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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

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Listening to coffee

coffee tasting notes
Do we pay attention long enough to discern tasting notes such as those in the cup profile here? My current coffee, from Amoret – where you can currently buy this coffee and see if you can ‘hear’ these tasting notes.

Do we taste and appreciate coffee in a similar way to the manner in which we would appreciate a complex piece of music?

Perhaps the idea seems fanciful, maybe even non-sensical. How could it be that the way that we appreciate flavour is similar to how we listen (and how is this related to physics)? Coming from someone who is a clear amateur in both appreciating coffee and appreciating music, you would be forgiven for being a little dismissive (though I’d hope that you would trust me on the fact that there will be a link with physics). But, by being an amateur in taste, I think it is possible to see a first connection: it is in how much attention and learning (training or practise) we give to our perception of our sensation.

A great nineteenth century physicist, Hermann von Helmholtz, was also a medical doctor (and a keen amateur musician). In thinking about how we listen to sounds, Helmholtz suggested that “sensation” was physiological – the effect of the note on our ear or the chemical on our taste buds – but “perception” was psychological – how we hear the notes together or discern the flavour notes of a particular coffee.

Think about how you recognise a type of coffee that you love, or distinguish between a washed and a natural? Or how you know that the instrument that you can hear through the speakers is a violin. With the latter, it is because the fundamental note played is accompanied by a set of harmonics that are distinctive to that instrument. A flute or a piano will have a different set of harmonics and so a different sound. It has been through listening to different instruments that we have learned to identify them, but it is through training and practise (or experimental physics) that we can start to discern the various harmonics.

The way that we hear the different harmonics concerns the way that their waveforms add together. This is underpinned mathematically by Fourier analysis, which describes how any wave form can be made up of a summation of sinusoidal waves. Incidentally Joseph Fourier was also the scientist who proposed the idea of a greenhouse effect back in 1824 (which you can read more about here, or in relation to coffee here). Where you may have experienced these wave combinations is in tuning a guitar (or similar instrument). When you play two notes that are nearly exactly the same, but not quite, the waves of each will add together as they make their way from the plucked string to your ear. As they travel, at some points the two waves will combine to form a large amplitude wave and at other points the two waves will exactly cancel out. We would hear it as a type of “beating” (on-off-on-off) that you can hear as you attempt to tune the two strings together to play the same note. When the two plucked strings play the same note, the two waves will only add together to be louder, they will not cancel each other out and you should hear one, continuous and smooth tone.

Guitar, coffee
From resonances to the way we sense the world around us, there are a number of connections between coffee and music.

You can be an amateur musician and still appreciate the physics that is underlying this aspect of your ability to play (tuneful) music. But Helmholtz had noted a bit more than this. Owing to the way that waves combine, and which in the simplest case gives the ‘beats’ that you notice as you tune the guitar, when you play two notes together, if you listen carefully you will not only hear the two notes, but a third, a so-called combination tone. Discovered by the organist Georg Andreas Sorge in 1740 (you can hear one of his compositions here), this third note has the frequency of the first minus the second note. So, for example, if you were listening to C4 and G4 (at 264 and 396 Hz respectively), you would additionally hear a note at 132 Hz (C3). It is incredibly difficult to be able to discern such a combination tone which maybe part of the reason that it took so long to discover them. To learn to hear the note would take a lot of practise and no less attention when listening to a piece of music. How often do we truly listen to a piece of music to be able to do this?

Where Helmholtz came into this was that, not only did he explain the origin of this combination tone (in terms of the way the waves combined), he invented a device that allowed us mere amateurs to be able to hear it. One end of a tube was designed to fit snugly into the listener’s ear, with the other end open to the sound. The size of the tube determined which frequency of sound would reach the ear. Using these devices Helmholtz showed that, not only was the combination tone a real phenomenon, it had a mathematical basis in physics. And of course there was more. If you could hear the note of the subtraction of the two sound frequencies, you should be able to hear the note of the sum of these two frequencies too. In the example above, you should hear a note at 660 Hz. This combination tone had never been heard before, it came as a prediction of Helmholtz’s theory of how sounds added, itself sparked by a profound attention that he paid to listening to music.

Using a similar resonator to that used for distinguishing the combination tone based on difference, Helmholtz showed that this note too was audible. It was a prediction of what we should be able to hear based on the physics of what was going on. It extended our ability to perceive music.

The beat of a drum or the resonance on our coffee – the links between music and coffee go further than this.

In what way is this linked to tasting coffee? It is in how we learn to distinguish our taste. Just as a musician can, with time and attention, learn to discern at least a difference combination tone so, with practise, we can train our palette to discern intensities of sweet, of sour and subtleties of acids. We amateurs can hone our skills using the SCAA coffee flavour wheel, tasting each coffee we prepare to detect the sweet, roasted or floral notes that we read about on the packs of coffee we buy. To actually describe these coffees requires skill and a large amount of practise in cupping coffee. But to develop those skills to the point of being Q-grader requires an attention to detail that is quite incredible (you can read about the training needed to become a Q-grader here). Just as with music, for some of us, even a lot of practise will only ever allow us to appreciate the work of others rather than produce it ourselves.

Of course, training our palettes requires drinking a lot of coffee, but it also means making mixtures of salty or sweet liquids and thinking about how they taste. Cupping hundreds, thousands, of coffees and paying attention to the complete flavour profile of them. Is there a flavour equivalent to Helmholtz’s summation combination tone that is waiting to be discovered? It will need someone skilled in matters of coffee appreciation and experimental science. Someone who has demonstrated the attention required to carefully listen to the taste of our coffee but who can also work on the theory of how those flavours are perceived. There are many people working on the physics, chemistry and physiology of taste and smell. Could you be one of them?

This is the third in a series of the contributions of Hermann von Helmholtz to our appreciation of the physics in coffee – it goes far beyond the vortices he may be famous for. The introduction is here while the contribution of Helmholtz to our understanding of colour and vision is here. Future posts will consider hot coffee and of course, what happens as we stir it. Much of the material for this post has been found as a result of reading Michel Meulder’s excellent biography of Helmholtz: “Helmholtz: from enlightenment to neuroscience” (2001).

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Coffee review Observations slow

Constructive interference at Frequency, Kings Cross

exterior of Frequency Kings Cross
Note the tiles. Frequency, Kings Cross on a rainy day.

It was a rainy afternoon when we ventured to Kings Cross and into Frequency. Suggested by the London’s Best Coffee App as the closest café to our then location, we made our way through puddles and rain onto Kings Cross Road. At that point, a brain-freeze meant that we couldn’t see where Frequency should be. The map on the app was implying that we were extremely close but there didn’t seem to be a café around. Then we saw it in front of us! The striking black and white tiling on the floor somehow hiding this shop-front from view.

The tables inside matched the tiling outside. Black and white triangles meeting at a point. My long black (from Workshop) was placed close to the intersection of these triangles. The coffee arrived in a mug, more cylindrical than standard coffee cups and so closer to mathematical models of coffee cups that are used in explanations of convection and rotation in the cups. An interesting change of aesthetic that also changes the internal dynamics of the coffee. A nice touch was that the mugs were also coordinated with the tiling, though to be fair I hadn’t noticed that at the time.

The coffee itself was extremely fruity, a lovely warming brew to enjoy while watching the rain outside. The interior of the café meanwhile was decorated with a lot of wood around together with a couple of music stands. Perhaps the music stands make sense in a café named Frequency. Indeed, according to the review on London’s Best Coffee (or as it is now known, Best Coffee), there are plans to build a music recording studio here as well as having live musical performances. However, also mentioned in that review was the fact that this café had been designed and built from scratch with the help only of online tutorials. Which makes a particularly resonant connection with something I noticed here.

mug of coffee at Frequency
Coffee at Frequency.

What caught my eye as I contemplated this café was the one bit of bright colour on the ceiling. It was also something that hints at problems that can crop up when you design and build your own electrical circuits: Parallel wires (in this case leading to the lightbulbs). Perhaps in the café, these were intended to represent music staves, certainly that would fit in the theme. However to an experimental physicist who dabbles in designing pieces of kit for electrical measurements, these parallel lines leading to a light mean something entirely different.

They mean noise.

When you are designing a piece of electrical equipment to be used for measuring voltages across an unknown material, there often ends up being a lot of wiring in the probe as well as the bit at the end of the instrument that you are actually interested in. Some of this has a practical purpose. Often we want to measure something when it is very cold so it has to be on the end of a metal rod that is inserted into a vat of liquid nitrogen or helium or that is held in a strong magnetic field. When designing the probe, the bits of wire leading to the interesting bit at the end of the rod can be almost as important to consider as the measuring bit itself.

To see why, perhaps you remember putting compasses around a wire carrying an electric current? As the electric current is switched on, the compass needles move indicating that the electrical current generates a magnetic field. The basis of electric motors and dynamos, the idea is that an electrical current will generate a magnetic field and a moving magnetic field would generate an electrical current.

transmission lines, electrical noise
The wires to the light bulbs in Frequency Kings Cross. Memories of transmission line lab experiments.

Now, imagine two parallel wires each carrying an electrical current. Both of them will produce a magnetic field, but if there is a varying current in one or other of the wires, the magnetic field will also be varying. And if there’s a varying magnetic field, it can induce a current in the neighbouring wire. In this way, electrical noise on one of the wires can be transmitted to the other.

Such electrical noise can be inconvenient if we are trying to speak on the phone and just hear a ‘hiss’, or if we are trying to listen to the radio and just can’t tune in. It could also be more problematic, imagine if there was a lot of electric noise on a machine measuring the electrical activity of your heart, an ECG. Consequently, there are whole books written on how to reduce electrical noise pick up. However one simple way to reduce a lot of the noise is to get rid of those parallel lines the like of which are on the ceiling at Frequency by twisting them together. The ‘twisted pair’ is a great way of making more sensitive electrical measurements. And if you wanted to reduce the noise further, you can shield the twisted pair with another conductor and ground (or earth) it.

The twisted pair works by reducing the magnetic coupling between the two wires. Of course, it may not be quite as immediately aesthetically pleasing as parallel wires on a ceiling but there is something quite elegant about a well made and shielded twisted pair properly grounded in an electrical circuit. And when you put everything together, ground it properly and see the noise from the electrical mains (at 50Hz) disappear, there is a certain pleasing effect from that too.

Café design as a clue to electrical design. Frequency can be found at 121 Kings Cross Road, WC1X

 

Categories
Home experiments

The hot chocolate effect

hot chocolate effect, Raphas
A ready prepared hot chocolate

This is an effect that reveals how sound travels in liquids. It enables us to understand the milk steaming process involved in making lattes and yet, it can be studied in your kitchen. It has an alternative name, “The instant coffee effect”, but we won’t mention that on this website any further. To study it you will need,

1) a mug (cylindrical is preferable),
2) some hot chocolate powder (no, instant coffee really will not do even if it does work)
3) a teaspoon
4) a wooden chopstick (optional, you can use your knuckle)

Make the hot chocolate as you usually would and stir. Then, remove the spoon and repeatedly tap on the bottom of the mug with the wooden chopstick (you could instead use your knuckle). Over the course of about a minute, you will hear the note made by the chopstick rise (not having a musical ear, I will have to trust that this can be by as much as three octaves).

resonator, mouth organ
The length of the pipes in this mouth organ determine the note heard. Photo © The Trustees of the British Museum

What is happening? Well, just like an organ pipe, the hot chocolate mug acts as a resonator. As the bottom surface of the hot chocolate is fixed in the mug and the top surface is open to the air, the lowest frequency of sound wave that the hot chocolate resonator sustains is a quarter wavelength. The note that you hear depends not just on the wavelength, but also on the speed of sound in the hot chocolate, and it is this last bit that is changing. When you put in the water and stir, you introduce air bubbles into the drink. With time (and with tapping the bottom surface), the air bubbles leave the hot chocolate. The speed of sound in a hot chocolate/air bubble mixture is lower than the speed of sound in hot chocolate without air bubbles. Consequently, the frequency of the note you hear is higher in the hot chocolate without bubbles than in the former case.

Let’s use this to make a prediction about what happens when a barista steams milk ready for a latte. At first, the steam wand introduces air and bubbles into the mixture but it is not yet warming the milk considerably. From above, we expect that the speed of sound will decrease as the bubbles are introduced. This will have the effect of making the ‘note’ that you hear on steaming the milk, lower. At the same time the resonator size is increasing (as the new bubbles push the liquid up the sides of the pitcher). This too will act to decrease the note that is heard as you steam (though the froth will also act to damp the vibration, we’ll neglect this effect for the first approximation). At a certain point, the steam wand will start to heat the milk. The speed of sound increases with the temperature of the milk and so the note will get higher as the milk gets warmer.

So this is my prediction, musically inclined baristas can tell me if there is any truth in this:

1) On initially putting the steam wand into the cold milk, the tone of the note heard as the milk is steamed, will decrease.
2) This decrease will continue for some time until the milk starts to get warm when the note increases again.
3) Towards the end of the process, the note heard on steaming the milk will continue to increase until you stop frothing.
4) It should be possible, by listening to the milk being steamed, to know when the milk is ready for your latte just by listening to it (if you are experienced and always use similar amounts of milk per latte drink).

So, let me know if this is right and, if it is wrong, why not let me know what you think is happening instead. I’d be interested to know your insights into the hot chocolate effect in a milk pitcher.