liquid nitrogen

Questioning my assumptions at Everbean, Marylebone

Coffee cake Everbean
Coffee and cake at Everbean.

Alerted by Caffeine Magazine (on Twitter) to the opening of the second branch of Everbean, we arranged a quick visit into central London. A fair few had beaten us there. Initially, it seemed that the cafe was quite small with limited seating but a sign on the staircase pointed us to an entire area downstairs. Although there are tall stool-type seats upstairs fronting the window, there are more chairs and cushion backed bench seats downstairs (together with a comfy arm chair but more on that later). Downstairs was clearly the place to be on that day and is certainly a comfortable space for enjoying your coffee. As you enter, the counter upstairs is quite large and features a number of tempting cakes. Too tempting. Together with my Americano, I enjoyed a delicious vegan mandarin and chocolate cake.

Downstairs could be described as cosy. Cushions with birds embroidered onto them line the bench running down one side wall. A bookshelf with an eclectic collection of books is in the corner of the room next to the arm chair, suggesting a great (phone-free) way of spending an afternoon. I would share with you some of the titles but in some ways, that would be to judge the books by their cover (titles). Which in some way connects with the thought train that we encountered here at Everbean.

Mirror at Everbean, coffee Marylebone
Mirror, mirror on the wall: We can see ageing effects in metals but taste them in coffee.

On the wall behind us a lattice effect mirror reflected the room to itself. The lattice was painted but bits of paint had aged leading to rust and corrosion effects on the metal lattice work. Age, in the form of oxygen and moisture, affecting metal work in a similar way to how age affects the flavour of coffee. At this point, my thought train at the time went towards the ways in which different materials oxidise and the use that this can be put to. But a different thought train occurred to me when I started to think about this cafe later as I came across Brian’s Coffee Spot’s thoughts on coffee bean storage and specifically, should you ever store your beans in the freezer.

In addition to showing that, depending on your defrosting conditions, it was perfectly fine to store your coffee beans in the freezer, Brian’s Coffee Spot had highlighted a Twitter poll concerning coffee storage. The results of the poll had been definitive. Of 118 voters, 99 had ticked the “never store coffee in the freezer” option. I admit I was one of them. In hindsight, I can self-justify: I could say I was thinking about the (very real) problems with moisture affecting the ageing of coffee and the possibility of water already in the bean causing structural issues for the bean. However these are also problems that are avoidable, as Brian’s Coffee Spot outlined. If I am honest, in reality, I saw the poll, had a negative view towards the freezer option and so clicked “never”.

After reading Brian’s Coffee Spot, doing a little bit more reading about it online and then sitting back and actually thinking about it, I realised that I had perhaps been hasty. Is there still time to change my mind now I know more about the issue? We need a second vote!

But reading about the issues of freezing coffee beans also alerted me to a study that had been done a couple of years ago about the effect of the temperature of the coffee bean on grind size. The question was, when we grind coffee, does the temperature of the bean matter?

books at Everbean
You could sit here all day. Imagine what you would learn.

To test this question the authors subjected batches of 20g of coffee beans to two hours of four different temperatures: liquid nitrogen (-196C), dry ice (-79 C), freezer temperature (-19C) and room temperature (20C). Following this, the beans were immediately ground using a Mahlkonig EK43 grinder. They found that, under otherwise identical grinding conditions, the colder beans showed a smaller grind size and a reduced particle size distribution.

The authors of the study suggested their results as a possible explanation for the need in many coffee shops to tune the grinder to a closer grind size as the day progresses: they argued that the beans are warming up while sitting in the hopper on the grinder and that this results in a change in the way that they grind. They also suggested a possible long term solution for the storage of coffee beans: liquid nitrogen. Just a little bit colder than a freezer.

Which takes us a long way from the basement at Everbean on Seymour Place. Or does it? Perhaps you need to take some time out and sit in the armchair, questioning and investigating your perspective.

Everbean (2) is at 21 Seymour Place, W1H 5BH

Reality bites at Chin Chin Labs, Camden

Coffee grinder at Chin Chin Labs Camden

Nitro-brew? Not this week. Coffee and liquid nitrogen at Chin Chin Labs (a nitrogen dewar is on the table behind the coffee grinder).

It is true that Chin Chin Labs is not really a coffee-based café (although it does serve decently prepared, Monmouth roasted, coffee). Nonetheless, there is no question but that it has to be included as a cafe-physics review on Bean Thinking. Why? The answer is in the photo of the coffee grinder, though you may have to look carefully. You see, Chin Chin Labs is offering a different sort of café experience. Not coffee nor tea, but ice cream, indeed, Chin Chin Labs in Camden Lock advertises itself as the ‘future of ice-cream’ and the reason it does so is because here, all the ice cream is made with liquid nitrogen.

There are only 3-4 tables inside Chin Chin Labs which makes it more of a take-away bar than a sit down café. As you enter, a large dewar of liquid nitrogen is on your left, just behind the counter. Arranged behind this large dewar are a set of smaller dewars while on one of the ice cream preparation tables another (small) dewar sits with a pipe in it, ready for the nitrogen to be decanted out. If all these dewars are full, that is a lot of liquid nitrogen. The coffee is decent and prepared in the normal styles (espresso, Americano, cappuccino, latte), though this place is really not about the coffee (one of the staff expressed surprise that I’d ordered a coffee and not an ice cream). Next to the espresso machine were a set of glass beakers and glass containers as you would expect to find in a chemistry set, while the aprons worn by the staff had “Chin Chin Labs” written in a glittery, (futuristic or disco?), font.

Various dewars of nitrogen

Nitrogen, nitrogen everywhere…

There are many fun things that can be done with liquid nitrogen. From creating ice cream, through to shattering flowers and even to a possible solution for the energy storage problem (info here). Not to mention its important use as a coolant in all sorts of physics experiments and for biological storage. I have spent many hours decanting liquid nitrogen into buckets for basic experiments or into the first cooling stage of very strong magnets (such as are used in MRI machines).

However, at -196ºC, liquid nitrogen is not a liquid that can be treated flippantly. Although it can be fun, and handled correctly there is no problem, it can nonetheless be very dangerous. Which is why something else about Chin Chin Labs struck me quite hard. While there were glass beakers and containers that a cartoon may feature as part of a science ‘lab’, there was none of the equipment that you would actually expect to see in a real lab where liquid nitrogen is used. In our lab, oxygen monitors beep (annoyingly) every 60 seconds*, eye goggles and proper cryogenic-suitable gloves are stored in a highly visible position easily accessible to anyone in the lab. Risk assessments are prominently displayed so that everybody is aware of the risk of oxygen depletion (leading to suffocation) were the nitrogen dewars in the lab to fail and suddenly vent all that liquid nitrogen into nitrogen gas in the lab. These things are not fun, but are a necessary part of running a lab in which cryogenic liquids (including liquid nitrogen) are stored and used.

Ice cream at Chin Chin

The final result: vanilla nitrogen-ice-cream.

It is this contrast, between what is expected of a lab (glass beakers and complicated looking valves on the dewars) and what is in a lab (safety equipment and complicated looking valves on the dewars) that struck me. What do people, the public, café owners, think a lab looks like? What do they (you?) think a scientist looks like? Do we prefer indulging in our stereotyped ideas of a lab rather than think about the reality of life in a real science lab?

I am sure (or at least I hope) that the safety equipment, oxygen monitors etc. are present, but hidden under the counter, at Chin Chin Labs. It should always be possible to have fun with liquid nitrogen, whether in a lab or a café. And the ice cream is definitely worth trying (according to the person I visited Chin Chin Labs with). But, if you happen to pass by Camden Lock and try some nitrogen ice-cream, please do spend a minute to ask yourself, what you think a scientist, or a lab looks like. And do let me know what you think, I’d be interested to know.

Chin Chin Labs is at 49-50 Camden Lock Place, NW1 8AF

* In the event of the failure of a liquid nitrogen dewar, the oxygen in the room would be displaced. The resulting decrease in oxygen concentration can cause sleepiness, mental confusion or in the case of severe oxygen depletion, coma and death (more info here, opens as pdf). Oxygen monitors check the oxygen level in the room is at a safe level. The beep is annoying but tells us that the monitor still has battery and is checking the oxygen level in the room.

Super cold brew

Cold brew coffee with ice

Cold brew coffee served with ice. Image from pixabay.com

How cold do you drink your cold brew? Poured over ice? As an experimental physicist who works with liquid nitrogen (& helium), I was initially quite intrigued to learn of nitro cold brew coffee. Could it be coffee that somehow uses liquid nitrogen to fast-cool it, what would that do to the taste? You would expect liquid nitrogen (at -196ºC) to rapidly cool the coffee below its freezing point, after all, it is how Heston Blumenthal makes ice cream. To make a drink-able cold-brew with liquid nitrogen would require great skill, especially given the potential health risks. It would be another situation where you may well ask yourself, “what’s the point?”

However, it turned out that the reality was far more mundane, gaseous nitrogen is passed through cold brew coffee to create a drink with a silky mouthfeel. A smooth drink that comes straight from the tap just like stout. Such a drink is going to behave as an ordinary liquid and chilled only to the point that it is kept in the vat. The novelty would presumably come from the mouthfeel introduced by the many tiny bubbles distributed through the drink. Just as with water, if you cooled the nitro-brew below its freezing point it would solidify and form coffee cubes. No real difference to get excited about. But what if there was a very different sort of liquid, a “super liquid”, that didn’t behave like water, coffee or even liquid nitrogen but one that could leak through solid cups?

Superfluid helium is such a liquid. Like water, oil or even liquid nitrogen, when you cool helium (the same gas that is in party balloons)∗, it becomes an ordinary (but very cold) liquid at -269ºC. But unlike those liquids, when you cool it further, below -271ºC, it does something very odd indeed. It becomes a superfluid in which the liquid moves with zero friction or equivalently, zero viscosity (honey is very viscous, water is very much less so).  And it is because of these properties that it can do some astonishing things such as stream through cracks in containers that were thought impermeable (see the video at 0:52m), or even climb the walls of the container it is in (1:13m)!

 

To explain the behaviour of superfluid helium it is necessary to use quantum mechanics. Indeed, Fritz London (1900-1954) is said to have described both superfluidity and superconductivity (which happens in solids) as “quantum mechanisms on a macroscopic scale”. At the heart of the theory of superfluidity is the idea that the helium atoms fall into the lowest energy ground state possible, a Bose-Einstein condensate. To form a Bose-Einstein condensate, the particles (atoms of helium) have to  be bosons rather than fermions. All particles in nature can be categorised as either bosons or fermions. The difference between the two types comes from another quantum property of particles, the spin. Spin is related to the angular momentum of the particles and, this being quantum mechanics, can take only discrete values, either whole number or half integer numbers.

cold brew, doublemacbex

Another photo of cold brew coffee, this time from Bex Walton (flickr) – note the condensation around the rim, much could be said about that. Image CC licensed.

Bosons are particles with integer values for spin, fermions are particles with half integer values. Most of the elementary particles you will have heard of are fermions: electrons, protons, neutrons, they’re all fermions. Some particles however, such as the photon (the particle of light) are bosons. Helium 4 atoms are effectively composite bosons, because of the combination of 2 protons, 2 neutrons and 2 electrons that make up the atom. When you add their individual (half-integer) spins, you will get an integer spin, hence a boson not a fermion. The distinction is important because while bosons can share a lowest energy state (the Bose-Einstein condensate), fermions cannot. Quantum mechanically, no two identical fermions can share an energy level (the Pauli exclusion principle), so you can never get to a state where all the fermions are in the lowest energy state. There are practical, every day consequences of this for us, such as the way metals such as copper conduct electricity and heat, the fact that the electrons in the metal are fermions turns out to be crucial for us to understand how metals ‘work’. In contrast, the fact that the helium atoms are in the lowest energy state in super-fluid helium means that the ‘liquid’ behaves very strangely indeed.

We seem to have come a long way from the idea of a cold coffee. But perhaps next time, if someone offers you a “super cold brew” take a moment to think of the physicists who get to play with some real super cold superfluids†. Hope you enjoy the video.

 

*Technically it is Helium 4 that becomes superfluid at 2.2 K (-271ºC). The rarer isotope, Helium 3, does not become superfluid until much lower temperatures and even then, the superfluidity has some very special properties.

†Although I do get to work with liquid helium (and although it is mostly helium 4), I work at the relatively ‘hot’ temperatures at about -269C. At this temperature the interest is not so much in the liquid helium itself but its use as a coolant for other materials.