Categories
Coffee review General slow Sustainability/environmental Tea

Coffee and a horse box at Blue Tin, Oxfordshire

coffee Nuffield Oxfordshire Blue Tin
The cafe is in here. The new farm shop at Blue Tin.

Blue Tin is not an easy café to find, one that you can wander into just off the street. In fact, although it serves coffee and cake, Blue Tin is not really a café at all but a friendly place for a drink attached to a farm shop. Open to walkers and passing cyclists, horse riders and drivers, Blue Tin seems to be almost in the middle of nowhere. Approximately 4km by road from Nuffield, Blue Tin can be found just off a single lane country road. You will know when you actually arrive at the farm because of the sign and the box advertising fresh eggs (complete with honesty box for when the shop is closed).

We first came across Blue Tin (when it was a shop in a shed rather than a shop/café in a building) while walking in the area. There are some good walks in the area which can be very pretty when the bluebells are out and so it is well worth combining a visit to the café with a walk in the Oxfordshire countryside. Despite only opening in December 2017, the café associated with Blue Tin has put a lot of effort into ensuring that their coffee is ethically sourced, great tasting and locally roasted. The coffee is roasted by Horsebox Coffee and is of course also available to purchase in the shop. The espresso based drinks use the Dark Horse espresso blend (though I wasn’t sure whether this was occasionally rotated when the seasonal espresso is available). We had an Americano and a latte. The Americano indeed had the chocolate notes described on the coffee bag, while the milk of the latte really complemented the espresso base. Cakes are also available though we didn’t try on this occasion.

Provenance Information Blue Tin, old board, no coffee info
On the wall of the cafe is a schematic showing where each product sold in the shop originates. Seen here is the earlier version that does not include the coffee (roasted within 5 miles). Everything is local and the meat is particularly local having been brought up in the farm next to the shop.

There is plenty of space to sit down inside and contemplate the shop while enjoying your coffee in this welcoming environment. The arrangement also gives you time to consider the farm and space for your mind to wander. One place my mind was wandering that day was to the importance of our beliefs in our decision making, even while they are informed by science.

For example, it is often said that we could significantly help climate change by becoming vegetarian or including one meat free day per week in our diet. In a 2013 paper, the authors calculated the emissions associated with farming, producing, packaging and storing 66 categories of food item that were sold in a (modelled) medium sized supermarket. In order to calculate this various assumptions about the produce had to be made¹.

To summarise the paper (though it is well worth taking the time to read it), the study suggested that avoiding meat altogether could reduce our individual carbon footprint due to food by 35%. However even introducing a meat free day (combined with a switch to poultry rather than beef and significant reduction in the amount of food we waste/packaging used) could introduce a reduction of 26%.

Horsebox coffee Oxfordshire
Americano, Latte and shop. The coffee-space at Blue Tin farm shop, Oxfordshire

Does the science therefore “say” that we should all go vegetarian? It is worth looking more closely at the paper and considering our own belief systems. In the report, beef had a total CO2 equivalent emissions of 25.13 Kg per kg of food¹. One suggestion of the authors was to swap beef for poultry. Poultry has a total emissions of 4.05 Kg CO2 equivalent per Kg. But looking through the table of calculated emissions for each food type, “spirits and liqueurs” had a total emissions of 3.16 Kg CO2e per Kg. Perhaps (hopefully) you could say you would take a long time to drink a kg of spirits, but even wine has 2.41 Kg CO2e per Kg. As a rough estimate, 1 bottle of wine (750 ml) is 3/4 Kg, so the bottle of wine with dinner is contributing roughly equivalently to the shared roast chicken. There are nutritional arguments for eating meat. Can we say the same of drinking wine? What of coffee? (not included in the table I’m relieved to say!)

The study shows the quantity of emissions associated with each type of food stuff. It does not show us how to act. Each decision we make (eliminate meat/go teetotal/all things in moderation) is based on what we believe about the world. Even the idea that it would be a good thing to reduce our greenhouse gas emissions in order to try to limit climate change is a moral one, not a scientific one. These decisions depend on what we think is ‘good’, what is ‘bad’, what life is about. In short it depends on our beliefs about the world and our place in it rather than purely the facts. These are philosophical, or dare I say it, even religious questions. Science can inform us of the damage that we are doing but it cannot help us to decide whether that matters, nor even if it does matter, what we should do about it.

Interior of Blue Tin with flower
You won’t need the sugar. Another view of the cafe at Blue Tin.

Whether we decide to buy better quality² meat less frequently, go vegan or even do nothing are not decisions that we are making entirely based on the science. Although informed by the science they are nonetheless based also on our existing beliefs about the way the world is and the way the world should be. We may decide for example that, while we should reduce our consumption of “cheap” beef/imported lamb, we should take care to buy more expensive meat from somewhere that takes care of their animals throughout the farming (and slaughtering) process but eat it less often. Depending on the rest of our diet, this could similarly reduce our food-related greenhouse gas emissions (if for example we mostly ate vegetarian with occasional meat consumption). We may similarly decide that eating meat is intrinsically wrong and so go entirely vegetarian.

These are choices we make, informed by the science but based on our ideas of morality. They are not easy choices nor are they choices we will necessarily agree with each other about. To make these choices requires time set aside to think about what matters to us, about what we believe in. And this means that there is no intrinsic conflict between science and religious belief any more than there is a conflict between science and the decisions we make in general. We need science to inform our beliefs but we need also to recognise the role of our beliefs (conscious or subconscious) in our decision making.

In short, we need to slow down, pause and really think about things. And where better to do so than in quiet and comfortable places with good coffee (and cake) such as Blue Tin?

 

¹Interestingly, the authors assumed that for beef, the effective emissions were increased owing to deforestation and land clearance that is associated with beef production in some places. If this is not accounted for, the effective emissions from beef are still calculated to dwarf much of the other food stuffs but not by quite so much. The footprint would therefore be less for beef raised on an existing local form, slaughtered and purchased locally. Similarly, the ‘vegetarian’ diet that was modelled by the authors contained dairy (with similarly high emissions as beef).

²Again ‘quality’ is a subjective term that cannot be easily ‘scientifically’ quantified, instead it is argued based on what we believe ‘good’ means. Do I mean that the animal had healthy conditions during life? Was well cared for? That it tastes good? That I could speak to the people who farmed the animals? I’ve left it deliberately slightly ambiguous here.

Blue Tin Produce is at Garsons Farm, Ipsden, OX10 6QU

Categories
General Observations

Coffee (beans) in the blood?

Brazil nut effect
A green bean ‘floating’ in coffee grounds. When you pour your beans into your grinder, do they behave like a liquid flow or do they have their own type of ‘granular’ flow?

When you first learn about liquids, solids and gases, you may learn about the fact that a solid keeps its shape whereas a liquid flows. A solid is rigid and can be moved as one block whereas a liquid will spread and change shape. Solids can be stacked up like bricks though this is not true of liquids.

A slightly unfair question is then put to you. What about sand? (Or, in the context of this website, what about coffee beans?). A pile of beans will initially stack but as the pile builds, avalanches will occur to prevent the tower being too vertical. When you pour your beans into your grinder hopper, the beans will level out, in much the same way as the eventual coffee will in the cup. Do the collection of coffee beans move more as if they are a liquid or a solid?

Clearly to some extent the question is wrong, the beans represent their own class of structure but perhaps a better way of asking the question would be, how do a collection of coffee beans flow? It is a question with consequences beyond the coffee hopper. From pharmaceuticals to civil engineering projects and beyond, understanding how granular materials flow is an important topic.

Beans on a plate. The aspect ratio of the coffee bean is similar to that of the particles used in a new study to analyse granular flow.

And yet it has apparently been difficult to analyse this problem owing to the difficulty in tracking individual coffee beans (tablets or particles of cement) as they are pushed in one direction or another. A start was made nearly 20 years ago when a team at the University of Chicago used Magnetic Resonance Imaging (MRI, yes, the same MRI as you get in hospitals) to image individual mustard and poppy seeds as they flowed between two cylinders. The imaging allowed researchers to track the position and velocity and packing density of the seeds as they moved around the cylinders. Then, last year a new study used X-ray tomography to watch individual particles in a rectangular box as they were subjected to being pushed at various pressures in different directions. This, more recent study used plastic ellipses with a minor axis of 6.35mm and an aspect ratio of 1.5. Sadly, not real coffee beans but a fairly large plastic equivalent. While the aspect ratio will of course vary from varietal to varietal and even bean to bean, the coffee beans in my hopper at the moment have an aspect ratio of 1.3 (and a minor axis of 4.5mm) which makes them pretty close to the plastic used in the study.

Brew&Bread, latte art Sun, KL latte art
The structures in milk allow the milk to be ‘frothed’ and so enable latte art. They also make milk an example of a complex fluid.

By tracking each bean, the study discovered that such granular collections moved as if they were “complex fluids”. Which is all very well but does makes you wonder, what is a complex fluid? Is coffee a complex fluid?

Does the definition help? The definition on the Physics (APS) website says that: complex fluids “can be considered homogeneous at the macroscopic (or bulk) scale, but are disordered at the “microscopic” scale, and possess structure at an intermediate scale.”. What does that mean? Well, it seems to mean that complex fluids contain things that are larger than the molecules that make up the liquid and so affect how the fluid flows. Milk has long chains of proteins and fats (which give it the foam like qualities when it is frothed in a cappuccino) and so is a complex fluid. Chocolate and blood are other complex fluids as are emulsions and gels. Pure water would not be a complex fluid and my guess is that coffee (which contains water molecules and various molecules associated with the coffee itself) is also not a complex fluid. Were you to have a latte or a cortado though, the milk would transform your coffee into a complex fluid. Although I much prefer to keep my coffee simple, it would seem that there is more to the saying “you have coffee in your blood” than it would at first appear, particularly as regards the coffee beans. It may be time for some experimental tests of coffee bean (and coffee or latte liquid) flow….

Categories
Coffee review General Observations Science history Tea

Time standing still at VCR, Kuala Lumpur

VCR chalkboard
A trip down memory lane via a new cafe. VCR in Bangsar, KL

One of the first science-based talks I gave was about how VCR tapes worked. Depending on how you viewed it (and whether you had to listen), this was either an achievement given that I was at school and didn’t really understand magnetism nor magnetoresistive devices, or a thing to be suffered through (for much the same reasons). So when I learned that a new café called VCR had opened in Bangsar in Kuala Lumpur, it prompted a series of fond (and a few embarrassing) memories.

Moving on, it is clear that this second branch of VCR (the first is in Pudu, in the main part of KL), aims to provoke such memories of times past. From the name of the wifi to the pulleys behind the counter and the wooden screen at the back of the café, various details around the café pull your memory in different directions. However the coffee is very much in the present. With three types of coffee available to try as a pour over as well as the standard espresso based drinks, this café has a lot to offer. The coffee is roasted by VCR themselves in their Pudu branch. There is also an extensive food menu with an interesting Chawan mushi as well as an intricate avocado toast (topped with pomegranate seeds, toasted quinoa and feta).

coffee at VCR Bangsar
Coffee and pour over jug. But is the number 68 or 89?

The friendly baristas were happy to advise on which coffee to match with which brewing device (though there seemed a marked preference for V60s on the days I visited). In total I tried 4 pour-overs, one with the Kalita Wave and the others by V60. These coffees were all excellent but very different. A couple were fruity, one was sweet and full bodied, one reminded me a bit of the local fruit durian, not I hasten to add because of its taste, but because the aroma from the cup was so different from the flavour of the drink. It was a great privilege to be able to try these different coffees consecutively and to really experience the variety of flavours in coffee. Great care was taken while making the pour over before it was brought over to the table, together with a jug of water, it also seemed to me that the baristas kept a discreet eye on me afterwards to ensure I enjoyed the coffee. So it was a good experience to have had the opportunity both to enjoy one of those pour overs and to observe the people and the surroundings of VCR when I had to wait for 1 hour for someone with no phone and no book. If you get the opportunity to do this I would very much recommend it. Find a comfortable café, order a coffee and then sit, without distractions, and watch what your mind notices and where it wanders for an hour.

An obvious place for a mind to wander would be to the mechanism of tape recording (and why mini-disks are the superior recording medium for the elegance of the physics involved). However, in an hour a mind wanders far further than the name. Supporting the cakes (and a display case for the 2nd place award of the brewers cup), was a table with a concertina type decoration around its edge. Was this a nod to the Kalita Wave brewing device? This is a significant difference between the V60 and the Kalita Wave: the ridges (or wave pattern) on the filter of the latter. How does coffee flow past these ridges? Does this difference in flow dynamics make a difference to the taste of the coffee?

variables grind size, pour rate, pour vorticity
It seems that there would be a lot of physics to observe in the fluid flow in a Kalita Wave filter.

A few weeks previously a friend had made a (lovely) coffee with her Kalita Wave. It was interesting to note the different dose of coffee she used and the way the grinds built up in the ridges (compared with my ‘normal’ V60). Why do the grinds end up in the ridges? Why is there a layer of dust on the blades of a fan? Why do some corners of a building collect more dust or leaves than others? Are these questions related and does it change the flavour of the coffee in the Kalita?

In fact, there are many subtleties in understanding how fluids move around solid objects. One of these is that at the interface of the fluid with the solid, the fluid does not flow at all, there is a stationary layer. Known as a boundary layer or Prandtl boundary layer (after the person who first suggested their existence, Ludwig Prandtl), realising these layers existed revolutionised the field of aerodynamics. The problem had been how to model the drag experienced by a solid object in a fluid flow. Although perhaps only of academic interest in terms of the flow of coffee around a Kalita filter or a spoon, by the end of the nineteenth century and particularly, with the invention of airplanes, how to calculate fluid (i.e air) flow around a solid (i.e. wing) object became very important for practical reasons.

vortices, turbulence, coffee cup physics, coffee cup science
Another cool consequence of boundary layers:
Vortices created at the walls of a mug when the whole cup of coffee is placed on a rotating object (such as a record player).

Prandtl introduced the concept of a boundary layer in 1904. The idea allowed physicists to treat the main body of the moving fluid separately to the layer, very close to the solid, that was dominated by friction with the solid. This meant that the Navier-Stokes equations (that are used to describe fluid flow and ordinarily do not have an analytical solution) are simplified for this boundary layer and can be quantitatively solved. Although simple, by the 1920s Prandtl’s layer (and consequently the solvable equations) were being used to quantitatively predict the skin friction drag produced by airplanes and airships.

The boundary layer allows us to understand how vortices form behind cylinders or around the corners of buildings. I suspect a mix of the boundary layer, turbulence caused by the coffee going over many of the ridges and the brick like stacking/jamming of the coffee grains would combine to explain the difference in the grind shape around the Kalita Wave and the V60 filters. What this does to the flavour of the coffee and whether better brewing would involve more agitation, I will leave to Kalita Wave coffee lovers to investigate. And when you do, I would love to hear of your results, either here on Facebook or Twitter.

 

Categories
General Home experiments Observations Science history slow Tea

A tense moment for a coffee…

capillary bridge
A bridge formed by water between a cup and a cafetière.

Each and every coffee represents an opportunity to uncover an unusual bit of science. Sometimes the connections between what happens in your cup and the wider world are fairly obvious (e.g. the steam above your coffee and cloud formation), but sometimes the connections seem a little more obscure. On occasion, your observations may lead to philosophical speculations or stories from history. Every coffee is an opportunity to discover something, if you just slow down and ponder enough.

It was with this in mind that I looked at my freshly made French Press coffee a few weeks ago. I had positioned my cup very close to the cafetière such that a small water bridge had formed between the cup and the cafetière (see photo). Such “capillary bridges” have been studied for a couple of centuries and yet there is still more work to do. Caused by the surface tension of the water, understanding the way these bridges form and the shape of the surfaces produced is important for fields such as printing and powder processing. Yet it is only in the last 150 years or so that we have started to understand what surface tension is. Moreover, much of the pioneering work on this subject was done by an amateur scientist who just noticed things (and then designed some very clever experiments to discover more).

Agnes Pockels (1862-1935) is now regarded as a surface science pioneer but in 1891 she was a complete unknown. Although she had wanted to study physics, she was prevented from going to university because she was female. Consequently, all her study of the subject had to be through her brother Friedrich’s books and letters. It is not known what prompted her investigations but from 1880 she had been experimenting with a device to measure the surface tension of water. The device used a sliding weight to measure the force required to pull a 6mm diameter wooden disk off of the surface of a trough of water.¹ The design of this device was so successful that, a few years later, Irvine Langmuir adapted it slightly in order to study the surface of oils. He went on to receive the Nobel Prize for his work in 1932. Yet it is a device that could also be built in your kitchen, exactly as Agnes Pockels did².

reflections, surface tension
The effects of surface tension can be seen in the light reflected from a coffee

Pockels measured the surface tension of water contaminated by oil, alcohol, sugar, wax, soda crystals and salt (amongst other things)¹. She discovered how the surface tension of the water could be affected by pulling the surface or introducing metal objects onto it. She discovered the “compensating flows” that occurred between regions of different surface tension (you can see a similar effect with this soap boat). Yet all of this remained hidden from the wider world because Pockels was unable to publish. Not having access to the contemporary literature about surface tension and moreover unknown, unqualified and female, no journal would look at her work let alone publish it. Nonetheless, she was clearly a brilliant experimentalist and capable physicist.

Things changed when Pockels read a paper by John William Strutt (Lord Rayleigh) in about 1890. Rayleigh was quite the opposite of the unknown Pockels. As well as his work on sound, electricity and magnetism and the (co-) discovery of Argon, Rayleigh is known for his work on understanding why the sky is blue. (Which is another phenomenon that you can see while preparing your coffee if you drink your coffee with milk.) In his paper on surface tension, Rayleigh had come to similar conclusions as Pockels’ work but Pockels had gone further. Unable to publish herself, she instead wrote to Rayleigh, in German, detailing her experimental technique and results. Rayleigh responded by forwarding her letter to the scientific journal Nature together with an introductory paragraph:

“I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behaviour of contaminated water surfaces. The earlier part of Miss Pockels’ letter covers nearly the same ground as some of my own recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels’ experiments.”¹

Coffee Corona
You may have seen white mists form over the surface of your coffee (seen here by the rainbow effect around the light reflection). But what are they and how do they form? This is still not really known.

Rayleigh’s introduction and Agnes Pockels’ letter were published in Nature on 12 March 1891. The paper enabled Pockels to publish further results in both Science and Nature as well as in other journals. In 1932 she received an honorary doctorate in recognition of her work.

It seems that this coffee-science story has two main messages. The first is to emphasise how much we gain by ensuring everyone has access (and encouragement) to study physics (or indeed whatever subject they are motivated by). What would we have lost if Agnes Pockels had not had the books of her brother and made the decision to write to Rayleigh? But the second message is that Agnes Pockels managed all this, at least initially, by merely noticing what was going on in the liquids around her. Being curious she designed and built a piece of equipment that enabled her to measure what she was intrigued by and by taking a systematic series of data she discovered physics that was unknown to the wider community at the time. So the question is, what do you notice when you look at your coffee? How does it work, what can you discover?

Please do share any interesting physics that you see in (or around) your coffee either here in the comments section below, on Facebook or on Twitter. Tea comments would also be welcome, but whatever you do, slow down and notice it.

 

¹Rayleigh, Nature 1891, 43, 437-439, 12 March 1891 (full text here)

²Reference to the kitchen is here.