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Pure Over Brewing

The Pure Over brewing balanced on my V60 jug. It may seem an odd thing to do, but brewing into a clear glass container that can then be poured into a mug makes a better coffee. Firstly, the brew speed can more easily be monitored, and secondly, any fines that do fall through the glass filter basket are left in the bottom of the jug and do not make it into the final coffee cup.

The kickstarter project promised an all glass coffee drip-brewer without the need for paper filters: great coffee and an elegant brewer, all without waste. But how does the Pure Over perform in practise?

Created by coffee loving glass blower, Etai Rahmil in Portland, Oregon, prototypes of the Pure Over were developed with “The Crucible”, a non-profit art-school in the area. The Pure Over was designed partly to avoid the need for disposable coffee filters during coffee brewing. Although the 275bn disposable filters/year claimed in the kickstarter video sounds an overly high estimate of the number of filters used (though do let me know if you have a referenced value for this), it is true that disposable filters do come with an environmental cost, which could build up and be appreciable. So, if we can reduce our impact on that, it would be a good thing to do.

Now available to purchase online, I got my Pure Over in the initial Kickstarter campaign. When it arrived in early March 2021, everything about it was elegant: the glass had an aesthetic to it that was quite striking. It is easy to understand how the inventors of the Pure Over can describe their ambition as “to make our world a more meaningful and beautiful place”. But there was an immediate puzzle: the holes for the filtration basket seemed larger than I would have expected, would this really work?

I have in the past tried changing a Chemex paper filter for a metal Kone in an effort to reduce my use of paper filters. However, I never got on with the Kone. The filter in the metal was fine enough that the coffee grounds became stuck in it and it was consequently a bit of a pain to clean. At the same time, I never managed to optimise the cup it brewed. I should say that some people have found metal filters and the Kone great products, but I was not one of them. Seeing the glass filter basket therefore made me concerned that this elegant brewer would be pleasing to the eye but never to the palette.

I am happy to say that I was wrong. The Pure Over can make a great cup of coffee and look good too, but it does have a couple of quirks.

The funnel from the Aeropress is brilliant at directing the coffee grounds into the base of the Pour Over. Filling the grinds over a bowl means that any fines that fall through the glass holes can be rescued and put back into the top of the coffee bed. Thereafter the bed is quite stable.

Firstly the grind. The temptation (mentioned in some of the user-reviews of the Pure Over) is to assume that because the holes in the glass filter basket are quite large, a fairly coarse grind would be preferable so that the coffee does not fall through. This is a mistake. The Pure Over works because the water filters through the coffee bed. When the grind is too coarse, rather than produce a thick matrix of coffee for the water to percolate through, the grounds cannot pack closely and what happens is that a large amount of empty space opens up through the coffee percolation ‘bed’. This means that the water flows through the coffee bed too quickly, barely extracting any of the flavour compounds. The resultant cup is weak and unpleasant. If the grind is too fine on the other hand, it will indeed fall through the holes which ultimately block during brewing and the coffee becomes over extracted. The answer is to use a fairly fine grind but not too fine, I use ever so slightly coarser than the grind I use for making V60s. Of course, some coffee grinds do fall through initially, but if you hold the Pure Over over a bowl while you put the coffee grounds into it, you can then catch those that fall through and put them back in at the top. As these are finer grinds anyway, this has the effect of blocking some of the holes (vacancies) that form in the coffee bed and enhances the extraction of the coffee.

Secondly, the part-filter, part-immersion style of the Pure Over means that the water temperature is critical. Because you are using a fairly fine grind within what is partially an immersion brewer, using water that is too hot can result in the coffee being over extracted and bitter. Therefore, in addition to playing with the grind size, it is important to experiment with the brew temperature.

Lastly, the Pure Over comes with a diffusion basket which slows the pour of the water and spreads it over the coffee grounds. This turns out to be important because if you pour the water directly from a kettle it can lead to cratering within the coffee bed and result in a non-uniform percolation through the bed.

The diffuser on top of the Pour Over. The design is supposed to reduce the speed at which the water lands on the coffee bed as well as distributing the pour across the whole coffee bed. There is a lot of physics here, it will have to wait for another post.

When you have optimised these parameters (grind size, water temperature and speed of pour through the diffusion basket), the resultant cup is very much worth it. I found the coffees I made with it to have a character similar to the character that was apparent when I brewed with the V60 and different to the character that the coffee acquired when I brewed the same coffee with an Aeropress. The oils and some fines do come through, which is why I brew the Pure Over into my V60 jug and then pour that into my mug. This has the dual benefit of my being able to see how fast the coffee is filtering through the Pure Over basket and it resulting in a ‘cleaner’ cup as the fines are left at the bottom of the jug when I pour the coffee into the cup.

Over all, a really good cup of filter coffee without a filter. You can read another review of it in Barista Magazine here.

There is additionally a lot of physics involved in how the coffee brews. Although I didn’t mention it here, there is a link to traffic jams and filtration, a link to some novel methods now used in the organic farming of coffee beans and a connection to steam engines. There are also other links that I think do help to contribute to a more meaningful and beautiful world, so please do return in future weeks for an exploration of some of the physics involved in this interesting new addition to coffee brewing.

Coffee Elephants

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.

Thought bubble

inverted Aeropress and coffee stain
A problematic inversion with the Aeropress. This brew method offers plenty of physics connections for those who look.

The Aeropress is not a brewing technique that creates many bubbles on the surface of a coffee. Unlike the crema of an espresso or the iridescent bubbles on top of a black coffee prepared using a cafetiere, the surface of an Aeropress coffee could be thought of as a bit, well, dull. The paper filter within the Aeropress removes many of the oils while this calm brew method generally does not create the turbulence needed to produce bubbles that cling to the side of the resultant cup. Yet it is this brew method that can provide a bubble link to climate change and coffee roasting, and to see why, we need to pay careful attention to our brew.

Although there are many techniques for brewing with the Aeropress (you could try the guide here or here), one step common to most brew guides is that you will need to rinse the paper filter in the basket before you brew. The rinsing step removes a potential paper-y taste from the filter as well as helping it to stay fixed in position (the reason for this could be the subject of another post). Importantly for this particular post though, it also traps air within the holes of the filter, which you can see in the photograph.

The bubble is trapped owing to the strong surface tension of the water dripping from the basket. You could perhaps test this by adding soap to your brewing water in order to reduce the surface tension and watching to see if the number of trapped air bubbles you produce decreases. Or perhaps there are limits to what you are prepared to do with coffee in order to see some physics. Whichever way, the fact that the bubble is there at all can lead us down several thought alleys.

Perhaps we start to think about air that is trapped within water. In a way, this air is characteristic of what is around us now: the pollutants, the oxygen level etc. Which, while it may seem an obvious statement has an immediate consequence. Air that is trapped in water that is then frozen remains as a record of the composition of the air at the exact point of time that it was trapped. So if layers of ice form trapping layers of bubbles of air, and this happens for many years, we can analyse the composition of the trapped air bubble to discover what the atmosphere was like 100, 1000 or 100 000 years ago. This offers a way of understanding how concentrations of carbon dioxide, for example, have varied over the millennia.

An example of air bubbles within the Aeropress filter. In addition to the long bubble caused by incorrect filter placement, you can see two air bubbles in the hollows of the plastic basket under the paper filter (circled with a dotted red line).

But maybe your mind stays with the coffee: what about air bubbles within a coffee bean? In order to turn the green coffee bean into the aromatic substance that we all appreciate, it needs to be roasted. Roasting coffee is a fantastic mix of science and art: using the knowledge of what happens during roasting and applying (and playing with) that knowledge to produce great tasting coffees. At its core, the roasting process involves heating the beans for a certain amount of time in order for the water to come out of the green bean, the sugars to turn in the Maillard reactions and for the various aromatics to develop chemically. The green bean also undergoes physical changes. The colour is altered, the bean expands and the internal gases (first water, then carbon dioxide) build up pressure within the bean and then crack open some of the cell structures during roasting. And while this sounds fairly simple, there are ‘arts’ involved in roasting: how long do you let the beans dry? How fast do you take the bean through the Maillard processes? Do you let the beans cool slowly or cool them really fast to stop any further chemical reactions immediately? Each of these has effects on the final flavour of the bean, some which are fairly similar across the industry, some which rely much more on the creativity and discernment of the roaster.

There are obvious analogues to materials physics and materials chemistry. In order to make the different materials that are studied, raw materials are often heated to a high temperature and left for a significant time before either being cooled slowly or suddenly, by quenching. There is the science: the temperature at which different reactions occur and the way that materials form together in order to produce grains that get larger as they are heated for longer. And then there is the art, how fast to heat, how long to leave it for, whether to cool or quench, even what gas should be used to flow over the forming compounds. Small differences in how the materials are heat treated can have large consequences on the applicability and strength of the final material, with applications from gear cogs to airplane engines.

Kamwangi and Gelana coffee under the microscope
A fluorescence microscope image magnified 20x of two types of coffee after roasting. The microstructure (including pore development) will depend on the type of coffee as well as the style of roasting.

To return to the coffee roasting, the effect of the temperature has a similar marked effect on the microstructure of the resultant bean which will have consequences for how the roast ages. For example, a study about 20 years ago showed the differences between coffee beans roasted to an equivalent level (measured by moisture loss and colour analysis of the roast) at two different temperatures. The physical properties of the final roasted beans were very different. Not only did the higher temperature (260C) roasted beans show a larger volume increase compared to the low temperature (220 ) roasted beans, the pore structures of the beans were also different. For the higher temperature roasts, larger micropores had opened up within the cell walls of the roasted coffee. These pores connected to regions deep within the bean that would otherwise be cut off from the air: trapped bubbles within the bean that, with the higher temperature roasting, now have a way of escaping to the outer surface. Indeed, one day after roasting, the authors of the study saw, under a microscope, many tiny spots of coffee oil seeping from the interior of the higher temperature roasted bean and to the surface.

This has consequences for how the bean will age after roasting and so how we as consumers will appreciate the drink. Roasting is a dark art indeed, and one that I’m grateful for the many skilful practitioners that we now have around. Roasters who help us to appreciate the flavour of our coffee, as well as the directions of thought it takes us on.

In search of origins

Amaje coffee
Buriso Amaje Coffee from Ethiopia via Amoret Coffee in Notting Hill. The Jimma 74158 and 74160 varietals are selections from coffee grown in the wild.

It was a goat herder named Kaldi, so the story goes, who first noticed the effect of coffee beans on the the energy levels of his goats. After telling the local abbot of his observations, the monks at the nearby monastery realised that this drink could help them stay awake during prayer and so the reputation, and consumption, of coffee spread from Ethiopia and then throughout the world.

While the details may be questionable, there is evidence that the coffee plant originated in Ethiopia. Coffee still grows wild in parts of Ethiopia and the oldest varietals are also to be found there. And so, when I realised that my latest coffee was an Ethiopian Natural of varietal Jimma 74158 and 74160, roasted by Amoret coffee in Notting Hill, I thought, why not do a coffee-physics review rather than a cafe-physics review? For there are always surprising links to physics when you stop to think about them, whether you are in a cafe or sampling a new bag of beans.

This particular coffee was grown by Buriso Amaje in the Bensa District of the Sidama region of Ethiopia. The varietals were selections from the Jimma Research Centre from wild plants that showed resistance to coffee berry disease and were also high yielding. Grown at an altitude of 2050m, the naturally processed coffee came with tasting notes of “Blueberry muffin, white chocolate” and “rose petal” among others. Brewed through a V60, it is immediately clear it is a naturally processed coffee, the complex aroma of a rich natural released with the bloom. Indeed, the bloom was fantastically lively with the grounds rising up with the gas escaping beneath them in a manner reminiscent of bubbling porridge (but much more aromatic). And while I lack the evocative vocabulary of Amoret’s tasting notes, the fruity and sweet notes were obvious, with blueberry a clear descriptive term while I would also go for jasmine and a slight molasses taste. A lovely coffee.

Brewing it again with an Aeropress, the tasting notes were different. We could start to ponder how the brew method affects the flavour profile. But then we could go further, how would this coffee taste if brewed using the Ethiopian coffee ceremony? Which leads to further questions about altogether different origins. Where did this come from and how do our methods of experiencing something emphasise some aspects while reducing others? Ethiopia offers a rich thought current if we consider how things originated because it is not just known for its coffee, Ethiopia is also home to some of the world’s oldest gold mines. Today, one of the larger gold mines in Ethiopia lies just to the North West of where this coffee came from, while a similar distance to the south east is a region rich in tantalum and niobium. We need tantalum for the capacitors used in our electronic devices. In fact, there is most likely tantalum in the device you are using to read this. While niobium is used to strengthen steel and other materials as well as in the superconductors within MRI machines. Where do these materials come from?

The Crab Nebula is what remains of a supernova observed in 1054AD. Explosions like these are the source of elements such as iron. Image courtesy of Bill Schoening/NOAO/AURA/NSF

Within the coffee industry there has been a lot of work done to demonstrate the traceability of the coffee we drink. But we know much less about the elements that form the components of many of the electronic devices that we use every day. And while this leads us into many ethical issues (for example here, here and here), it can also prompt us to consider the question even more fundamentally: where does gold come from? Indeed, where do the elements such as carbon and oxygen that make coffee, ultimately, come from?

The lighter elements, (hydrogen, helium, lithium and some beryllium) are thought to have been made during the Big Bang at the start of our Universe. While elements up to iron, including the carbon that would be found in coffee, have been formed during nuclear fusion reactions within stars (with the more massive stars generating the heavier elements). Elements heavier than iron though cannot be generated through the nuclear fusion reactions within stars and so will have been formed during some form of catastrophic event such as a stellar explosion, a supernova. But there has recently been some discussion about exactly how the elements heavier than iron formed, elements such as the gold, tantalum and niobium mined in Ethiopia.

One theory is that these elements formed in the energies generated when two neutron stars (a type of super-dense and massive star) collide. So when the LIGO detector, detected gravitational waves that were the signature of a neutron star collision, many telescopes were immediately turned to the region of space from which the collision had been detected. What elements were being generated in the aftermath of the collision? Developing a model for the way that the elements formed in such collisions, a group of astronomers concluded that, neutron star collisions could account for practically all of these heavier elements in certain regions of space. But then, a second group of astronomers calculated how long it would take for neutron stars to collide which led to a problem: massive neutron stars take ages to form and don’t collide very often, could they really have happened often enough that we have the elements we see around us now? There is a third possibility, could it be that some of these elements have been formed in a type of supernova explosion that has been postulated but never yet observed? The discussion goes on.

coffee cup Populus
Where did it all come from? Plenty to ponder in the physics of coffee.

The upshot of this is that while we have an idea about the origin of the elements in that they are the result of the violent death of stars, we are a bit unclear about the exact details. Similarly to the story of Kaldi the goat herder and the origins of coffee, we have a good idea but have to fill in the bits that are missing (a slightly bigger problem for the coffee legend). None of this should stop us enjoying our brew though. What could be better than to sip and savour the coffee slowly while pondering the meaning, or origin, of life, the universe and everything? That is surely something that people have done throughout the ages, irrespective of the brew method that we use.

As cafes remain closed, this represents the beginning of a series of coffee-physics reviews. If you find a coffee with a particular physics connection, or are intrigued about what a connection could be, please do share it, either here in the comments section, on Twitter or on Facebook.

Coffee quakes

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

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

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

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

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

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

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

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

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

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

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

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

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

Filtering

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Coffee and the stars

cold mug
There are many ways that gazing at a cup of coffee can help with sky gazing.

There is a problem looming on the horizon concerning how astronomers can continue to look at the sky as the effects of global climate change become more pronounced. Some of these issues are an extension of those that have been affecting amateur astronomers since the invention of telescopes. Fortunately for those with portable telescopes, many of the issues can be minimised, but some effects will be a problem for our larger observatories. And of course, for this website, we can gain an insight into what the problems are by gazing more closely at our coffee.

It’s time to make a hot coffee. Or a tea. In fact, for some of the following observations a cup of green tea or a herbal tea would be perfect. You are after a brew that is light and allows you to see through to the bottom of your mug. But if you want to keep with coffee, worry not, there are still important clues to be seen above the coffee (and you can always use the spare brewing water to pour plain hot water into a cold cup).

If you have made a tea, you should be able now to look into your tea to the bottom of the cup. If it is a sunny day, or if you have a light on behind you, you will hopefully be able to see lines of light starting to form and then dancing around the base of the cup. If you have made a coffee, this will be more difficult for you to see. In addition to pouring any spare brew water into a cup to see the same effect in plain water, you could also look at the top of your cup and notice how the steam is making the air above more turbulent, changing the way you see things on the other side of the mug (is there an allegory there?).

The dancing light patterns and turbulent steam clouds are similar to conditions in the atmosphere that can make observing the stars difficult for amateurs and professionals alike. It is perhaps easier at first to think about the keen amateur astronomer who takes their telescope from the warmth of their indoors to the cold of a cloudless night. We can perhaps immediately see analogues with the (hot) tea in the (cold) cup and the steam clouds above the coffee.

Shortly after pouring hot tea into a cool cup you should be able to see these bright lines dancing over the base of the cup. They indicate how the refractive index of the tea changes as a function of temperature and so show the convection zones within the tea cup.

We can start by thinking about the turbulence in the air movement of the atmosphere being similar to the turbulence in the steam clouds above the cup. It is hard to focus on point objects through the steam clouds; the star light twinkles as it travels through our atmosphere. But then, just as we see the light patterns form in our tea cup as regions within the tea that have ever-so-slightly different temperatures mix in a convective pattern, so the hot air within the tube of the telescope will mix with the air at the edge of the tube that has been cooled by contact with the night-temperatures. The refractive index of air and water varies as a function of temperature (fluid density). And so with the telescope as with the tea cup, these regions of hotter and cooler fluid (air and tea respectively) have different refractive indices, meaning that any light travelling through those regions gets bent by different amounts as a function of the temperature of the medium it flows through. In the tea cup, this means that we see bright lines dancing across the bottom of the cup that trace the convection zones in the tea. In the telescope we would get a wobbly image.

For the amateur with their portable telescope the solution to the convection problem, if not the atmospheric turbulence, is relatively simple. Take your telescope outside for a good amount of time so that the air inside the tube can reach a similar temperature to the air outside. Convection will subside and the image will be more stable. If we wanted to drink cold tea, we could see the same thing with our tea cup: leave the tea to cool to room temperature and those dancing light lines on the bottom of the cup should subside (this is admittedly a thought experiment on my part. I have generally finished the tea before reaching this point).

But unfortunately, similar phenomena also affect professional observatories, and a recent study suggests the problems are likely to get worse as the effects of global climate change become increasingly apparent. One of the first problems is exactly the same as for the portable telescopes: the telescopes are frequently warmer than their surroundings. Observatories such as the European Southern Observatory facility in Cerro Paranal, Chile, have in the past compensated for this by cooling the domes housing the telescopes during the day to match that of the air outside. The problem is that the feedback circuits do not work to cool to a temperature higher than 16C and, as the atmospheric temperatures rise, so it becomes harder to maintain the temperature equilibrium between the telescope and the atmosphere. As the atmosphere becomes warmer, it also becomes more turbulent, causing further problems for observations done with ground based telescopes.

Edmond Halley, Canary Wharf, Isle of Dogs, view from Greenwich
The view towards the Isle of Dogs (and Canary Wharf) from Greenwich. In the 17th century it was thought that the Isle of Dogs floated on the tidal Thames because of how it seemed to rise and fall with the tide. The reality is far more interesting and involves the same physics that affects tea and telescopes. You can read about that aspect here.

More difficult however is the effects of water vapour in the atmosphere for observations being made in the infra-red. As the atmospheric temperature increases, so the water vapour content in the atmosphere will increase. One measure of the water vapour in the atmosphere is known as the integrated water vapour (IWV). The IWV is the total water vapour in a column of air stretching vertically from the Earth’s surface to the top of the atmosphere. High IWV levels affect observations in the infra-red and are particularly frequent during El Nino events. It is not just that climate change will cause there to be, on average, more water vapour in the atmosphere. It is known that the frequency of El Nino events is increasing as a consequence of the effects of the climate change we are already seeing. This will lead to more frequent occasions when the observing conditions are unfavourable for ground based telescopes.

The authors of the study conclude that we will need to think about the effects of climate change on the local conditions before we can build any new ground based observatories. We will need to adapt to the new conditions that climate change forces on us. As to how we can minimise the effects of climate change altogether, that will require gazing into our coffee and tea and thinking a lot more deeply. There are things we can do, individually and collectively. Is it too much wishful thinking to wonder if we will start to do them in 2021?

Gallery of fluid motion, 2020

Ever wondered about the shape of the splash formed as your pour over coffee drips into the brew? Or considered what it looks like if you blast falling drops with a high powered laser? Well, now you can discover these and more in this year’s videos submitted to the annual meeting of the American Physical Society, Division of Fluid Dynamics. You can see the full gallery here, and this year’s prize winners here, but below are some of 2020’s entries that have a particular relevance for coffee or cafes.

I hope you enjoy watching some beautiful physics.

Brewing a pour over? Watch the drips

As you watch each drop falling into the coffee below, some produce a splash, some bounce on the surface and some just fall without much effect. Watch drops entering a puddle of water in slow motion to see what happens as each drop splashes:

Rain falling into puddles, or coffee into your V60 brew?

Mocha Diffusion: An experiment you can do in your kitchen

Mocha diffusion is a process for decorating ceramics, but if you have some food colouring and some time, perhaps you can do similar experiments at home.

Mocha Diffusion: from ceramics to the kitchen

Levitating boats with a beat

If you came along to the first Coffee & Science evening at Amoret coffee in June 2019, you will have an idea what this is about. For those of you who didn’t make it, a similar experiment can be done at home (instructions here) and while we didn’t adapt it at the time to the artificial boats shown here, there is no reason that you cannot improve upon that experiment and replicate this one. But if you do, please do let me know how you get on.

Another experiment you can do at home.

Can we do this with coffee?

How does a liquid flow down a string? In this experiment, the authors varied the diameter of the liquid flow and the position of the string to show some beautiful effects with fluid flow. It would be tricky to adapt this to coffee as I think that in order to see the effects shown here, you would need to have a very viscous fluid. On the other hand, why not try and let us know how you get on.

Coffee on a string?

Coronavirus and masks

It is 2020 after all. There were quite a few videos imaging the air flow around breathing, talking and coughing people. Some of the videos compared types of mask, some imaged singers in addition to the coughing people. You can see other videos in the full gallery here. But, as many of us are having to, or deciding to wear masks while we pop into get a coffee, you may want to see the effect that they have on the air flow surrounding the mask wearer.

To mask or not? Is it even a question?

And finally. Don’t try this at home

Ever wanted to smash a droplet with a highly focussed laser? Now you don’t have to but can watch what happens here:

Smashing a falling droplet with a laser. Why not.

Smelling collectively

You can see the steam rising above the cup in this coffee at Carbon Kopi. But you will have to imagine the aroma.

It is hard to choose the best thing about coffee, so many aspects combine to make a good cup. But one of the key things about drinking coffee, particularly if you have had a difficult meeting or have just come in from the cold, is the aroma that wafts up as you grind the beans, add water to bloom the coffee and then brew. In happier times, we may be walking down the street preoccupied about something that is going on and then suddenly get hit by a fantastic aroma that signals our proximity to a good cafe. We perhaps ‘follow our noses’ to the source of the smell and then breathe in the scents as we enter the cafe. Which brings us, in a round about way, to moths and a recent paper that appeared in Physical Review E.

It is not that moths have been shown to have a particular liking for the smell of coffee. That may be an area of future research for somebody. But they do need a very good sense of smell because they need to be able to ‘follow their noses’ in order to find the source of a smell that they are interested in (typically a pheromone released by a female moth). This female moth may be located 100s of metres away from the male and probably does not emit that much odour, so how do the male moths find her?

In a similar manner to our approach to the aromatic coffee shop, the moths first travel against the wind, aware in some sense that the smell is carried downstream. If they lose the scent, they then fly perpendicular to the wind flow in an attempt to sniff the aroma once more. This pattern of zig-zagging flight allows them to approach the source of the smell fairly quickly*.

Eggs of a large cabbage white butterfly. No real links with coffee and few with moths, but the adult pair may well have had to find each other using the sense of smell.

It’s a clever method that is perfect if the wind flows in one direction without any turbulence. But how many times have you watched as leaves have been swept up in the wind flow and danced a swirling vortex pattern before falling back to the ground? Or, as you approach the side of a tall building, you get hit by a gust of wind that seems to come in a number of directions all at once because of the way that it is being affected by the presence of the building wall? We can see a similar thing in babbling streams and in our coffee as the convection currents swirl in vortices. The real world is not so simple as a linear wind flow, in the real world the wind is turbulent.

And yet still the moths find their way to the source of the smell that they are seeking. How do they do it, and could we design a robot (or robots) to emulate the moths in order to find, for example, chemical leaks? It was these questions that were addressed by the recent paper in Physical Review E. In the study they used mathematical calculations to look, not at the behaviour of an individual moth, but at the behaviour of a swarm of moths, a group of moths all searching for a mate.

In the computer model, each individual moth could discern the wind speed and direction and also detect odour molecules. So, left to their own devices, the individuals in the model would follow the zig-zag pattern of individual moths observed in nature (this was a deliberate element of the model). But the model-moths were given another ‘sense’: the ability to see the behaviour of their fellow model-moths. Which direction were the others going in? How fast were they moving?

The model-moths were then provided with one final behaviour indicator, a parameter, β, which was called a ‘trust’ parameter. If β = 0, the model-moths did not trust what the others were doing at all and relied purely on their own senses to reach the prize. Conversely, if β = 1, the model-moths completely lacked confidence in their own ability to discern where the smell was coming from and followed the behaviour of their peers.

We find our way to a cafe via visual cues or perhaps the sounds of espresso being made. But can we also follow the aroma?

Running the model several times for different wind conditions including a turbulent flow, the authors of the study found that the moths reached the destination smell best if they balanced the information from their own senses with the behaviour of their peers. In fact, the best results were for a trust factor, β ~ 0.8-0.85 meaning that they trusted their peers 80-85% of the time and relied on their own decisions 10-15% of the time. If they did that, they reached the smell source in only just slightly longer than it would take a moth to fly directly to the source of the smell in a straight line. An astonishingly quick result. As the authors phrased it, the study indicated that you (or the moths) should “follow the advice of your neighbours but once every five to seven times ignore them and act based on your own sensations”.

Now it would be tempting to suggest that this study has no relevance for us individuals finding a coffee shop and minimal relevance to coffee. But that I think would be premature. For a start, a similar result was found when the question was not about moths but about the best way for a crowd of people to leave a smoke filled room. If everyone behaved individualistically, or conversely, if everyone behaved in a purely herd like manner, the crowd took longer to escape the room than if people balanced their individualistic needs with a collective behaviour. It is a push to suggest that the same thing may be relevant for us finding cafes, but who knows what may happen post-lockdown(s) as we collectively attempt to find a well made flat white to enjoy outside our homes. Maybe we too need to trust our own senses some of the time but be open to taking the advice of those around us too.

*You can read more details in the paper Durve et al., Phys Rev E, 102, 012402 (2020)

Packaging, all about substance

The OK Vincotte or OK Compost HOME labels are for items that are suitable for “home” composting. This label was on a coffee bag from Amoret Coffee

Who would have thought that buying coffee to drink at home could be such a moral minefield? There are issues of sustainability: for the people involved in the coffee process through to the planet. Issues of transportation and the balance between supporting local independents or larger companies with different sustainability policies. And in amongst all this are issues of packaging the final product. How does your freshly roasted coffee arrive? Is it in a bag that you have no choice but to dispose of in the ordinary rubbish, or in a bag (or even bottle) that can be re-used and recycled or composted?

As many of us are buying more coffee on-line at the moment, I thought that it may be helpful to have a list of roasters who have gone to some effort in thinking about the sustainability of their final packaging. Of course many other issues are involved in your decision about which coffee to purchase. This list is only intended as a place to collate information on coffee bean packaging. The list is not definitive, so if you know of a roaster (or if you are a roaster) who is not currently featured on this list but you think ought to be, please let me know as I will be updating the page regularly. Similarly if you notice a mistake, please get in touch (e-mail, Twitter, Facebook).

One more caveat. We each need to decide what we consider a ‘good’, or sustainable packaging. The issue is highly complex. Some of us will have the ability to compost at home, some will have access to an industrial composting bin, some will go to supermarkets regularly and would prefer to recycle plastic together with other plastic bags. And then of course there is the problem that packaging is just one part of a whole relationship between farmer, supplier, roaster, customer and planet. It requires thought and consideration on our part as consumers, on the part of the coffee roasters and, I think, it requires kindness on all our parts, appreciating the efforts of those who are trying to improve things while recognising that there is currently no perfect solution.

In alphabetical order:

Compostable (Home)

Very few items marked “compostable” are, in reality, “home” compostable. Properly home compostable items are certified by the “Ok Compost, Vincotte“/OK compost-HOME labels.

Amoret – Notting Hill, London and online. Coffees (including directly traded coffees) are supplied in bags certified as home compostable (OK Compost). Owing to supply problems during the pandemic, some bags of coffee have been packaged in EN13432 (industrially) compostable bags instead but a recent addition of a new supplier should hopefully solve these supply problems.

Coromandel Coast – online. Shade grown coffee from India, coffee orders online come in a Natureflex bag within a recyclable cardboard box. Natureflex is certified as ASTM D6400 but also listed as “home” compostable and indeed composted in my worm bin composter in 17 weeks (packaging was from Roasting House in that instance).

Roasting House – online. Delivery by bike in the Nottingham area. Ground coffee is supplied in home compostable packaging. Whole beans are supplied in recycled and recyclable bags (see below). You can read more about their latest packaging policies here.

Compostable (Industrial)/Biodegradable

Most packaging that is marked compostable (or biodegradable), but that is not marked as home compostable, will require specialist facilities to compost/degrade such as industrial composting. Compostable items should be certified by (BS) EN 13432 and/or ASTM D6400.

Coromandel Coast – Croydon and online. Bags of coffee purchased in Filtr, the coffee shop associated with Coromandel Coast in Croydon, are supplied in industrially compostable packaging. For coffee purchased online see above.

Dear Green – Glasgow and online. “Together we can all make a difference”. Next year, COP26 will go to Glasgow and Dear Green are ready, organising the 2018 Glasgow Coffee festival to be re-usable cup only. Coffee is supplied in biodegradable packaging.

Glen Lyon Coffee – Perthshire and online. Glen Lyon coffee made a commitment to zero waste in 2017 and use OK Compost Industrial certified coffee bags for their 250g and 500g packaging. 1kg bags are designed to compost within 3 months in a home composting environment. They offer a ‘drop box’ for customers to return their bags for composting. You can read further details about their dedication to sustainability here.

Recyclable

Several roasters have opted for recyclable packaging and quite a few are using the Dutch Coffee Pack bags which are additionally carbon neutral (via offsetting which you can read about here). Be careful with the “recyclable” label as it may, or may not, be suitable for collection with your household waste. Look for the recycling labels on the bags. PET plastic (label 1) is often collected with the street based collections but LDPE (label 4) should be taken to a supermarket where they provide recycling for plastic bags.

Atkinsons – Lancaster, Manchester and online – Established in 1837 as a tea merchant in Lancaster, Atkinsons now sell tea and coffee using recyclable packaging which is also carbon neutral.

Casa Espresso – online – Great Taste award winner for 3 years in a row, coffee is supplied in recyclable and carbon neutral packaging.

Chipp Coffee – online – In addition to using recyclable packaging, you can read more about the ethical and sustainability policies of Chipp Coffee here.

Fried Hats – Amsterdam and online – recyclable but also re-usable. The coffee comes in bottles that can be re-used before ultimately being recycled.

Good Coffee Cartel – online – Coffee in a can, but this time a re-usable and recyclable can containing speciality coffee beans.

Manumit coffee – online – “Manumit”, a historical verb meaning to set a slave free. Manumit coffee works with people who have been subject to exploitation and modern slavery so that they can rebuild their lives. Their coffee comes in recyclable and carbon neutral, Dutch Coffee Pack packaging

New Ground – Oxford, Selfridges and online. Providing opportunities for ex-offenders to develop new skills and employment, coffee is provided in recyclable packaging.

Paddy and Scotts Suffolk based, various outlets and online – Coffee packaging is described as PET recyclable or compostable. Check labelling on package. More info here.

Rave Coffee – Cirencester and online – Rave coffee have been conscientious in describing the reasoning behind their policy of using recyclable (LDPE (4)) bags, You can read about the rationale here.

Roasting House – For whole beans, Roasting House supply the coffee in (recycled and) recyclable paper packaging. Ground coffee is supplied in home compostable packaging (see composting section).

Steampunk coffee – online. I’m reliably informed that their coffee is supplied in recyclable packaging but have been unable to confirm.

This list will be updated regularly. Please do get in touch if you would like to suggest a coffee roasting company who should be included: email, Twitter, Facebook.