physics of smell

Details at The Italian Coffee Club, Shepherd’s Bush Market

Italian coffee club, Shepherd's Bush Market
The Italian Coffee Club. Plenty of chairs both inside and out.

What’s in a name? A hundred impressions and assumptions, an idea that to know somebody is to know their name? And so it was that The Italian Coffee Club thew me. Towards the Uxbridge Road end of Shepherd’s Bush Market, The Italian Coffee Club is in a wooden lined chalet. A few tables outside and some prominent signage leave you in no doubt as to the fact that coffee is served here. A sign asks if you would like to try the signature Italian blend, while another informs you that the aroma of the coffee “comes from here”.

Which goes part the way to explain why I was surprised when I walked in. Inside, a number of chairs and tables line the, fairly narrow, space leading to the counter. Towards the counter are various large jars of freshly roasted coffee beans ready for retail. Perhaps this should have given me a clue to check my assumptions. The roasts were varied with a good choice of origins, including several single origin. The coffee menu offered the usual choices and…. V60s of any of the various coffees that they sold (sadly I noticed this only after I had ordered an Americano). The coffees are roasted by The Italian Coffee company and include several direct-trade relationships. Although I had the “signature” Italian blend on the day, I did purchase 200g of the La Abuela washed Colombian to take home with me as beans. La Abuela means grandmother and apparently this coffee farm (which is one of those with which The Italian Coffee club has a direct trade relationship) is run by an 80 year old lady growing coffee that scores 83+ in the speciality quality score.

The aroma of coffee comes from here, The Italian Coffee Club, Shepherd's Bush
There were several signs about the aroma of coffee. This was one of them outside the cafe.

Looking around this chalet/cafe, the first thing that caught my attention was a sign about “smelling the aroma”. This immediately conjured up thoughts as to how it is that we actually perceive smells. In some ways an incredibly basic sense, in others, something that we still do not understand. It also prompted me to think about anosmia (smell blindness) and its allegorical relevance to my assumptions as I had entered the cafe about the coffee I would find.

The jars of coffee were the sort of transparent bottle with a rubber seal, reminiscent of vacuum physics. A (presumably decorative) manual coffee grinder at the bottom of the shelves could have prompted thought trains about automation and whether the coffee making process is improved by the uniformity of grind obtained by industrial grinders or the imperfections (but connections) that we would have through a fully manual brew (I think it may depend on what we mean by ‘improve’).

And then I looked down at my coffee and noticed a hair floating on top of it. I knew it was mine because it hadn’t been there originally and it was of the right length and colour. But I could tell it was there due to the indentations on the liquid surface around the hair, much as you can see the indentations around the feet of a pond skater. How much force was the hair exerting on the surface of the coffee to make such indentations? And when would it ‘fall through’?

Hair, surface tension, coffee
I wasn’t worried: it was definitely mine! But look at the way the surface of the coffee is affected by the hair. Why does it bend in such a way?

The surface tension of the coffee is caused by the water molecules in the liquid being attracted by the other water molecules into the coffee but not having anything above the surface to balance that force. Consequently, there is a net attraction for the molecules at the surface into the coffee and a ‘skin’ is formed on the surface, rather like an elastic sheet. This ‘skin’ takes a certain force to break it, which can be measured and which is called the ‘surface tension’. My hair, about 5cm long, as a typical human hair, weighs about 168 micrograms. Which means the gravitational force acting on it is F = mass x gravitational acceleration = 1.68 microNewtons. Expressed as a Force per unit length, this works out as 34 microNewtons per meter. In comparison, at 60 C, the surface of water requires a force of https://www.engineeringtoolbox.com/water-surface-tension-d_597.html0.067 Newtons per meter to break through it. My hair would be no match: the surface tension supports the hair.

What about a pond skater? That has a slightly larger mass (at 0.02 g) and it is also slightly shorter (20 mm), so its force per unit length is also larger at 0.01 Newtons per meter. So although it is going to push down more on the surface of a pond (or my coffee) than my hair is, it still won’t break the surface.

cat in Shepherd's Bush Market
It’s the little things….

As this is a coffee blog, what if we took the example of a coffee bean and, neglecting for one minute any other considerations, calculated the force it exerts on the water/coffee. Beethoven’s 60 beans of coffee had a mass of 9 g. So one bean has, roughly, a mass of 0.15 g. Each bean is about 1cm long and so it exerts 0.15 Newtons per meter on the water surface. Certainly enough to break it: so we could use coffee beans to measure surface tension. A novel purpose for the coffee bean, but I prefer my more traditional approach of grinding and drinking it.

Which took me back to the Colombian, La Abuela that I purchased from The Italian Coffee Club and tried, at home, as a V60. Sweet and syrupy, with cherry fruit: an enjoyable coffee for some time to ponder.

The Italian Coffee Club can be found in Shepherd’s Bush Market, Shepherd’s Bush.