How specialty coffee woke up to water’s role in flavour

James Harper:

Welcome back to Filter Stories, I'm James Harper, and before we get into today's episode, a quick note. This episode is actually a reworked version of an episode I released back in 2022 called Water for Brewing Coffee. That original episode is still up if you want to check it out, but what you're going to hear here is a clearer, more comprehensive version.

In case you haven't done it yet, what I strongly suggest you do first is listen to the two episodes before this one. The first episode, A Beginner's Guide to Good Water for Coffee, is a simple practical walkthrough to figure out how good your tap water is for brewing coffee, and then how to fix it. Then the next episode, the episode right before this one, that's an episode where I get you familiar with two important concepts when it comes to water for coffee, calcium and hydrogen carbonate.

And it's this fun, crazy story where I take you back millions of years to explain how these ancient sea creatures accidentally ruined your coffees. And this episode is like part three. What we're going to look at here is the story of how the coffee community figured out that water actually affects the flavors of our coffee in big, noticeable ways.

Because for the longest time, the coffee world only cared about water's impact on equipment. Limescale buildup, corrosion, flavor never entered the picture. This is the story of how that changed, and how we came to define what good water for coffee is.

And my partner sponsor for all these episodes on water is the water filtration manufacturer, BWT.

James Harper:

Hope you enjoy it.

So let me introduce to you a professor of chemistry I spoke to.

Professor Christopher Hendon:

My name is Professor Christopher Hendon. I'm a professor of chemistry at the University of Oregon.

James Harper:

So 10 odd years ago, Christopher was a budding young chemist, and he was doing his PhD at the University of Bath in the UK. While working on his PhD, he stumbles across, you know, the beauty, the delicious world of specialty coffee.

Professor Christopher Hendon:

When he tasted... A coffee that tasted so unusual. And at the time it was just a naturally processed coffee, but I'd never had something like that before.

James Harper:

And so he frequents this cafe more and more often. And the cafe is Kelowna and Smalls, run by Maxwell Kelowna Dashwood. And it's here where his world of computational chemistry collided with the specialty coffee industry.

Professor Christopher Hendon:

Basically what happened was, Maxwell used to be a multi-roaster cafe, and that involved him buying beans from all over the place. And I think the story goes that Kelowna and Smalls purchased a coffee from Square Mile. A London-based coffee roastery co-founded by James Hoffman, the now YouTube celebrity.

And there was a disagreement about whether that coffee was defective or not. And in essence, Maxwell tried to dial this thing in and was arriving at flavors that he perceived as negative. The coffee went back to James, and James cupped it back in London and arrived at it being perfectly fine.

They're good tasters. They definitely are not disagreeable people. And so when there's a difference in opinion that's so dramatic, there must have been some other scientific basis for that.

And so we began to look at what possibly could have happened and arrived, obviously, at water chemistry differences.

James Harper:

And so Maxwell, the coffee shop owner in Bath, got busy trying to understand water science himself. And at one point, he asked one of his regulars, Christopher Hendon, a chemistry question.

Professor Christopher Hendon:

Yeah, so his original question was, what does TDS mean, and how can it tell us about quality of coffee? And I immediately responded with something along the lines of, it means nothing. And I have no idea why this ever evolved to be a metric that people would use.

James Harper:

Okay, now here's the thing. At the time, the coffee industry's understanding of what good water is for coffee essentially boiled down, no pun intended, to TDS. Now let me unpack why that's a problem.

First up, there's a lot of confusion around the term TDS, because it means different things in different parts of coffee. In brewing, when we talk about TDS, we use a refractometer, and that measures how strong a cup of coffee is. Because what the refractometer is measuring is how much coffee material is dissolved in your brew, how busy the liquid is with coffee stuff.

But when it comes to water, it's a different TDS. When it comes to measuring TDS in water, you use a conductivity meter, right? And that's just this device with these two forks that measures the electrical current that passes in between them.

It measures how much charged stuff there is, things like calcium, magnesium, sodium, chloride. But the thing is, when it comes to good water for coffee, we don't care about a lot of that stuff. We mostly care about calcium, magnesium, and hydrogen carbonate.

And so a TDS meter is just like measuring things we don't frankly care about. It can give us readings that seem quite high, like for example 150 ppm, parts per million, but if it's 150 ppm of the wrong minerals we don't care about in our coffee, then who cares? It's not relevant.

And that's why Christopher Hendon said this when Maxwell brought up TDS.

Professor Christopher Hendon:

It means nothing, and I have no idea why this ever evolved to be a metric that people would use.

James Harper:

But nevertheless, there it was. TDS was the measure, the only measure about water quality that was being communicated at all by the coffee industry's largest trade groups at the time.

Professor Christopher Hendon:

So the idea originally in the coffee world was that water had to have a TDS of less than 135, or at 135, right? And they'd broken it down a little bit more, plus and minus in some areas, but the point was 135 was the number. And the reason that they gave was because anything above that was risky to your machine and anything below that was risky to your machine.

James Harper:

But to someone in professional academia, like Christopher Hendon, TDS, it was an overly simplistic measure. And so he and Maxwell decided to write a book, Water for Coffee, and one of the big things Christopher Hendon did was he replaced that whole concept of TDS and instead focused on two other specific ways we can measure our water, total hardness and alkalinity, two concepts that we are still using today. And if you've heard the previous two episodes, you should be pretty familiar now with these two concepts.

Total hardness measures how quickly your machine can get gunked up with limescale, and alkalinity looks at how quickly the water neutralizes acids in our coffee. And of course, we don't want alkalinity too high because then it takes away those beautiful acids in our coffee. But what's interesting about the book is that it's not so much a practical guide as like a crash course in chemistry.

Professor Christopher Hendon:

So what we started with in the book was a discussion of where atoms come from and understanding the process of creating atoms which you can then use to build molecules, which you can then understand function of molecule once you've got a collection of them together in a liquid.

James Harper:

The book was essentially an undergraduate water chemistry textbook for coffee people.

Professor Christopher Hendon:

But we were trying to teach people more than water. We were trying to teach them scientific process and reasoning.

James Harper:

And it was such a novel concept at the time that they bootstrapped the publishing of it.

Professor Christopher Hendon:

Yeah, we self-published the book because we felt as though we were talking about a scientific topic that people did not have a resource at the time.

James Harper:

So the book, it's making waves in the coffee community. But another thing that makes an enormous splash is what Christopher's partner in the project, Maxwell Colonna Dashwood, the cafe owner in Bath, did on the World Barista Championship stage.

World Barista Championship Announcer:

Please give it up for the barista champion of the United Kingdom, Maxwell Colonna Dashwood.

James Harper:

This was the 2014 World Barista Championship in Rimini, Italy. And I wasn't there personally. But Sergio Barberisi, a former part of the BWT leadership team, was in 2014.

I'm sure you remember.

Sergio Barberisi:

He was there and remembers that moment like it was yesterday. 2014 in Rimini, it was the moment when at the World Barista Championship, a guy from the UK, it's Maxwell Colonna Dashwood, went onto the stage.

Maxwell Colonna-Dashwood:

Speciality coffee takes each of us to some strange places. For me, it was a chemistry lab at the University of Bath about a year ago. Now, the purpose of my visit was to collaborate with a computational chemist to try and answer some of the mysteries about the way brewing water impacts on the flavor of coffee.

Sergio Barberisi:

In front of the judges, he started to talk about the fact that he that he roasted this coffee for the competition according to the water that he knew he was going to find in Rimini in the competition.

Maxwell Colonna-Dashwood:

And after testing the water here today and noting that the buffer is high, the roast I'm choosing to serve you has a lower end temperature and a shorter development time. I want to make sure that the complex sweet acidity that makes this coffee so special comes through that buffer.

James Harper:

And by the way, what Maxwell was saying on stage was that the water in Rimini, he knew that it had a very high alkalinity, which as we covered in the first episode, getting great water for coffee step by step. A high alkalinity means that the coffee's acids are going to get wiped out. And so what Maxwell did for the competition was roast his coffee in a way that brought out more acidity.

And so when he brewed his coffees on stage, like even though the water was neutralizing a lot of acids, he had so much acid in the first place that quite a lot of it still got through so we could taste it.

Maxwell Colonna-Dashwood:

What I've done here is I've actually taken water and my understanding of it back to the roasting level. Because when you think about it, water probably impacts on a roaster more than anybody else. In essence, they're actually roasting their coffee to a given water.

Sergio Barberisi:

And that was absolutely astonishing for the people. And the rumors spread so quickly into the halls of the World of Coffee show that everybody were rushing to the stage to hear this guy talking about the water. That was the real turnaround.

James Harper:

So the book Water for Coffee and Maxwell's presentations, they're making huge waves in the world of specialty coffee. And this is all great, although the book did have its critics. More on that coming up next.

So Christopher Hendon and Maxwell Colonna Dashwood, they've released this book Water for Coffee. It's a groundbreaking piece of work for the coffee community. It's creating a lot of buzz.

And of course, Maxwell is presenting Water for Coffee on the World Barista Championship stage, creating even more buzz. And as a result of all this, the book sells a lot of coffees. Well over 10,000.

But of course, it's not just specialty coffee people who are reading this book. Other academic chemists who had a strong interest in coffee also got hold of the book. For example, it landed on the desk of Professor Shahan Yeretsian at the University of Applied Sciences in Zurich.

Professor Shahan Yeretsian:

I'm Shahan Yeretsian. I'm a professor in the Institute of Chemistry and Biotechnology. I'm heading the Coffee Excellence Center, which is a center focusing on the science of coffee.

James Harper:

Okay. So a book came out a few years ago by Christopher Hendon. When you read it, what were your thoughts?

Professor Shahan Yeretsian:

Well, that's essentially where we decided to go into that subject. Because when you read it, we realized that there were some major scientific errors that would be misleading the whole community.

James Harper:

Now the reason Shahan is quite critical of the book is because Christopher's approach and the way he presented his recommendations for Water for Coffee are quite different from how a more conventional academic chemist would approach the topic. And listen, I don't want to go into the deep, deep details of this. It's really a case of like a lot of small critiques building up into a larger critique.

And to give you like one tiny example, when discussing a good mineral concentration in water, Christopher used milligrams per liter.

Professor Christopher Hendon:

So we recommended an upper limit of something like 70 milligrams per liter of bicarbonate as the ion floating around.

James Harper:

Now quick translation, bicarbonate is just an older term for hydrogen carbonate. And as you might remember from the first episode, Getting Great Water for Coffee Step by Step, hydrogen carbonate is the thing that neutralizes acids. As in, water with a lot of hydrogen carbonate has a high alkalinity.

And so what Christopher is saying here is that the amount of hydrogen carbonate in water for coffee should not be more than 70 milligrams per liter. Because more than that is going to neutralize a lot of acids and make our coffees taste lame. And here's the thing, in chemistry, you can express the amount of hydrogen carbonate in water in lots of different ways.

One is weight, milligrams per liter, which is what Christopher used. You could also use moles, which is like the number of them.

Professor Christopher Hendon:

But Christopher used weight because... It was to teach people that water starts out with nothing in it. And you can go ahead and weigh out stuff and then you can taste the difference yourself.

That's on you to figure out what you like. But you're going to do it by weighing it.

James Harper:

But to more conventional chemists, such as Chahan, he didn't think milligrams per liter was the appropriate unit.

Professor Shahan Yeretsian:

It's not linked to the reality of what the coffee community needs.

James Harper:

And why would it be problematic if we use milligrams?

Professor Shahan Yeretsian:

It's absolutely correct. You can measure the weight of magnesium and calcium, but it doesn't help you to develop a story that goes into application.

James Harper:

And so other chemists have explained to me that if Christopher had used a different measure, for example, if he'd chosen to use moles, which is the number of hydrogen carbonate molecules floating around in the water rather than their weight, then water compositions could be more accurately defined. And it'd be more easy to compare waters in different cities and their respective mineral compositions. But despite all of that, the academic chemists in Zurich did start a dialogue with Christopher, raised their concerns.

And in some cases, he does agree with the feedback.

Professor Christopher Hendon:

He was right in saying that if we still go by mass, we can't decouple calcium and magnesium, which is true. And we have fixed that.

James Harper:

And Christopher told me that he's planning to incorporate these changes in a new edition of the book that he's currently working on. And during my conversation with Christopher, when we took a step back and reflected on the impact of his book, Water for Coffee, the way he sees it, it contributed to what has become a total sea change in the world of coffee science.

Professor Christopher Hendon:

Because what it resulted in was the beginning of the SCA directly investing in science. SCA, the industry's major trade group, the Specialty Coffee Association. So even if it was inflammatory and even if I didn't make friends initially, those people that I didn't make friends with initially are now very close friends.

James Harper:

So what did the coffee trade bodies actually do after the publication of Christopher Hendon's book?

Frank Neuhausen:

Well, I spoke to somebody who was on the board at that time. I also joined the SCA in the board of directors. A senior leader at BWT.

My name is Frank Neuhausen. I'm working for BWT Water & More since about 17 years. The publication of Christopher's book was personally a wake-up call for him.

This was, let's say, one of the starting points of getting deeper and deeper in all the discussions about water for coffee. And what we also did in parallel is we worked together with the University of Zürich and prepared, I think it was in 2015, the first booklet on water for coffee.

James Harper:

So essentially, BWT, a water filtration manufacturer, partnered with the Coffee Excellence Center at the Zürich University of Applied Sciences, headed up by Caghan Yeressin, who we heard earlier, and together created the Specialty Coffee Association's Water Quality Handbook. Link in the show notes. The approach of the book was very different to Christopher Hendon's.

They didn't try to teach the fundamentals of water chemistry. It was a much more practical manual. Here's Caghan Yeressin again of the Coffee Excellence Center.

Professor Shahan Yeretsian:

And we developed the concept of measure, aim and treat.

James Harper:

Measure the minerals in your water. Aim towards where you would like the mineral composition to be. And treat.

Apply appropriate filtration to get you there. And they also established what might be a good range for the mineral composition in your water.

Frank Neuhausen:

A zone that ensures both a very good extraction and avoiding corrosion and avoiding limescale.

James Harper:

And just kind of curious, does this sound familiar to you? Because my first episode in this little mini-series, Getting Great Water for Coffee Step by Step, I framed my entire episode around this approach. This measure, aim, treat approach.

It's basically the SCA's Water Quality Handbook in audio. Okay, but now I want to look at the question, What exactly is the ideal range for great water for coffee? Okay, well, the two most important things are, How hard is the water?

As in, how likely is it to gunk up your special machine boiler or your kettle with limescale? This is the total hardness of the water. And also, how likely is the water to neutralize acids?

This is known as the alkalinity of the water. Now, the SCA and Christopher Hendon's recommendations overlap quite a lot on these two measures. And if you want those specific numbers, there's a link in the show notes.

And this is all well and good. These two measures, total hardness and alkalinity, they are the most important things for water for coffee. But they're not the whole story either.

There are other things too that contribute to flavor in more subtle ways. The specific minerals in your water. And the thing is, there are many types of minerals you could have in your water.

You could have calcium, magnesium, sodium, potassium, chloride. Each of them will affect your coffee in subtle ways. For example, the water mineral sachet company, Third Wave Water, they've determined that for lighter roasted coffee, the best minerals are magnesium, calcium, and sodium.

With a little added bit of citrate. But I want to focus on the first mineral in that ingredient list, magnesium. Because a growing body of evidence suggests that magnesium is what we want in our water for coffee.

For example, after publication of the Specialty Coffee Association's Water Quality Handbook, Frank Neuhausen at BWT partnered again with the University of Applied Sciences in Zurich to study how magnesium affects coffee's flavor.

Frank Neuhausen:

And the outcome, more or less, is that the typical flavor of a coffee that is, let's say, desired or the target of a roaster, more or less easily can be achieved if you have a high ratio of magnesium versus calcium.

James Harper:

And this research was published in a whitepaper, which I've linked in the show notes. So the emerging consensus is that magnesium tends to make specialty coffees more vibrant. And now, I want to take a moment to clear up three common misconceptions I see floating around in coffee internet.

Misconception number one. Magnesium is not the only mineral that matters. Different minerals add different things to the coffee.

And we think the best water for coffee is actually a combination of many minerals. But for sure, magnesium is a very important one and might be the largest one. Okay, now, misconception number two.

Minerals don't add flavor to the coffee. You know, when we add magnesium to water, it's not like we're adding flavor to the coffee. It's not the same as adding something like sugar.

You know, if you add sugar, then it tastes very sweet because you can taste the sugar. But you can't really taste the magnesium. These minerals interact with the coffee in very subtle ways to bring out the intrinsic flavors of the coffee.

We're not adding flavors. It's more like it's helping bring out flavors from the coffee. And now, here's my third and final misconception I want to clear up.

We don't really know why minerals impact coffee flavors. Out in the coffee blogosphere, you'll find a theory that's often quoted for why certain minerals impact coffee flavors. The theory is called binding energy.

And it is just that. It is a theory. But it may not be the right theory.

And this theory of binding energy actually came from a paper that Christopher Hendon wrote in and around the time the book Water for Coffee was published. Maxwell Colonna-Dashwood then also spoke about that theory on the World Barista Championship stage, helping popularize it. The idea is, you know, there are magnesium molecules that are missing a couple of electrons floating around in the water and they bind better with some of the organic acids in the coffee, thereby kind of bringing them out into the coffee brew, making the coffees taste fruitier.

But binding energy as a theory has its critics, like Samuel Smerquet of the Coffee Excellence Center. Now, he wasn't denying that binding energy is a thing. It's a real phenomenon.

And it absolutely has an effect on coffee flavor. He even brought up a little bit of research he had read recently about binding energy and how it interacts with acids in coffee. But the problem was the water they used in those tests had extremely high levels of magnesium, much higher than you'd find in a cafe.

And then he suggested a totally different explanation entirely. Maybe magnesium is playing around with something on our tongues instead. So, all this to say, minerals matter for the flavor of our coffee.

But why? What they're actually doing? We just don't know.

This is an area of ongoing research. So, I hope you've enjoyed this journey into water for coffee these last three episodes. What I've shared here is a simplified version of a much more deep, complex world.

I didn't even cover things like ions, electrical balance, pH, and how all these things might interact with coffee extraction and our flavor receptors. If you want to go deeper, I strongly recommend reading the SCA's Water Quality Handbook. And also Christopher Hendon says he's coming up with a new updated book, Water for Coffee, which I strongly suggest you pick up once it comes out.

You can find him on Instagram at chhendon. And if you just want to have some nerdy fun, there are corners of Discord and Reddit where homebrewers and professionals are experimenting and tweaking water recipes. And what you could also do is take the Certificate in Coffee Excellence offered by the Coffee Excellence Center in Zurich.

It's a virtual course where you will have trained academics taking you into the science, especially water science. Link in the show notes for that. And if you want a practical guide on how to get good water for coffee, listen to the end of my episode, A Beginner's Guide to Good Water for Coffee.

Now, if you want to keep following along with my work, you know, the stories behind these episodes, the ideas that I didn't quite manage to fit into the audio, my personal journey with this podcast, I share all that on my Substack newsletter. You can subscribe to my Substack through the link in the show notes. And you can also follow me on Instagram at filterstoriespodcast, where I post infographics, visuals, that will help explain and cement a lot of the concepts that we explored across these episodes.

James Harper:

My Instagram again is at filterstoriespodcast. Link in the show notes as well. Filter Stories is produced by me, James Hartog, and I also write and play the piano music.

Thank you again for listening, and I'll speak to you next time.