Month: February 2019

Categories
Coffee Roasters Observations

An effective medium for coffee roasting?

Pulp, Papa Palheta KL
Electrical boxes in Pulp by Papa Palheta KL. The moisture meter at Amoret is much smaller than these old boxes at this ex-printing works.
coffee bowl pour over
How would you measure the moisture content of a coffee bean?

Recently I had the pleasure of a tour of Amoret coffee in Notting Hill. In addition to discussing an upcoming event that Amoret are kindly hosting (an evening of coffee physics, sign up to the events list to find out more), it was great to see the coffee roaster that is installed there. Fascinating, with what looks to be a really interesting series of coffees lined up ready to roast. And in the course of all this, we came upon the moisture meter, which got me thinking.

Measuring the water content of green (and then roasted) coffee beans is quite critical to gaining an understanding of your roasting process apparently. Sitting on the shelf next to the roaster at Amoret, a small box contained an instrument designed for measuring exactly this. Although it looks as if it is a giant ice cream scoop with a central pillar in the middle, it is actually designed to measure the water content of the coffee beans capacitively. How does it work and, knowing how it works, can we make any predictions as to anomalous results that it may occasionally provide?

The simplest style of capacitor consists of two metallic plates with a gap between them. The capacitance changes depending on the size of the metallic plates, the distance between them and, crucially for this subject, the material that fills the space between the plates. When you apply an electric field between the two plates, the electric moments of the material within the capacitor will tend to align with the electric field. Different materials will react differently depending on their “polarisability”. You only have to think about how a stream of water reacts to a statically charged balloon to see why.

Pulp, Papa Palheta KL
Electrical boxes in Pulp by Papa Palheta KL. The moisture meter at Amoret is much smaller than these old boxes at this ex-printing works.

What this means in practise is that a capacitor formed of plates filled with water will have a different capacitance to the same capacitor filled with air. We say that the ‘permittivity’ of the air is different from the ‘permittivity’ of the water. Measuring the capacitance tells us the permittivity of the material between the plates and so whether the capacitor is filled with air or water. Now fairly obviously, it’s not quite as simple as this because a coffee bean is neither air nor fully water and the moisture meter is not two parallel plates. But in terms of the physics of the measurement, the shape doesn’t really matter here while another bit of physics called “effective medium” theory helps us with the fact that the bean is neither fully air nor fully water. Effective medium theory tells us that the relative permittivity of the mixture is simply proportional to the sum of the individual contributions from the polarisability of each set of molecules. So, merely changing the number of water molecules between the plates will change the capacitance. By knowing what the contribution of the dry beans are, we can calculate the moisture content of the coffee beans as a percentage. Or at least, the instrument can do this calculation internally and provide you with a number on the display.

But. This is what got me thinking about the measurements of the coffee at Amoret. Coffee beans come in a range of sizes and shapes, as you can see by taking a look at the online selection at Amoret (here). Some of these coffees are small, tending towards a more spherical shape while some are significantly larger and more conventionally bean shaped. Is it obvious that the moisture content measured for different coffees is directly comparable? This is not to diminish the use of the moisture meter. As a comparative tool to measure before and after roasting for example, it should be a fairly good indicator. But what should we expect for the absolute accuracy of the instrument? Is a 16% moisture content measured in a small bean really equal to a 16% moisture content measured in a big bean?

At first sight it may seem a silly question, after all, the moisture content is expressed as a percentage; why should size matter? But perhaps we could have a little further think about this. The moisture meter will be optimised for a dense packing of coffee beans. So if we filled it with small beans such that there were very few air gaps between the beans, we would expect a fairly accurate moisture content measurement. If on the other hand, the beans were larger such that there were quite a lot of air gaps between the beans, the actual volume fraction of water molecules in the meter would be reduced (16% of 100% full is greater than 16% of 90% full). And as the capacitance is directly related to the number of water molecules in the sample, the water content that was measured would be less than the true value in each individual bean. So this leads to my first question for roasters using capacitive moisture meters:

  • Do your large beans, that don’t pack well into the moisture meter, often show lower moisture contents than your smaller beans?
variables grind size, pour rate, pour vorticity
Coffee roasting is part-science, part-art and requires great skill and attention. But can thinking about a little extra physics help to understand some of what goes on with the process?

A second point is slightly more subtle. Consider that I had two beans of equal moisture content (%). But one of those beans packs more fully into the moisture meter than the other larger, more irregularly shaped bean. On roasting these beans, they both lost the same volume fraction of water so, say, they went from 16% to 12% water content on roasting. Would both beans show that they had lost the same amount of water?

We could start by thinking about packing these beans into the meter. The one that was densely packed would show a moisture content that was close to the real value (in our example 16%).  The one that was less densely packed however would have a lower volume fraction of water and so show a lower water content. If we assume that the beans filled 90% of the space, the percentage that we measure would be 16% of 90% = 14.4%. On roasting, the two beans are again loaded into the meter and again the densely packed one will show a moisture content close to the real value (in our example 12%). The loosely packed one will show a moisture reading of 12% of 90% of the volume which is 10.8%. Crucially, if we are looking at moisture difference, the densely packed bean will appear to have lost more water (16% – 12% = 4%) than the loosely packed bean (14.4% – 10.8% = 3.6%). Which leads to my second question for roasters:

  • Do small beans that pack well into the moisture meter appear to lose more water for an optimised roasting profile than your larger, less densely packed beans?

Clearly, different beans will have different moisture contents anyway and so it may be difficult to discern any pattern between two specific coffees. The moisture readings may genuinely reflect the fact that the smaller beans have higher water content or vice versa. And also obviously, the measured moisture content is only one part of determining a successful roast profile. However the question is one of statistics. On average, do your larger, less well packed beans have a moisture level lower than you expect? And on average, do they seem to lose less water (measured capacitively) on roasting?

I’d be fascinated to hear your thoughts, here, on Twitter or Facebook.

Categories
Coffee review General Observations

Semi skimmed at Full Fat, Balham

exterior of Full Fat Balham
The shopfront almost seemed to skinny for the name of this cafe.

Just around the corner from Balham tube station, on Chestnut Grove is a new (old) café, Full Fat. Although it has only been in its current location since September 2018, it was previously known as the Balham Kitchen and was apparently quite popular, not just because it was a friendly local café, but also because of the coffee and the chapatis.

We had chanced upon Full Fat while in Balham and took the opportunity for a chapati brunch. During our coffee break several customers came in and had a chat with the two people behind the counter. With coffee roasted by Workshop and an excellent range of homemade chapatis, along with friendly people, what is not to like? We enjoyed an Americano and an oat milk hot chocolate together with two chapatis. My egg chapati was perfectly done, just the right amount of pepper-to-egg balance. And the coffee was also very well made with plenty to think about just by gazing into it.

Although the café itself is quite small, there are three tables and several seats, enough to be able to ensure that you can probably perch somewhere to enjoy your coffee and chapati. There are even entertaining drawings on the walls of the café that make me wonder whether these are previous customers, immortalised on the walls enjoying a cup of coffee with their morning paper? Certainly they are a good reason to put down your smart phone and just soak in the atmosphere here.

pencil drawings in Full Fat
Pencil drawings at Full Fat Balham

Apart from the drawings, the other decoration in the café that caught my attention was behind another table: a striped piece of woodwork that was reminiscent of a type of cake served in Malaysia and Singapore, kueh lapis. It is a layered cake, the idea being that you peel each layer off to eat it, extending the enjoyment that you can get out of a cake. Although the layers peel easily, ordinarily the cake holds together as a cake, the layers do not glide over each other as if they are wholly separate, perhaps like chapatis stacked on top of each other. No, whether the cake works or not, as a kueh lapis, is down not just to the flavour, but also to the texture and to the way that each layer peels from the next, the subtle tug of one layer held, but not quite, by the last.

These interlayer or interface effects are often, ultimately, an atomic phenomenon. Just as when you drop a drip of coffee on the table, the thing that ultimately determines the shape of the droplet is the attraction between the molecules in the water and the atoms on the table surface*, so the stickiness of the cake has to be occurring, ultimately, at the atomic level.

Interface effects can be crucial in other solids too, not just coffee and cake. Consider sapphire. Sapphire has the molecular formula Al2O3. Ordinarily it is colourless and transparent, it becomes blue when impurities are added to it. But sapphire has another property which is that it is electrically insulating: a sapphire would not conduct any electricity if you tried to use it to connect to your light bulbs. This insulating behaviour is shared with another oxide, strontium titanate, SrTiO3, which is also a colourless and transparent material. Nothing of any interest there then. But, and this is the key thing, if you took a piece of strontium titanate and grew the sapphire on top of it, under certain growth conditions, this bilayer becomes extraordinarily electrically conducting, far better than many metals that you can think of. And it is because of the atomic effects that occur at the interface between the strontium titanate and the Al2O3.

Layering of wood at Full Fat
Can you see the layering on the wooden panel behind the table? Thought not, you’ll just have to visit Full Fat and see for yourself.

But then another example, a new finding that is perhaps more closely associated with coffee. When you take the semiconductor molybdenum ditelluride (MoTe2) and sandwich a thin layer of it between two sheets of graphene, some atomic-level interactions occur. In the case of MoTe2, the “band gap” of the semiconductor (which determines how it conducts electricity when light is shone on it) is altered by the van der Waals forces associated with the graphene layers: the interface effects are changing the way that the semiconductor reacts to light. Ordinarily if you shine a pulsed laser at such a semiconductor, the electrons† that get excited across the band gap are few enough that they behave as a gas within the semiconductor. This means that if you add more electrons (by pulsing the light on the semiconductor again), the density of the electron ‘gas’ will increase. What researchers have just shown is that for this 2D layer, if you shine very high powered lasers at the MoTe2 layer for a short length of time, so many electrons get excited that the semiconductor no longer behaves as if it contains an electron gas, but an electron ‘liquid’. A sort of droplet of electrons in the locality of the laser beam. And because of the way that the band structure had been affected by the interface layers, they managed to obtain this behaviour at room temperature. Although such liquids had been created before, the new thing about this result was that previously these experiments were usually done at very low (-269C) temperatures. Quite a temperature increase on previous results!

Droplets of an electron-hole excitation may seem a far step from the droplets of coffee that you could be enjoying at Full Fat. However, it is just a short hop for the imagination if you stopped to give it time to think. What will you notice next time you are in a café?

Full Fat is on Chestnut Grove, literally just around the corner from Balham tube station.

*Assuming that the table is flat. If the table is nanostructured, the structure itself can influence the ‘wettability’ of the table.

†Yes, and holes.

Categories
Coffee cup science General slow Sustainability/environmental

Coffee and science: a problem shared?

coffee and Caffeine at Sharps
What is the future of coffee? Science? Our society? Are these things held together more closely than we imagine?

There is a lot of science in coffee (and a lot of coffee in science). And there are also many scientists who are keen coffee drinkers and vice versa. But is there more in common between these two fields than even this? Could a shared problem be hiding a different (shared) problem?

One issue for coffee drinkers is reliability and reproducibility. How can we ensure that we get a good cup each time we visit a café or brew our own? In a similar way, how do we ensure that our experimental results in science are correct and reproducible? It is a fairly fundamental tenet of science that an experiment should be able to be reproduced in another lab with similar equipment. The suggestion is that this is not always happening, we have a ‘reliability’ problem in science (and sometimes in coffee).

A possible solution, in both fields, is some form of automation. In the world of coffee this is quite obviously just by making coffee via a machine. There have been several attempts to make reproducibly good coffee using an automated pour over machine. In the world of experimental science, it is not quite so clearly an automation process but is described instead as “data sharing”. The results of all experiments, or at least those that are published, should be shared (uploaded with the published paper) so that others can examine the data in more detail and form their own conclusions†.

For both coffee and science, it is suggested that this opening up of our process so that it is more transparent or reliable, will increase the reproducibility of good results and, crucially, mean that we get those results faster. We will get reproducibly good coffee without having to queue so long in the morning; we will make discoveries more quickly and have faster progress in science.

It seems that the problem that we thought we had, reproducibility, is perhaps not the one that we are actually aiming to solve. The problem we seem to be interested in is ensuring faster progress.

coffee under the microscope
We can look at coffee under the microscope (here are two different coffees ground to the same degree). But do we need to look more closely at the process of making good coffee or of doing science?

But an emphasis on faster progress can undermine our initial ideal of a reproducibly good result. For scientific research the emphasis on getting results quickly (at least within the time frame of the science funding cycle) has led to predictable problems. There are cases that I know about where results that were contrary to those that were wanted were suppressed. Not permanently. No, that would be demonstrably scientific fraud. No, suppressed just long enough for the first ‘ground breaking’ paper to be published. Then, after a suitable length of time, the second paper showing the problems with the first can follow up. Those involved get two papers (at least), and rapid progress is shown to be happening in the field. Would data transparency help here? Clearly not, because the initial set of data would still be suppressed until it was wanted those few months later.

What we need is a change in the structure of how science is done. We need to value scientific integrity and so trust that other scientists do too. We know that the current situation whereby promotions, funding etc are determined by the number of papers in ‘good’ journals, can act to undermine scientific integrity. This needs to change if the reliability issue is to be addressed. In the type of case described above, there would be no consequences for the people who kept their names on the paper(s) published. The only consequences would be if anyone refused to have their name on the paper as they knew it was misleading. And even then, the consequences would be to that person/those people in terms of their CV, and publication list, not those who published the paper and of course, shared the data.

coffee at Watch House
A good pour over takes time.
What are we looking for in coffee, in science? Is progress an aim of itself?

For the coffee, there are already discussions about whether the increase in throughput offered by automated coffee brewing techniques really contributes to the coffee experience that the cafés are trying to encourage. Can we really expect someone to slow down, take in the aroma, the mouthfeel, the taste and flavour if we rush the cup through to them on a production line? Isn’t part of the enjoyment of something to have to wait for it (hence lent before Easter; fasting before a feast)?

It is not that automation necessarily is bad. We can get a genuinely all round good coffee in a café that utilises a machine based pour over (perhaps). We can also get genuinely reproducible data in a situation where data is routinely shared. It’s just that data sharing does not solve the reproducibility problem, nor does automation give us continually good coffee. What makes the difference is a café that cares about the product that they are serving; scientists that care about the integrity of the research that they are doing. Automation processes give us faster results, they do not, automatically, give us better science (coffee).

Moreover, our desire for faster progress obscures questions that we should be asking if we slowed down a little. What is a good coffee experience? Who (if anyone) should own the scientific data shared? Is our desire for good coffee, quickly and (relatively) cheaply obtained, an aspect of that consumerism that is damaging for the planet’s ecological health? How much do we need to trust each other (and take responsibility for our own integrity) for our society, including our scientific society, to function? Is faster progress in and of itself, a “good” to aim for?

And perhaps, there is a final, more fundamental question. Have we become so accustomed to seeing ourselves and our work as merely a cog in a machine that we have become inured to the dehumanisation of society which seems to us almost natural and itself progress? Is this what we want for society?

The process of making a good cup of coffee indeed shares many things with the process of doing science. Perhaps this should not be surprising, both are practises embedded in our society. Certainly our view of the society that we live in can be informed by slowing down with our coffee as we enjoy a little science (or should that be the other way round)?

 

†It is not quite an automation process in the sense that the data is taken by a machine and then uploaded. However, it is still a dehumanisation process. At the root of the concept is the idea that the human experimenter can be taken out of the process. I would be happy to expand on this in the comments but for the sake of readability haven’t done so here.

Categories
Coffee review General Observations slow Sustainability/environmental Tea

To stay or to go at Cafe from Crisis

coffee commercial St volcano
Cafe from Crisis on Commercial Street, E1. Notice the arches…

It was not what I had expected. Entering the door of the Cafe from Crisis, you go up a ramp with a bench running alongside it before the counter looms in front of you with a large café space opening up to your right (previously partially obscured from your view by the wall for the ramp). Perhaps it is fitting that my expectations were wrong. Many of us have ideas about the homeless (why they are homeless, what homelessness is etc) that may not match fully with the reality. And this café is, after all, in the head office of Crisis, a UK national charity working with the homeless and homelessness.

The coffee is roasted by Volcano and there are a large number of food options (including vegan and veggie) and cakes at the counter. A selection of keep cups are also arranged in a rack on the left of the counter, should you not have one yet. We ordered an Americano and tea (to stay) and took our numbered wooden spoon to the table so that they could find us. Although it was late lunchtime and busy, the drinks arrived fairly quickly with the coffee in a (Crisis themed?) red cup. Apparently serving coffee in red cups make us perceive the coffee as warmer than if it is served in a blue cup. Whether this is true or not, the warm brew was very welcome on this cold January day. The café is situated on a street corner which means that it has many windows, each topped with a shallow arch. The building looks fairly modern from the outside, but the arches were reminiscent of the way that older buildings can be dated by the window style, along with other features. The Cure played in the background which entertained my tea drinking companion but made me wonder about the ideas of Pythagoras on the psychological impacts of different sorts of music (and whether it affected the ability to find thought connections in a café).

plant in a coffee cup
It turns out there are many things to notice in this photo. From the bricks to the self-defence tactics of plants. But what about the nature of the home of the plant?

As we sat, enjoyed our drinks and looked around, we noticed that some plants had found a home in coffee cups placed on the tables around. Small plants in plastic pots (a nod to the anthropocene as pointed out by @lifelearner47 on twitter) were dotted around the café. Did they move from an espresso to a long black cup as they grew larger? Perhaps it was the spiky plant in one of the pots, but my mind immediately jumped to hermit crabs and their search for a new shell each time they grew a bit bigger. Marine hermit crabs  have been shown to be happy in any old discarded shell. Normally these are the ex-homes of gastropods that have, well, “moved on” would be a euphemism, but marine based hermit crabs have been known to make their shells out of all sorts of things including our plastic litter. Land based hermit crabs however are far more demanding and only move into shells that have been specially remodelled by earlier generations of hermit crabs for their own use. This means that land based hermit crabs have to develop a social awareness of other hermit crabs when they want to swap shells.

Apparently the interaction goes something like this: A group of hermit crabs come together in a small-ish area and begin to scope each other out. The loose collection becomes a cluster as the crabs explore whether one of the larger crabs can be evicted from its shell. As the process of eviction is about to occur, the remaining crabs (which can number quite a few, 10 or more) literally ‘line up’ in order of shell size so that, when the largest is evicted, each crab can move up to the next sized shell leaving the smallest, most undesirable shell on the seashore and the poor evicted crab, shell-less.

Several questions arise but one is, do the crabs make decisions, “to stay or to go” based on how advanced the eviction process is? So, say a crab wanders into an area with an unusually large number of crabs in it (perhaps 4) but the crabs are all lined up in a queue ready to swap into each others shells. Do the crabs coming into the area stick around for a long time or do they head off somewhere else? Or, conversely, what if they enter an area where there are more than the usual number of ‘colleagues’, but they are all scattered about, not yet ready to evict the largest crab. What would our incoming crab do then?

coffee red cup Crisis
What would you learn if you noticed the connections your mind was forming while enjoying a coffee?

These questions were addressed by a group working with the terrestrial hermit crabs of Costa Rica. By defining five cells on the beach, each with a different arrangement of (empty but inaccessible) shells that the incoming hermit crab may want, the researchers found that the incoming hermits were making some strikingly sensible decisions. When the crab came into a region of scattered shells (that the incomer mistook for fellow crabs owing to a trick with a combination of loctite glue and partially burying the empty shells that the researchers used to fool the incomers), the incomer tended to stick around, waiting for an opportunity to swap a shell. If the incomer came but saw that the queue of shells had already formed, it still stayed a bit longer in the region relative to a control area devoid of shells, but it did tend to leave it after some time, perhaps to look for new shells elsewhere. The researchers concluded that when the crab came into an area and thought it had a pretty good chance of inserting itself into a good queue position, it would stay in the area waiting for the eviction to occur and the shell swapping process to start. However when the crab came into an area where the queue had already formed, it was unlikely to be able to get a good position in the queue and so would investigate the situation for a bit before wandering off elsewhere in the search of a new shell in a different area.

Does this have any relevance to a café trying to do a bit to address the problems of homelessness and the homeless in our city and country? I will leave that to each reader to ponder. However, it was a great opportunity to learn something new about our world, which only happened because I stopped to notice something in a café and then wondered how hermit crabs get their homes. It’s always good to slow down and notice things. What will you see next?

Cafe from Crisis (London) is at 64 Commercial Street, E1 6LT.