A few months ago, news came that the coffee roasting company Old Spike had opened a new café, Spike and Earl, down in Camberwell. Operating on similar principles to Old Spike, Spike and Earl aims to serve excellent coffee (and food and cocktails) with a social conscience. By employing those who have previously been homeless, Spike and Earl offers an employment (and training) route for people who may not easily otherwise have the opportunity. So although Camberwell is a bit of a trek, I was looking forward to trying this new place. As it was a late afternoon in November and the menu suggested that the dairy alternatives were only soya or oat, I decided to try a soya latte. (For any reader with a nut allergy, the current fashion of using almond milk means that you should always ask first if your cappuccino contains nuts). The baristas were friendly and confident in assuring me that they do not use almond milk (no danger of nut-cross contamination) but that their brownies did contain nuts (so I sadly had to pass on the brownie opportunity). My partner in these café reviews opted for a ginger beer.
There were a series of high tables with stools on the left hand side of the café. Presumably many people can therefore be accommodated when it gets crowded. However, at the time of our visit, it was fairly empty and we made our way to the rear of the café. Behind us, and behind closed glass doors, was a coffee roaster that we later discovered was part of the Old Spike roasting expansion. It’s always a nice touch to see coffee roasting happening as you drink but perhaps we needed to arrive earlier for that.
Drinks arrived together with complementary water and the soya latte was very smooth. Almost caramel like in the sweetness and very drinkable. It makes a pleasant change to have a latte once in a while. Light was playing tricks around the room as the sun was setting and the inside lights were becoming more prominent. But the striking thing about Spike and Earl was that the bricks used to support the tables and line the walls all had holes in them. On the wall running along the side of the café, (windows were on the other side), pot plants were placed in the holes giving the impression of the beginnings of a green wall. The holes in the bricks supporting the table meanwhile made an excellent footstool and were complemented by holes in the stools. A latte of course is largely made up of holes, or at least bubbles. The foam structure consisting mostly of air. How is it that some structures can be made better owing to what they don’t contain rather than what they do?
For example, if you imagine the difference between a latte and a cappuccino (but made out of metal rather than milk) that can be the difference between a successful tooth implant and a failure. We know from our coffees that bubble size can have a significant structural effect. But how about more fundamental properties, can the holes in bricks change things such as the way sound propagates?
You may have heard about how different structures can be engineered to make materials “invisible” to certain frequencies of light. Imaginatively named “invisibility cloaks” are made by designing materials with patterns on them that change the path of an incident light beam. Because the effect on the light beam is due to the structure in the material rather than purely from the material itself, these materials have become known as ‘meta-materials’. When you remember that microwaves are a form of light, it is perhaps easy to see some of the applications of this research and one reason that it has attracted a lot of funding.
However there is an acoustic type of metamaterial that is far more similar to the bricks in Spike and Earl and that may find applications in medical imaging (ultrasound). Earlier in 2017, a team from the universities of Sussex and Bristol published a study about acoustic metamaterial ‘bricks’. Each brick had a differently shaped hole through the centre of it which delayed the incident sound wave by a specific phase interval (you can say it ‘slowed’ the wave). In order to work efficiently, the brick had to be of a height equal to the wavelength that the researchers were interested in and a width equal to half that wavelength. As they were investigating ultrasound, the bricks were therefore about 4.3mm square and 8.66 mm high.
By assembling the bricks together, the researchers found that they could steer a focussed beam of sound or even change the shape of the sound beam. This would have applications as diverse as targeting cancer cells with ultrasound to levitating a polystyrene bead. You can read more about their research here (or, if you have access to Nature Communications, their paper can be downloaded here).
Just for fun, assuming that the bricks supporting the table at Spike and Earl could be similarly turned into acoustic metamaterials, we could calculate the musical note that they would best work with. Estimating the brick at about 15cm square and remembering that is approximately half the wavelength (λ/2) and using the speed of sound in air to be 330 m/s, we can calculate the frequency to be:
f = c/λ
f = 330/0.3 = 1100 Hz
As I finished my soya latte, strata of milk lined the cup. Reminiscent of the Earth’s layers or perhaps, metaphorically, our strata of understanding, there is certainly plenty more to ponder at this interesting new(ish) addition to the London café scene. So next time you are in Spike and Earl, do let me know what you end up thinking about, you never know where these thought trains may take you.
Spike and Earl is at 31 Peckham Road, SE1 8UB