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Questioning my assumptions at Everbean, Marylebone

Coffee cake Everbean
Coffee and cake at Everbean.

Alerted by Caffeine Magazine (on Twitter) to the opening of the second branch of Everbean, we arranged a quick visit into central London. A fair few had beaten us there. Initially, it seemed that the cafe was quite small with limited seating but a sign on the staircase pointed us to an entire area downstairs. Although there are tall stool-type seats upstairs fronting the window, there are more chairs and cushion backed bench seats downstairs (together with a comfy arm chair but more on that later). Downstairs was clearly the place to be on that day and is certainly a comfortable space for enjoying your coffee. As you enter, the counter upstairs is quite large and features a number of tempting cakes. Too tempting. Together with my Americano, I enjoyed a delicious vegan mandarin and chocolate cake.

Downstairs could be described as cosy. Cushions with birds embroidered onto them line the bench running down one side wall. A bookshelf with an eclectic collection of books is in the corner of the room next to the arm chair, suggesting a great (phone-free) way of spending an afternoon. I would share with you some of the titles but in some ways, that would be to judge the books by their cover (titles). Which in some way connects with the thought train that we encountered here at Everbean.

Mirror at Everbean, coffee Marylebone
Mirror, mirror on the wall: We can see ageing effects in metals but taste them in coffee.

On the wall behind us a lattice effect mirror reflected the room to itself. The lattice was painted but bits of paint had aged leading to rust and corrosion effects on the metal lattice work. Age, in the form of oxygen and moisture, affecting metal work in a similar way to how age affects the flavour of coffee. At this point, my thought train at the time went towards the ways in which different materials oxidise and the use that this can be put to. But a different thought train occurred to me when I started to think about this cafe later as I came across Brian’s Coffee Spot’s thoughts on coffee bean storage and specifically, should you ever store your beans in the freezer.

In addition to showing that, depending on your defrosting conditions, it was perfectly fine to store your coffee beans in the freezer, Brian’s Coffee Spot had highlighted a Twitter poll concerning coffee storage. The results of the poll had been definitive. Of 118 voters, 99 had ticked the “never store coffee in the freezer” option. I admit I was one of them. In hindsight, I can self-justify: I could say I was thinking about the (very real) problems with moisture affecting the ageing of coffee and the possibility of water already in the bean causing structural issues for the bean. However these are also problems that are avoidable, as Brian’s Coffee Spot outlined. If I am honest, in reality, I saw the poll, had a negative view towards the freezer option and so clicked “never”.

After reading Brian’s Coffee Spot, doing a little bit more reading about it online and then sitting back and actually thinking about it, I realised that I had perhaps been hasty. Is there still time to change my mind now I know more about the issue? We need a second vote!

But reading about the issues of freezing coffee beans also alerted me to a study that had been done a couple of years ago about the effect of the temperature of the coffee bean on grind size. The question was, when we grind coffee, does the temperature of the bean matter?

books at Everbean
You could sit here all day. Imagine what you would learn.

To test this question the authors subjected batches of 20g of coffee beans to two hours of four different temperatures: liquid nitrogen (-196C), dry ice (-79 C), freezer temperature (-19C) and room temperature (20C). Following this, the beans were immediately ground using a Mahlkonig EK43 grinder. They found that, under otherwise identical grinding conditions, the colder beans showed a smaller grind size and a reduced particle size distribution.

The authors of the study suggested their results as a possible explanation for the need in many coffee shops to tune the grinder to a closer grind size as the day progresses: they argued that the beans are warming up while sitting in the hopper on the grinder and that this results in a change in the way that they grind. They also suggested a possible long term solution for the storage of coffee beans: liquid nitrogen. Just a little bit colder than a freezer.

Which takes us a long way from the basement at Everbean on Seymour Place. Or does it? Perhaps you need to take some time out and sit in the armchair, questioning and investigating your perspective.

Everbean (2) is at 21 Seymour Place, W1H 5BH

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On mountains, molecules and coffee

A tea plantation in the mountains of the Cameron Highlands, Malaysia. But how high would you need to climb in order to boil water at the perfect temperature to prepare your brew?
A tea plantation in the mountains of the Cameron Highlands, Malaysia. But how high would you need to climb in order to boil water at the perfect temperature to prepare your brew?

Walking in the hills or, if you are lucky, the mountains, we can easily be reminded that atmospheric pressure decreases with height. We just have to look at the way that the plastic water bottles we may be carrying have been crushed, or open a yoghurt pot slightly too close to our face. We may remember that the boiling point of water decreases with decreasing atmospheric pressure and so that a kettle boils more quickly at the top of a mountain than at the bottom. But how high would we need to climb to make a perfect cup of coffee with just-boiled water? And what has this to do with the reality, or not, of molecules?

Although the effect appears obvious to us, it is not trivial to calculate exactly how the atmospheric pressure varies with height. To see why, we could think about what pressure is. The pressure exerted by a gas on an object is proportional to the number of gas molecules colliding with and recoiling from the object concerned. These collisions create a force on the object and pressure is just force ÷ area. So why would this change with height?

Small waves seen from Lindisfarne
Think about a layer of air with air pressure above and below it but further acted on by gravity pulling it down. What happens?

Think about a layer of air. Above it, the molecules in the gas are exerting a pressure, pushing down on the air. Below it, there are molecules pushing upwards and keeping it up. But there is one more force that we need to consider: gravity. In physics, we like to think of things in equilibrium, perfectly balanced. So when we think about our layer of air, the forces acting down on the layer of air (the pressure from above and the gravity of the earth) have to be perfectly compensated by the force acting up, i.e. the pressure from below. If this were not the case, the layer of air would sink. Perhaps it is starting to become clearer, why the density of the atmosphere decreases with height. The only thing that remains is to work out exactly how it does it.

And while we could do the calculation here, it has (fortunately) already been done for us by a remarkable physicist called Jean Perrin back in 1910. He was remarkable not just because of the detail of his experiments but also because of the connections he made.

“It appeared to me at first intuitively [that]…. Just as the air is more dense at sea-level than on a mountain top, so the granules of an emulsion, whatever may be their initial distribution, will attain a permanent state where the concentration will go on diminishing as a function of the height from the lower layers and the law of rarefaction will be the same as for the air.”

Jean Perrin, Brownian Movement and Molecular Reality, 1910
coffee at Watch House
In search of the perfect coffee. How far would you travel?

Perrin realised that to calculate the balance of forces acting on our imagined layer of air, one has to assume molecules exist, just as we have done above but something that was not obvious at the turn of the 20th century. But he also realised that this calculation would be the same for any fluid containing a suspension of particles whether that was the atmosphere or a drop of water colour paint. Assuming that the molecules exist allows us, and allowed Perrin, to make quantitative predictions for the variation of pressure with height or, in Perrin’s case, the variation of the number of granules in an emulsion with depth. Perrin considered a paint pigment suspended in water under the microscope, but his theory is also valid for the (non-soluble) matter in coffee. The fact that these quantitative predictions matched so extraordinarily well with the experimental observations of thousands of water droplets containing suspended paint pigment (the poor PhD students of Jean Perrin!) went a long way to proving the existence of molecules. Hence Perrin’s book “Molecular Reality” and the ceasefire in a philosophical disagreement about whether physics should seek to understand what was happening or merely describe phenomena such as pressure (but that’s another story).

Which takes us back to how to brew coffee properly. Calculating the variation of pressure with height is the first part of the problem. The second is calculating what that means for the boiling point of water, which actually is done by extrapolating from experimental data. But it does mean that we can calculate, for a small range of temperatures near 100C, the altitude at which you would need to boil a kettle for the boiling temperature to be identical with the optimum brewing temperature for your drink. Listed below are a few recommended mountains on which you can prepare your drink of choice. I will leave it to someone else to calculate the energy saving (and hence the saving in CO2 equivalent emissions) of boiling your kettle on top of a mountain rather than in your kitchen. We’ll assume that there’s electricity on top of Mont Blanc.
 

Drink – Recommended brew temperature – Equivalent Altitude – Suggested mountain

Coffee – 93.3 C* – 2000 m – Kebnekaise (Sweden),

Coffee – 96 C** – 1000 m – Any of the Scottish Munroes

Oolong tea – 87.8 – 93.3 C*** – upwards of 2000m – Mont Blanc (France) could be good

Pu’er tea – 93 – 100C| – why leave your living room?

*Coffee Detective

**The Kitchn/Blackbear coffee

***The Spruceeats

|The tea leaf journal

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Coffee review Observations slow Tea

Rosie and Joe, St Giles churchyard

Coffee in a Wake Cup at Rosie & Joe in St Giles. The space rewards those who notice.

There is a long history of hospitality on the site of St Giles in the Fields stretching back far earlier than the Notes coffee barrow. But Rosie & Joe is a lovely iteration to that tradition. There’s a definite focus on tea at Rosie & Joe but the coffee is roasted by Square Mile and prepared on a La Marzocco machine. There is also a good selection of food to nibble on (as well as more food stalls nearby on weekday lunchtimes). And although it is a cart, there are a few seats and tables dotted around so it is easy to sit back and enjoy your coffee while the world races by.

St Giles High St is a very busy road and yet, sitting in the churchyard of St Giles is strangely peaceful. Despite the traffic and the occasional siren, it is one of those rare places in London that you can find the stillness to listen. A beautiful place to enjoy a coffee from an independent stall in fact! And if you have your own cup with you, there is even 10p off your coffee. The coffee was smooth and sweet, fruity but definitely a sweet and full bodied type of fruity cup. But why was it so peaceful? Was it merely that it was a lovely (but breezy) spring morning when I tried Rosie & Joe? Or was it that it is a small bit of nature in a built up environment? Both of these helped but I think it is also the way that the place rewards those who notice by offering more each time you look.
The ghost sign hidden behind the tree just outside the churchyard.

There’s the, perhaps slightly grim, history suggested by the fact that the ‘garden’ is significantly raised above the level of the pavement in parts. There’s the brickwork and stone walls of the church itself of course. The ‘ghost sign’ on a nearby building that is revealed to the coffee drinker by the fact that the tree between us and it has not yet got its summer leaves. And then the nod to the history of the site hinted at by the coffee cart itself: Since Matilda, wife of Henry I founded St Giles’ leprosy hospital on the site, a “cup of charity” was given to condemned prisoners as they made their way past St Giles on their way to their execution at Tyburn*. Very different now, but the tradition of refreshment for the traveller is continued.

But then a fire engine’s siren reminds you that you are in a cosmos, a universe filled with beautiful physics. You know whether the fire engine is approaching or has passed away from you from how the pitch of the sound changes as it goes past. The Doppler shift meaning that sound waves travelling towards you have a shorter wavelength (higher frequency, higher pitch) than those travelling away (longer wavelength, lower frequency, lower pitch). And part of the beauty of physics is that it is so universal; what works for sound also works for light. If an object emitting light is moving away from us, the light appears to have a longer wavelength (lower frequency, it is red-shifted) than if the same object were stationary or moving towards us where it would appear as if it emitted light with a shorter wavelength (higher frequency, blue shifted).

signboard at Rosie and Joe
Doesn’t a right imply a duty? There’s a lot that could be said about #supportindependent
So, similarly, if we were to look at the surface of a rotating planet and saw how the light reflected off that planet’s surface, the side of the planet that was rotating towards us would look ever so slightly bluer than the side rotating away from us which would look slightly redder. And if the planet’s surface was like Venus and obscured by clouds (rather like the ghost sign at Rosie & Joe will be obscured by leaves in a couple of months time) we could use the reflection of radio waves from the surface rather than visible light to see the same red-shift/blue-shift in the radio waves as the planet rotates**. In this way we could determine the direction of rotation of the planet and how fast it was rotating just as we get an indication of the speed of the fire engine from listening to the sound of the siren.

The siren takes us from a consideration of inner stillness to a recognition of the scale of the universe. Which is rather apt for a cafe in a churchyard, where the architecture of a church is often designed to be read symbolically, from the person to their place in the grand scheme of things***. One great thing about this particular cafe though was how much there was to see that cannot be included in this cafe-physics review for reasons of space. The location truly rewards those who pay attention to what they notice here. I can only recommend that you take some time out, take your re-usable cup and go to find some time to enjoy your coffee (or tea) in this quiet space in central London.

*The London Encyclopaedia, 3rd Edition, Weinreb et al., 2008

**Astronomy, the evolving universe, 6th Edition, Zeilik, 1991

***How to read a church, Taylor, 2003

Rosie and Joe can be found in St Giles in the Fields churchyard, Monday-Friday.