angstrom – Bean Thinking

coffee Coromandel Coast, Indian Shade grown coffee — The coffee from Coromandel Coast. Chocolate, ginger and nougat. I got the chocolate and the nougat, though the taste profile changed quite significantly between brewing by a V60 or an Aeropress

The coffee from Coromandel Coast arrived in a box, in bags that were suitable for industrial composting, each printed with an elephant on the packaging. The elephant is the logo of Coromandel Coast and is a nod to the fact that all of their coffees (which include single origins and blends) originate in India. All of the coffees have been shade grown which helps with the carbon footprint of the coffee, hence the slogan “Climate solution in your cup”. Which means that it would have been easy to do a coffee-physics review based on the different ways that coffee can be grown and why shade grown coffee can be part of a climate solution for coffee. But that would have been too quick; one of the motivations for cafe-physics reviews (and the related coffee-physics reviews) is to slow down and explore how sitting down and contemplating a cafe (or just coffee) can lead to so many different but connected thought trains. Given that your attention is drawn to the issues of climate change, and what you can do, from the instant you order from Coromandel Coast, this seems to be too obvious, even if an incredibly useful, thought train. So, if you would like to follow that thought train while contemplating the coffee you are drinking, you can read more about the environmental impact of coffee growing here or here and the importance of shade grown coffee here. An alternative thought train may be provided by the elephants.

I purchased two coffees from Coromandel Coast: Ganga and Chalukya. The Ganga was a washed catuai peaberry coffee with tasting notes of “chocolate, ginger and nougat”. The chocolate definitely comes through when brewed in the V60 and the pureover while the Aeropress produces a somehow cleaner taste profile that I find characteristic of washed coffees. Coromandel Coast was established in 2017-8 and is both a coffee roaster and a cafe based in Croydon. All of the packaging is recyclable or compostable, including the box it arrives in which is additionally re-usable (and will be reused again a couple of times before it is eventually recycled).

The elephant stamp. Is every copy identical? Could we use one elephant to understand the others?

The ink-stamped elephant on the box is a nice touch and echoed on the coffee bags. You could perhaps start to think about ink printing, dyes and the invention of the printing press, there are plenty of thought-paths that open themselves out. But a chance conversation over the coffee provided a different direction into the ways in which physics is taught at schools.

It appears that the school of my interlocutor that day initiated the physics course with a very boring set of classes on units. I was asked that morning: why would the teacher have started teaching physics with such a boring set of lessons? But I wondered a separate question, how can units be boring? How sad that they were made to be so. For although they are of fundamental importance in how we explore and understand our world, and could perhaps be quite dry, they can also link elephants to the Sun and to the work we now do to understand coffee better. For if we start with elephants, it was a favourite unit of my physics teacher. Used for all manner of things when we omitted to include the units in our answers. Consider the coffee: it comes in bags of 250 what? 250 elephants? or 250 grammes? The elephant became a unit of frustration for the lack of stated proper units. But we can push the Coromandel Coast elephant link a bit further, for each elephant on the packet is an ink-stamped copy. They are different but identical, they serve as a standard.

neon sign, light emission — Light is emitted from different chemicals at certain, definite wavelengths. This is an effect you will have seen on many a high street in these neon signs where the colour is determined by the composition of the gas within the sign. We can use the reverse of this to identify chemicals based on what wavelengths they absorb. But to do that, we need to know that we are all measuring in the same units.

And the standards are important for units because we need to know that we are all measuring the same thing. When Anders Angstrom was measuring the absorption and emission spectra of the Sun and of different gases, he quoted the absorption lines in units of 1/10 of a nanometre (a unit now called the Angstrom). Different gasses will absorb (or emit) light at very specific frequencies or wavelengths. Being a very careful experimentalist, Angstrom had ensured that his measurements of the wavelengths that were absorbed or emitted were checked against the standard measure of length of the day, the metre. But at the time, the metre was defined by the length of a metal rod stored in Paris. All other standards of the metre were copies of this original one, including the metre kept at Uppsala where Angstrom was doing his experiments. An issue with metals is that they will age. With time you will get some shrinkage and some expansion owing to the formation of oxides etc. on the metal. The metre in Paris had aged in a different way to that in Uppsala which was just a tiny bit shorter than the Paris metre*. These differences would not be noticeable were Angstrom measuring the size of elephants, but instead he was concerned with measurements that were one ten-billionth of a metre. And at this scale, it mattered a great deal. Angstrom was aware of the systematic error in his results but it wasn’t until after his death that the error was fully hunted down and corrected for.

The position of the lines that Angstrom had been measuring reveal the chemical composition of the gases, and so knowing whether a line appears at 700 or 710 nm, reveals information about the chemical studied. We still use these spectroscopy techniques, not just for understanding gases, but also for checking the composition of medicines and for understanding the differences between Arabica and Robusta coffees. Which brings us back to the coffee, for while we no longer use a physical measure of length as our standard metre, we still use a standard definition of the metre that allows us to compare coffees and stellar spectra. It also allows us to appreciate the beauty in the uniformity of an ink-stamped elephant on a box housing an interesting and flavourful, climate sensitive, coffee.

You can order from Coromandel Coast here, or (post-lockdown) visit the cafe at Filtr, 53 Limpsfield Road, S. Croydon,, CR2 9LB

*To read more about the history of the definitions of units including the metre, click here. This anecdote was originally recorded in a book that I do not have physical access to at the moment owing to coronavirus restrictions. As soon as I get the name/author of the book, I’ll include it here.

Setting standards at Brill, Exmouth Market

Brill, Exmouth Market, neon, architectural history — The neon lit “Brill” from the back of the cafe. You can also see evidence of an old arch in the brickwork, an old doorway?

Brill on Exmouth Market has quite a history. Originally a record store, it has evolved into a music shop/cafe more recently. On my recent visit, I ordered a very good Americano (beans from Officina Coffee Roasters) and although cakes were on sale, it was a small bar of Green & Blacks chocolate that appealed to me a bit more that day. It is a small cafe and so the few seats that are upstairs were occupied. This turned out to be a good thing though because I noticed a sign indicating that there were more seats downstairs, which actually meant that there was seating in a lovely little courtyard/garden at the back of Brill. Although it was originally locked (it was February and fairly dismal when I visited, who in their right mind would want to sit in the garden?), the friendly staff unlocked it and quickly cleaned one of the tables so that I could enjoy my coffee and chocolate in peace in central London. Indeed, the occasional (inevitable?) sound of sirens in the distance only served to emphasise the tranquility of the courtyard. The courtyard has four tables and a glitter-ball in the corner hanging from a tree. There was a lot to appreciate outside, both in terms of the science and the history of the place: Leaves deposited by vortices in corners of the yard with brickwork that suggested a significant re-build has occurred to this cafe.

But from my vantage point, it was the word ‘Brill’, lit up in neon lighting inside the cafe, that caught my attention. Neon lights are always interesting to me because their colour is so suggestive of the atoms that make up the light. The colour of a neon light is determined by the energy levels of the atoms that make up the light, the gas ‘neon’ shines red, hence neon lights. But if you wanted blue ‘neon’ lights you could use mercury as the vapour in the tube instead of neon, it is all about the energy levels of the atoms in the gas in the tubes.

glitter ball, disco at Brill Exmouth Market — A glitter ball in the corner of the courtyard at Brill

Under certain conditions, cadmium also emits a red light which brings us to the subject of this cafe-physics review: The definition of length. How is it that we can all agree on what ‘one metre’ is, or even one ‘inch’? Perhaps you are wondering how the red light emitted by cadmium, (or neon), relates to the definition of the metre? It’s about standards and definitions. Up until about 1960, the standard unit of length (the metre) was measured with reference to an actual, physical, metal rod kept in Paris with two scratches carved into it, one metre apart. Any arguments about the precise length of a metre could be settled by referring to the metre, this metal bar in Paris. But of course there were problems, the first of which was that the metre was in Paris. Perhaps you would think it easy to make copies? Yet in the nineteenth century this was already becoming a problem, the measurements that were being made were becoming too precise. Anders Ångstrom’s pioneering work with spectroscopy (investigation of elements by the colours that they emit/absorb) revealed a small difference between the metre kept in Uppsala (where Ångstrom was based) and that kept in Paris. Although the difference was tiny, when it was compared with what people had started to measure, it became significant. Then there was the question of the scratches: Would you measure the metre between the furthest two points of the scratch? Or the closest? Then an even worse problem was discovered: The rod was shrinking! If you’re tempted to abandon metric units and hark back to Imperial units, bear in mind that the UK Imperial Yard was shrinking even faster. No, something had to be done and that something involved changing the definition of the metre fundamentally.

It is here that cadmium comes in to the story. Rather than use a physical length that we could all measure, the people whose job it is to define our base units decided that the definition of the metre would be with reference to the wavelength of the red light of Cadmium. I do not know why they did not want to use the red of neon lights but even with cadmium it quickly became apparent that there was a problem. The problem was that cadmium exists as several isotopes, all having a very slightly different ‘colour’ of red light that they emit. So, rather than cadmium, in 1960 they settled on the orange line of Krypton as the definition of the metre. One metre was then defined as 1650763.73 vacuum wavelengths of Krypton. That was the definition for over twenty years before the definition of the metre was updated again in 1983. It is now defined as “the length travelled by light in a vacuum during a time interval of 1/299792458 of a second”.

Perhaps it is not a definition that you or I could use, we’d probably still refer to our metre rule! Nonetheless this definition does allow people to perform experiments that need very precise and very accurate measurements of lengths. These standards are important for extremely sensitive measurements such as that needed to detect gravitational waves with the LIGO experiment, reported a few weeks ago. The neon lights at ‘Brill’ do indeed suggest a story that goes way back in time, both for the cafe and for the science.

Brill is at 27 Exmouth Market, EC1R 4QL

Spectroscopy information from “Spectrophysics”, by AP Thorne, Chapman and Hall Ltd, 1974