Tag: coffee physics

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Coffee whispering

coffee and cassette tape in Batch and Co
What does listening to your coffee tell you? Would a long black sound different to an Americano?

How does your coffee sound? Does an espresso sound different to a latte? Could you deduce how the milk had been frothed, or what milk had been used, by listening to your coffee before you drank it?

To see why there may be an effect, it’s worth thinking about your coffee for a moment. The tiny bubbles in the crema of an espresso are different from the larger bubbles of a milk froth made of semi-skimmed milk in a cappuccino. Bubbles of non-dairy milks may be different too, particularly if the initial small bubbles have combined to form larger bubbles as the froth ages. Indeed, sound is used as a characteristic of coffee: think about the sounds made by a steaming wand in milk. Somehow the environment of a café would not be the same without the constant hiss and whistle of a cappuccino being made. But can we use it to experience our coffee more fully? Not just the aroma, taste, sight and feel but also, can we start to listen to our coffee?

Take the example of the sound of a dripping tap: each drop of water falling into a bowl of water left under the tap ready for washing up later. Each “plink” is telling you something about the size of the drop coming from the tap. Intuitively, or perhaps from experience, we know that small drops produce a higher pitch, a higher frequency, than large drops: small drops ‘plink’, large drops ‘plonk’. But there is something wrong with this example, because, despite what we may think, we are not hearing the drops at all, only a consequence of the drops.

Drops on a coffee can reveal a lot, but this time we’re interested in the sound that they make.

As the drop falls, it creates a hole in the surface of the water, a dent that grows and then closes in on itself, so that the drop of water has formed a bubble of air under the water surface. As this bubble is unstable, it pulsates under the water just before it collapses and it is this pulsation that we hear. As the frequency of the pulsation will depend on the radius of the bubble, air cavities of different sizes will produce different sounds. And because a larger drop will generally produce a larger hole under the water, the larger drop will generate deeper sounds: plonks rather thank plinks.

How does this relate to the sounds made by your coffee? Well, it turns out that the sound of a bubble bursting reveals a lot about the surface tension and the size of the bubble. A recent study published in Physical Review Letters measured the sounds made by bursting soap bubbles through 24 microphones placed around each bubble. Analysing the sounds, the group found that not only could they ‘hear’ how the air escaped the bubble, by analysing the sounds recorded in the microphones they could determine, quantitatively, the movement and forces of the bubble ‘skin’ as it retreated back and the bubble burst. They suggested that listening to bubbles and liquid surfaces could be a complementary tool to high speed photography for understanding the forces on a liquid. This may prove useful for example when thinking about how a pond skater moves on the surface of the water.

To think about what this may mean for coffee, take the Aeropresses I’ve been making recently. First, I wet the grounds and allow a first stage of de-gassing to start. The sound here is of an almost continuous hiss, not entirely dissimilar to the sound you hear when you put an empty seashell to your ear.

latte art, hot chocolate art, soya art
Could we detect a difference between a semi-skimmed milk latte and an oat milk hot chocolate by the sound that they make? Some people listen to their bread in order to know when it is cooked. What does listening to coffee reveal?

At this point it was hard to know whether what I was hearing were the grinds or the ‘sound’ of the Aeropress ‘shell’. Topping up the chamber with water, the bubbles on the surface of the coffee became larger, and of a different form. And they sounded different too! A few pops, and a hiss.

Did I learn anything (apart from that putting one’s ear to the top of an Aeropress does get quite hot and a steamed ear is a strange experience)? I learned that there was much more to my coffee than I had appreciated, that there is always more to discover. It was almost as the author of the 1933 paper about determining the size of bubbles in water by the sound said:

“As a matter of fact we know very little about the murmur of the brook, the roar of the cataract, or the humming of the sea.”

What will you hear in your coffee? Do let me know, in the comments below, on Twitter or over on Facebook.

Categories
Allergy friendly Coffee review General Observations Science history

Thinking space at Le Peche Mignon

Coffee in Le Peche Mignon, Highbury, Islington
Le Peche Mignon in Highbury, hidden down a side street.

It was a balmy February morning when I met an old friend at Le Péché Mignon on Ronalds Road near Highbury and Islington. I had first come across Le Péché Mignon a few months ago when I had had a lovely coffee (and a great cake, I remember the staff being very helpful to check the ingredients for my nut allergy) but too little time to properly think about the space. So, when the opportunity arose to meet a friend (who I have known since we were both 5 but haven’t seen for many years) near Islington, I jumped at the opportunity to meet there.

This small but delightful café seems to be very popular. Both the bench seat in the window (where I had sat last time) and the long, sharing-table in the middle of the café were practically full by the time we arrived in the mid-morning. Fortunately, there was plenty of space in the quiet garden at the back for us to catch up for a couple of hours (and a couple of coffees!). The coffee is roasted by Monmouth, the Americano was very well done and there were quite a selection of pastries and salads on offer. One wall of the café was lined with bottles of wine while Carambars were available to purchase next to the counter.

brick wall at Le Peche Mignon
A join between two brick walls at Le Peche Mignon. How exactly are bricks made and why are they made that way?

The garden behind the café had plenty of tables and, even though it was February, it was warm enough for us to sit comfortably outside. One of the walls of the garden was formed by two sets of brick walls that had a join between them. The appearance of a separation between the walls, together with the weather, reminded me of the crack and the imminent demise of the Larson C ice shelf. However as this was probably too close to recent posts about climate change, I started thinking about defect structures in crystals instead. While pondering this though, my thoughts turned to an entirely different subject matter, the unusual toilet at Le Péché Mignon.

Just as the toilets in our old primary school, the toilet at Le Péché Mignon is outside, in the garden. This got us reminiscing about our old primary school which, during winter, regularly closed when the outside toilets froze (hopefully not a problem for the toilets at Le Péché Mignon!). And while the school has undergone significant renovation since then, it does get you thinking about the history (and engineering/science) of toilets. While this may seem an unpleasant subject for, what is after all a café review, please do bear with me because thinking about toilets can lead to surprising connections. For example, a recent New Yorker article about confirmation bias featured quite a discussion on toilets. How? It seems that while people generally tend to think that they understand how a toilet flush works, when asked to explain it step by step, they suddenly become far less confident. Our knowledge is not so great as we tend to think it is.

cup of coffee in Le Peche Mignon
From coffee cups to aeroplanes, the hardness and porosity of materials depends on the temperature that the starting materials were ‘baked’ at.

Which brings me back to Le Péché Mignon. The issue of flushing toilets became a problem for London in the mid-nineteenth century when the introduction of the “water closet” increased the volume of water flowing into the rather inadequate sewage system (if you are interested in the history of the toilet you can click here). The great engineer Joseph Bazalgette (1819-91) was commissioned to design and build London’s sewer system in which a network of tunnels were built across the capital. Bazalgette’s northern branch lies about 5 minutes walk north of Le Péché Mignon and runs from Hampstead Heath to Old Ford in Stratford. A distance of just 9 miles (14.4 Km), this particular tunnel has a remarkably steep gradient dropping at least 4feet (1.2m) every mile (1.6 Km). Imagine water flowing down a plug hole. The turbulence and speed of the water (ahem) flowing down this ‘drain’ means that Bazalgette had to think very carefully about how he lined this particular tunnel. If he had used ordinary bricks, such as those that make up the wall around the café’s garden, they would have eroded quickly with the turbulent motion of the water. Consequently, Bazalgette specified Staffordshire Blue bricks¹ to line this tunnel. During the manufacturing process, Staffordshire Blue bricks are baked at very high temperature (and in a low oxygen atmosphere) making them particularly resistant to erosion and to water absorption. It should not surprise us that the hardness, brittleness and texture of materials should be affected by the temperature at which they are formed after all, great care is taken about the temperatures at which chocolate is melted and allowed to re-solidify. Indeed, a vast amount of research is done to understand how different materials (from ceramics to metals) respond under different heat treatments. This research is important for applications as diverse as the walls of sewer tunnels to the design of aeroplanes. And, of course, to the design of better coffee cups, a thought with which we can return to thinking about this great little café.

Le Péché Mignon can be found at 6 Roland’s Road, N5 1XH

¹”The Great Stink of London…” Stephen Halliday, Sutton, 1999

 

 

http://www.plumbing-geek.com/howdoesatoiletwork.html

http://www.baus.org.uk/museum/164/the_flush_toilet

Categories
Coffee review Coffee Roasters General Observations slow

Time for a slow coffee?

enamel mug, teh halia, Straits Times kopitiam
This enamel mug connected glass to the Giants Causeway (Straits Times kopitiam)

Every two weeks, the Daily Grind on Bean Thinking is devoted to what I have called a cafe-physics review. The point of these reviews is to visit a café, slow down and notice what has been going on in a cafe physics-wise. I focus on physics because it is my ‘specialist’ area but the point is to notice the connections between the coffee, or the cafe and the world around us. To see how what is going on in your mug is reflected in the science of the wider universe. Realising that things that seem disparate are in fact connected: It is the same maths that describes electrons moving in a metal and the vibrations on the surface of a cup of coffee. That sort of connection to me is mind boggling. Yet there is more. Thinking about the connections between physics and coffee can lead to meditations on the environment and sustainability, or considerations about how our attitude to drinking coffee changes our perception of it.

Everything is connected.

Parquet floor at Coffee Affair
How many people have walked on this floor? The story of evolution at Coffee Affair

It is my strong belief that whenever we go into a cafe, order a coffee and then proceed to sit down with our smart phones or tablets and check our e-mail or our Twitter accounts we lose a fantastic opportunity. It is the opportunity to be properly present and to notice what is going on around us. It is the opportunity to slow down and to appreciate what life has given us and the surprising things that the world has to offer. To look at the beauty and the complexity of the world and to say ‘wow’.

This appreciation is open to us all, provided we seize the opportunity to slow down and take that time to enjoy our coffee.

So, this week’s Daily Grind is an invitation. It is an invitation open to anyone who sits down with a coffee. If you notice anything peculiar, or interesting, that you feel deserves a mention as a cafe-physics review why not write an edition of the Daily Grind? It does not matter where in the world you are or what your level of science knowledge is. If a full Daily Grind article is too much but you have a great observation, write a paragraph review of your favourite cafe and I’ll add it to the cafe-physics review map. Think that you don’t know enough science? Never mind, share your idea with me and we can work on it together.

Hasten coffee, long black, black coffee, espresso base
Sometimes the link with physics/science is a little bit tenuous, as it was at Espresso Base

Your observations need not be physics-based. It would be great if it is based on some aspect of science, but, as past examples have shown, this link can be a little tenuous if the cafe/subject warrants it.

So, over to you. I hope that someone will respond to this invitation. Please do contact me if you would like to pen a review or if you have any questions. It is my hope that you are all enjoying such great coffee in the huge variety of cafe’s that we now have that there will be plenty of opportunities for people to slow down and to notice and then to share it with the Daily Grind.

Please contact me here, or in the comments section below. I look forward to hearing from you.

 

Some brief guidelines for a cafe-physics review:

1) The cafe should, preferably, be a good independent.

2) Any science/history etc. needs to be verifiable but, as mentioned, if you’ve noticed something great but are unsure of the science, get in touch and we’ll work something out together.

3) If you have noticed something fascinating with your coffee but at home and not in a café, contact me anyway.

4) Please do not write a cafe-physics review of any cafe you are financially associated with. I will have to refuse/delete any ‘reviews’ that I find are adverts.

Categories
Coffee review Observations Science history slow Sustainability/environmental

In the Greenhouse at CoffeeGeek

Coffee Geek and Friends, Coffee Victoria
Coffee Geek and Friends

Earlier this year, a new café opened up in Victoria. Coffee Geek and Friends is located at the far end of Cardinal Place as you enter from Victoria Street. Cardinal Place is an odd sort of shopping centre, a small collection of shops with a glass roof. The building site near Coffee Geek as well as the constant stream of people rushing to and fro make Coffee Geek an ideal place to spend some time watching the world go by. Coffee is by Allpress espresso and is served in very individual mugs. Apparently there is a range of geek-ery in the cafe including a ‘centre piece’ water filter but I admit I missed that as I was too focussed on my coffee. Coffee Geek and Friends is definitely a cafe to keep in mind (along with Irish & June’s) if you need a good place to meet near Victoria Station.

It was a very humid day when I enjoyed my coffee at Coffee Geek and, because the mug had not been pre-warmed before my Americano/long black (my notes don’t specify which) was poured into it, condensation quickly formed around the rim of the mug. The condensation forms for the same reason that dew forms after a cool night: the vapour pressure of the water above the coffee (or the ground) has reached the dew point at the temperature of the mug. The lower the temperature, the lower the vapour pressure has to be for the water in the atmosphere to start condensing into liquid droplets. Hence you will often find that your coffee is more ‘steamy’ on a winter’s, rather than a summer’s day.

Condensation on mug in CGaF
Look carefully at the rim of the mug. Do you see the condensation?

Just over two hundred years ago, William Charles Wells made a study of dew. He observed the weather conditions under which dew formed. He observed on which surfaces dew collected. He noted whether the dew formed on space facing surfaces or ground facing surfaces. After several years of careful study he published his “Essay on Dew” in 1814. His work, showed that the earth radiated heat at night (when it was not being kept warm by the Sun) and therefore that space was cold. Cloud cover reduced the amount by which the ground cooled which implied that cloud cover was acting as a type of blanket for the Earth, keeping the heat trapped inside. Later calculations of the balance between the heat radiated by the Earth and the heat received by the Sun confirmed that, without some heat getting trapped by clouds and ‘greenhouse’ gases in the atmosphere, the earth would be a good 30 C cooler than it is observed to be. Although these calculations are just rough, “back of the envelope” figures, detailed calculations confirm that the Earth is in a delicate balance, heated by the Sun, cooled by radiation and kept warm (and live-able) by a layer of natural greenhouse gases. This “natural greenhouse effect” has been necessary for our development, the problem is that now we are adding yet more greenhouse gases to the atmosphere which threatens to tip the established delicate balance by a few degrees.

Cardinal Place roof, greenhouse
The roof of Cardinal Place shopping centre. A very appropriate place for a meditation on the greenhouse effect

What we now call the greenhouse effect are these extra gases, which are more efficient at trapping heat within our atmosphere. If you can imagine what has been happening over the past three hundred years or so as we have been pumping yet more of these gases into the atmosphere at an accelerated rate, we are in danger of tipping this delicate balance towards further heating of the earth. The 2015 Paris Climate Conference is being held with the aim of requiring all nations to agree to a legally binding commitment to reduce the amount of extra greenhouse gases that we emit to a level that will only result in a temperature increase of 2C. To achieve this requires all of us to work together to reduce our own ‘carbon footprint’. Each of us will have to find our own, individual ways to reduce our emissions but perhaps when we look at the condensation on the rim of our coffee cup, we could remember William Charles Wells and his essay on dew and just think, what can I do, at this moment, to reduce my carbon footprint? Maybe it could be something as simple as turning off that phone (to conserve the battery) and watching what is going on in a café instead. A small gesture but one that would be good for us as well as the earth.

Coffee Geek and Friends is at the northern end of Cardinal Place shopping centre (opposite Westminster Cathedral).

As a Coffee Geek note, I would like to just comment that my notes on Coffee Geek and Friends were written using a “linux-sure” ball point pen. Not particularly environmentally friendly but definitely quite geeky.

Categories
General Home experiments Observations slow Sustainability/environmental

An opportunity to become a cafe-scientist

coffee, Timberyard, wooden tray
A great place to sit and do some citizen science: Timberyard, Seven Dials has plenty of seats outside.

There are many things to be gained from putting down your smart phone when you enter a café. Firstly, there is the opportunity to fully experience the coffee. The sounds as it is made, the smell, the taste, even the feel of the coffee. Then there is the opportunity for people watching; their behaviour as they order their coffees or have their meetings or try to alleviate boredom while playing with their smartphones. Of course, there is also the opportunity to look at the history of the café and its surroundings, to think about a café-physics review or just slow down and notice things. There’s always something interesting going on.

If you are lucky enough though to be in Athens, Barcelona, Belgrade, Berlin, Copenhagen, London, Manchester, Milan or Rome there is now even more reason to put down that phone while you savour your coffee. By doing so, you could be helping scientists with a few questions that they have about atmospheric pollutants. If you are not in one of those cities, you miss out this time, but you may want to keep reading because if enough people get involved now, perhaps next time the iSPEX-EU project may come near you.

contrail, sunset
What sort of aerosols and pollutants are floating in the atmosphere above your head at this moment?

The question is, what are the atmospheric pollutants that are in the air near where you are now? Perhaps you are in a café on a main road and the answer seems obvious, it is those cars and buses that keep passing by. But there are in fact many forms of atmospheric aerosols or particles and they range in size from a few nanometers to tens of microns (which, in terms of coffee grind is from much smaller than the smallest Turkish coffee to approximately the size of a small particle in an espresso grind). Is it really so clear that where you are, in the centre of that big city, is that polluted? If on the other hand you are on the coast in Barcelona, just how salty is that salty sea air? The iSPEX-EU project allows you to measure it and find out.

These particles of dust, salt and soot etc. can have  an effect on human and animal health, so clearly we want to know more about their distribution and their prevalence. But there are also, more subtle reasons why we may want to know about them. They may have an effect on global warming and they are certainly needed in order for clouds to form, (though as yet we still do not fully understand this process). We need more data about what aerosols are around and where they are to start to know what questions to ask (let alone answer) about health, the climate and cloud formation. Yes, we have satellite measurements and pollution data at specific locations, but what people are missing is that local information. What are you actually breathing? When you look up at the blue sky, what pollutants (or other type of aerosol) are you looking through? Can we get enough data to know how the air quality varies between the cafés of Hackney and those of Hammersmith?

Skylark Wandsworth
Another ideal cafe for iSPEX-EU measurements, great coffee and a lovely outdoor seating area at Skylark cafe, Wandsworth Common

To get this data the scientists involved in iSPEX-EU need people, many people. People who are willing to spend 5 minutes turning their iPhone (sadly it is an iPhone-only project) into a pollution detector. The more people that they can get measuring, the more data that they will be able to obtain. All you need is an app from the App-store and a (free) device that fits over your iPhone camera which you can pick up from somewhere local to you. Then, you just take a seat outside the café on a lovely blue sky day between now and the 15th October, aim your phone at the sky and take a series of photographs which are shared back with the scientists coordinating the project. If you are curious to know how your air quality compares with that in another participating city, you can check the live map to see how the measurements are going across Europe.

The device works by looking at the colour spectrum as well as the polarisation of the light reaching the camera as a function of angle. This information gives tell-tale clues as to the size of the aerosols as well as their prevalence. There is a lot more information on the website of the iSPEX-EU project and so I would recommend that if you do want to know more, you click their link here. In the meantime, why not sign up with iSPEX-EU, take a seat outside in that café and enjoy a great coffee knowing that, as you do so, you are contributing to our understanding of atmospheric science.

If you do decide to participate, please let me know of any great locations that you find, both for the coffee and the measurements, or share your pollution measurements with me in the comments section. I look forward to seeing some great data on the live map.

To get involved with the iSPEX project, you can follow the link here.

 

Categories
Coffee cup science Observations

The attractive power of coffee

Just imagine, you are trying to fill 3 espresso cups at once but all you have is a portafilter with two spouts and a balloon? Ok, that sounds unlikely. The experiment that I’m going to describe however will allow you to bend a stream of coffee with a balloon. Moreover, in order to work it relies on sub-atomic particles. What a party trick; investigating sub-atomic physics while filling two cups with one stream of coffee. It could be mind bending, instead it is coffee bending.

What happens?

When you rub an inflated balloon on your (dry) hair, electrons are transferred from your hair to the rubber balloon. Electrons are, of course, sub-atomic particles and, together with protons and neutrons, they build up atoms. As these electrons carry an electric charge, the balloon becomes the source of a static electric field.

Thanks to Artemisdraws for the schematic
The electric field from the balloon aligns the water molecules such that the coffee gets attracted towards the balloon.

Water molecules are composed of two hydrogen atoms and an oxygen each. They are electrically neutral. However water is also a strongly polar molecule, meaning that when it is subjected to an electric field, the molecules will tend to align such that they are more positively charged closer to the negatively charged balloon and more negatively charged further away from the balloon. This charge distribution means that the stream of water gets attracted towards the balloon. The amount that the coffee stream bends is dependent on the strength of the electric field from the balloon and the mass of the stream which is still being pulled down by gravity.

The video suggests using cold brew coffee when you test this at home. There are two reasons for this. Firstly, if the balloon gets too close to the coffee stream, it can get splashed. There is a chance that this may burst the balloon. Secondly, and more fundamentally, the water molecules are more agitated at higher energies (temperatures). This means that thermal agitation weakens the average dipole moment of the water thereby weakening the attraction between the coffee stream and the balloon. In this effect as in its taste, cold brew is a stronger drink than your ordinary hot filter.

Let me know if you try this and how you get on. It would be particularly interesting to see any attempts made on bending coffee from an espresso machine. My thanks, as always, to artemisdraws for the helpful schematic shown here.