Do you and I taste the same flavours?

James Harper: It's June 2023. I'm in Athens, Greece. It's a really hot morning. Sun high in the sky. And I step off a bus at the airport. No, I'm not catching a flight, I'm actually attending the Specialty Coffee Association's World of Coffee trade show, which is taking place next door to the airport. And I'm here very early in the morning, because later in the day, I'm going to be doing an experiment by putting a question to the test. What's going on inside my head, different to you, when we taste the same coffee? In the last episode, I explored how our sense of taste and smell works. In the previous series, I explored how things like sounds affect what we taste, and I got to wondering, are we actually living in the same flavor universe? Because I began to come across a lot of genetic evidence, cross modal evidence, cultural evidence, to suggest that when we drink the same coffee, we might actually be tasting different things.

So here in this coffee trade show in Athens, I'm gonna give the same coffee to lots of different people and discover whether they're actually tasting the same thing. But for this experiment to work the coffee has to be the same, which is why I walk across the trade show to the Marco Beverages stand.

Marco is the sponsor of this episode Because they are a leader in making brewing equipment for cafes. And at the stand I meet Renee Callis. Rene is going to help me brew up many, many batches of the same filter coffee. But here's the thing: It's actually very difficult to do consistently. I explored in the previous series how there are so many variables that can make a simple pour over coffee quite inconsistent from batch to batch. Temperature. Time. Flow rate. But Marco developed a solution to this – The SP9.

It's a countertop brewer for cafes that automates a very delicately made hand-poured filter coffee. It delivers a very precise amount of water in a very precise amount of time, at a very precise temperature. So Rene showed me how to make many, many pots of the same coffee on the SP9, and he was assuring me that all these brews would be the same. But I needed even more certainty, so I decided to test these coffees with a refractometer, a device that measures how strong a coffee is. And then came the results.

Coffee number one. The first coffee had a TDS of 1.48 basically in this water, 1.48 percent of it. Has coffee compounds floating around in it. Then, coffee number two. And finally. Coffee number three. Now I knew my TDS meter had a margin of error to it. So I did even more tests and I was satisfied that every batch of coffee was going to be almost identical and so much more consistent than if Rene and I had stood there making these coffees ourselves, pouring this water out of a kettle ourselves, batch after batch. And I mean, you would have to be spot on with your hands, which is almost impossible to do and to replicate that.

René Kallus: So I think if we know that's now three brews, if we did say a thousand brews, that would still be spot on. But in a thousand brews with a human being, you would see massive differences.

James Harper: Okay, so I had many pots of the same coffee and then over the next couple of days came some Filter Stories listeners. I'd done a shoutout on Instagram and a whole bunch of people had raised their hands saying, "Hey, yay, I'd love to be a taste tester for your experiment, even though I don't really know what you're going to do to me." And then I gave everybody an identical coffee and I got very, very different answers.

Bram De Hoog: It's sweet.

Callum Gilmour: This is quite chemically.

Emmanuel Dias: There is a bit of orange taste, orange peel.

Miroslav Ocenas: Maybe something green in.

James Harper: Dark chocolate.

Abbie Manning: Almost tea-like.

Jeff Daou: Woody astringent finish.

James Harper: This is the same coffee. But it was being described as sweet, chemically, orangey, green, dark chocolate, tea-like, and woody. I mean, I couldn't believe it. How can this exact same coffee taste so different to different people? I needed to know, what on earth is going on? Is my tasting reality the same as your tasting reality?

So, to begin with, we'll look at your flavor receptors on your tongue and in your nose. Are my receptors the same as your receptors? Are we getting the same information? Then I'm going to explore cross modal effects, other things in the environment which might change how you perceive coffee relative to me: the type of cup you're drinking it from, the music you were listening to. I finished by looking into the muddiest, most complicated aspect of all of them, and that is our lived experiences, our cultural backgrounds.

Are you ready for this? Because we're about to get metaphysical.

James Harper: I'm James Harper, and this is The Science of Coffee. A spinoff series from my documentary podcast Filter Stories and a journey into coffee's hidden microscopic secrets.

So, first question, genetically speaking, are my smell and taste receptors the same as yours? Now, back at the trade show, in Athens, at the Marco Beverages stand, I did an experiment and got some weird results. So, I had just brewed up many pots of coffee on Marcos SB9 brewer, and I was satisfied they tasted the same, they were brewed consistently, but then I added different types of artificial sweeteners. You find artificial sweeteners everywhere. Monster Energy Drinks, Coke, you name it. But it turns out, you and I could perceive it quite differently. For example, when I added the artificial sweetener stevia to coffee…

Carolina Pirola: It's sweet. It's not bitter.

James Harper: A group of people said, "Yep, this is very sweet."

Miroslav Ocenas: This is loaded up with sugar.

Callum Gilmour: Yeah, very, very sweet.

James Harper: But then this other group of people said, "Yeah, okay, it's sweet, but it's also bitter."

Jeff Daou: I'm confused here. It's, um, sweet and bitter. Bittersweet.

James Harper: And that's the group I fall into. I find Stevia, yeah, sweet, but also horribly, horribly bitter as well. So, here we have a situation where some people find Stevia sweet, and others, like myself, find it sweet and bitter. And then things got even more strange because in a different pot of coffee, I added in a different kind of artificial sweetener. Ace K, a sulfan potassium. It's like people just traded places, right? So, the group that said Stevia was sweet, not bitter, just sweet, now they're telling me that Ace K, this different type of sweetener, is also bitter.

Callum Gilmour: This is more bitter than the last one. Uh, for sure.

James Harper: And then the other group of people who found Stevia horribly bitter and sweet, now the bitterness disappeared and it was just sweet.

Jeff Daou: Too sweet.

James Harper: What on earth is going on? So I got inspiration for this test when I spoke to Professor Helena Hopfer.

Helene Hopfer: I'm associate professor in the Food Science Department at Penn State.

James Harper: She suggested I do that experiment, because it shows that genetically speaking, the receptors on your tongue are different to the receptors on my tongue.

Helene Hopfer: John Hayes, my colleague here, he has shown that bitter taste receptor R31 is activated by certain non-EU sweeteners where people get the sweetness but they also, depending on the genetic variant, might get quite some bitterness from it too.

James Harper: So yes, genetically speaking, you and I might have different taste receptors. We might be drinking the same thing, but it literally tastes different to you and me. But it doesn't stop at the receptors in our mouths; there is also genetic variation in the aroma receptors in our nose. For example, Naglich, professional Taster and author of the excellent book, How to Taste.

Mandy Naglich: One that I talk about in the book is beta ionone, the scent of violets.

James Harper: She told me about violets.

Mandy Naglich: You could obviously live your whole life very happily without ever being able to smell a violet. You would never know. There's about a third of the population who can't smell that compound.

James Harper: You and I could be drinking the same coffee And I could say, ooh, I have a nice note of violet and because of your genetics, you're never gonna know what that smells like.

Mandy Naglich: No matter how much training you do, if you don't have the gene for beta ionone, you're not tasting it.

James Harper: So genetically speaking, your receptors are different from mine, but how big is that difference? We have hundreds of different types of aroma receptors in our nose. Is it just one or two which are different? And to get an answer, I spoke with Joel Mainland of the Monell Chemical Senses Center.

Joel Mainland: On average when we looked at these receptors in the lab, we found that about 30% of yours are functionally different from mine.

James Harper: And when he mentioned 30%, I was like, "Oh my Lord! That's enormous!" If we were talking about color, that's like, I'm looking at a wall, and I say it's painted blue, and you say it's painted red. However, Joel went on to explain that actually it's not that dramatic.

Joel Mainland: So there's a lot of difference, at this sort of low level for specific compounds, but once you get to sort of complicated mixtures, it blends away a little bit. So your perception of something and my perception of something will be different, but usually not dramatically different.

James Harper: So, although there are cases where one very specific aroma, like the aroma of violet, you might be able to smell it and I just can't, the thing is, most aromas we encounter are really complicated. There's a whole mixture of different sorts of aromas all coming together. Take the example of coffee – coffee is not just one specific aroma.

Joel Mainland: You have these nutty notes, these purines that give you the nutty notes. You have different esters that add these fruity notes to it.

James Harper: There are so many different types of aroma within coffee. And so when we breathe it in, it triggers a suite of different receptors, not just one receptor. And even though the aroma receptors are different in my nose compared to you, our brains get enough information to be able to say conclusively, okay, yep, you and I, we can both agree, this coffee is fruity. However, it could also be the case that, you know, in that coffee you might have this really distinct smoky note coming through and that specific aroma I may not get because I just don't have the receptor for it.

Joel Mainland: At the same time, you might have individuals who think the coffee is very smokey and another person thinks it's not very smokey at all. And that might be just some genetic difference.

James Harper: And what I find really weird about this is that smokey note. It is absolutely there in the coffee and it's also not there in the coffee. Both are true at the same time. It just depends who's tasting it and what their experiences are. It's really trippy to think about, and I start to wonder how do we come together as a society, as coffee lovers, and say, this is what this coffee objectively tastes like. The way that Joel gets a handle on what's going on here is he gets as many people in a room as possible to taste the same thing and then look at what the average flavor experience is.

Joel Mainland: You have around 15 people on the panel, they will look about the same as another panel of 15 people.

James Harper: And so what Joel sees is that on average experiences of a coffee are the same, on average. Zooming out, do genetic differences in our receptors explain why I got such a variety of responses to that same coffee? After exploring it this far, I've landed in a place where, on the whole, we do broadly perceive the same thing, but there are subtle differences, and sometimes quite major differences. The analogy I use is, imagine you and I were staring at a white wall. I say, "it's more of an eggshell white, you know, slightly warmer." And you say, "mmm, to me it's a bit cooler. It's more like snow reflecting a blue sky on a winter's day." You and I, we both see this wall as white. They're just slightly different shades of white. and then our friend walks into the room, stares at that same wall, and says, "you know, this wall, it's a white wall, but it's got this distinct green sheen to it." You and I look at each other and we're like, "uh, okay, well we don't see that, but who are we to tell you what you are seeing?"

If this were a coffee, you and I say, "hmm, yeah, this is a medium roasted coffee, it has notes of chocolate," and along comes our friend, and says, "I'm getting a distinct smoky note, we might not taste it, but we can't deny that our friend is experiencing that smoky note." Now I have also come to the conclusion that genetic differences alone do not explain how I can give the same coffee to many different people and they give me such a crazy array of flavor notes. No, there must be other things going on. And so next, we're going to explore cross modal effects – how our environment shapes what we're experiencing.

The second question I explored was, when you and I drink the same coffee, was there something in our environment, what we saw, what we heard, what we felt, that changed the flavors of the coffee and back in Athens, at the Marco Beverages stand, I tried out another experiment. I used the same bag of coffee and brewed a few batches of filter coffee using the SP9, so I was happy with how consistent they were going to taste. Part one of the experiment, I just gave this coffee to my taste participants and asked them what it tastes like. Now, the coffee itself was a high scoring, naturally processed red bobon from the Café de Maman's Women's Project in Northern Rwanda, roasted by my favorite roasters here in Berlin, 19 Grams. And as predicted, everyone said, Yep, it's quite lovely.

Bram De Hoog: That's nice. That's very good. Um, definitely a lot of fruity notes in it.

Miroslav Ocenas: I get sweetness. Not much bitterness.

James Harper: Then came part two. I asked them to put on a pair of headphones, and then I played them some super angry, intense rock music. And here's the thing, a lot of my taste testers suspected they were tasting the same coffee.

Linda Bartoshuk: Are you giving me the same coffee?

James Harper: But despite that, the music changed their perception.

Carolina Pirola: It's more bitter than the previous one. I mean, it might be the same one, but the music is making me angry. I feel like the bitterness is starting to cancel out the sweetness a little bit.

James Harper: Other taste testers, like Miroslav, were fans of this royalty free track that I just plucked off the internet.

Miroslav Ocenas: Yeah, it sounds like my playlist.

James Harper: Oh, really?

So angry rock music, no surprises, coffee tasted more bitter. This is an example of a cross modal effect, how one of our senses affects the other sense. For example, what you hear affects what you taste. And I was inspired to do this rock music experiment after I spoke with cross modal researcher Janice Wang.

Janice Wang: I'm an assistant professor of Food Science at university.

James Harper: And she spoke about some experiments she did looking at music and how it changes what we're tasting. In one experiment, she gave participants this juice that was both sweet and sour and asked them to put on a pair of headphones.

Janice Wang: They heard a little melody that was either harmonized with consonant interval or dissonant interval. And what we found was that the fruit juice tasted more sweet when they were listening to the constant music and the juice tasted more sour when they were listening to the distant sound Genesis' theory is that we associate sweetness with pleasant emotions, and sour and bitter with unpleasant emotions.

James Harper: Music stirs our emotions, which can lead us to focus on different aspects of a complicated drink, like coffee which can be at the same time bitter, sour and sweet. And when I think back to that tasting experiment at the Athens trade show, at the Marco Beverages stand, where I did the tastings. They were very close to a coffee competition stage, and you could hear the music from the stage. Could that have influenced what people were tasting?

And here's another thing, too . In the last series, I showed you a study done by Felipe Reynoso, where he asked people to put on these headphones and he played very loud, cafe sounds like up to 85 decibels. And the majority of the participants told him that their coffees tasted more watery. Here we are in this loud environment near a coffee competition stage. Was that making people's coffees taste more watery? Or stronger, because about 20% of his participants said, when they were listening to very, very loud cafe sounds, the coffee was more intense. They tasted more sweet, bitter and acidic. So you have more than half the group saying that coffee tastes more watery. But there's a proportion of people, 20% or so, who say, "actually, we think coffee tastes more intense in a loud environment." Sound influences different people in different ways. And these cross modal effects, they go well beyond sound, you know, even the shape of the coffee cup can influence what you taste. I learned this speaking with Brazilian researcher Fabiana Cavalho of the Coffee Sensorium.

Fabiana Carvalho: I am a neuroscientist. I've been doing research in neuroscience for 23 years.

James Harper: And I want to tell you the story of a really interesting experiment she did in 2017. Now in the world of wine, this is a very well known phenomenon.

Fabiana Carvalho: So there are lots of articles that demonstrate that the shape of the wine glass can affect the way people perceive the wine.

James Harper: But does that same effect translate in the world of coffee? So, for this test, Fabiana needed different types of coffee cups. So she went clicking around the internet and discovered there is a well known specialty coffee roastery in Norway called Tim Wendelboe, founded by a guy called Tim Wendelboe, and Tim and his team had designed these quite unusual looking coffee cups, which they said would bring out different attributes in a coffee.

Fabiana Carvalho: So these cups should be used for, uh, more acidic coffees. This one should be used to sweeter coffees.

James Harper: And I want you to picture two of those cups. The first was shaped like a tulip bulb.

Fabiana Carvalho: Bulbous cup, wine glass shape.

James Harper: Wider at the base, and then getting narrow towards the top. That's the first cup, the second cup is what Tim Wonderbo called the split cup. Because it resembles an hourglass.

Fabiana Carvalho: So it's a cup that has an indentation in the middle.

James Harper: The tulip bulb cup and the hourglass cup. And on the website, Tim Wunderboe stated that the cup that looked like the tulip bulb would be good for enhancing sweetness and that the hourglass shape, the split cup, would be better for... acidity. Fabiana was a bit curious. What kind of tests had Tim and his team done to make these claims.

Fabiana Carvalho: So he replied to my email saying that, wow, we did some in-house testing, you know, with my team. So around six, seven people.

James Harper: With so few people doing the test, Fabiana wasn't convinced about these claims.

Fabiana Carvalho: So it's not really a scientific sampling size, and also biased because they participated in the development of those gaps.

James Harper: Now, Fabiana had plans to visit a coffee trade show in Brazil.

Fabiana Carvalho: And then I asked him if he would be willing to put those cups into a test, actual test, you know, with hundreds of people. And he said, oh, absolutely.

James Harper: And so these cups which had been developed in Norway made their way to Brazil. And Fabiana got some rather intriguing results.

Fabiana Carvalho: But what we observed was that the bulbous cup enhanced the aroma perception.

James Harper: So the cup that looked like a tulip, you know, the classic kind of wine glass shape, for Tim and his team, it enhanced sweetness, but Fabiana's participants said it enhanced aroma instead.

Fabiana Carvalho: And that was our hypothesis in the beginning, because it's very similar to, uh, windless shape. And then regarding the hourglass shaped cup…

James Harper: Tim's team for them said it increased acidity, and for Fabiana's participants, it too increased acidity, but also sweetness.

Fabiana Carvalho: The coffee was perceived as sweeter and more acidic when tasted from the split cup.

James Harper: And so Fabiana discovered that, yes, the shape of cups do influence your perception of a coffee, but for her participants, not the same way that Tim and his team had described it. So, those sound experiments, the cup experiment, they're just some of the many ways in which our environment affects our perception of a coffee. But going back to that tasting at the Marco Beverages stand, where my participants gave me very different descriptions of the same coffee. These cross modal environmental effects, how big of an effect do they really have? Going back to my white wall analogy, are these cross modal effects big enough that you know I will look at a white wall and say that looks white to me and you look at it, and you say, no way! That wall is blue! So here's the thing. In Fabiana's experiment…

Fabiana Carvalho: The differences were statistically significant…

James Harper: She had low p values, which is a good thing, because it means that there's a very low probability that the result she got was just from random chance. But the issue is more the size of the difference. I mean, it's not nothing, but it's not earth shattering either. For example, she found the differences in the intensity of aroma went from level five to level six on a ten-point scale. Like I said, it's definitely an effect, but it's not night and day either. and that's roughly the same level of change that I saw in Jannas Wang's sweet sour music experiment. So going back to those very different responses I got to the same coffee, how much of what we've just learned explains these differences? Genetic differences between my receptors and your receptors? Okay, yeah, there's a small difference there. Cross modal influences and things in the environment that affect us all differently? There is a small effect there too.

But you know, both of those combined don't explain just how dramatic the differences were in what flavors people were experiencing. And so I continued looking around and then came across another possible explanation.

The third explanation I investigated for why I was getting such a wide range of responses to the same coffee is differences in our lived experiences. This is a very, very broad category. Catches a lot of different things but it boils down to the fact that I have lived a different life to you, everything that I've experienced and learned in my life and how that's wired my brain is going to be different to you, and to show this effect, I did one final experiment at the Marco Beverages stand in Athens. One morning while I was waiting for the bus to take me to the convention center, I dived into a local Greek supermarket, and I picked up a bottle of local liquor, 40% alcohol. This thing had a punch. And then at the end of my tasting experiment, I gave each participant a shot of this alcohol. And for some of my taste participants like Bram, "Yeah, I like it. Okay. Lovely. Yeah." Honestly, he could have been describing a dessert.

Bram De Hoog: Elderflowers, citrus seed. Sweet. It's super, super nice.

James Harper: However for another taster, Carolina, she's someone who doesn't drink very often and when she does, sticks to a light sweet mojito.

Carolina Pirola: Oh my God. What is this? This is like vodka times three. Is it like pure alcohol? What are you giving me, James?

James Harper: Could not get over that alcoholic punch!

Carolina Pirola: Paint thinner. There you go. That's what it is. I'm poisoned.

James Harper: So how is it that Bram drinks this, tastes elderflowers, citrus, and then Carolina tastes it, and it tastes like paint thinner. You just can't get over the alcohol. Now I got inspiration for this test when I was speaking with Professor Helene Hopfer And she was mentioning to me some research done by Ilya Kroymets.

Helene Hopfer: She's a linguist.

James Harper: So the experiment had three groups of people: wine experts, coffee experts, and regular consumers. They each drank coffee and wine and were asked to name all the different flavors they were tasting.

Helene Hopfer: It found that coffee experts were really good at pulling out small differences within their products, but once they were faced with wine, they weren't so good. They were just like an average consumer. And same for wine experts as well. The coffee experts were really great at saying, "um, yeah, this coffee has got aromas of cacao and blueberries and a hint of tea."But when it came to wine, the coffee experts were like, "yeah, tastes nice, uh, kind of fruity."And the same thing happened with the wine experts.

James Harper: They'd drink wine and be like, "oh yeah, mmm, delicious, it's got these notes of elderflower and jasmine, ripe apples,"and then they'd taste the coffee and be like, "yeah, it's nice, it's uh, uh, fruity coffee" and so going back to the hard alcohol…

Bram De Hoog: Elderflowers, citrus seed. Sweet.

James Harper: Bram was getting all these flavor notes, because compared to Carolina, he's an expert who savors spirits on a regular basis. He even has a certificate from a rum tasting course he did almost 10 years ago. But Carolina, on the other hand, has no knowledge of the product. What Bram has that Carolina doesn't is language. A language around flavors for spirits, which he has spent a lot of time learning.

So, reflecting back on my tasting experiment where I got a whole range of different responses to the same coffee. One reason these responses are so wildly different is because some are more expert at putting names to flavors than others. So that's one explanation. Okay, so, moving on now, another reason that could explain why those flavor responses are so different is because you and I grew up in different places, and I got this insight when I spoke with a coffee tasting expert.

Freda Yuan: My name is Freda Yuan, I am the three times UK cup tasting champion.

James Harper: Freda Yuan is from Taiwan in Asia, but now lives in the UK, and she told me a story about how, when she came to the UK as an adult, she worked in coffee, and she'd see a flavor description on a bag of roasted coffee, and it would say blood orange. But the thing is, blood oranges? Very hard to come by in Taiwan.

Freda Yuan: So for me personally, again, I never tried blood orange before I came to the UK. So I never really know how it should taste like.

James Harper: So you probably have tasted foods that I have never tried, and when I encounter hints of those aromas in a coffee, you'll be able to name it and I'm gonna struggle. Now, another thing that might be going on too, is that, you eat apples, I eat apples, but maybe our apples don't taste the same.

Freda Yuan: My apple from Taiwan doesn't mean it tastes the same as your apple here in UK, and so therefore it's really, really hard to really put down a word saying this coffee tastes like apple.

James Harper: Now, fortunately, this problem is solvable. Joel Mainland from the Monell Chemical Sensor Center told me how to calibrate everyone so they have the same words for the same flavors.

Joel Mainland: When we train people to be panelists for us, we do sort of about four hours of training, and in that training we'll give them a kit of reference odors that they'll use to sort of learn what these words actually mean.

So when I say green, what does that mean to you? Right. The green smell. Here's a jar that has a green smell in it. You learn very clearly what the correspondence is between the word that you're using and what's in the vial.

James Harper: So I began this journey wondering whether when we taste the same coffee, are we actually having the same flavor experience? And this is where I've landed. There's a good chance that you and I will broadly taste the same thing in the same coffee but sometimes there will be a flavor in there that you pick up on, which I won't, which could be down to our genetics, crossmodal effects and how the same sort of background noise or music or the cups of drinking affect us differently. It has a small effect as well. And I think the differences in our lived experiences, how expert we are at putting names to different coffee flavors, I think that explains most of the differences in the terms I was hearing when people described the same coffee. Because maybe the craziest thing of all is that coffee can be all those things at once which is one of the many reasons I still love working in coffee. It's just so fascinating.

Now all the reasons I've covered in this episode for why people can use such different terms for describing the same coffee. There are many more reasons too that I haven't had time to cover and I would love to cover them in a future series, and one thing I haven't touched on today, but it is so fundamental to coffee, and I absolutely will cover it in a future series, is preferences. Do people like one coffee over another? What determines quality? What even is quality? I invested a couple of weeks digging into trying to answer that question for this episode, and I decided, no, no, no, no.

This is a huge task. I'm gonna leave it for the next series. So stay tuned for that. However, in this series, in the next episode, I'm gonna be covering the weird wonderful chemistry taking place inside our roaster, how you turn green beans brown and where flavors come from, chemically speaking. And I cannot wait to share it with you.