Categories
Coffee review General slow Tea

Data overload at The Gentlemen Baristas

coffee Borough
The Gentlemen Baristas in Borough.

Borough is always such a great place to wander. Walking around the backstreets with their bits of hidden history. The other day, we had visited the market, wandered down Redcross Way past the old Crossbones graveyard and hit upon The Gentlemen Baristas on Union Street. It is difficult not to have heard about these Gentlemen and my visit there was long overdue and so, we wandered in to try this famous venue.

The shop front advertised itself as a “Coffee House”. A very accurate description and a nod to the Coffee Houses of the past. As it was shortly after lunchtime, it was very crowded with a diverse bunch of people and felt a little cramped at the counter. Nonetheless, the queue was quick and friendly baristas soon took our order allowing us to retire inside to try to find a table (no chance) or a stool next to a bar (successful). Around us, people were either chatting over their coffees or working on laptops.

While waiting for my long black (intriguingly described on their website as a “well mannered coffee”), I noted the various posters describing different types of screw head or parts of the human skeleton. Enough detail to be a phone distraction but surely there was more physics waiting to be seen in this convivial back room of a coffee house? A blackboard at the end of the bar, offered details of the wifi as well as a quote (slightly adapted) from PG Wodehouse about the benefits to friendship of a shared taste in coffee. On a shelf opposite the blackboard were a number of books including a thick book detailing coffee trading in years gone by. From the fact that the books were stacked horizontally, it would appear that they are not consulted often.

shelf books hats Borough
The lighting made photography difficult but you can see the books (and the hats) on this shelf at The Gentlemen Baristas

Sitting between this juxtaposition of wifi information and old books, caused me to pause. I have heard it said that we “know” more now than we have ever known in the past. That we have access to an enormous amount of knowledge merely through our phones. Is this correct?

On one level it is certainly un-arguable. Ninety percent of the world’s data in 2013 had been generated in the previous two years. If you need to find anything out, a quick duckduckgo (or if you have to, a google) will often lead to websites detailing all sorts of quirky bits of information. If we want to know the radius of the Earth or the size of an espresso grind, we no longer have to remember the answer, nor even really to have a feel for the answer, instead we can almost immediately find webpages that tell us (here and here).

And yet, this answer seems unsatisfactory. While there is an awful lot of information available to us at the tap of a phone, it is questionable whether that information translates to our own knowledge. Although collectively we can understand amazing things such as gravitational waves, individually we may struggle to explain how a toilet works. We need the plumber’s knowledge as much as we need that of the cosmologists. Does it matter who knows? What level of knowledge does someone need to have to say that they ‘know’ something?

coffee long black gentlemen baristas
Taking time to stop and think about what it’s all about. My coffee at The Gentlemen Baristas

Perhaps this appears a very strange cafe-physics review, where is the physics? But part of the rationale behind Bean Thinking is also to slow down and contemplate and it seems that The Gentlemen Baristas offers the perfect environment in which to do so. A café that mixes the new with the old, a space in which the practices of one can inform the other.

So to return the thought train to the area local to the Gentlemen: Writing in the second century AD, the Stoic philosopher Marcus Aurelius wrote

In death, Alexander of Macedon’s end differed no whit from his stable-boy’s. Either both were received into the same generative principle of the universe, or both alike were dispersed into atoms.

It is a quote you will probably find very easily via a search engine, or slightly less easily if you read his “Meditations”. But it is perhaps worth pondering, in what sense we ‘know’ what he was meaning. Strolling past the ribbons and messages memorialising the (estimated) 15,000 people who lay buried in the ‘outcast’ graveyard of Crossbones, what about our own attitudes to our modern outcasts? And perhaps more tellingly, our attitudes to those in positions of power or influence?

Perhaps it will take a lifetime of understanding our personal reactions to the poor, the prostitutes, the homeless and the powerful to really know what Aurelius meant. It certainly requires of us that we stop, pause and reflect on the knowledge that we come by. So it is far from obvious that it benefits us to use the wifi password rather than sit, slow down and contemplate. And where better to do so than in a friendly café with good coffee and seats to ponder the moment?

The Gentlemen Baristas can be found at 63 Union St, SE1 1SG

 

 

Categories
General Observations slow Tea

Back of the envelope calculations with coffee

coffee at Watch House
Coffee is generally a great help for reading, but to properly see the clouds in your coffee, it may help if you prepared yourself a brew now.

To read this post it will help if you have a cup of lovely, hot, freshly prepared coffee or tea with you.

Got it? Ok, let’s begin.

A few weeks ago, there was a talk given by Prof. Paul Williams of the University of Reading about the Mathematics of turbulence and climate change. An entertaining talk about the importance of, and the effort of comprehension required to, use mathematics in order to understand climate change. There were several thought provoking comments through the talk that demanded further reflection. But one, almost throw-away comment has been bugging me since. Although I’ve forgotten the exact words, they went along the lines of

Of course mostly we think about the impact of climate change on the weather, after all, we live in the bottom few metres of the atmosphere and so that is what mostly affects us. What I would like to talk about is the effect of climate change on airplane turbulence…

The bottom few metres of the atmosphere? It’s true. The bit we’re most experienced with is just a tiny portion of it. It’s about perspective. To us, it seems the atmosphere is very big, we pump all sorts of exhaust fumes into it and they disappear. We have expressions such as “the sky is the limit” that suggests that the atmosphere is a huge volume of gas. We all know it is not really limitless, but day to day, on our human scale, it seems enormous.

Now the mathematics that Prof Williams uses to calculate the effect of changing temperature and carbon dioxide levels on the jet stream (and consequently the turbulence felt by planes) is way beyond the sort of back of the envelope calculation that we can do with a cup of tea (or coffee). Understandably, to even start to comprehend these mathematical models requires years of training in maths and physics. However, assuming that we are not ourselves atmospheric physicists, there are things that we can do to help us to see our atmosphere in a more realistic way. And this is where your coffee comes in.

Earth from space, South America, coffee
Clouds swirling above our common home. But if the atmosphere is represented by the white mists on the surface of a cup of coffee, what size coffee are we drinking?
The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler

Take a close look at that coffee. Assuming it is not cold brew, hopefully your coffee or tea is still fairly warm. Watch the surface of the coffee. You may start to see movement such as convection in the mug, perhaps you can see a film of oil on the surface. But do you see something else? In very hot tea or coffee, you should be able to see what appear as white mists hovering over the surface of the cup*. It is easy to miss them, but as you watch, cracks suddenly appear in the mists and then there is a re-organisation of them which allows you to start to see them dancing over the surface of your drink*.

These mists are the result of the levitation of many thousands of droplets of water just above the surface of the coffee. I have written about them elsewhere. No one knows quite how they levitate above the surface, but what is known is that they are at a distance of up to 100 μm (0.1mm) from the surface of the coffee.

Let’s construct a scale model of our coffee as the Earth and its atmosphere. These mists can then do a fairly good job of representing the atmosphere with its drifting clouds. So, assuming that the mists are the atmosphere and the coffee is the Earth (on the same scale), what size of coffee would you have to have? Would you be drinking:

a) an espresso

b) a long black

c) a venti

d) a ristretto

Think you know the answer? Let’s work it out with a “back of the envelope” calculation. The easy bit is deciding the radius of the Earth, it’s just under 6400 km, our first problem comes with the estimate of the thickness of the atmosphere. There are several layers in the atmosphere. The one that we are most familiar with, the one closest to us is the troposphere. This extends for the first 16 km above the surface of the Earth (though this varies with latitude, it is only 8 km at the poles). Most of our weather happens in this region and it is also the layer of the atmosphere that planes fly in. Above the troposphere is the stratosphere which extends until about 50 km. Beyond that, things get very rarified indeed though the boundary between our atmosphere and “space” does not happen for several hundred km (indeed, the orbit of the International Space Station is in this bit of our extended atmosphere).

Coffee Corona
Look carefully around the central (reflected) white light. Can you see a rainbow like spreading of the colours? Another manifestation of the white mists on the coffee surface.

As we are mostly concerned with the weather (and airplane flight etc) though, it seems sensible to define the atmosphere height to be the top of the troposphere. After all, most of us will tend to think that the Space Station is in, well, space. This definition is further justified by the fact that about 75% of the mass of the atmosphere is found within this region (the atmosphere gets thinner as you go higher).

What size coffee would we be drinking if the white mists (0.1 mm above the coffee surface) represent the 16 km of the Earth’s atmosphere? We’ll call the coffee height, hc. Our first step is quite easy, we can just use the ratios of the heights to calculate the coffee size:

(height of troposphere)/(radius of Earth) = (white mist height)/(height of coffee)

A bit of rearrangement:

height of coffee = (white mist height)*(radius of Earth)/(height of troposphere)

hc = (0.1) * (6400)/16

hc = 40 mm (4cm)

So for the mists to represent the atmosphere in your coffee, you would need to be drinking a 4cm tall coffee which is probably a smallish long black. I would leave it to you to calculate the coffee size for the atmosphere defined as outer space (beyond the orbit of the International Space Station). But perhaps this perspective gives us another way of looking at our atmosphere. Vast indeed, but fragile too.

*As I was writing this, I had a warm, very drinkable, cup of coffee but it wasn’t steaming and so showed no white mists over the surface. The mists are best seen in freshly made, very hot drinks.

Categories
Coffee Roasters General Home experiments Observations Science history slow Uncategorized

Chemical extraction in a V60

chromatography, paper chromatography, V60
Brewing a coffee, insight into analytical chemistry

Ever considered the connection between your morning brew and a century old technique that, it is fair to say, revolutionised analytical chemistry?

Last week, a new coffee arrived in the post from the Roasting House coffee club, followed shortly by an email with details about that week’s coffee. This is not unusual, the coffee club means that a different coffee arrives every two weeks. What was slightly unusual was the email which started:

“There are some brief tasting notes on the bag of coffee we sent you, but before you go on and read the more detailed description, have a good taste of the coffee yourself….”

The opportunity to do so finally arrived and I prepared a V60. First measuring out the freshly ground beans, rinsing the filter, watching the bloom, then slowly pouring the remaining freshly boiled water onto the grounds, all the while noting the aroma.

Taking this opportunity to slowly prepare (and appreciate) a coffee, I noticed that some of the soluble elements in the coffee climbed the filter paper during the pour. A few hours afterwards, the paper had gained a circular rim of coffee solubles around the top of the paper. Although in many ways quite different, this effect was very reminiscent of the technique of chromatography.

Roast House coffee, tasting chromatography
The coffee in question. What tasting notes would you get if you slowed down and tried this one?

The biggest difference between the behaviour of the V60 filter and “paper chromatography” is that in the former, the bottom of the filter paper is continuously immersed in both the sample (coffee) and the solvent (water). In chromatography on the other hand, a drop of the sample (e.g. coffee or ink) is put onto the filter paper which is then placed in a solvent (e.g. water, ethanol). Different components within the sample travel different amounts up the filter paper depending on how soluble they are in the solvent and how they interact chemically with the filter paper. So different components will travel different distances up the filter paper before they get stuck while the solvent continues to travel up the paper. All else being constant, each component always travels a certain distance relative to the solvent and so this provides a way of separating chemical components ready for further analysis or identification.

Perhaps you remember using chromatography to separate the colours in an ink pen at school? The ink was spotted onto a piece of filter paper and then immersed in water. We watched as it separated into various colours illustrating the number of different dyes that had been used to make up the ink. When used professionally though, the chromatography technique can be used to investigate trace impurities in soil, air, drinking water etc. It has even been used to analyse the components in coffee. From something that can be done in school science, it is an incredibly powerful chemical technique.

What was surprising was that the technique of chromatography was not invented until 1903, while the idea of using paper in chromatography only came about in 1944¹. Those who first used chromatography as a method to identify chemicals (in plants), did so using columns of powder rather than paper. Paper chromatography was invented to investigate the separation of amino acids and specifically was used to understand the composition of the antibiotic tyrocidin¹. Just as the ink in our school experiments separated into different dyes, so the chemicals that they were investigating would separate into different components, different chemicals would stay at different heights on the filter paper.

Since its invention, the technique had been extended to include gas chromatography rather than just liquid and has been developed to be extraordinarily sensitive. It is now possible to analyse chemicals with a mass of just 10^-15 grammes, a quantity which is too small to even easily imagine. Even just a couple of decades after the invention of the technique it could be said:

“Amino acids… could now be separated in microgram amounts and visualised…. (Paper chromatography) would allow one within the space of a week [to do some analysis]… which until then could very well have occupied the three years of a Ph.D….”¹

V60 chromatography chemistry kitchen
A few hours later and the coffee had travelled up the filter paper with the solvent (water).

However, to return to the coffee. Through tasting rather than chemistry, I obtained a toffee aroma, with earthy notes and hints of redcurrant that evolved as the coffee cooled into a sweet toffee taste. The tasting notes further down the email on the other hand said:

“There’s a rich chocolate base, a kind of woody pine taste, sweet summer fruits, even tobacco. Remember, taste it before you judge it! Tobacco notes and woody pine don’t sound particularly appealing and maybe you don’t taste them at all!”

Much more descriptive than my effort. It seems I need to return to my V60 and improve my tasting ‘chromatography’. There are so many ways to slow down and appreciate a good coffee, what do you notice in yours?

A ‘coffee tasting wheel’ can be found here if you, like me, would like to improve your coffee tasting ‘chromatography’.

¹Chapters in the evolution of Chromatography, Ed. John V Hinshaw, Imperial College Press, 2008

Categories
Coffee Roasters General Home experiments Observations

Coffee under the microscope

Inside Coffee Affair

There are many great cafés in London serving excellent coffee but inevitably a few stand out. One such café is Coffee Affair in Queenstown Road railway station which ‘inhabits’ a space that really encourages you to slow down and enjoy your coffee while just noticing the environment. An ex-ticket office that whispers its history through subtle signs on the parquet floor and in the fixings. The sort of place where you have to stop, look around and listen in order to fully appreciate it. And with a variety of great coffees on hand to sample, this is a café that is a pleasure to return to whenever I get the opportunity.

So it was that a few weeks ago, I happened to wander into Queenstown Road station and into Coffee Affair. That day, two coffees were on offer for V60s. One, an Ethiopian with hints of mango, peach and honey, the other, a Kenyan with tasting notes of blackcurrant and cassis. But there was an issue with them when they were prepared for V60s. The Ethiopian, “Gelana Abaya”, caused a considerable bloom but then tended to clog the filter cone if due care was not taken during the pour. The other, the Kenyan “Kamwangi AA”, did not degas so much in the initial bloom but instead was easier to prepare in the V60; there was not such a tendency to clog.

What could be going on?

So we had a look under the microscope at these two coffees. Each coffee was ground as if it was to be prepared in a V60 and then examined under the microscope. Was there any difference between the appearance of the Gelana compared to the Kamwangi? A first look didn’t reveal much. Magnifying both coffees at 5x, it could be said that the Kamwangi had more ‘irregular protrusions’ on the ground coffee compared to the smoother Gelana, but it was hard to see much more:

coffee under the microscope
The samples of ground coffee imaged under an optical microscope at 5x magnification. Kamwangi is on the left, Gelana on the right. “500 um” means 500 micrometers which is 0.5 mm.

So, the microscope was swapped to image the coffee in fluorescence mode. It was then that the cell structure of the coffee became clear. Here are the two coffees magnified 10x:

Fluorescence microscopy 10x, Ethiopian, Kenyan, Kamwangi, Gelana
Fluorescence microscope image of the two coffees at 10x magnification. Note the open structure in the Kamwangi and the more closed structure in the Gelana.

and at 20x

Kamwangi and Gelana coffee under the microscope
A fluorescence microscope image magnified 20x – not ‘um’ means micrometers (1/1000 of a mm), so the scale bar represents 1/10 mm.

So there is perhaps a clue in the cell structure. It seems as if the Kamwangi structure is more open, that somehow the cells in the Kamwangi break open as they are ground but the Gelana somehow keeps its cells more intact. Could this be why the Gelana blooms so much more?

Which naturally leads to a second experiment. What happens when you look at these two coffees in water under the microscope? Here the fluorescence images didn’t help as all you could see were the bubbles of gas in each coffee but the optical microscope images were of more interest.

optical microscope image in water
The two coffees compared under the microscope while in (cold) water. Magnfied 5x

‘Bits’ broke off the Kamwangi as soon as water was added but in comparison, there were far fewer bits of coffee breaking off the Gelana grains.

So what do you think has happened? If you remember our question was: when these two coffees were prepared with a V60, the Gelana bloomed a lot but then clogged in the filter (without extreme care while pouring the filter). Meanwhile the Kamwangi did not bloom so much but also did not clog the filter, what could be happening?

From the microscope images, it appears that

  1. Before adding any water, the cell structure in the Kamwangi is more open, the Gelana appears ‘closed’.
  2. When water is added, there are many more ‘bits’ that come off the Kamwangi whereas the Gelana does not show so much disintegration on the addition of water.

If pushed for a hypothesis, I wonder whether these two observations are linked. What is happening is that the cell structure in the Kamwangi is, for whatever reason, fairly fragile. So as soon as it is ground, the cells break up and a lot of the carbon dioxide is released. Consequently when water is added to it, the bits of broken cell quickly disperse through the water and it doesn’t seem to ‘bubble’ that much. In comparison, the Gelana cell structure is tougher and the cells only open up when water is added. I wonder if this means that the ground Gelana coffee will swell rather than break up and so ‘jam together’ as each grain tries to expand rather like trying to inflate many balloons in a bucket. They will push against each other and prevent water from easily percolating through the ground coffee.

Sadly, many more experiments would be required before we could see if there’s any truth in this hypothesis however that does provide a great excuse, were one needed, for many return trips to Coffee Affair. Meanwhile, what do you think? Do any of the images stand out to you and why? What do you think could be the cause of our V60 coffee mystery? I’d love to hear your thoughts so please let me know either here in the comments section (moderated and experiencing a lot of spam at the moment so please be patient), on Facebook or on Twitter.

Categories
General slow Sustainability/environmental Tea

Coffee cup recycling

a take away cup
It is recyclable, but not easily so.

That old subject again, the recyclability of take-away coffee cups. But before you groan about our disposable culture, there has recently been some great news, at least as far as the university sector is concerned. Regular readers may know of the Bean Thinking list of Top UK Universities for Coffee Cup Recycling. You may also be aware of just how short that list has been. Now though, there are signs of change. Perhaps because it is the start of the academic year, several universities including Oxford Brookes and the University of Bedfordshire have announced new schemes for recycling their cups with Simply Cups.

Owing to the way the cups are made it is extremely difficult to recycle them; although they are technically recyclable, very few companies have the capabilities. Consequently, the majority of the cups that we use for our take-away are just thrown-away, taking many decades to break down.

compostable, coffee cup, disposable culture
Using compostables can be a step in the right direction.

It is often our universities that do the research showing just how environmentally damaging our disposable culture can be. Nonetheless many university catering departments continue to serve coffee in “disposable” cups without putting in place any scheme to recycle them. Over a year ago I started a list of the UK’s top universities for coffee cup recycling. It would be thought that it should be extremely easy to be listed here. To be listed, all a university has to do is take a responsible attitude to it’s take away coffee cup use. Preferably, they would discourage take-away coffee cup use altogether. As Loughborough University recognises, slowing down, talking with colleagues over a stay-in (washable cup) coffee can be far more productive than scurrying away with your non-degradable cup.

However, often we feel that we don’t have time to sit down for a coffee and need to take-away. At this point, to be listed on the guide, all that a university would have to do is either invest in compostable cups (despite the caveats*, this is at least a step in the right direction) or institute a scheme to collect and recycle their coffee cups (as has been done at the University of Bath, Bedfordshire, Kent, Loughborough, Manchester Metropoliton and  Oxford Brookes University).

As may be apparent from the fact that the universities can be listed within this short article, the current list is woefully short. Even after the recent good news from Oxford Brookes and the University of Bedfordshire. Most universities, including my own are sadly still not on it. So, what can you do if your university is not listed here?

  1. If you think it should be listed but hasn’t been it is very highly likely that I just don’t know about it yet, please let me know by contacting me through email, Twitter or Facebook.
  2. If your university is doing very little to discourage disposable cup use: Write to the catering department and waste management department of your university to let them know your concerns. When writing, be aware of the fact that they have probably considered this problem before and are aware of the issues but have concerns/limitations that have prevented them from implementing a policy. Consumer pressure can help to change their minds but there may be (what appear to them to be) valid reasons that they have not yet done so.
  3. Use a re-usable cup. Even if your university does not charge extra for using a disposable cup/give a discount for using a re-usable (thereby encouraging the use of re-usables), systemic change starts with individuals. Be the start of the change you want to see. You can find a review of various re-usable coffee cups here.
  4. Refuse to buy your stay-in coffee if you are served it in a take-away cup. Good coffee deserves to be enjoyed in appropriate cups and poor coffee should be avoided anyway.

You can find the list of the UK’s top universities for responsible take-away coffee cup use here.

 

*The word ‘compostable’ does not necessarily mean that it will compost in a home-composting environment. For this situation to be preferable to the ordinary disposable cup, it would be necessary to have some form of industrial composting facility in place.

Categories
Coffee Roasters General Home experiments Observations slow Sustainability/environmental

How compostable is compostable?

the cup before the worm bin
“Completely compostable”
But how compostable is it?

So we’re trying to do our bit for the environment and ensure that we always get a compostable cup for our take-away coffee. But have you ever stopped to wonder, just how compostable is compostable?

It is a sad fact that most items that are described as ‘compostable’ do not compost as you or I may expect. Throw a ‘compostable’ cup in a compost bin (or wormery) and you may be surprised at how long it takes to disappear. The reason is that the legal definition of compostable generally refers to industrial composting conditions. In contrast to the worm bin, or the home-compost heap, an industrial composting facility is kept at (58±2)ºC. In these conditions, something defined as ‘compostable’ by the EU regulation EN 13432 or the US based ASTM D6400 needs to have completely disappeared within 6 months but have 90% disintegrated to fragments smaller than 2mm by 12 weeks.

Perhaps it is not hard to see why the legal criteria are defined this way. How would you define common criteria for home composting? Although there is a (Belgian led) certification called “OK compost” by Vinçotte, there are as yet no widely agreed definitions for home composting. However, some companies do try to seek out truly home-compostable packaging. In the case of coffee specifically, one coffee roaster trying to keep their environmental impact to a minimum is the Nottingham based Roasting House. Although most of their packaging is paper, (recycled and recyclable), they needed something less permeable for transporting pre-ground coffee by post. Apparently this took quite a search as many bags that said they were home-compostable turned out not to be. Eventually however they chose Natureflex, a packaging that provided a good moisture and air barrier to protect the coffee but that also broke down in a home composting environment.

But how quickly would it disappear in a worm-composter? On the 6th May 2017 my coffee from Roasting House arrived double packed. First in a Natureflex compostable bag and then in the standard (recyclable) paper bag/envelope. It was ready to be placed in the worm bin on the 8th of May 2017.

See the video below for how long it took to be eaten by the worms:

Seventeen weeks later, on 4th September, it was time to declare the bag composted. After 17 weeks, the bag had started to become indistinguishable from other items in the worm bin (such as garlic skin) and when I picked up what bits seemed to remain, they quickly disintegrated in my hand. It seemed time to declare it over for the bag. A truly home-compostable bag, but how does it compare to the ‘OK Compost’ label of Vinçotte.

Coffee bag genuinely home compostable
How it started.
The Roasting House bag before it went into the worm composter.

The definition used by Vinçotte is not for a worm-composting bin but a standard home-compost heap. Ignoring this fact for the time being, the certification requires that a compostable item disintegrates to pieces less than 2mm within 26 weeks and has fully gone within 365 days when held (in a compost bin) between 20-30ºC. Within these criteria, the packaging from Roasting House is certainly “home compostable” as determined by the worms. Although there were bits of greater than 2mm after 17 weeks, just handling them reduced their size to bits in the mm range. And that was only after 17 weeks, well within the 26 specified by the criteria used by Vinçotte.

So now we’re just waiting for the coffee cup. That went into the worm bin on the 20th April 2017 and is still going, 21 weeks later. Will it be home-compostable? Will the lining that’s needed to keep the coffee from leaking out prevent the worms from breaking it down? You’ll find out here! Make sure you sign up to the BeanThinking newsletter or follow @thinking_bean on Twitter or Facebook to be one of the first to find out when the coffee cup has finally gone.

In the meanwhile, if you’re looking for an environmental solution to your take-away coffee cup habit, it is worth investing in a re-usable cup. Most councils at the moment do not provide industrial composting facilities. Moreover, it is not safe to assume that compostable items will eventually compost in a landfill as modern landfills are water-tight and air-tight. As they say here, the modern land fill is not designed to mulch as much as to mummify. So,if you want to avoid green-washing, you may want to invest in a re-usable cup, for a review of these see Brian’s coffee spot here.

 

 

Categories
Coffee cup science General Home experiments Observations Science history

Coffee Rings: Cultivating a healthy respect for bacteria

coffee ring, ink jet printing, organic electronics
Why does it form a ring?

It is twenty years since Sidney Nagel and colleagues at the University of Chicago started to work on the “Coffee Ring” problem. When spilled coffee dries, it forms rings rather than blobs of dried coffee. Why does it do that? Why doesn’t it just form into a homogeneous mass of brown dried coffee? Surely someone knew the answer to these questions?

Well, it turns out that until 1997 no one had asked these questions. Did we all assume that someone somewhere knew? A bit like those ubiquitous white mists that form on hot drinks, surely someone knew what they were? (They didn’t, the paper looking at those only came out two years ago and is here). Unlike the white mists though, coffee rings are of enormous technological importance. Many of our electronic devices are now printed with electrically conducting ink. As anyone who still writes with a fountain pen may be aware, it is not just coffee that forms ‘coffee rings’. Ink too can form rings as it dries. This is true whether the ink is from a pen or a specially made electrically conducting ink. We need to know how coffee rings form so that we can know how to stop them forming when we print our latest gadgets. This probably helps to explain why Nagel’s paper suggesting a mechanism for coffee ring formation has been cited thousands (>2000) of times since it was published.

More information on the formation of coffee rings (and some experiments that you can do with them on your work top) can be found here. Instead, for today’s Daily Grind, I’d like to focus on how to avoid the coffee ring effect and the fact that bacteria beat us to it. By many years.

There is a bacteria called Pseudomonas aeruginosa (P. aeruginosa for short) that has been subverting the coffee ring effect in order to survive. Although P. aeruginosa is fairly harmless for healthy individuals, it can affect people with compromised immune systems (such as some patients in hospitals). Often water borne, if P. aeruginosa had not found a way around the coffee ring effect, as the water hosting it dried, it would, like the coffee, be forced into a ring on the edge of the drop. Instead, drying water droplets that contain P. aeruginosa deposit the bacteria uniformly across the drop’s footprint, maximising the bacteria’s survival and, unfortunately for us, infection potential.

The bacteria can do this because they produce a surfactant that they inject into the water surrounding them. A surfactant is any substance that reduces the surface tension of a liquid. Soap is a surfactant and can be used to illustrate what the bacteria are doing (but with coffee). At the core of the bacteria’s survival mechanism is something called the Marangoni effect. This is the liquid flow that is caused by a gradient in surface tension; there is a flow of water from a region of lower surface tension to a region of higher surface tension. If we float a coffee bean on a dish of water and then drop some soap behind it, the bean accelerates away from the dripped drop (see video). The soap lowers the surface tension in the area around it causing a flow of water (that carries the bean) away from the soap drop.

If now you can imagine thousands of bacteria in a liquid drop ejecting tiny amounts of surfactant into the drop, you can hopefully see in your mind’s eye that the water flow in the drying droplet is going to get quite turbulent. Lots of little eddies will form as the water flows from areas of high surface tension to areas of low surface tension. These eddies will carry the bacteria with them counteracting the more linear flow from the top of the droplet to the edges (caused by the evaporation of the droplet) that drives the normal coffee ring formation. Consequently, rather than get carried to the edge of the drop, the bacteria are constantly moved around it and so when the drop finally dries, they will be more uniformly spread over the circle of the drop’s footprint.

Incidentally, the addition of a surfactant is one way that electronics can now be printed so as to avoid coffee ring staining effects. However, it is amusing and somewhat thought provoking to consider that the experimentalist bacteria had discovered this long before us.

Categories
Coffee cup science General Home experiments Observations slow

On rings, knots, myths and coffee

vortices in coffee
Vortices behind a spoon dragged through coffee.

Dragging a spoon through coffee (or tea) has got to remain one of the easiest ways to see, and play with, vortices. Changing the way that you pull the spoon through the coffee, you can make the vortices travel at different speeds and watch as they bounce off the sides of the cup. This type of vortex can be seen whenever one object (such as the spoon) pulls through a fluid (such as the coffee). Examples could be the whirlwinds behind buses (and trains), the whirlpools around the pillars of bridges in rivers and the high winds around chimneys that has led some chimneys to collapse.

Yet there is another type of vortex that you can make, and play with, in coffee. A type of vortex that has been associated with the legends of sailors, supernovae and atomic theory. If you add milk to your coffee, you may have been making these vortices each time you prepare your brew and yet, perhaps you’ve never noticed them. They are the vortex rings. Unlike the vortices behind a spoon, to see these vortex rings we do not pull one object through another one. Instead we push one fluid (such as milk) through another fluid (the coffee).

It is said that there used to be a sailor’s legend: If it was slightly choppy out at sea, the waves could be calmed by a rain shower. One person who heard this legend and decided to investigate whether there was any substance to it was Osborne Reynolds (1842-1912). Loading a tank with water and then floating a layer of dyed water on top of that, he dripped water into the tank and watched as the coloured fluid curled up in on itself forming doughnut shapes that then sank through the tank. The dripping water was creating vortex rings as it entered the tank. You can replicate his experiment in your cup of coffee, though it is easier to see it in a glass of water, (see the video below for a how-to).

Reynolds reasoned that the vortices took energy out of the waves on the surface of the water and so in that way calmed the choppy waves. As with Benjamin Franklin’s oil on water experiment, it’s another instance where a sailor’s myth led to an experimental discovery.

chimney, coffeecupscience, everydayphysics, coffee cup science, vortex
In high winds, vortices around chimneys can cause them to collapse. The spiral around the chimney helps to reduce these problem vortices.

Another physicist was interested in these vortex rings for an entirely different reason. William Thomson, better known as Lord Kelvin, proposed an early model of atoms that explained certain aspects of the developing field of atomic spectroscopy. Different elements were known to absorb (or emit) light at different frequencies (or equivalently energies). These energies acted as a ‘fingerprint’ that could be used to identify the elements. Indeed, helium, which was until that point unknown on Earth, was discovered by measuring the light emission from the Sun (Helios) and noting an unusual set of emission frequencies. Kelvin proposed that the elements behaved this way as each element was formed of atoms which were actually vortex rings in the ether. Different elements were made by different arrangements of vortex ring, perhaps two tied together or even three interlocking rings. The simplest atom may be merely a ring, a different element may have atoms made of figure of eights or of linked vortex rings. For more about Kelvin’s vortex atom theory click here.

Kelvin’s atomic theory fell by the way side but not before it contributed to ideas on the mathematics (and physics) of knots. And lest it be thought that this is just an interesting bit of physics history, the idea has had a bit of a resurgence recently. It has been proposed that peculiar magnetic structures that can be found in some materials (and which show potential as data storage devices), may work through being knotted in the same sort of vortex rings that Kelvin proposed and that Reynolds saw.

And that you can find in a cup of coffee, if you just add milk.

 

Categories
General Observations slow

The impact of water on coffee

lilies on water, rain on a pond, droplets
What is the crater shape produced by falling droplets of water on freshly ground coffee?

Recently there has been considerable discussion about the impact of water on the taste of your coffee. Although this is interesting not only from a chemistry perspective, but also an experimental design and an environmental one, Bean Thinking is probably not the best place to explore such effects of chemistry on coffee taste. If you are interested, there is a recent article about it in Caffeine Magazine, click here. Instead, on Bean Thinking, the idea would be to go a little more fundamental and ask instead what is the impact of water on coffee? What effect does dripping water have on the craters produced in freshly roasted coffee grinds?

You may have noticed craters produced by rain drops on sand or paused while preparing your drip brew to think about the different ways that water percolates through a filter compared to an espresso puck. But have you stopped to consider what determines the shape of the crater that is produced as a falling droplet impacts a loose bed of granular material (such as coffee). Perhaps you have looked at images of the Chicxulub crater on the Yucatan peninsula and wondered about asteroid impacts on the Earth or craters on the Moon but what about something closer to home? What if the impacting object were liquid and the impact surface more sand like? It’s a problem that affects how rain is absorbed by soil as well as the manufacture of many drugs in the pharmaceutical industry. But it is also something that we could experiment with in coffee. Is there a difference between craters formed in espresso pucks compared to those in the coffee in the filter paper of a V60?

bloom on a v60
Bubbles in a V60 filter – but what is the impact of individual drops of water on the dry grains of coffee? The ultimate in slow coffee.

Recently, a study appeared in Physical Review E that investigated the crater shapes produced by water droplets on a bed of dry glass beads (imitating sand). The effect of the impact speed of the water droplet as well as the packing density of the granular bed (sand/coffee) was studied. A high speed camera (10 000fps) was used in combination with a laser to reveal how the shape of the craters changed with time, from the initial impact right through until the crater was stable. The authors came up with a mathematical model to consider how the energy of the falling droplet was distributed between the impacting drop and the sand bed. Does the droplet of water deform first or does the energy of the impact go into displacing the sand and so forming the crater?

Perhaps unsurprisingly, when drops of water fell onto dense beds of sand (think espresso pucks but not quite so packed), the craters produced were quite shallow. It would take a lot of energy to displace the densely packed sand but not quite so much to deform the droplet. But when the drops fell onto looser sand beds (think drip brew coffee) the crater produced formed in two stages and depended on the velocity of impact. A deep crater was formed as the drop first impacted the sand. Then as the camera rolled, the sides of the crater started to avalanche producing much wider craters that had different shapes in profile (from doughnut to pancake type structures). For looser beds of sand, the faster the impacting drop, the wider the final crater. You can read a summary of the study here.

So what would happen for craters produced during making an espresso compared to those produced making a drip brew? A first approximation would be that the espresso coffee is more densely packed, so the craters should be shallower and less wide than those produced in the loose packed filter coffee. However then we need to think that the water used in making espresso is forced through the puck with high energy. In contrast, in drip brewing techniques, the water used has a lower impact energy, (it could be said that the clue is in the name). So the energy of the impact would form larger craters in the espresso pucks and smaller craters in the drip brewers, an opposite expectation from that of the packing densities, which effect wins?

coffee ground in a candle holder
Early experiments with coffee grind craters: There are advantages to working with glass beads and high speed cameras.

But is there anything else? Grind size! Espressos are made using finely ground coffee beans, with a typical “grain size” being about 10μm (0.01mm). Drip brewed coffee is somewhat coarser, a typical medium grind being compared to grains of sand (which vary between 0.05-2mm, 50 – 2000μm but we’d expect ‘medium’ ground coffee to be at the lower end of that). This is fairly similar to the ‘sand’ used in the study in Phys Rev E which used grains of size 70-110 μm. A slightly earlier study had shown how the crater shape depended on grain size for ‘sand’ ranging from 98 to 257 μm. That study had revealed that how the water interacted with the different grain sizes depended in turn on whether those grains were hydrophilic (wettable) or hydrophobic (water proof). It is probably safe to assume that the coffee used in an espresso grind has the same hydrophilic properties as the coffee used in drip brew but even so, we still have those three variables to contend with, packing density, impact energy and grind size. So, happy experimenting! Let’s find out how the impact craters left in coffee change with preparation method. And whatever else, it’s a perfect excuse (if one were really needed) to drink more coffee while slowing down and properly appreciating it.

With thanks to Dr Rianne de Jong for pointing me in some interesting directions (not all of which fitted in this piece) towards the interaction of water with coffee, more coming soon I hope.

 

 

Categories
General Home experiments Observations Science history slow

Theme on a V60

bloom on a v60
V60 bubbles. There is much to be gained by slowing down while brewing your coffee.

Preparing a coffee with a pour-over brewer such as a V60 is a fantastic way to slow down and appreciate the moment. Watching anti-bubbles dance across the surface as the coffee drips through, inhaling the aroma, hearing the water hit the grind and bloom; a perfect brewing method for appreciating both the coffee and the connectedness of our world. The other week, while brewing a delightful Mexican coffee from Roasting House¹, I noticed something somewhat odd in the V60. Having placed it on the kitchen scales and, following brewing advice, measured the amount of coffee, I poured the first water for the bloom and then slowly started dripping the coffee through. Nothing unusual so far and plenty of opportunity to inhale the moment. But then, as I poured the water through the grind, I noticed the scales losing mass. As 100g of water had gone through, so the scales decreased to 99g then 98g and so on. It appeared the scales were recording the water’s evaporation.

science in a V60
Bubbles of liquid dancing on the surface of a brewing coffee.

It is of course expected that, as the water evaporates, so the mass of the liquid water left behind is reduced. This was something that interested Edmond Halley (1656-1742). Halley, who regularly drank coffee at various coffee houses in London including the Grecian (now the Devereux pub), noted that it was probable that considerable weights of water evaporated from warm seas during summer. He started to investigate whether this evaporating vapour could cause not only the rains, but also feed the streams, rivers and springs. As he told a meeting of the Royal Society, these were:

“Ingredients of a real and Philosophical Meteorology; and as such, to deserve the consideration of this Honourable Society, I thought it might not be unacceptable, to attempt, by Experiment, to determine the quantity of the Evaporations of Water, as far as they arise from Heat; which, upon Tryal, succeeded as follows…”²

Was it possible that somehow Halley’s demonstration of some three hundred years ago was being replicated on my kitchen scales? Halley had measured a pan of water heated to the “heat of summer” (which is itself thought provoking because it shows just how recent our development of thermometers has been). The pan was placed on one side of a balance while weights were removed on the other side to compensate the mass lost by the evaporating water. Over the course of 2 hours, the society observed 233 grains of water evaporate, which works out to be 15g (15 ml) of water over 2 hours. How did the V60 compare?

Rather than waste coffee, I repeated this with freshly boiled water poured straight into the V60 that was placed on the scales. In keeping with it being 2017 rather than 1690, the scales I used were, not a balance, but an electronic set of kitchen scales from Salter. The first experiment combined Halley’s demonstration with my observation while brewing the Mexican coffee a couple of weeks back. The V60 was placed directly on the scales and 402g of water just off the boil was poured into it. You can see what happened in the graph below. Within 15 seconds, 2 g had evaporated. It took just a minute for the 15g of water that Halley lost over 2 hours (with water at approximately 30 C) to be lost in the V60. After six minutes the rate that the mass was being lost slowed considerably. The total amount lost over 12 minutes had been 70g (70ml).

evaporation V60 in contact with scales
A V60 filled with 400g of water just off the boil seemed to evaporate quite quickly when placed directly on the scales.

Of course, you may be asking, could it be that the scales were dodgy? 70g does seem quite a large amount and perhaps the weight indicated by the scales drifted over the course of 12 minutes. So the experiment could be repeated with room temperature water. Indeed there did appear to be a drift on the scales, but it seemed that the room temperature water got moderately heavier rather than significantly lighter. A problem with the scales perhaps but not one that explains the quantity of water that seems to have evaporated from the V60.

control
Hot water (red triangles) loses more mass than room temperature water (grey squares).

Could the 70g be real? Well, it was worth doing a couple more experiments before forming any definite conclusions. Could it be that the heat from the V60 was affecting the mass measured by the electronic scales? After all, the V60 had been placed directly on the measuring surface, perhaps the electronics were warming up and giving erroneous readings. The graph below shows the experiment repeated several times. In addition to the two previous experiments (V60 with hot water and V60 with room temperature water placed directly on the scales), the experiment was repeated three more times. Firstly the V60 was placed on a heat proof mat and then onto the scales and filled with 400g of water. Then the same thing but rather than on 1 heat proof mat, three were placed between the kitchen scales and the V60. This latter experiment was then repeated exactly to check reproducibility (experiment 4).

You can see that the apparent loss of water when the V60 was separated from direct contact with the scales was much reduced. But that three heat proof mats were needed to ensure that the scales did not warm up during the 12 minutes of measurement. Over 12 minutes, on three heat proof mats, 14g of water was lost in the first experiment and 17g in the repeat. This would seem a more reasonable value for the expected loss of water through evaporation out of the V60 (though to get an accurate value, we would need to account for, and quantify the reproducibility of, the drift on the scales).

V60 Halley
The full set: How much water was really lost through evaporation?

Halley went on to estimate the flow of water into the Mediterranean Sea (which he did by estimating the flow of the Thames and making a few ‘back of the envelope’ assumptions) and so calculate whether the amount of water that he observed evaporating from his pan of water at “heat of summer” was balanced by the water entering the sea from the rivers. He went on to make valuable contributions to our knowledge of the water cycle. Could you do the same thing while waiting for your coffee to brew?

Let me know your results, guesses and thoughts in the comments section below (or on Twitter or Facebook).

¹As this was written during Plastic Free July 2017, I’d just like to take the opportunity to point out that Roasting House use no plastic in their coffee packaging and are offering a 10% discount on coffees ordered during July as part of a Plastic Free July promotion, more details are here.

²E Halley, “An estimate of the quantity of vapour….” Phil. Trans. 16, p366 (1686-1692) (link opens as pdf)