Category: Home experiments

Categories
General Home experiments Observations Science history slow Sustainability/environmental Tea

Coffee and the world

Welcome to the first post of 2018, Happy New Year! But before embracing 2018, perhaps let’s take a moment to remember those things that we discovered in 2017 that connect your coffee cup (or brewing device) with the physics of what occurs in the wider universe. Here are some of the highlights for me this year, if you want to share your highlight, please comment in the section below.

latte art, flat white art
A properly made latte. But what if you add hot espresso to the milk instead of the other way around?

1) Latte layering

In mid-December a study was published in Nature Communications that explored the complex, but elegant, physics involved in making lattes (ok, not quite by the technique that you would hopefully find in your neighbourhood café but keep with this…). When a hot, low density, liquid (espresso) was poured into a hot higher density liquid (milk) contained within a cold mug, the competition between the density gradients of the liquid (vertical) and the temperature gradient from the cup wall to the liquids (horizontal) produced multiple layers of varying coffee/milk concentration in the cup. Too late for a 2017 Daily Grind article, this looks to be too good an experiment to pass by, hopefully it will appear on the Daily Grind in early 2018.

 

science in a V60
Could this V60 mystery now be solved?

2) Bouncing drops

November 2017 saw research published about what happens when a cold droplet falls onto a hot liquid (think milk and coffee). The temperature difference causes currents to be established within the droplet (and in the main liquid) that in turn create air flows between the droplet and the liquid bath that prevent the droplet from merging with the bath. The research can explain why it is that you can sometimes see raindrops staying as spheres of water on the top of puddles. It may also explain a puzzling phenomenon that I have seen while brewing coffee in a V60.

 

Vortex rings get everywhere.

3) Vortex rings in coffee

June 2017 and it is again about adding milk to coffee (why do I drink coffee black?). When one liquid (such as milk) is dripped into another (such as coffee), it is very likely that you will observe the milk to form “vortex rings”. These rings are related to smoke rings and have, in the past, been proposed as an atomic model. This year however it was suggested that these vortex rings could form as a type of magnetic nanostructure. Mathematically impressive, beautiful, perhaps quite useful and mathematically similar to something you can find in your coffee.

 

bloom on a v60
How do craters form?

4) Crater shapes

April 2017. What happens while brewing a pour over? As you drip water onto a granular bed (or, in coffee terms, ground coffee in a V60 filter), each drop will create a crater. The size and shape of the crater will depend on the density of the granular bed (espresso puck or loose grounds in a filter) and the velocity of the falling drop. Fast frame photography revealed how the shape of the crater changed with time for different scenarios.

 

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

5) A home experiment

Perhaps not quite in the theme of the other four stories but this is an experiment that you can do at home. Some have proposed compostable coffee cups as a more environmentally conscious alternative to ordinary, disposable, coffee cups. But how “compostable” are compostable cups and compostable packaging? Between May and September 2017, #howlongtocompost looked at how long it took the Natureflex packaging (used by the coffee roasting company Roasting House for their ground coffee) to compost in a worm composting bin. This one worked quite well. Within 17 weeks, it had been eaten by the worms. In comparison, the “completely compostable” take away coffee cup is still in the worm bin (although considerably degraded) 37 weeks after the start of the experiment. If you are interested, you can follow #willitcompost on twitter. Will it finally compost? I’ll leave you to place your bets but you may decide that a link to Brian’s coffee spot guide to re-usable cups will be helpful.

 

What will 2018 bring? Certainly there will be more composting experiments as I have a coffee bean bag from Amoret coffee, 3 different compostable cups and a compostable “glass” to try with the worms. But in terms of the science? We’ll have to wait. Meanwhile, if you have a coffee-science highlight from 2017, please do share it either here in the comments section, on Twitter or on Facebook. Happy New Year to you all.

 

 

 

 

 

Categories
General Home experiments Observations slow Tea

Coffee and cream baubles – not just for Christmas

floating, bouncing drops
Drops of water can be stable on the water’s surface for many minutes if you put the water on a loudspeaker, more info on how to create these at home here.

You may have noticed them before: balls of liquid dancing on the surface of your coffee (or tea) that seem to last for ages before being absorbed into the drink? Perhaps you have added milk to your coffee and noticed that it took some time before the milk entered into the brew?

It turns out, there’s some very interesting physics that is happening whenever you add milk to your tea or when you are preparing a pour-over. It can link coffee to wine and to quantum mechanics. It is worth taking a closer look at these drops.

You may remember that you could use a loud speaker to make droplets of coffee bounce on a cup of the same. The vibrations in the cup meant that the air between the droplet and the drink never got squeezed out of the space between them. So, rather than coalesce, the drop jumped up and down on the coffee surface before finally disappearing under. This type of bouncing bauble has been shown to behave in similar ways to quantum particles in wave-particle duality. An analogue of quantum physics in the macroscopic droplets on the surface of your drink.

But that type of bauble required the use of a loud speaker (or some similar way of generating vibrations on the surface of the coffee). What if you could ‘bounce’ a drop of coffee on a cup of coffee without any external props like speakers? Well, it turns out that you can. In November 2017 a group of researchers showed how a temperature difference between a drop falling into a drink and the drink itself could result in the drop appearing to float on the surface of the drink for many seconds. The obvious example was cold milk into a cup of coffee (or tea). But I think that it may also happen in a V60 when you prepare a pour over, more on that below.

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

The idea is quite simple. If there is a temperature difference between the drop and the coffee, when the drop approaches the coffee, there will be thermal gradients across the drop/cup system. Surface tension is temperature dependent: the higher the temperature, the weaker the surface tension. Differences in surface tension across the surface of a liquid result in compensating liquid flows (one of the best places to see this is in a glass of wine, but there’s also a great party-trick experiment you can do to demonstrate it which is here). So, because there is a temperature difference across the surface area of the droplet (owing to the difference between the droplet and the cup), there will be liquid flows set up within the drop. These flows are like circulating vortices which draw the surrounding air into the gap between the drop and the cup and so prevent the existing air between the drop and the cup from escaping. If the air has nowhere to escape to, the drop can’t merge with the drink, in fact it ‘levitates’ for a number of seconds.

The authors suggest that this is a reason that you can often see rain drops staying on the top of puddles or ponds before being subsumed into the water, or why you can see the cream (or milk) stay as globules on the surface of your coffee (or tea). And so I wonder, could this also be the explanation for an odd phenomenon that I sometimes notice while brewing coffee in my V60. Perhaps you have seen this too? After some time, the new drops of filtered coffee impacting on the surface skit along to the edge of the jug. They stay as balls of coffee on the coffee’s surface for quite some time before becoming part of the brew. You can see a photo of some of these droplets above. Initially I thought that this was because the surface of the coffee had started to vibrate with the impacting droplets. But it is also possible that it could be this temperature effect. As the (brewed) coffee in the jug would be cooler than the water dripping into it from the filter, there would be a temperature difference between the droplet and the coffee but the reverse of the milk-coffee situation. The drop would be warmer than the coffee it’s dripping into. The authors of the study suggested that it was the magnitude of the temperature difference that was the key, not the sign of the temperature difference. So that would fit with the V60 observations seen previously. However how would you show which effect (vibration or temperature difference) is responsible for the behaviour?

Enjoy playing with your tea, coffee and V60s. Do let me know the results of your experiments. Is it a vibration thing or does the temperature difference have to be there to begin with? Let me know what you think is going on.

I am also grateful to Amoret Coffee for alerting me to this story in the first place through Twitter. If you come across some interesting coffee-science, please let me know, either here in the comments section (moderated, please be patient), or on Twitter or Facebook.

 

 

 

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
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 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)

Categories
Allergy friendly cafe with good nut knowledge Coffee cup science Coffee review Home experiments Observations Tea

Coffee chemistry at Estate Office Coffee

Could it really be true that the tables were reclaimed school science desks? I had read a review of Estate Office Coffee by Beanthere.at on London’s Best Coffee that had made this surprising claim (together with favourable comments about the coffee and cakes). Like a red flag to a bull, a visit was inevitable. Would there be any clues left on the tables as reminders of the past history? In the absence of many photos of the interior of the café, my mind wandered to images of long wooden benches like the physics labs in my old school. I imagined enjoying a coffee at such a bench, seated on a wooden stool, my feet not able to reach the ground. So when I arrived outside the cute little building, I was a bit puzzled as to how a whole lab could fit inside! Going in, my images of rows of coffee-table-lab-benches were metaphorically thrown out the window. Instead, a set of modern looking (small) tables were arranged so that several groups of 2-4 people could sit and enjoy their coffee together or individually. A lovely, friendly, space for conversation with friends but not quite the lab I had imagined. The counter, which was on the right as we entered, had a great array of muffins and cakes arranged on it which proved irresistible (and they knew which allergens were in which cake, so a definite tick in the ‘allergy friendly’ café box). The coffee (from Allpress espresso) was also very good and we ‘retired’ to a table to enjoy coffee and cake together.

interior Estate Office Coffee
Clearly science labs have changed since I was at school! The tables in Estate Office Coffee are reclaimed lab benches.

Although warm that day, sitting near the window was a very pleasant way of slowing down and noticing things. Moreover, the local history that is framed on the wall near the door, provided an interesting diversion for understanding how this quirky building came to be (and to survive in its present form). Copies of Caffeine magazine were also lying around adding to the large number of things that you could think about rather than revert to checking your phone. Finally though, curiosity got the better of me and I asked, were the tables really old school science lab benches? The helpful barista wasn’t absolutely sure and so texted the owner to enquire. Fairly quickly an answer came back: yes indeed, the wood had been reclaimed and used to be laboratory benches. Either school science labs have changed a bit since I attended or the tables have undergone a refurbishment as well as a reclaim, but nonetheless what a feature! Together we looked underneath the tables and noticed the parallel grooves running along the underside of the wood. What were they used for? Pens? Drainage channels for spilt chemicals? The mind boggled. But then returning to our table, we noticed that despite the lovely varnish and careful refurbishment, our table showed evidence of previous science lab use. Two circular stains as if the wood varnish had been etched by a strong acid. Immediately this took me back to experiments-gone-wrong with a home chemistry set but then it set off a whole different thought train through a slightly lateral connection to acidity and coffee.

table detail, inside Estate Office Coffee
Evidence of a past life?
Two rings in the varnish on one of the tables at Estate Office Coffee.

The issues and science associated with acidity in coffee have been discussed many times elsewhere and so if you would like to follow that train of thought you can do so here or here. Instead, I was reminded that the Arrhenius definition of acidity was that of a substance that, when in solution, increased the concentration of H+ ions in the water. For reasons that will become clear, this reminded me of stories I had heard of expert coffee-tasters who always use the same spoon when cupping coffee. Were there actually very good reasons that these coffee tasters always insist on using their own, same spoon, in every cupping session?

The connection between acidity and the spoons used for cupping comes via the ability of substances to gain or lose electrons to become ions. In the case of acids, the ion is H+ but different elements form their ionic counterparts more or less easily. This means that it is easier to take two electrons from the element copper (Cu) to form Cu2+ than it is to remove one electron from gold (Au) to form Au+. The ‘ability’ of a substance to gain (or lose) electrons is measured by the standard electrode potential. A few years ago, a group at the Institute of Making investigated whether different teaspoons made from different metals tasted different. In a blind taste test involving 32 participants, not only did they find that the spoons tasted different (as measured by bitter, metallic, strong etc), those metals that were more likely to form ionic species in solution (as indicated by the standard electrode potential) consistently tasted more bitter and more metallic than the rest: copper and zinc teaspoons tasted metallic, chrome and stainless steel tasted the least.

coffee at EOC Streatham
The important thing is how this tastes. What is the influence of cup size, shape, colour on your perception of the taste of coffee?

What was more interesting though was that the investigators then turned to the question: does the type of spoon used influence the taste of a substance? Although they investigated ice cream rather than coffee, the tastes they were looking at (bitter, sweet, salty, sour) are very relevant to coffee tasting. Again, the authors did a study involving a series of blind taste tests, this time involving 30 participants. Again, the teaspoons used were identical to each other apart from the fact that each had been electroplated with a different metal (gold, copper, zinc or stainless steel). Again there appeared to be a dependence between the taste of the substance (ice cream) and the standard electrode potential of the metal used for the spoon. When the ice cream (which had been separately flavoured to be more salty, bitter, sweet, sour or left plain) was blind-tasted with zinc or copper spoons, the ice cream was consistently rated more bitter than when tasted with stainless steel spoons. But there was more, it seemed that the sweetness of sweet ice cream was enhanced by the copper and zinc spoons. Indeed, copper and zinc spoons seemed generally to enhance the dominant taste of the ice cream (sweet became more sweet, salty more salty etc). Although spoons made of these two metals were also rated as tasting metallic, the most pleasant blind-tested ice cream-spoon combination was the sweet ice cream tasted with the copper or zinc spoons.

So it would appear that the material that the spoon is made from could influence our perception of the taste of the food or drink we consume with it. The taste of coffee could be influenced by the type of metal spoon that is used to taste it with. Other studies have emphasised the psychological importance to taste of the appearance or weight of the spoon. For consistent cupping therefore, it may very well be a good idea to stick to your favourite spoon.

However, this seems an area in which anyone can do a bit of kitchen-top coffee science experimentation. Have you blind taste tested several coffees? What about different coffees with different spoons? For those who cup coffee regularly it would be fascinating to hear your thoughts on the influence of the spoon on the taste of coffee. For those of you new to coffee cupping, you can find a how-to at the bottom of this post and then please do share your experiences. In the meanwhile, you may be pleased to return in our imaginative journey to Estate Office Coffee where a great tasting coffee can be enjoyed in a non-metallic cup and where you may additionally pause to ponder the influence of your surrounding environment on the pleasure you derive from your coffee.

Estate Office Coffee can be found at 1 Drewstead Road, Streatham, SW16 1LY

 

 

 

Categories
Coffee review General Home experiments Tea

Communities at Wilton Way

exterior of Wilton Way, Hackney Coffee
Wilton Way cafe on Wilton Way

There are two things that may strike you as you walk past Wilton Way café. The first is the prominent La Marzocco espresso machine on the counter. The second is the “ON AIR” sign in the corner next to the window. Indeed, it is best to look out for these two as there didn’t seem to be any other sign indicating that this café was the Wilton Way cafe, home to the London Fields Radio that is broadcast from here (hence the “on air” sign). In the late afternoon, the café offered some shade on a sunny day and so we popped in for a tea, though there is seating on a bench outside should you wish to enjoy the Sun. Although this website is supposed to be about coffee (which is roasted by Climpson & Sons), sometimes a fresh mint tea is what is needed. This particular mint tea was very refreshing with plenty of mint leaves in the cup. Sadly though, in what seems to be a common pattern at the moment, this was another café at which there were few cakes on offer, presumably as it was late afternoon by the time we visited. However, what is sad for the mind is perhaps good for the waistline, we’ll have to revisit in the morning for the cakes next time.

Corrugated iron supported the counter while the (plentiful) seats inside the café appeared to be made of recycled wood and boxes. Interestingly, this is mentioned in the description of the Wilton Way café on the London Fields Radio website, apparently the interior was designed to be a mix of modern and reclaimed materials. Choosing a seat at the back allowed us to survey the space and people-watch while sipping the tea. On the counter was an old-style Casio cash register while in the far corner at the front of the café, the microphone and broadcasting equipment stood waiting to be used for the London Fields Radio.

the broadcasting equipment at the WW cafe Hackney
London Fields Radio, broadcast from Wilton Way cafe

In the book “Radar, how it all began” the author, Jim Brown reminisced about how he had played with a crystal radio set as a child in the 1920s¹. Many scientists can remember making their own radio sets as children (or indeed as adults). It seems playing with things, taking them apart and building them again is part of the personal-history of many scientists and engineers (particularly experimental ones whether they be ‘professional’ scientists or not). The Lunar Society (which was active at the end of the eighteenth century and into the early nineteenth) featured a group of keen “tinkerers”. These were people who experimented with nature and invented new devices in order to explore their understanding of the world. Though each of them were only doing science ‘on the side’ as they each had other day-jobs, individuals within the group did make some important contributions to our understanding of the world. One such contribution was by Josiah Wedgwood who by observing the “waviness of flint glass” noticed its resemblance to “that which arises when water and spirit of wine are first put together before they become perfectly unified”². The reference is to mixing fluids of different density. Isn’t this experience of tinkering with things similar to our enjoyment and appreciation of coffee? The more we experiment, the more coffee we try (including cupping coffee as with this how-to from Perfect Daily Grind), the more deeply involved in coffee we become and the more we value it. Isn’t it actually true that in order to deepen our relationship with coffee we need to explore it (and experiment with it) more fully? Cannot the same be said for our relation to our world?

interior of Wilton Way cafe
The view from the corner. Spacious and quirky, the Wilton Way cafe has plenty to offer the coffee (or tea) drinker who wishes to slow down and appreciate the moment.

But then a second thought that, to some extent flows from the first. No development would be possible without a community, each contributor bringing a different talent but each contributing to an idea of a greater good. The London Fields Radio would not be possible without the scientists and engineers who design and optimise the broadcasting (and receiving) equipment. But neither would it be possible without talented DJs and musicians, thinkers, poets and performers to give us something to listen to. Two more groups of people are needed for London Fields Radio to be a success. Those who provide the space for the broadcasting equipment (i.e. the café) and those who listen in. Again there is an analogy with coffee. No cup of coffee could be there for us to enjoy without the farmers, the traders, the roasters, the baristas and finally many other people like us who enjoy a good cup. And the more each of us tinker with appreciating another’s work (cupping the coffee like a roaster or tending an allotment to appreciate the growth), the more of a community we become and the better coffee we get for it. We do not imagine while ‘cupping’ coffee that we are really about to take on the role of the coffee trader or roaster, yet by playing at their job we can appreciate their importance and skill more and so realise more effectively our own role too. We could go full-cycle here and consider how playing with radios and experiments can help us to understand the role of technology and science in society and our participation in it, but perhaps that is left as a point to ponder in another café: How can we each contribute to a better society, understand our role in it and appreciate the contributions of others?

One final thought that came from the Lunar society but appears to have a very contemporary relevance. Wedgwood once said to Richard Lovell Edgeworth “But in politics… as in religion, hardly any two people who thought at all, thought exactly alike on everything.” The main thing was “to agree to differ, to agree on impartial investigation and candid argument”.² It appears the Lunar men still have a thing or two to teach us.

Wilton Way cafe can be found at 63 Wilton Way, E8 1BG

¹Radar, How it all began, Jim Brown, Janus Publishing Ltd, 1996

²The Lunar Men, Jenny Uglow, Faber & Faber, 2003