Coffee review Coffee Roasters General Observations slow

Time for a slow coffee?

enamel mug, teh halia, Straits Times kopitiam
This enamel mug connected glass to the Giants Causeway (Straits Times kopitiam)

Every two weeks, the Daily Grind on Bean Thinking is devoted to what I have called a cafe-physics review. The point of these reviews is to visit a café, slow down and notice what has been going on in a cafe physics-wise. I focus on physics because it is my ‘specialist’ area but the point is to notice the connections between the coffee, or the cafe and the world around us. To see how what is going on in your mug is reflected in the science of the wider universe. Realising that things that seem disparate are in fact connected: It is the same maths that describes electrons moving in a metal and the vibrations on the surface of a cup of coffee. That sort of connection to me is mind boggling. Yet there is more. Thinking about the connections between physics and coffee can lead to meditations on the environment and sustainability, or considerations about how our attitude to drinking coffee changes our perception of it.

Everything is connected.

Parquet floor at Coffee Affair
How many people have walked on this floor? The story of evolution at Coffee Affair

It is my strong belief that whenever we go into a cafe, order a coffee and then proceed to sit down with our smart phones or tablets and check our e-mail or our Twitter accounts we lose a fantastic opportunity. It is the opportunity to be properly present and to notice what is going on around us. It is the opportunity to slow down and to appreciate what life has given us and the surprising things that the world has to offer. To look at the beauty and the complexity of the world and to say ‘wow’.

This appreciation is open to us all, provided we seize the opportunity to slow down and take that time to enjoy our coffee.

So, this week’s Daily Grind is an invitation. It is an invitation open to anyone who sits down with a coffee. If you notice anything peculiar, or interesting, that you feel deserves a mention as a cafe-physics review why not write an edition of the Daily Grind? It does not matter where in the world you are or what your level of science knowledge is. If a full Daily Grind article is too much but you have a great observation, write a paragraph review of your favourite cafe and I’ll add it to the cafe-physics review map. Think that you don’t know enough science? Never mind, share your idea with me and we can work on it together.

Hasten coffee, long black, black coffee, espresso base
Sometimes the link with physics/science is a little bit tenuous, as it was at Espresso Base

Your observations need not be physics-based. It would be great if it is based on some aspect of science, but, as past examples have shown, this link can be a little tenuous if the cafe/subject warrants it.

So, over to you. I hope that someone will respond to this invitation. Please do contact me if you would like to pen a review or if you have any questions. It is my hope that you are all enjoying such great coffee in the huge variety of cafe’s that we now have that there will be plenty of opportunities for people to slow down and to notice and then to share it with the Daily Grind.

Please contact me here, or in the comments section below. I look forward to hearing from you.


Some brief guidelines for a cafe-physics review:

1) The cafe should, preferably, be a good independent.

2) Any science/history etc. needs to be verifiable but, as mentioned, if you’ve noticed something great but are unsure of the science, get in touch and we’ll work something out together.

3) If you have noticed something fascinating with your coffee but at home and not in a café, contact me anyway.

4) Please do not write a cafe-physics review of any cafe you are financially associated with. I will have to refuse/delete any ‘reviews’ that I find are adverts.

Coffee review Coffee Roasters Observations Science history slow

Wonders of the World at Espresso Base, Bloomsbury

Hasten coffee, long black, black coffee, espresso base
‘Has Bean’ coffee at Espresso Base

Espresso Base is exactly the sort of café that you want to make sure that you know about, but part of you is selfishly quite happy if not too many others do. It is not that the the place is small, far from it. There is plenty of space in the courtyard at Espresso Base, beside St George’s Church, to sit and enjoy your coffee. The thing is, it is great to have the place almost entirely to yourself. With few others around, the oasis-like quality of the place is emphasised, astonishing as it is so close to the busy Bloomsbury Way. Only this oasis serves great coffee. Their coffee is roasted by Has Bean, which I admit is the reason that I first dropped into Espresso Base a few weeks ago. The black coffee that I had was certainly very good and the environment in which to enjoy the coffee was thought provoking which, for me, is an important aspect of any café. Cafés need to be places that you can go, slow down and notice things and Espresso Base certainly falls into that group of cafés that I would highly recommend both for the coffee and the café.

stone recycling, slate, slate waterfall, geology
The purple slate waterfall feature in the courtyard area at Espresso Base. You can just see the stone with the rectangular holes carved into it at the bottom of the wall.

On the day that we arrived, it had been raining. For a café with seating outside this may have posed a problem but the chairs had been thoughtfully folded so that they remained dry. The rain had however seeped into some of the paving slabs around the chairs and so that was the first thing to notice, the fact that many objects when wet appear darker, why? Opposite our seating was a rock feature that to me looked like a waterfall made out of slate, the slate had a purple tinge which again, had been made slightly more purple by the rain. Below the slate ‘waterfall’ and forming a wall, were a series of stones that had clearly been taken here from somewhere else. I say ‘clearly’, because the stone at the bottom had two holes that had been carved out of it, one square, one slightly more rectangular. Presumably the stone had been used as part of a gate post in the past and yet there is no evidence of the remains of a gate on the other side of the courtyard (I think that a gate post would have to be deeper than the square indent in the paving slab that is at the other side of the courtyard). It is therefore more likely that the stone had been used somewhere else beforehand and ‘recycled’ for use in this wall. This juxtaposition of slate above and recycled stone below reminded me of the early geologists and how they identified the Great Glen fault that runs through Loch Ness in Scotland. Slate is a metamorphic rock, meaning that it has undergone changes due to the high pressure and temperatures within the Earth. Slate is however quite a low-grade metamorphic rock so, compared with higher grade metamorphic rocks, it has not been subjected to that much pressure or that much temperature. By mapping the lower grade and higher grade metamorphic rocks along the Great Glen, the early geologists noticed a line that sharply separated the metamorphic rock types. This fault would have, in the past, caused earthquakes as the ground slipped along the fault.

Replica of Mausoleum of Halicarnassus
The steeple of St George’s church, Bloomsbury Way. The statue on top is of King George I rather than King Mausolus in  his chariot. The statue of Mausolus, his wife/sister Artemisia and a horse from his chariot can be seen in the British Museum.

On leaving Espresso Base I turned and looked up at the church. If you get a chance, take a look at the steeple. Particularly ornate, the stepped steeple is apparently built to the description of the Mausoleum of Halicarnassus by Pliny the Elder. This monument was one of the seven wonders of the Ancient World and was built to be the burial chamber of King Mausolus of Karia. Described as standing approximately 40 m in height, this massive stepped, marble pyramid stood on top of 36 columns surrounded by statues. Topping the pyramid was a statue of King Mausolus himself, in a chariot. This ancient wonder is thought to have been destroyed by an earthquake in the fourteenth century after which the stones were ‘recycled’ by the Knights of Malta to build a fortress. A history that is aptly mirrored in the geology and stone recycling evident in the courtyard of Espresso Base.


Espresso Base can be found in the courtyard of St George’s church, Bloomsbury Way, WC1A 2SE

Artefacts from the Mausoleum of Halicarnassus can be seen in room 21 of the British Museum (conveniently just around the corner from Espresso Base).

Geology help from: “Geology Today, Understanding our planet”, Murck/Skinner, John Wiley & Sons, 1999

Coffee Roasters Home experiments Observations

Coffee bean degassing

coffee, Roast House
Coffee from the Roasting House, one light roasted one dark roasted. They were roasted within an hour of each other.

How long do freshly roasted coffee beans take to  degas? Should you let the beans lose the carbon dioxide inside them for 24h, 72h, one week, more? Do dark roasted beans degas for fewer days than light roasted beans? As readers of Bean Thinking will hopefully know, one of the aims of Bean Thinking is to bring science, and particularly experimental science, onto everybody’s coffee tables. Is there an experiment (or experiments) that you can do to measure the amount, and duration, of degassing with equipment that you will have in your kitchen?

To help me in my coffee bean degassing experiments, I got in contact with the very helpful people at Roasting House. Based in Nottingham (UK) they will deliver freshly roasted beans to you by bicycle if you live in the Nottingham area or, for the rest of us, by Royal Mail. Together with the cycling aspect of their business, they also have a commitment to supporting those people who produce the coffee. It is important I think, not just that coffee tastes good, but that everybody involved in the coffee process (from grower to consumer inclusive) gets a good deal. Lastly, and very importantly for the degassing experiment, Roasting House offer their beans roasted to the degree that you specify. While they helpfully recommend a particular style of roasting for each bean (dark roast for one bean type, a lighter roast for another), they do give you the option of choosing which you would prefer.

They are also very knowledgeable about their coffee. As I was discussing the degassing issue with them, they suggested a coffee (Daterra, Bourbon Yellow) that they thought would degas quite a lot. Not just that, but the coffee concerned would taste great as both a dark and a light roast (I do drink the coffee after all). All in all, this experiment could not have been done without the help and input from Roasting House and I am very grateful to them for their support in my little project. So, onto the experiment.

The Experiment:

water acidification via coffee beans
Red cabbage liquid approx 96h after roasting and then being sealed in a jar with coffee beans. Note the colours.

To discover the time period over which the beans degas, I decided to utilise an effect that (for reasons unconnected to coffee beans) is currently having an alarming environmental effect: the acidification of water by carbon dioxide. Carbon dioxide dissolves in water to form carbonic acid. With the rising atmospheric levels of CO2, this is leading to ocean acidification, which is another factor in the “global weirding” phenomenon. For the degassing experiment however, if the roasted beans are sealed in a jar with some water, appreciable CO2 degassing will lead to the water becoming acidic, something that is easily measurable.

Experiment 1 – Red Cabbage, Do the coffee beans really degas CO2?

red cabbage, acidity, indicator, natural indicator, coffee bean degassing
The colours of the red cabbage liquid on tissue. Control sample is on the left, light roast in the middle, dark roast on the right

An acidity indicator that you may well have in your kitchen is red cabbage. Liquid extracted from red cabbage is initially purple but will turn blue in the presence of an alkali or red if it is exposed to an acid. For the experiment, three (identical) jars were prepared each containing 60 ml of red cabbage indicator and three (identical) shot glasses. Each shot glass contained either 10g of dark roast, 10g of light roast or nothing (as a control). The coffee beans were kept dry and out of the water by placing them in the shot glasses. The jars were closed, sealed with sellotape and then left. On opening the jars, (approximately 96h after roasting) the two that had contained the coffee beans had turned red (indicating acidity) while the control jar remained purple – see pictures. It is a pretty way of showing the acidification of the water by carbon dioxide and confirms that the beans are degassing. To establish the duration of degassing, it would be necessary to refresh the red cabbage liquid and measure for a further period of time.

Experiment 2 – testing the pH more systematically.

I headed off to a pet shop to get a pH indicator used by people who keep fish (Nutrafin Test). As with experiment 1, the coffee (10g) was sealed in jars (with 30 ml of water) together with a control. When the jars were first opened (at the same time as the red cabbage jars), the jars containing the coffee showed really low (acidic) pH values (approx 6.0 – 6.5). The control water was neutral or slightly alkali (approx 7.5). The water in each jar was then emptied, the jar rinsed and the water replaced with 30 ml of fresh water which was then sealed in the jar, again for 48h. The picture below shows the evolution of the pH with time (measured as hours after roasting) for the jars containing both roasts. The jar containing the dark roast showed a reduced acidity by 192h (8 days) after roasting (the test tube in the picture is greener), compared with about 288h (12 days) for the light roast. Even after this amount of time however, the water was still becoming slightly more acidic than the control, indicating that the beans were still degassing a little.

pH testing, coffee bean degassing
Testing the pH of the water exposed to the coffee bean degassing. The light roasted beans are on the top row, the dark roast on the bottom row. The ‘hours’ is the number of hours after roasting. The pH is measured by comparing the colour of the liquid in the tube to the colour chart.

Experiment 3 – using a bubble system to ‘catch’ the CO2

A third experiment to try to ‘catch’ the CO2 degassing from the beans (in an adaptation of this experiment) sadly did not work on either occasion that I tried it. If you try it and get it to work with with equipment that you can find around the house, please let me know via the comments section below.


The coffee tried here, Daterra, Bourbon Yellow, degassed significantly for 6 days after the roasting date. The time over which the beans degassed, was dependent on the roast type, with the dark roast degassing for less time, consistent with the thoughts expressed here. Degassing certainly continued for many days after the critical ’72’ hours. Even 10 days after roasting, some degassing was still occurring. To be pedantic about things, the gas was not identified in these experiments. However, the acidification of the water in proximity with the coffee beans is consistent with the gas being CO2.

Please do try this at home and send me your results and pictures. Let me know what you find out, whether you use red cabbage or a bubble system that works. One thing that these experiments did not do at all of course was monitor how the beans tasted over a similar time frame to the degassing experiment. Perhaps you have thoughts on this. Please send your comments via the form below, comments are moderated but will (hopefully) be approved pretty quickly after you submit them.

Thanks again to Roasting House for being very efficient about sending me freshly roasted coffee and also to Tyla for helping to independently test the red cabbage experiment.