Categories
Coffee cup science General Observations Science history slow

Drip coffee

The universe is in a cup of coffee. But how many connections to different bits of physics can you find in the time it takes you to prepare a V60? We explore some of those links below while considering brewing a pour-over, what more do you see in your brew?

1. The Coffee Grinder:

coffee at VCR Bangsar
Preparing a V60 pour over coffee. How many connections can you find?

The beans pile on top of each other in the hopper. As the beans are ground, the bean pile shrinks along slipping layers. Immediately reminiscent of avalanches and landslides, understanding how granular materials (rocks & coffee beans) flow over each other is important for geology and safety. Meanwhile, the grinding itself produces a mound of coffee of slightly varying grain size. Shaking it would produce the brazil nut effect, which you can see on you breakfast table but is also important to understand the dynamics of earthquakes.

Staying at the grinding stage, if you weigh your coffee according to a brew guide, it is interesting to note that the kilogram is the one remaining fundamental unit that is measured with reference to a physical object.

2. Rinsing the filter paper:

V60 chromatography chemistry kitchen
A few hours after brewing pour over, a dark rim of dissolved coffee can be seen at the top of the filter paper. Chromatography in action.

While rinsing the filter we see the process of chromatography starting. Now critical for analytical chemistry (such as establishing each of the components of a medicine), this technique started with watching solutes ascend a filter paper in a solvent.

Filtration also has its connections. The recent discovery of a Roman-era stone sarcophagus in the Borough area of London involved filtering the excavated soil found within the sarcophagus to ensure that nothing was lost during excavation. On the other hand, using the filtered product enabled a recent study to concentrate coffee dissolved in chloroform in order to detect small amounts of rogue robusta in coffee products sold as 100% arabica.

3. Bloom:

bloom on a v60
From coffee to the atmosphere. There’s physics in that filter coffee.

A drop falling on a granular bed (rain on sand, water on ground coffee) causes different shaped craters depending on the speed of the drop and the compactness of the granular bed. A lovely piece of physics and of relevance to impact craters and the pharmaceuticals industry. But it is the bloom that we watch for when starting to brew the coffee. That point where the grinds seem to expand and bubble with a fantastic release of aroma. It is thought that the earth’s early atmosphere (and the atmosphere around other worlds) could have been helped to form by similar processes of outgassing from rocks in the interior of the earth. The carbon cycle also involves the outgassing of carbon dioxide from mid-ocean ridges and the volcanoes on the earth.

As the water falls and the aroma rises, we’re reminded too of petrichor, the smell of rain. How we detect smell is a whole other section of physics. Petrichor is composed of aerosols released when the rain droplet hits the ground. Similar aerosols are produced when rain impacts seawater and produces a splash. These aerosols have been linked to cloud formation. Without aerosols we would have significantly fewer clouds.

4. Percolation:

A close up of some milk rings formed when dripping milk into water. Similar vortex rings will be produced every time you make a pour over coffee.

Percolation is (almost) everywhere. From the way that water filters through coffee grounds to make our coffee to the way electricity is conducted and even to how diseases are transmitted. A mathematically very interesting phenomenon with links to areas we’d never first consider such as modelling the movements of the stock exchange and understanding the beauty of a fractal such as a romanesco broccoli.

But then there’s more. The way water filters through coffee is similar to the way that rain flows through the soil or we obtain water through aquifers. Known as Darcy’s law, there are extensive links to geology.

Nor is it just geology and earth based science that is linked to this part of our coffee making. The drips falling into the pot of coffee are forming vortex rings behind them. Much like smoke rings, they can be found all around us, from volcanic eruptions, through to supernovae explosions and even in dolphin play.

5. In the mug:

Rayleigh Benard cells in clouds
Convection cells in the clouds. Found on a somewhat smaller scale in your coffee.
Image shows clouds above the Pacific. Image NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

Yet it is when it gets to the mug that we can really spend time contemplating our coffee. The turbulence produced by the hot coffee in a cool mug prompts the question: why does stirring your coffee cool it down but stirring the solar wind heats it up?

The convection cells in the cooling coffee are seen in the clouds of “mackerel” skies and in the rock structure of other planets. The steam informs us of cloud formation while the condensation on the side of the cup is suggestive of the formation of dew and therefore, through a scientific observation over 200 years ago, to the greenhouse effect. The coffee cools according to the same physics as any other cooling body, including the universe itself. Which is one reason that Lord Kelvin could not believe that the earth was old enough for Darwin’s theory of evolution to have occurred. (Kelvin was working before it was known that the Sun was heated by nuclear fusion. Working on the basis of the physics he knew, he calculated how long the Sun would take to cool down for alternative mechanisms of heating the Sun. Eventually he concluded that the Sun was too young for the millions of years required for Darwin’s theory to be correct. It was the basis of a public spat between these two prominent scientists and a major challenge to Darwin’s theory at the time).

 

Of course there is much more. Many other links that take your coffee to the fundamental physics describing our world and our universe. Which ones have you pondered while you have dwelt on your brew?

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