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Coffee Chat with Bean Thinking

Written by . Published on under the Coffee Interviews category.

The photo for this article was provided by the interviewee.

Close-up of bubbles on the edge of a cup of coffee

A few weeks ago, I discovered Bean Thinking, a blog devoted to the intersection of science and coffee. Karen, the owner of Bean Thinking, has conducted various experiments that describe effects we can see in a cup of coffee. In this interview, I talk with Karen about how she plans and executes experiments and the philosophy behind her blog.

For my readers who have not read Bean Thinking, could you tell them a bit about your blog?

The universe is in a cup of coffee. By which I mean, the laws of physics are the same throughout the universe, so what applies to the universe applies to your coffee too. Appreciating coffee has many levels, the taste, the aroma, even the feel of the warmth of the cup. That five or ten minute break that we take to really enjoy our coffee can lead us on journeys of imagination to the countries where the coffee was grown or to the cafes where we enjoy cups of coffee outside. Thinking about the science of the cup can extend that enjoyment further, as we see the connections between our cup and, say the evidence for the Big Bang theory. That is my hope for Bean Thinking anyway.

You are dedicated to exploring the world of science “though the lens of a mug of coffee.” Could you tell me what inspired you to think this way?

I drink a lot of coffee and have a background as an experimental physicist researching how magnetism and superconductivity interact with each other. I find it thrilling to realise that two things are connected to each other in some way, be that scientifically, historically or indeed something other way. There are many connections between coffee and physics and I hope that some people may be similarly excited to find a connection that they had not realised was there.

Some of your posts, like your one on degassing coffee, feature experiments. Can you talk me through how you come up with ideas for your experiments?

I think physics should be accessible for anyone with some patience, curiosity and some basic kitchen equipment. So all of the experiments on Bean Thinking can be done with items that can usually be found around the home. But then there are different types of experiment. To take your example of the de-gassing experiment. There I was given a problem - for how long does a coffee degas after roasting (and is there a difference for the same bean type roasted in different conditions)? Then, I had to think, how could we test this with items that we can find at home?

Red cabbage is a great indicator (for showing what is acidic and what is alkaline) and carbon dioxide (which is what degasses out of the freshly roasted coffee) makes water acidic when it dissolves in it. This is the problem for the ocean acidification that we are experiencing at the moment, but it also means that any of us can see how much carbon dioxide escapes from our coffee beans as a function of time.

In the case of some of the other experiments, for example making ‘smoke rings’ appear in a glass of water, they are experiments that I have seen described in other contexts and have thought, that looks really cool, can we make it work with coffee.

What happens after you come up with an idea for an experiment?

It is really important that any experiment that I describe on Bean Thinking works and that anyone could copy it and try it for themselves. So I test it and test it again. Sometimes the experiment does not work and so these experiments do not make it onto the website. Often it works but not quite in the way that I had originally planned it. Sometimes, not often, it works exactly as I had hoped. And then it’s a case of making a video and editing it, or taking photos, to show how the experiment was done and so (hopefully) someone can replicate it in their own kitchen.

You also talk about general physics effects on your blog, such as the effect behind “wine tears.” How do you balance coffee and non-coffee related articles?

Everything is ultimately related to coffee somehow! In terms of the articles on the website though, sometimes an effect is more interesting in a different drink, such as wine. So take the ‘wine tears’, this has to do with the surface tension of a liquid and how liquids flow in response to a difference in surface tension between one part of the liquid and another (for example if you add alcohol or soap to water). In wine this gives a lovely effect where you can see what appear to be ‘legs’ or ‘tears’ above the wine level after swirling the glass a bit. With coffee, the effect is part of what drives the suspended coffee particles into the rings that form coffee stains. For that experiment, it was more fun to be drinking wine and watching the effect than to wait to watch coffee dry (though I’ve done that for the website too).

What is your favourite coffee-related science experiment that you have done?

Making liquid globules bounce on the surface of a liquid. It’s an amazing effect, you can actually stabilise a drop of water on a bath of water 1 so that it remains as a drop, not merging with the bath, for many minutes. I’ve managed 2 minutes on my kitchen work top. When I took the experiment to a “Coffee and Science evening” at Amoret Coffee in Notting Hill, London, one of the participants stabilised the droplet for about 10 minutes. It should be possible to make it last for much longer than this.

You can also do it with coffee and one of the beautiful moments in the video of the experiment (from my point of view) was when a drop of coffee, stabilised on the surface of a bowl of water, merged with a drop of milk. The way they merged was just fascinating.

What was the most transformative coffee experience you have had?

Transformative? When I was growing up there were no proper cafes in the town where I lived. If you ordered a coffee it was instant. A cafe in the local city started serving coffee in cafetieres. It was the start of a great journey.

What is your go-to order when you go out for a coffee?

Long black

Do you brew at home? If so, what device do you mainly use?

Of course. Typically a Hario V60 but I still also rely on the Aeropress and cafetiere.

The Bean Thinking blog is available at I recommend the posts on degassing and Aeropress bubbles.

  1. Although it will work with water for a short amount of time, to actually stabilise the droplet for longer durations, it is best to add a bit of soap to the water. 

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