June 2019 – Bean Thinking

A first coffee & science evening at Amoret

intro board for Amoret evening — An evening of coffee and science at Amoret Coffee in Notting Hill

A couple of weeks ago we hosted a first “coffee and science” evening at Amoret Coffee in Notting Hill. Designed to explore a physics concept that you could notice in your coffee cup with people from a diverse range of backgrounds, in some ways, the evening itself was an experiment. Would anyone turn up? Would the experiments be interesting? Was I just making my coffee badly?

This last question referred to the fact that the connection for that particular evening had been the dancing drops that skirt across the surface of a V60 (or other pour over) as you prepare your coffee. I had noticed these a couple of years ago but at that point had not appreciated their significance. To answer that question, we were prepared two excellent pour overs by people who really knew what they were doing. And we were spoiled for the coffee which was a recently roasted Nicaraguan washed coffee grown by the Baltodano family who also came along for the evening. The two pour overs were prepared very slightly differently and produced drinks that highlighted different aspects of the flavour of the coffee (though sadly I only managed to try one). This led to a fair amount of discussion amongst those present, not just about which they preferred, but how the preparation affected and highlighted different flavour notes.

Pour overs at Amoret — Preparing pour overs by two (slightly) different techniques. But would we see the dancing drops? (Yes x 2)

The pour overs showed that the dancing drops were there (in both techniques) when coffee was made properly. This was a relief for me! But did they also supply a clue as to how these drops were able to survive, as liquid drops, on the surface of the coffee?

Ordinarily, when a drop drips into a bath of liquid, you would expect it to quickly coalesce with the liquid bath. Once the drop gets close enough to the surface, the van der Waals forces in the drop and the liquid bath will overcome the surface tension effects and the drop will be subsumed into the liquid. If the drop does not coalesce, but instead appears to ‘float’ on the surface there must be a reason.

The first reason that the drop may survive for a while on the surface is because there is a temperature difference between the drop and the bath. This sets up stresses within the drop that pull air into the region between the drop and the bath and keep the drop ‘floating’ for a little while.

Secondly, if you increase the surface elasticity of the droplet, you can stabilise it on the liquid bath for longer. This is usually done by adding soap to the water, not something we did with the V60. But could there be an effect of the coffee oils or some other aspect of coffee chemistry that is keeping these droplets afloat?

Experiments at Amoret — You can see a drop almost ‘sitting’ on the surface of the water here (circled). This particular drop was stabilised for about 15 minutes. I think if you look carefully you can see a ripple pattern around the droplet in addition to the standing wave pattern on the surface of the water caused by the loud speaker underneath (indicated by the red arrow).

Lastly, if you vibrate the surface of the liquid bath, you can create conditions whereby the droplet ‘bounces’ on a cushion of air on the bath. It was interesting, that in the preparation of both pour overs at Amoret that evening, the times that we observed the dancing drops coincided with those times that the pour over was dripping into the coffee bath, causing a noticeable ripple on the surface.

This last condition was the subject of an experiment in the corner of the upper room at Amoret where we used a loud speaker to generate vibrations to two different liquid baths (water and soap water for example) to see if we could obtain stable drops on the surface. Astonishingly, some of the participants on that Tuesday managed to keep a droplet stable for about 15 minutes, you can see their droplet in the photo. The photo is interesting because if you look closely, not only can you see the wave on the bath of water caused by the vibration of the speaker, but you can also see a circular ripple pattern around the droplet. Is that the ripple caused by the droplet’s bounce?

Conversations led on to the fact that these drops were not just seen in pour overs but could occasionally be seen in espressos too. I’m definitely looking forward to the video of that one. While we also got to discuss the importance of different parameters on the stability of the drops – it turns out droplet diameter, as well as the forcing amplitude (which translates to, how loud you have the volume on the loud speakers) are key parameters that affect the behaviour of the drop, something that has been pointed out elsewhere.

V60 droplet floating bouncing sitting on coffee — A drop in-situ

The evening also emphasised just how much we have to talk to each other about! One topic that kept coming up was fermentation, specifically with how the coffee cherries are processed. Hopefully this could become the subject of a future conversation.

Future events are planned (in theory but not yet in practise) and so if you’d like to make sure you hear about them, you can sign up to the Bean Thinking events list here. Also, if you didn’t get chance to take part in the evening but would like to continue the discussion and maybe add your videos & comments about the droplets, you can sign up to the Virtual Coffee House which will be discussing this topic (until the next coffee & science evening).

Digital information at Kape and Pan, St Giles

coffee Kape and Pan — My pour over coffee at Kape and Pan.

The area around St Giles has changed significantly in recent years. As old haunts have disappeared, new ones spring up in that regenerative evolution that seems to characterise parts of London. Kape and Pan is in the foyer of one of these new buildings (that apparently also homes Google). In some ways it is very much in tune with the new buildings surrounding it and yet there are a number of touches if you take the time to sit and wait attentively for your coffee to arrive (and more that I discovered on researching the cafe later). I was alerted to the opening of Kape and Pan by its mention in Caffeine Magazine and, as I was in the area, it seemed an opportune moment to try it (once I had found which of the glass buildings was number 1, this does not seem to be an area where an address helps!).

Some interestingly titled non-coffee drinks shared the menu with the usual combination of espresso based drinks. Kape and Pan focus on coffees from South East Asia and edibles that are influenced by the flavours of that region. Three coffees were highlighted for the pour over menu. The ‘house’ coffee from Myanmar, an Ethiopian and one that I didn’t make a note of (but as these last two are on rotation, it will have changed by the time you try it). I ordered an Ethiopian pour over, with notes of peach and tea, found a table, and then waited for my coffee.

Light was pouring through the glass windows of the front of the building and so I sat towards the back of the space, with a good view of the pour over being made. That day, a technical problem had meant that payment was by cash only and watching each new customer arrive and encounter this problem, it was great to watch the relationships that had already built among regulars and the baristas and how that contributed to solving it in each case. It is interesting to see how new places develop a sense of community.

Clearly not stainless steel. Does the spoon affect the taste of the coffee? (Answer: yes it can and it has a chemical basis but you have to be drinking your coffee from your spoon)

One of the themes of the cafe appears to be a coffee drinking Buddha. Coffee in one hand, something to eat in the other, he is clearly enjoying his coffee while he contemplates it. And perhaps you may have imagined that the ‘digital’ referred to in the title would be connected with the fact that Kape and Pan is in a Google building, with associated physics connections of data processing and analysis, AI, etc. But no. The digital information comes from the representation of this sage.

As I enjoyed my (definitely tea like, though I did not ‘get’ peach) pour over, my non-coffee drinking companion studied the sugar jar. And gazing at the Buddha’s hand, commented about the perspective that the artist had taken of the fingers and then considered the evolution of the fully opposable thumb in tool use. This is a connection that would not have occurred to me as I don’t spend time drawing and emphasised the importance of listening to the experience of others (something that also was apparent in the evening of coffee & science held at Amoret on 11th June, more details about how this went next week).

It turns out that our idea of the evolution of the thumb and the human hand is still a debated issue and the story of our understanding is, in some ways, an interesting illustration of how science is done, together with the human prejudices and ideas that go together with that.

The idea had been that humans had split from our ape relatives fairly early on in the evolutionary time scale. And that, after that point, we had developed thumb use and other advantages that allowed us to develop tools and to become, as a species, fairly successful. But a spanner in the works came in the 1980s and 1990s when biologists were able to show by looking at the DNA of living primates, that humans were actually a lot closer to the chimpanzee than had been realised. So the model was adapted, humans and chimpanzees had a common ancestor but then the human hand structure evolved a longer thumb relative to the chimpanzees and so we acquired tool use etc. So far, so easy but how can we be more quantitative?

Buddha Kape and Pan coffee drinking — Happy coffee drinking contemplation.

The relative length of the thumb of a primate can be quantified by measuring the length of the thumb (down to the base of the hand) compared with that of the ring finger. Humans have a ratio of thumb length to ring finger length of about 0.75 compared with about 0.35-0.6 in other living apes (I challenge you not to measure yours!). And it is here that there is an issue when people look at the fossil record. There we find ratios that are similar to that of modern humans suggesting that while human hands differ significantly from currently living apes, our hands are not so different from some primates that lived long ago. This would mean that our hand evolution was not there for our specific evolutionary advantage.

But there is more, even the phrasing of the first question is telling as it implies an assumption of further evolution on the part of human beings “human thumbs are longer“. But are they really longer or is it that our other digits are smaller relative to other living primates? And the answer to that got increasingly complex as that depends also on body mass, how can this be estimated in the case of fossil creatures for which we only have skeletons?

As I finished my coffee, I thought again about how Crossrail has changed this area and how new spaces are developing. Perhaps it was apt, given the direction of the thought-flow that I had chosen an Ethiopian coffee to sample that day. Thought to be the origin of coffee, the coffee plant can still be found growing in the wild in parts of Ethiopia. Other coffees, other varietals, have developed (or been developed) since the coffee plant was taken from there to grow elsewhere, giving us an enormous range of flavours to try. The human thumb may not have evolved specifically to enable us to develop tool use, but it does enable us to pick up our cups of coffee.