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Exploring the sound of coffee

coffee at Watch House

We’re used to thinking about the aroma of coffee and how it looks, tastes, even how it feels, but what about how it sounds?

How much attention do you pay to your brewing coffee? You know the aroma, how the coffee blooms, you anticipate the taste and feel the warmth of the steam rising off the brew. But what about the sound? Admittedly this depends on your brew method, but what about the sounds as you filled the kettle or prepared a pour over brew? It turns out that the sound of dripping water was the subject of a recent paper in Scientific Reports.

Perhaps take time to watch a tap dripping into a bowl of water. Or maybe use this as an excuse to make another coffee by drip brewing. Each drop falling onto the water (or coffee) below first deforms the water’s surface then, as far as we can see, rebounds up with a splash of a returning drop or droplets. The phenomenon of what causes the characteristic sound of the drip has been investigated for over 100 years but in 1959 it was established using high speed photography that there were four key phases to any drip sound. First, the drop fell on the liquid, then a cavity formed just under the water surface and an air bubble formed just under that. Finally the water surface recoiled leading to a jet of droplets returning from the surface. It has been thought that the sound, that ‘plink’ of the dripping tap, was caused by that trapped air bubble expanding and contracting as it moved through the water under the water’s surface¹. But this has now been confirmed, along with some other interesting, coffee related, observations using ultrafast video recording (30 000 fps for most of the work, 75 000 fps for some of the extra details).

lilies on water, rain on a pond, droplets

Like the sound of falling rain? What causes the dripping sound of a tap?

The authors of this recent paper describe what must have been a fun experiment to do, dripping water into a tank below. You can see some of the videos of the droplet entering the water by scrolling down to the “supplementary information” in the paper. Two microphones (one above, one below the water surface) recorded the sound waves coming from the dripping ‘tap’ simultaneously with the video recording so as to match the timing of the sound with what was happening in the video. The microphone above the water surface largely recorded the same sound waveform as the microphone under the water with one crucial exception. When the authors lined the tank with MDF wood, the underwater sound was ‘damped’ quite quickly, in comparison the bare tank amplified the sound and so the sound wave took much longer to decay. Above the surface however, it didn’t matter whether the tank was lined or not, the sound signal remained the same. This may sound somewhat insignificant, but it means that it cannot be the sound created by the wobbly bubble itself merely propagating through the surface of the water. If this were the case, the microphone above the water surface should show the same signal as the microphone under the water’s surface. Instead the authors suggest that the oscillating bubble causes the surface of the water immediately above it to vibrate (in the bit that is depressed owing to the droplet having fallen into it) and it is this that we hear above the water surface.

science in a V60

Droplets on the surface of a brewing V60 may also form owing to a temperature difference between the dripping drops of coffee and the coffee ‘bath’ underneath.

It is a beautiful set of experiments but how can it link to coffee (apart from with the dripping)? It is in the way that it gives us the chance to experience our coffee with experiments involving more of our senses than just smell, touch and taste. Firstly, the study emphasises the connection between the drop’s diameter and speed to the sound of the drip (the best sounds are for drops between 1mm and 5mm diameter). This suggests that by changing the brewing parameters (whether you prepare your V60 in a jug or a mug or change the filter paper to a metal kone for example), you may hear a change in the sound of the drips. Do you? Secondly, it has been suggested that the sound that is formed is dependent on the temperature difference between the dripping drop and the water bath underneath. A temperature difference between drop and bath would also explain an odd phenomenon I noticed in the V60 a while back. Do you notice a difference in the sound of the brewing coffee when you prepare cold brew pour over as opposed to a standard breakfast brew? Lastly, the authors of this study found that they could suppress the sound of the plink by reducing the surface tension of the water bath that they were dripping water into. In their case they added washing up detergent to the bath. This seems an awful waste of coffee but is it possible that something intrinsic to our coffee brew could do the same thing? Oil will also change the effective surface tension of the water and different coffees (and different roast strengths) change the oil content of the brewed coffee. Have you noticed any change in the sound of the drips of the coffee depending on how dark a roast coffee you use?

It may not make ground-breaking science but it does offer us an opportunity to pay even more attention to our coffee. Does the sound of your coffee reveal the beauty of the physics at work just under its surface?

¹ Some history of the investigation into the dripping sound as well as the experiments can be found in: Phillips et al., “The sound produced by a dripping tap is driven by resonant oscillation of an entrapped air bubble”, Scientific Reports, 8, 9515 (2018)

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

Celebrate the positive: University cafes helping to reduce waste

It is finally up! A list of UK universities that are trying to cut the coffee cup waste.

Wa cafe, Ealing, pottery, ceramic, bamboo spoon, glass tea pot

Is your university helping to reduce disposable coffee cup waste by only serving coffee “to stay”?

So many of our universities are doing some really good research into the environmental effects of green house gas emissions or plastic pollution. Yet, one big concern for anyone who drinks coffee must be the standard, disposable, coffee cups that we are frequently given if we order our coffee to “take away”. Recent research has shown that these coffee cups could take a very long time to degrade. So how many of these universities are taking the lead and showing that if we are concerned about this, we should be doing something about it too? How many recycle or otherwise act to reduce their disposable coffee cup usage in their university-run cafés?

So in order to highlight the positive, there’s now a list on Bean Thinking of those UK universities that are either recycling their coffee cups (with eg. Simply Cups) or are otherwise acting to reduce the number of disposable coffee cups that they are responsible for sending to landfill. Sadly, at the moment, there are shockingly few on the list. Surely there are more? Does your university do something, anything, to reduce coffee cup waste? I would love to hear from you, in fact, I would love to be inundated with all the great things that our educational sector is doing to help us address this problem, email me here, contact me on FB or on Twitter. So please do let me know and in the mean time, take a look at this list. Is your university there? And if not, take action and feel free to keep me in the loop with what you are doing. The more we work together on this, the better our world will be.

Plastic, coffee and ethical consumerism

“[W]hile 30% of UK consumers claimed to espouse ethical standards only 3% of purchases examined reflected those standards”∗.

Earth from space, South America, coffee

The Blue Marble, Credit, NASA: Image created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler

Most of us are aware of the growing number of environmental problems facing our planet and many of us want to do something. The question is what? Take the packaging that we use for freshly-roasted coffee. It often comes in metallised plastic bags with aroma valves on the front. Is this packaging good for the environment, or for our coffee?

Many factors will influence our decisions as consumers. Even our ‘ethical’ decisions can be based on different arguments. One factor though is, hopefully, the insights gained from scientific studies on the environmental effects of different types of packaging. Today’s Daily Grind examines some of this science.

Types of coffee packaging available

When you order coffee from a roaster, or buy it at a supermarket, mostly it will arrive in a metallised plastic bag. Some companies will supply coffee in compostable ‘plastic’ packaging, or paper, but most bags are still made from ordinary plastic. Some, larger, coffee roasters supply their coffee in cans. Although these are 100% recyclable, the increased weight compared to plastic packaging and the limited re-usability of the cans mean that plastic packaging can be more environmentally friendly than canned coffee. This article is therefore only going to consider smaller roasters and the plastic vs paper debate.

The problems of packaging

It is helpful to clarify the environmental concerns with respect to packaging. For the case of paper vs plastic, three major areas of concern are:

  • Depletion of a limited resource, recycling and re-usability.
  • Carbon dioxide emissions – in the manufacture and transportation of packaging.
  • Degradability – in both landfill and as litter.

Recycling and the Limited Resource problem

air valve, plastic, environmental coffee packaging

Disposable products make up about 37% of plastics produced‡. Are we wasting limited supplies by wanting our coffee as fresh as possible?

Paper comes from wood but plastics are generally a by-product of the petroleum industry (5% of petroleum in the US is used to produce plastics). Perhaps you will say that not all plastics are made from petroleum by-products. It is true. “Compostable” plastics are typically manufactured from starch based products (corn etc). However other bio-degradable plastics are petroleum based. “Oxo-biodegradable” plastic is ‘ordinary’ plastic with a small amount of catalyst added to it during manufacture. The catalyst causes the plastic to break down more quickly than the conventional plastic without the additive. Typically oxo-biodegradable plastic will be manufactured to degrade after 18 months compared with many years for ‘ordinary’ plastic.

Both compostable and oxo-biodegradable plastic are sometimes called ‘biodegradable’, but there are crucial differences between the two. For the sake of this article, I’ll be comparing ‘ordinary’ plastic with ‘compostable’ plastic (conforming to EN 13432) and oxo-biodegradable plastic (regulation ASTM D6954).

So the first part of the question would be to ask if the coffee packaging is made from recycled material. Paper can clearly be made from recycled material as can ordinary plastic and oxo-biodegradable plastic. Compostable plastic cannot be recycled and so cannot have been made from recycled material.

The second part of the question is whether you can recycle the packaging after using it. Again, paper packaging can obviously be recycled (provided it is not lined with plastic). Although both ordinary and oxo-biodegradable plastic can, in principle, be recycled, the multilayered and metallised design of the coffee bag means that it is not normally recyclable. Some coffee roasters however have started using specially designed plastic packaging that can be recycled in normal recycling centers. It would be great if more followed suit.

Two questions for your coffee supplier: Are the bags used to package the coffee made from recycled material and are they recyclable?

Greenhouse Gas emissions and energy costs

paper bag roasted coffee

Is a paper bag necessarily better for the environment?

Perhaps it is greenhouse gas emissions that concern you and so want to choose an environmentally sound packaging in terms of its CO2 emissions? Paper or plastic? You may be surprised. The environmental cost of a packaging type as measured by its CO2 emissions depends mostly on the energy that is required to manufacture it and the energy that is required to transport the packaging material to the point at which it is used (ie. the delivery of the bags to the roaster).

A few years ago, the Environment Agency performed a lifecycle analysis of different types of shopping bags (plastic, paper, cloth). Plastic bags are typically significantly lighter than the heavier paper bags. So, in addition to the cost of making the bags, it is going to require more energy to transport paper bags to the point of use. The report calculated that the manufacture and transportation of paper bags consumed so much more energy than plastic bags, that paper bags had to be re-used 4 times in order to have the same CO2 emissions as an ordinary supermarket plastic bag, re-used as a bin liner. The situation for a cloth bag was even worse.

Although the plastic used for coffee packaging is much heavier than a standard supermarket shopping bag, the analysis suggests that if your concern is CO2, paper is not necessarily better than plastic. It depends on how you are going to re-use the bags before you eventually recycle them.

Litter and Degradability

I hope that no one is deliberately discarding their used coffee packets onto the street or onto the beach! But litter and bio-degradability are big issues for plastic based packaging materials, particularly at sea. There are horrific stories about marine animals being starved due to consuming plastic or being drowned because they are entangled in it. Paper will degrade very quickly and so clearly does not suffer from the same problems as the plastic packaging in this topic. However, as mentioned above, not all plastic is the same. As well as ordinary plastic, your coffee could come roasted and packaged in a degradable plastic, either compostable or oxo-biodegradable.

sea no litter

There is a big problem with plastic litter ending up in the oceans

The name ‘compostable plastic’ (EN13432) is, to me, a bit disingenuous. It suggests that it breaks down in a composting facility such as my worm bin. But the standard EN13432 does not refer to such home-composting at all. For a plastic to be deemed compostable it has to break down under industrial composting conditions (ie. it is held at 58 C for the period of its degradation). Not all countries/councils offer such facilities for their waste disposal and so a compostable plastic sent to landfill offers little advantage over ‘ordinary’ plastic. However, in the marine environment it has been shown that the compostable plastic bag did degrade quickly relative to ordinary plastic bags‡.

Oxo-biodegradable plastic on the other hand works very differently. At the time of its manufacture, metal-salt catalysts are added to the plastic that determine how long the plastic survives before it breaks down. As long as it is exposed to light and oxygen, the oxo-biodegradable plastic will break down after, typically, 18 months (though the usable time can be made longer than this). Recent studies have shown that it is safe to recycle oxo-biodegradable plastic together with conventional plastic recycling†. Provided that the bag does not get covered in algae, an oxo-biodegradable plastic will break down after 18 months (if that was the time specified at manufacture) whether it is on land or on sea.

Therefore if litter is what you are worried about, you have to ask where you think that the plastics are going to end up and whether you want to be able to recycle them or just re-use them.

So what should you do?

There’s no point me answering this question for you. Ultimately I do not know your individual circumstances and concerns, nor how you are buying and consuming your coffee. Moreover, these considerations have been solely based on some of the environmental problems associated with different packaging. Coffee consumption has other factors, such as the major issue of how the coffee tastes. Earlier this year, Roasting House conducted an experiment to blind-taste the coffee after it had been stored in different types of packaging. You can find the results of that interesting study here.

a take away cup

The next problem. What should we do about take-away cups?

Personally, my concerns are principally the greenhouse gas emissions and the litter/degradability problem. I also buy coffee that is delivered to me very soon after it has been roasted. So I tend to favour packaging that uses unbleached, recycled paper. There is a caveat though. The CO2 emissions caused by paper manufacture and transportation means that I need to find a way to re-use the bags as often as possible before recycling/composting. Fortunately, I think there is a great use for old paper coffee bags: They are the perfect size for carrying loose vegetables or uncooked fish/meat products in supermarkets (rather than use the plastic bags that can be supplied for these products). Each paper coffee bag can be reused multiple times before it finally becomes unusable.

If I were drinking coffee that wasn’t quite so freshly roasted, I would be in favour of using oxo-biodegradable plastic (preferably from recycled material). I do not currently have an opinion on compostable (EN13432) plastic. The results of the degradation of compostable plastic in a marine environment were encouraging and if it starts to become genuinely compostable (as I understand the word in terms of home composting) it would definitely be a type of packaging to consider.

You may come to different conclusions, if you do so, please do let me know what you think in the comments section below. In the meantime, a map of coffee roasters who are trying to improve the environmental footprint of their packaging in a variety of ways can be found here.

 

I am grateful for discussions with Oh Ying Ying of Miracle Spectrum Sdn Bhd who helped me to navigate the minefield of environmental plastics. There is much more to write about plastics, the environment, litter & the Paris meeting, the whole issue of take-away cups for example!

∗ Yeow et al., “Bags for life: the embedding of ethical consumerism” J. Business Ethics, 125, 87 (2014)

‡ O’Brine et al., “Degradation of plastic carrier bags in the marine environment”, Marine Pollution Bulletin, 60, 2279 (2010)

† A report by the Transfer Centre für Kunststofftecknik GmbH (“TCKT”) dated 12 November 2013 on behalf of European Plastic Converters (EuPC), Roediger Agencies.

ª Plastics and the Environment, Ed. AL Andrady, Wiley-Interscience Publications, 2003

Predicting the weather with a cup of coffee?

What do the bubbles on the surface of your coffee tell you about the weather?

weather, bubbles, coffee, coffee physics, weather prediction, meteorology

There is a lot of physics going on with the bubbles on this coffee, but can they be used to predict the weather?

You have just poured a cup of freshly brewed coffee into your favourite mug and watched as bubbles on the surface collect in the middle of the cup. It occurs to you that it is going to be a good day, but is that because you are enjoying your coffee or because of the position of the bubbles?

There are a large number of sayings about the weather in the English language. Some of the sayings have a basis in fact, for example the famous “red sky at night, shepherd’s delight, red sky in the morning, shepherd’s warning“. Others though seem to verge on the superstitious (“If in autumn cows lie on their right sides the winter will be severe; if on their left sides, it will be mild”), or unlikely (“As August, so the next February”).  In 1869, Richard Inwards published a collection of sayings about the weather. “Weather Lore” has since undergone several new editions and remains in print although Inwards himself died in 1937. Amongst the sayings contained in the book is one about coffee:

When the bubbles of coffee collect in the centre of the cup, expect fair weather. When they adhere to the cup forming a ring, expect rain. If they separate without assuming any fixed position, expect changeable weather.

A quick search on the internet shows that this example of weather lore is still circulated, there is even a ‘theory‘ as to why it should be true. But is it true or is it just an old wives’ tale? Although I have consumed a lot of coffee I have never undertaken enough of a statistical study to find out if there could be an element of truth in this particular saying. The number of bubbles on the surface of the coffee is going to depend, amongst other things, on the type of coffee, the freshness of the roast and the speed at which you poured it. While the position of the bubbles will depend on how you poured the coffee into the mug, the surface tension in the coffee and the temperature. It would appear that there are too many variables to easily do a study and furthermore that the mechanism by which coffee could work as a weather indicator is unclear. It is tempting to write off this particular ‘lore’ as just another superstition but before we do that, it is worth revisiting another old wives tale which involves Kepler, Galileo, the Moon and the tides.

tides, old wives legends, Kepler, Galileo, Lindisfarne, bubbles in coffee

The pilgrim path between Lindisfarne and the mainland that emerges at low tide is marked by sticks. But what causes the tides?

Back in the mid-17th century, Newton’s theory of universal gravitation had not yet been published. It was increasingly clear that the Earth orbited around the Sun and that the Moon orbited around the Earth, but why exactly did they do that? Gilbert’s 1600 work De Magnete (about electricity and magnetism) had revealed what seemed to be an “action at a distance”. Yet the scientific thought of the day, still considerably influenced by Aristotelianism, believed that an object could only exert a force on another object if it was somehow in contact with it. There was no room for the heavenly bodies to exert a force on things that were found on the Earth. Indeed, when Kepler suggested that the Moon somehow influenced the tides on the Earth (as we now know that it does), Galileo reproached him for believing “old wives’ tales”: We should not have to rely on some ‘magical attraction’ between the moon and the water to explain the tides!

The point of this anecdote is not to suggest that a cup of coffee can indeed predict the weather. The point is that sometimes we should be a little bit more circumspect before stating categorically that something is true or false when that statement is based, in reality, purely on what we believe we know about the world. We should always be open to asking questions about what we see in our daily life and how it relates to the world around us. It will of course be hard to do a proper statistical study of whether the bubbles go to the edge or stay in the centre depending on the weather (whilst keeping everything constant). Still, there are a lot of people who drink a lot of coffee and this seems to me to offer a good excuse to drink more, so perhaps you have some comments to make on this? Can a cup of coffee predict the weather? Let me know what you think in the comments section below.

 

Weather legends taken from “Weather Lore”, Richard Inwards, Revised & Edited by EL Hawke, Rider and Company publishers, 1950

Galileo/Kepler anecdote from “History and Philosophy of Science”, LWH Hull, Longmans, Green and Co. 1959

Footprints

Climate march, greenhouse effect

The People’s Climate March, London, 21st September 2014

A couple of weeks ago, People’s Climate marches were held in cities across the world. Held immediately before the UN climate summit, thousands rallied to emphasise the fact that we all need to work to lower our carbon dioxide emissions before it is too late. It is often said that we can “do our bit” by boiling only enough water to make the amount of tea/coffee that we want. So the question is, how much carbon dioxide is emitted as a result of preparing my morning cafetiere? And a related question, will it really make a difference if I boil the kettle efficiently?

A small cafetiere holds, roughly, 500ml of water. We need to increase the temperature of the water by approximately 80 C (from room temperature around 20 C to boiling point) in order to make the coffee. It is a property of water that, to raise its temperature by 1 C, we need to supply 4.186 Joules of (heat) energy per gramme (ml) of water (ref). To boil the amount needed for a cafetiere therefore takes 167 440 Joules of energy. (In practise it will take more than this owing to the efficiency, or inefficiency, of the kettle but this gives us a “ball-park” figure and a lower estimate).

How to turn this “energy” into a carbon footprint? Perhaps the simplest estimate would be to use the CO2 emissions guide for different electricity generation methods (link). The amount of CO2 emitted during electricity generation depends on the way that the electricity is generated. A wind farm is clearly going to produce far less CO2 than a coal fired power station. However, as a lot of electricity is still generated by burning fuels, let’s calculate the CO2 emissions for a ‘dirty’ fossil fuel such as (hard) coal and a ‘cleaner’ fossil fuel such as natural gas. According to estimates, (link) hard coal emits 115 kg of CO2 per GJ (ie. per 1 000 000 000 Joules) of energy produced. Natural gas emits 63 kg/GJ. This means that for one cafetiere (167 kJ), 19g of CO2 is emitted if your kettle is powered by a coal burning power station, or 11g (if your electricity supplier largely relies on natural gas).

chemex, coffeeBut what do these figures mean in terms of our carbon footprint? In the UK in 2010, 7900 kg of CO2 was emitted per person, according to the World Bank (link). This means that one cafetiere is the equivalent of 0.1% of an individual’s footprint for one day. This does not seem much but let’s phrase it differently. According to the British Coffee Association, 70 million cups of coffee per day are consumed in the UK and approximately 2 billion per day world wide. For the sake of simplicity in our calculations, let us assume (not unreasonably I think) that one cafetiere is the equivalent of two cups. Then, if we take the worst case (electricity generation from hard coal), each day there are 665 metric tons of CO2 produced in the UK from people enjoying their coffees (19g x 35 million cafetiere equivalents). Worldwide this equates to 19 000 tons of CO2 per day. If each person was boiling twice the amount of water that they needed for their coffee, more CO2 would be emitted each day due to our coffee making than the total annual CO2 emissions of the country of Lesotho (2010 figures, ref).

Something to think about while enjoying a coffee.

A coffee cup loud speaker

In the blog post “Musical Coffee”, I used a loud speaker that I had made out of a coffee cup.  This (hopefully brief) post is just to explain how the speaker was made in order that you can make it at home.  Firstly though I need to thank Jose Pino who had posted instructions for a very similar speaker (link) and from whom I got the idea for this speaker. Secondly, I ought to say that this video is the making of the actual speaker used in Musical Coffee.  Some further optimisation is clearly possible.

To make a loud speaker out of a coffee cup you will need

  1. A take-away coffee cup
  2. Paper and some scissors
  3. Sticky tape
  4. OLD ear-phones
  5. copper wire (0.28mm diameter worked well)
  6. superglue
  7. a magnet (a rare-earth magnet is best)

Instructions

Step 1: Make a paper “jacket” for the magnet. This jacket is there so that, eventually, we can pull the magnet out from the coil that we are going to wrap around the magnet.

Step 2: Make a second jacket with feet.  This jacket is to support the coil.  The ‘feet’ will allow us to easily superglue the jacket to the bottom of the take-away cup.

Step 3: Protect the magnet with a piece of paper. This paper just sits between the magnet and the cup.  It is to stop the magnet from getting glued to the cup in the next step.

Step 4: Glue the jackets to the cup. This is where the feet in step 2 come in.  Glue the outer jacket to the cup, the magnet should still be inside the jackets at this point but DO NOT glue the magnet to the bottom of the cup.

Step 5: Wind the coil. I used 100 turns of 0.28mm diameter (enamel coated) copper wire.  This worked quite well but could easily be optimised.

coffee cup loud speaker, cup speaker

The coffee cup speaker in an improved design

Step 6: Attach the legs. If I were to do this again, I would use cocktail sticks as in the photo here. In the video Musical Coffee though, I used bits of polystyrene cup stuck on with glue after having tried using straws. The aim is to make the cup fairly rigid so that the vibrations from the coil at the bottom of the cup are transmitted into the fluid of the coffee. The legs made out of bits of polystyrene cup worked well enough to hold coffee in the cup while it was being used as a loud-speaker but the cocktail stick design worked much better.

Step 7: Remove the inner paper jacket.  This is so that when you turn the coffee cup over and mount it onto a piece of card, the magnet will fall out onto the card centred with the coil.

Step 8: Glue the speaker and magnet to the card. Look again at the picture.  See that the magnet is on the card and directly below the coil? This is how it should be attached. Depending on what you used for legs, either superglue or wax (as used in the photo of the speaker with cocktail stick legs) would be good to hold the speaker in place.

Step 9: Be brutal with your ear-phones. Cut an ear-bud off.  There should be two wires left exposed.

Step 10: Solder the ends of the coil to the wires from the ear-phones. If you are not happy soldering, remove the enamel coating of the wire used for the coil with a sharp blade and then twist this wire with the ear-phone wires before fixing it with tape.

You are ready to go.  Let me know how you get on in the comments section below. Have fun.