stop us from trying to reduce our plastic consumption and what hope is there that new technology can help us? These are questions we may like to ponder with a cup of coffee.

What is the problem for those of us who mostly brew and drink coffee at home? Here, the major sources of plastic packaging are likely to be in the bags that the coffee arrives in and in the packaging of the milk that we may use to accompany our coffee. Many speciality roasted coffee beans now arrive in LDPE plastic packaging. This is recyclable although most household collection services will not be able to process it. Fortunately there are places that you can take your coffee bags for recycling such as supermarket plastic bag recycling points. Alternatively, some coffee suppliers or roasters (eg. Dog & Hat) will offer to arrange recycling for you via Terracycle if you return the empty bags to them.

If you decide to buy your coffee in compostable packaging, look out for the “OK compost, home” label by Vincotte

Another popular packaging material for coffee bags is “compostable” packaging. This falls into two types, the compostable according to EN13432 and packaging that is fully home compostable (occasionally certified with the Vincotte OK Compost label). You can read more about the relative compostability of each type of packaging here, but it is worth noting that the majority of us do not have access to an industrial composting facility, nor can these bags be recycled with other plastic. Packaging that is only certified to EN13432 will not compost easily in a home composting environment. Be very careful when buying “compostable” packaging. Less commonly, coffee could arrive in cans, paper or even (in the case of supermarket instant coffee) glass packaging. These can be easily recycled but may have higher carbon emissions costs associated with them, both in terms of the cost of transport and in terms of the cost of manufacture of the packaging.

Milk cartons are often recyclable or even, in the case of glass milk bottles, reusable and then recyclable. Those of us using non-dairy ‘mylks’ could try to eliminate the plastic altogether by buying oats or soy beans from a zero waste shop and then making our own according to recipes you can find online.

So it seems that we have a problem: we still have a lot of waste material when we drink coffee. Can technology help us? Recently, a new form of plant based ‘plastic’ material has been demonstrated. This material is able to be formed and used in a similar way to commercial plastics and may be suitable for food packaging. Not only that, but the material is fully degradable, though more details are needed here before we can know whether this is degradable as we would understand it or degradable under certain conditions similar to the ‘industrially compostable’ packaging. Nonetheless it is highly encouraging that work is being done on materials that will provide the low carbon footprint and food-safety aspect of plastic combined with the reduced problems of landfill waste. While still a few years off, such technology may provide a longer term solution to our current waste/emissions problem.

There is a good (physics based) reason that dairy milk is often supplied in semi-opaque bottles: the packaging protects the milk within from UV light that would otherwise cause it to spoil.

Which leaves us with the initial objection. Given the state of our climate emergency with regards to greenhouse gases, should we really be concentrating on reducing greenhouse gas emissions rather than on reducing plastic waste? Fortunately, there are choices that you can make that will reduce the carbon cost of coffee, regardless of the packaging it arrives in. There are some well researched and thoughtful articles available about the carbon footprint of coffee and what you can do, including this series from United Baristas. However, it is worth noting that even if we do decide to prioritise greenhouse gas emissions, recent work has shown that the methane emissions of plastic as it degrades has been previously under appreciated. Perhaps what we can do is make choices that reflect our concern for the planet that we call home. Clearly this means reducing as far as practicable our greenhouse gas emissions, but it also means living as sustainably/zero waste as possible. We each need to find the balance that is suitable for the situation that we each find ourselves in. A significant benefit of Plastic free July is that it gives us an opportunity to examine how much of our lives are made easier, or in some cases possible, by the use of plastic, in short, how much we rely on it. It is not necessarily about changing our lives forever, though maybe we will find some changes good to carry on with, but becoming more aware of the problems that we really have.

Have you signed up for Plastic Free July? What are you doing to reduce the environmental impact you have while still enjoying a cup of coffee? And do you have a good recipe for oat milk? Do let me know either on Twitter, Facebook or in the comments below. In the meanwhile, a happy Plastic Free July to you all.

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.