#86 | Elucidating the Bitter Taste of Coffee | Expo Lectures 2019

#86 | Elucidating the Bitter Taste of Coffee | Expo Lectures 2019

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Coffee shows an appealing bitterness when properly roasted and prepared. But how do the compounds that make coffee taste bitter develop during roasting and how do you analyze and identify them? What lessons can be learned from academic research on coffee roasting to make coffee even more pleasantly bitter-tasting? And after a century of intensive research, why does research still not know exactly what makes coffee bitter at all?

Learn more as Dr. Sara Marquart, curator of the “Cosmos Coffee” exhibition at the Deutsches Museum, shares excerpts of her academic research into bitterness during her Ph.D. at TU Munich in Food Chemistry focused on the highly sophisticated elucidation of reaction pathways and kinetics leading to bitter tastants in roasted coffee. 

Also, I will jump in occasionally to help you follow along. 

Special Thanks to Softengine Coffee One, Powered by SAP 

This episode of the Expo 2019 Lectures podcast is supported by Softengine Coffee One, Powered by SAP.  Built upon SAP’s business-leading Enterprise Resource Planning solution, Softengine Coffee One is designed specifically to quickly and easily take your small-to-medium coffee company working at any point along the coffee chain to the next level of success. Learn more about Softengine Coffee One at softengine.com, with special pricing available for SCA Members. Softengine: the most intelligent way to grow your business.

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Episode Table of Contents

0:00 Introduction
2:00 An overview of coffee’s sensory universe
8:15 The different types of bitterness and Sara’s work discovering what bitter compounds are in a cup of coffee
19:15 How to control for bitterness during roasting
24:30 Audience Questions

Full Episode Transcript

0:00 Introduction

Heather Ward:  Hello everyone! I’m Heather Ward, the SCA’s Senior Director of Content Strategy, and you’re listening to the SCA Podcast. Today’s episode is part of our Expo Lecture Series, dedicated to showcasing a curated selection of the extensive live lectures offered at our Specialty Coffee Expo. Check out the show notes for relevant links and a full transcript of today’s lecture.

This episode of the Expo 2019 Lectures podcast is supported by Softengine Coffee One, Powered by SAP. Built upon SAP’s business-leading Enterprise Resource Planning solution, Softengine Coffee One is designed to quickly and easily take your small-to-medium coffee company working at any point along the coffee chain to the next level of success. Learn more about Softengine Coffee One at softengine.com, with special pricing available for SCA Members. Softengine: the most intelligent way to grow your business.

The episode you’re about to hear was recorded live at the 2019 Specialty Coffee Expo in Boston. Don’t miss next year’s lecture series in Portland – find us on social media or sign up for our monthly newsletter to keep up-to-date with all our announcements, including ways to get involved in next year’s Expo and early-bird ticket release!

Coffee shows an appealing bitterness when properly roasted and prepared. But how do the compounds that make coffee taste bitter develop during roasting and how do you analyze and identify them? What lessons can be learned from academic research on coffee roasting to make coffee even more pleasantly bitter-tasting? And after a century of intensive research, why is it that still do not know what makes coffee bitter at all?

Dr. Sara Marquart is curator of the “Cosmos Coffee” exhibition at the Deutsches Museum. In this lecture, she shares excerpts of her academic research into bitterness during her Ph.D. at TU Munich in Food Chemistry focused on the highly sophisticated elucidation of reaction pathways and kinetics leading to bitter tastants in roasted coffee.

Also, I will jump in occasionally to help you follow along.

Alright, let’s get started.


2:00 An overview of coffee’s sensory universe

Sara Marquart:  I think we can start on time. I think if the title of this lecture would be like the acidic taste of coffee or the fruity tastes, they will be way more people because nowadays bitter in coffee is not so fancy anymore. So I did a Ph.D. about the elucidation of bitter taste in coffee. Why is coffee tasting bitter? What happens during the roasting? and this topic seems like from the last decade because bitterness isn’t a thing anymore. Nowadays, specialty coffee and coffee research, but as I did this research for Nespresso, it’s something different. So bitterness is still a thing there.

I’m a post-doctorate M.S., like Master of Science, food chemist and as I already told you, I did my Ph.D. about the taste of coffee, the bitter taste of coffee and what happens during the roasting? Right now I’m a culture girl, so I’m making an exhibition about coffee. So it’s something completely different, but still, I’m having some science background.

So what am I going to talk today about? It’s about aroma and taste. What is the difference? What is tastes? What is aroma? I will give a short introduction about roasting chemistry and like acidity versus bitterness and some analytics for all the geeks in here. All the guys who want to have some methodology. Then I will go like take into the formation of nature bitter compounds, the sensory evaluation of those and give a short overview. As I’m a chemist and I’m not a roaster, please don’t ask me for recipes afterwards, like how you can make the perfect coffee. I will try to give good answers, but yes I’m a chemist. I’m not a roaster.

So we’re starting off everyone is always citing like, there’s some thousand flavors and coffee and when I first entered the scene, I was like, wow, a thousand flavors. This must be such a highly diverse product. But actually, sorry, I need to be a myth-buster here because actually it is not a thousand flavors. It’s a thousand volatiles, a thousand semi-volatiles so they’re not actually for the flavor active.

Heather Ward:  Sara has a very complex chart up on screen. It looks like it came from a space satellite.

Sara Marquart:  and we did some research… you don’t have to mind about this diagram. It looks like quite messy. What it is, it is a meta-analysis of pretty much every publication made in the previous, like 40, 50 years on flavor of coffee. We did like a heat map and we did a cluster analysis in it and it turned out that coffee flavor can be described with 23 flavor compounds. So there’s not much magic behind.

So from my perspective, from a chemistry perspective, the flavor of coffee is pretty boring. So yes sorry. But. So what I like more of what’s more interesting for me is like the taste, the acidity, the bitterness, and is bitter always bad? So in specialty coffee. bitterness is like a dreaded word nowadays it’s all about acidity, blueberry, these kinds of thing, and everyone’s saying like, your life is bitter, your coffee shouldn’t be. And I think most of us agree that if our coffee wouldn’t be bitter, we wouldn’t like it that much. There’s a difference in bitterness. It’s not this like there’s not a single bitterness. There’s a variety of bitterness. And so for me, when it comes to taste, bitterness, it’s like a symphony. You have the acidity, you have the sourness, you have the bitter taste, and this all comes together to this beautiful, beautiful, highly diverse, complex beverage, which we enjoy on an everyday basis.

For the definitions What is aroma? What is taste? So aroma, we perceive it in the nose. Taste you perceive in the mouth, and when it comes to aroma we have like two different ways to perceive it. We have ortho-nasal which is like through the nose. When we drink the coffee, we can already smell it through our nose and we have retro-nasal when we have it in the mouth, it’s getting to our nose and there we smell it, but we call it commonly tasting. Like when we’re saying, actually it’s tasting like blueberries we’re smelling blueberries because it’s the blueberry flavor in our mouth. It’s getting to our nose and it makes us feel like we are tasting blueberry, but it’s actually smelling. What we do taste as just five basic tastes. It’s salty, sour, acidity, bitterness, sweetness, and umami.

I think most of you are nowadays are already familiar with umami. Like if this is the savory MSG broth, meaty tasting thing, which is like, Oh yummy when you eat like chips or something like that and you can’t just stop. The science behind is, we have a craving in our brain telling us when we eat umami MSG we are getting protein and carbohydrate. So if we are having like this umami reaction is like, Oh yeah give me more from this protein and carbohydrate. Because if there’s a like starvation phase, we will have enough energy for those days to dig into.

And a small little teaser from my research when I quit my chair, there’s also like, we’re in into discussion nowadays if there’s a sixth sense, like six taste sense and it’s called Kakuma and another Japanese name, and it is all about mouth fullness, long lastingness. Like how long this tastes stays in our mouth. For example, if you have a good red wine and you pour it down and you have this like two minutes after taste of like, yes and the same for coffee. Also having some Kakuma taste to it.

Coming back to this crazy thing. So it turned out that you can describe pretty much every food in this world, the aroma by 220 flavor compounds. As I said, flavors pretty boring. 220 sounds much, but it is not. So if you have those 220 you can pretty much do everything. Where it comes to taste, it just seems simple if five tastes about five taste receptors, but do you have millions of compounds who can activate those? and that’s, I think the other way around where olfaction, we have a lot of olfaction receptors and just 220 compounds activating them.

8.15 The different types of bitterness and Sara’s work discovering what bitter compounds are in a cup of coffee

Coming to bitter. So bitter is not just bitter taste. There’s a lot of bitter taste qualities. We have harsh, bitter-tasting and this I don’t know if I should name it, like Starbucks dark roast coffee. This is like super harsh I really hope there was no Starbucks person in here, I love Starbucks coffee. Sometimes I need that. Actually on yesterday after coffee expo and I had so much like acidic coffee that I went to some deli around the corner of my Airbnb on, bought up a box of Folgers Dark Roast classic and it and it made a French press like super strong and like let it infuse for five minutes and it was so, yummy I mean bitter. Like sometimes I need that bitter taste too. Anyways, so this rounded bitterness, which is pleasant. We have a metallic coin-ly like coin tastes like bitterness, have a sharp one, which is already like a little bit painful, velvet-like bitterness and stringent dry bitterness.

Coming to the chemistry, coming to my part now. When you do coffee roasting, you start with the green bean and 60% of the green bean is made up with carbohydrates. There’s like a little lipids, a little bit of protein. But what’s happening during the roasting is those compounds are all converted into something else. As you can see, the shares are shifting. So the most obvious changes is like carbohydrates and proteins are decreased and I think most of you already heard like this Maillard reaction behind proteins and carbohydrates mixing together. So there’s a breakdown of those two, making new compounds, making the coffee brown, caramelizing it, making it flavorful, making it yummy.

Same for the taste during the roasting. Acidity first goes up a little bit and then drops. So in later stages of the roasting, the acidity drops sharply, whereas the bitterness increases dramatically. So I think everyone knows that if you like ever roasted coffee before. So that’s not something fancy, something new. Now there’s my research, so I use two principles. I use mass spectrometry and I use nuclear magnetic resonance spectroc, spectroc, spectroc or whatever German native speaker so sorry. And I did qualification, which is checking what is in the coffee and quantification to check how much is in the coffee. And, so we have this tool here called LM NMR. It’s a huge magnet. It weighs 15 tons and we use like two, three, five milligrams of compound in the small tube put on the magnet and then we got a fancy looking spectra, which looks like that.

Heather Ward:  Sara has is showing a photo of a four-metre high canister underneath a giant fan. This is the Nuclear Magnetic Resonance Spectroscopy machine. Next to this photo is a chart of the results. The chart is a spiky square containing blurry splotches of black.

Sara Marquart:  And from that, we can draw out information, how the compound looks. And by that, if you know how a compound looks like, we can draw conclusions, how this compound might taste like and how this compound might being formed during the roasting, like which reaction lies behind.

If you start an analysis, you first or I did, I did untargeted analysis. So I first gathered information, just I got everything, what I wanted, like dig, dig, dig, so I had a huge pool of data. Then I did statistical analysis evaluation and then I draw like decisions or I draw conclusions, what does this mean for me and for my analysis? When it comes to roasting, it’s a mystery. Like when I started my PhD, my professor told me like, Hey Sarah, do you really want to open this Pandora’s box? Like if you open it, you might not be like satisfied with your research and actually I’m not because bitterness is like really still a mystery after four years of research, I can’t tell you exactly, like what is making coffee all bitter? I can just give you a small part of it.

So how did I start? I took Chlorogenic acid. I don’t know if you’re familiar with Chlorogenic acid. It’s a polyphenol it’s in green coffee. It’s making up to 12% in green coffee itself, it’s tasting sour, but when you roast it, it’s turning into something bitter called Chlorogenic acid Lectone. So something sour, turning into something bitter during the roasting, and it is a temperature and time-dependent reaction. How do we know that?

Now I’m coming to the geeky part, if it’s not already too geeky enough. So we took green beans, we extracted this compound, Chlorogenic acid. So we draw it all out, all 12% so the beans were empty, There was no Chlorogenic acid anymore. Then I sentisize, and modified Chlorogenic acid, which was isotope modified. So it is the same chemical and physical properties, different isotopic methods, slightly weighing different, and you can detect it with the methods I showed previously later on. Now we have like the original Chlorogenic acid. We have the modified one, we make a 50:50 ratio, and I stuff it back into the bean. Like, so then it’s like 12% CQA back in the bean, but 50% labeled 50% originally, and then I roast the bean and there’s the magic happening. What’s happening is that Chlorogenic acid degrades this breakdown molecules. There’s rearrangement molecules and this 50:50% ratio I can always track down. Like every molecule being generated is also showing this 50 50 ratio. So that’s the beauty about it. Like with that technique, you can find out novel compounds. You can trace reaction pathways because you always find your label. You always find your 50 50 no matter where you are in the reaction process, no matter where you are in the roasting process, you always have like different stages of your Chlorogenic acid or your breakdown or your novel compounds.

Anyway, I told previously that you have to speak data and you have to do statistical evaluation analysis. So you have to bring all those data points into our orders so you can draw out a conclusion. This is just an example. So this is called S plot because it looks like an S.

Heather Ward:  Sara has a graph on screen. It has an X and Y axis going through the middle, so it’s equal parts positive numbers and negative numbers. There are many data points scattered into what looks like an S, beginning in the lower left quadrant and moving into the upper right quadrant. The beginning and end of the “S” shape is very thin, with only a few dots, whereas the middle of the “S” shape is thick with dots.

Sarah Marquart: And, what you can see here is like the dots occurring on the outer part there or there are the same compounds and if it’s symmetrical, you will know like yes, you will know that this occurred from your precursor, like the modified thing you put into the bean. Like all this compounds here I don’t know 20 dots and here 20 dots are all like coming from my modified chlorogenic acid. So it’s a breakdown product and yes, what I could find out is like this harsh bitter-tasting phenylindanes are formed from  hlorogenic acid from various stages of the roasting and later stages of the roasting and is actually adding answers getting more and more bitter but it’s just more for clarification those graphics they don’t do any better for you. I just thought there might be like some chemist in here are like ‘oh yeah’.

Heather Ward:  Sarah has picture of eight chemical flasks. The colours of the liquids inside the flasks range from clear, to deep red, to yellow to brown.

Sara Marquart:  So this is how my daily life look like so quite colorful, but actually it was like just fractionation work. So I roasted the coffee, I fractionated the coffee, like cutting it in samples, cutting it in smaller samples, smaller and smaller and smaller. So what happened is I had three Bachelor students, two Masters students, and they were fractionating coffee for me for almost like three years and in the end, I had 5 million gram of compound which I was analyzing and I found something new, or we found something new it’s called Mozambioside. This compound itself is not tasting bitter, but it is a bitter-tasting enhancer and it can be only found arabica coffee. So it’s a mark of Arabica coffee. This is for benefit. For example, for coffee industry or adulteration analysis, if you want to track, like if it’s for, for example, instant coffee. It’s often said that, yes, they are using robusta coffee and with that marker compound you could track down if the company cheated on you or not.

Back the bitter and tasting part. So this company itself is in the coffee on a marginal level, like very, very small amount but it’s enhanced enhancing the other bitter compounds in the coffee. In the end of my four years, I pretty much came to this reaction scheme and some more compounds, which I’m not allowed to show due to like, European research is funded by companies. So we have the chlorogenic acids we’re doing the roasting, we are forming the bitter Lectone and in later stages of the roasting, we are forming various pathways, harsh, bitter-tasting compounds. The Phenylindane and we don’t want them actually, this is this Starbucks tasty thing and we don’t usually want, sometimes we want it, and the underlying reaction principle is a radical mechanism.

Why is this so interesting? Radical mechanism means that the reaction will never stop to occur. So if you roast your coffee and if you like cool it down, if you store it. If you brew it, if you have it in your can, this reaction will go on and on and on. So that’s why your coffee is getting bitter and more bitter and more bitter. The longer you have it on your heating plate, the longer you have it anywhere, so it’s getting bitter, more bitter, and more bitter due to this reaction be behind forming of those Phenylindanes. So the best is you try to not have as much in your roasts, so, later on, it might not form as fast, but you cannot prevent it.


19.15 How to control for bitterness during roasting

Sara Marquart: Anyways, theory to practice because this is was already quite boring.

What does it mean for our roasting high temperature versus low temperature? You like what I always say, you have like two Xs. You have temperature, you have time. If you make the, the one short, you have to make the other longer. Both ways lead to Rome, but not like the same entrance of Rome. So it looks different in the end, I would prefer a long roast with a low temperature to prevent from forming those Phenylindanes, then later in life, when I’m unpacking this coffee or my consumer unpacks it, it might not be as bitter, not as harsh bitter. So roasting time and bitterness there we have caffeine. As you can see, not much happens. Caffeine will not be degraded during the roasting, but caffeine also does not make our coffee bitter. Anyone of you ever drank decaffeinated coffee? I don’t think so because we were all coffee junkies, but someone was nodding over there. I saw you. I saw you. Yes so was it bitter? Yes so yes, caffeine is not making our coffee bitter because like until 1950 or so, people thought like it’s, yeah, the caffeine making coffee bitter, but it’s not. Only 10% comes from caffeine. So Chlorogenic acid is degraded sharply. But it’s sour. As I told the Chlorogenic acid lactones are formed, but later in the roast degraded. This is the bitterness we want. This is the pleasant bitterness we want. So we want to be somewhere around here, it depends on how much bitter we want our coffee.

Heather Ward:  Sara has a graph of how many chlorogenic acid lactones form the longer a coffee is roasted. Chlorogenic acid lactones are a more pleasant type of bitterness that are smooth and velvety. Her graphs suggest the chlorogenic acid lactones in her trials peak at three minutes of roast time and drop significantly by the 5th minute of roast.

Sara Marquart: And then the Phenylindanes we want not. So the optimum roast degree and concentration is around here, so we can have like slightly bitter. Like a strong bitterness but pleasant or then decreasing what we don’t know, but don’t want to be here where it’s like harshly bitter and not very balanced.

Heather Ward:  Sara has a new graph showing how phenylindanes increase dramatically after the 3rd minute of roast and plateau at a high level by the 7th minute. Phenylindanes give coffee an unpleasant harsh, metallic bitterness.

Sara Marquart:  In the end, we have this scheme, so around 60 to 70% of the bitterness comes from the chlorogenic acid lectones 10% from the caffeine, 10 to 15 from phenylindanes. It depends on the roast actually, but I was just picking out a medium roast and there’s the unknown part and that’s what makes me upset. After four years of research there’s an unknown box and yes. So please don’t ask me, I will not give you any answer and minor compounds, which I will show you in the outcome, but you don’t do it. Just like structural identification. You not only do like reaction pathway. So you also have to do a sensory analysis.

These pictures are from our sensory booths in Munich. So what we did, we did a sensory analysis. All of the identified compounds, we check the taste qualities, like which kind of bitterness is it or is it even bitter? Then we spiked those compounds to actual coffee beverages to see if it’s like adding up. Like for example, the spirit enhancing thing. You have to add it back to your coffee to see if it’s actually enhancing the bitterness or not. Then you determine the tastes threshold, like how much has to be in the coffee beverage so we can taste it then you correlate it with your previously quantitative concentration.

So the thing is just because a compound is, for example, tasting bitter. If you eat like one kg of it, but there’s only 100 milligrams in your coffee, so it’s not relevant for your everyday life and that’s like with most things. So if you find something you think ‘eureka, I found something’ and then, ‘Oh damn it, it doesn’t play any role in my coffee’. So in the end as I said there is a saying that life is bitter, coffee shouldn’t be, shouldn’t it be bitter or is not about  all like the balance, isn’t it acidity balancing out the bitterness, balancing out the sweetness, isn’t it that we want this yummy tasting in coffee which is like so perfectly like without sharpness this overview of bitter tastes and and I think Adam, like I’m more, more speaking for this everyday coffee, like the daily coffee. I’m not for this, like best of red wine in the evening. Specialty coffee which is like so very. That is fine for me, but for my everyday life when I stand up in the morning 6:00 AM I want to have my filter coffee, three cups, and I want to have it balanced, perfectly bitter. So it’s all a matter of balance and all of when it comes to roasting and bitterness, it’s all about temperature and time and balancing this one out. So thanks for your attention. It was quite short. So it’s 20 minutes, but maybe you have some questions and if not, you can have lunch more early.


24:30 Audience Questions

Heather Ward:  An audience member is asking whether Sara’s research can be transferred to Robusta beans too?

Sara Marquart:  Yes. It can. You just have like slightly different concentration when it comes to chlorogenic acids, they are lower in Robusta beans. But do you have, like, for example, double the concentration of caffeine also impacting the bitter taste as well? Like, as I said, caffeine was making up 10% of the bitterness if you have double the concentration of caffeine. So we have not double the bitterness of the caffeine, but so more bitterness from caffeine in Robusta, but less from the chlorogenic acids. Yes.

Audience member 2:  Have you pushed your research more into the consumer side where you maybe identify popular brands that do actually have this sort of sweet spot a bitterness without being too harsh and so forth?

Sara Marquart:  No, actually, this was basic research performed for Nestle and they wanted to know what they can do to make a pleasant, rounded bitterness doing the roast and how they can optimize the roasting. It’s more for like, I think you call it commodity coffee. Also like the ‘commodity’ term’s from within the specialty coffee scene, so it’s always hard to tell. Like for commercial coffee, I would name it. Yes, so when it comes to bitter sensitive there’s a genetic .prevalence for it. Like 50% are like bitter sensitive, 50% are not. And those who are better sensitive, they will always tend to drink coffee more with sugar and milk. And we can reach out to them anyways. If it’s like harsh, bitter-tasting or around bitter-tasting, they will always drink it with milk and sugar because they’re so bitter sensitive. They would not even touch the Starbucks roast, for example. I think only if they add like syrup or milk. Any further questions?

Audience member:  In terms of your research, did you find in terms of temperature and time, did you find certain temperatures where you saw a dramatic increase or a more significant increase?

Sara Marquart:  it’s always actually dependent on the bean, on the roasting process, which roasting you’re using. If it’s a drum roaster or Air FP, like fluid, I sped roasting. That’s one thing. And the other things, if you’re above 205 210 degrees, and you have a very long roasting time there, if you have a long development time. They’re like, I don’t know. So I can say it in general, like after three minutes you will produce phenylindane I just can’t do that. But generally speaking, if you’re sticking too long above 205, 210 then you will generate those. But even worse, if you’re going too fast above 220 like if you’re like making your time short, that going above 220 you will have those harsh bitter tasting in compounding. So I would rather stick within 205 to one ten two hundred fifteen but not too long. Like there’s, those roasts were like, I don’t know, 20 minutes or so. Yeah. Yeah.

Audience member:  With that being said, with your time and temperature, did you also add, it sort of sounds like you, did you play with your rate of rise?

Sara Marquart:  That’s an interesting thing. So I’m like super old fashioned. I’m coming from Europe. This research was done in the years 2013 to 2017. On the rate of rise wasn’t a thing back then. And actually, I must be honest, it isn’t a thing in academic science. I know it is a thing as specialty coffee, but for me, I think if you have temperature, if you have to weight loss, if you have time, if you have color measurement, and if you have these analytical political tools, you can pretty much do it the same way. But I know like previously I was working with the Ikawa roasters and I love their rate of rise because it’s a powerful tool. And that’s why I do not know why academic research is not supporting it more because, from my perspective, I love it if I would bring it up, they would be like, ah, let’s stick to this old traditional ways of measuring.

Yes, so I was using a pro drum roaster for this research, and I was measuring the weight loss, humidity, color, those kinds of things. The old fashioned stuff. Yes.

Heather Ward:  An audience member is asking what are the practical implications of discovering Mozambioside aside from being a marker of arabica coffee.

Sara Marquart:  Actually no It’s basic research. Like I think no one will ever need it. And as it is not like it is already in the green coffee bean, it is in the roasted coffee bean, it is pretty much not degraded. So it’s not a roasting thing, which comes from the roasting process, but, so it’s just pretty much not changed during the roasting. It’s just in the, in the bean enhancing, enhancing the bitter taste you can’t change it. It’s there. So, accept that that’s the sad story behind. I was, I wanted to try to not talk about it because it sounds more fancy for at least this out. Yes.

Heather Ward:  A member of the audience is asking whether growing conditions affect coffee’s bitterness compounds in coffee.

Sara Marquart:  Oh, yeah. Yep. There are so many varieties with so many different levels of chlorogenic acid. So it’s, Munis had like 12% up to 12%. It can be between six and 15% and it depends also on how those flower organic, like chlorogenic acids, is like more like a group. It’s like 25 different types, and they all form different and different bitter-tasting compounds. So in the end, the more organic assets you have, the more later on food and phenylindanes you’re going to have. So, but I would never advocate for dropping down for organic acid because it’s so important for a pleasant around I bitter tasting coffee that I would rather go like for just like, just don’t change it. It’s good how it is. Any further questions?

Audience member:  Any variation for the water content of the bean?

That’s the best one. So when I was talking about radical mechanism, stuff like that for a radical mechanism, this is taking place when the water content, water activity in the bean is low. So what do you need for radical reactions is like low water content and high heat, which is occurring 210 degrees. So the bean is super dry, you have high-temperature radical mechanism is kicking in like it starts so. Being set with that. It’s like the dryer, the Venus, the higher the temperatures, the more of those competencies will get the harsher the coffee will taste like later on.


31:00 Outro

Heather Ward:  That was Dr. Sara Marquart at the Specialty Coffee Expo in April 2019. Remember to check our show notes for a full episode transcript of this lecture and a link to coffeeexpo.org for more information about this year’s event.

This has been an episode of the SCA Podcast’s Expo Lecture Series, brought to you by the members of the Specialty Coffee Association, and supported by SAP’s Softengine Coffee One. Thanks for listening!


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