#53 – A Scientific Approach to Coffee Freshness | Chahan Yeretzian | Expo Lectures 2018

Since the early days of the specialty coffee movement, freshness has been one of its central pillars. It is best defined as coffee having its original unimpaired qualities. It is often understood as freshly roasted, ground within a few days, immediately extracted and consumed. In spite of this pivotal role of freshness for high-quality coffee, the scientific measurement of freshness has been vague and elusive.

In today’s recorded lecture, Chahan Yeretzian outlines two approaches. One is based on the degassing of freshly roasted coffee – Chahan discusses the link between CO2 content and degassing to freshness, processing, and cup quality – while the other approach looks into the evolution of the aroma profile during storage.

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Presentation Slides

This presentation gets very technical, so we recommend listening while looking at the presentation slides.

Table of Contents

0:00 Introduction
3:00 How freshness forms part of the specialty coffee story
9:00 How do we define freshness?
12:00 How to measure the freshness of roasted coffee through CO2
34:45 How does Co2 release affect processing and the cup
49:00 How to measure the freshness of roasted coffee through volatile aroma compound
1:06:00 Presentation conclusion

Audience questions

1:10:15 Is flushing freshly roasted coffee bags with nitrogen a waste of money?
1:11:00 With different CO2 values from different roast values, which is more important:  the absolute CO2 concentration or the percentage loss?
1:13:15 During the CO2 experiments, what purging testing through a GCMS was done to see they were getting any of the VOCs out, or is the weight is solely CO2?
1:15:45 Once a coffee’s temperature was dropped to reduce the CO2 release in the freezing experiments, were experiments done studying the what happens when temperature is increased again.
1:18:15 Outro

Full Episode Transcript

0:00 Introduction

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

As we’re taking some time to work through our 2019 lecture recordings from Expo, we thought we’d take this time to share some absolute gems from 2018 that haven’t yet been released. If you want to get in on some live lectures action, there’s still time! Visit worldofcoffee.org for a full schedule of our lecture series in Berlin this June.

Since the early days of the specialty coffee movement, freshness has been one of its central pillars. It is best defined as coffee having its original unimpaired qualities.  It is often understood as freshly roasted, ground within a few days, immediately extracted and consumed. In spite of this pivotal role of freshness for high-quality coffee, the scientific measurement of freshness has been vague and elusive.

In today’s recorded lecture, Chahan Yeretzian outlines two approaches. One is based on the degassing of freshly roasted coffee – Chahahn discusses the link between CO2 content and degassing to freshness, processing, and cup quality – while the other approach looks into the evolution of the aroma profile during storage.

Here, Chahan introduces a series of freshness index suited to assess the evolution of freshness of roasted coffee during storage. While these ratios have shown to evolve during storage, the speed at which this freshness indices increases/decrease depends on packaging, barrier properties and storage temperature. This has opened the possibility to use both degassing and freshness-indices to assess the freshness of roasted coffee and compare the quality of different packaging materials and storage conditions for preserving the freshness of coffee.

Chahan Yeretzian is Professor for Analytical Chemistry, Bioanalytical Chemistry and Diagnostics at the Zurich University of Applied Sciences (ZHAW) in Switzerland, and has earned an MBA from the University of Lausanne, Switzerland.

His lifelong passion for coffee began in 1996, when he joined Nestlé R&D in Lausanne, Switzerland. Here, his research covered everything from liquid coffee and coffee concentrate to soluble coffee and single-serve systems.

In 2008, he founded the Coffee Excellence Center at the Zurich University of Applied Sciences – the first ever public research institute dedicated to coffee. He initiated in 2010 the first post-graduate degree on the “Science and Art of Coffee”. Professor Yeretzian is a driving force behind the shift towards an innovation-driven coffee industry and is a board member of several coffee organizations.

This presentation gets very technical, so we recommend listening while looking at the presentation slides. There’s a link to them in the episode description. I’ll jump in occasionally to help you follow along.



3:00 How freshness forms part of the specialty coffee story

Chahan Yeretzian: Thank you, Peter, and thank you for coming today early nine o’clock for this lecture on coffee freshness. A subject that we have been working now since probably more than two years that we took up in our group and really the origin or the motivation of this work was thinking about what is actually specialty coffee. What is it you know? And when you think about quality or specialty coffee, it’s really difficult to define what it is at least to me. You cannot define the flavor profile but at some point going particularly into history of specialty coffee. I realized that freshness is actually one of the key attributes of specialty coffee together with another attribute which I would consider a little bit more technical which I call consistency. Consistency is also an attribute of quality because if you roast in a special way you have to have the skills to reproduce that every time again and again. So, for me really two quality attributes for specialty coffees is freshness, consistency, and perhaps more but I will call that things that I would be able to identify.

So, I like to talk about this subject, and I like to mention first of all a booklet, a handbook that just came out now for this Expo event. It’s called “The Coffee Freshness Handbook.”  As I said, this is work that started more than two years ago. There are papers have been published book chapters written so it’s not like new, but we have now summarized that and put it together into a booklet. It’s a Special Coffee Association booklet that you can also buy at the SCA shop. I’d like to mention also, the author’s just to mention Samo, Marco, myself Chahan. We are all from the Coffee Excellence Center. Marco is also here. He is giving a Water Workshop later and he’s working mainly extraction. He is a Q grader water specialist and Emma is SCA specialist in the science group was and she really contributed important chapter, which is sensory part which we didn’t have done. We are more scientist, so this the booklet if you have time and if interested, please go and get the booklet.

Just to mention also the second booklet that came out right now, which is called “The SCA Water Quality Handbook.” It’s a follow-up on a former booklet that was called “SCA Water Chart.” A little bit more content. We simplified our problem always as a scientist is that we’re always a little bit too complicated and we lose the people very fast. So, I’m going to try to be simpler again. I don’t know if I succeed until now, I think it’s fine. So, the water booklet also you can acquire and it’s a really interesting subject. Water ae a subject, lot of people have worked on it in the past and I think it’s an important thing.

Now, let me go to freshness, our subject of today. As I said, I think freshness has a lot to do with what specialty coffee is and if you go back into the history of specialty coffee, you have to say where did specialty coffee really start and I think you have to recognize that it started really by a person called Peet, Alfred Peet. He was the origin. I mean we can debate but that’s for me quite clear that he is the first person who really had the spirit of specialty coffee. He inspired people and he was the person who did it. He is actually already European. He moved to Berkeley and started his shop in Berkeley and as you see really what he really wanted to do is to offer fresh beans to customers and as simple as that sounds, that was a turning point actually at the time. It wasn’t really around people thinking to offer fresh coffee to customer in order to prepare fresh brew and so Peet really established his concept and he wanted, as written here the shortest between the roaster and the customer. And he inspired, of course, people who then found, in Seattle, Starbucks. They actually learn from him how to roast and they are also in the same spirit create a  Starbucks. The same thing to offer fresher coffee to customers and the customer freshness has been since then always at the heart of the specialty coffee movement.

It’s really important to be to offer fresh coffee and I can go on with this example Many other people have followed up but clearly, if you should go back to the origin, you will see the concept of freshness as an important concept for the movement. You can talk about micro lot is also important, all of that it. Sure, it’s not all but it is a very important quality that people have mentioned on and on. So, now why do we care about freshness. As I said, it is at the origin of the specialty coffee movement. It is where it all started in a way. It’s today highly sought-after quality. If you go on web pages, you see a lot of roaster saying that their coffee is fresh, a lot of people who advertise on freshness. So, freshness today is quite a well-known property. You see in capsule systems, in a lot of marketing language.

Freshness has now become kind of mainstream and it’s a competitive advantage in the business.



9:00 How do we define freshness?

Chahan Yeretzian: But, what is really, how do we define freshness? That’s the question. You know today when you talk to people very often what you get is people who define the process. How do I ensure that my coffee is fresh? So, if I roast and then I grind it very fast and then I extract my coffee fast and drink it fast. So, if I have small short times in between then I end up having a fresh coffee, but it’s not a definition in the cup. It’s not like that you can have a cup and then say this coffee is fresh because something in that cup is like that and that. It’s very often defined by the process that you prepare your cup. Not only, of course, things are moving but has been a little bit like that when we started a few years ago. Freshness is a kind of enigmatic secret thing, you know, everybody, it’s kind of a religion. You know, everybody is, “My coffee is fresh.” Why is it fresh? “Oh, I did it. I roast it yesterday or I roast it four days ago.” But how can you describe the freshness in your cup became a little bit more difficult for the people to say what makes freshness and it is difficult. It is not a simple concept.

So, the project that we or the work that we started, its many different projects is how can you measure freshness and by measuring freshness make it more rational, accessible to people in a more rational scientific way and so most of my talk will address that but not only. There are, of course we as scientists, scientific group we have a lab, we have instruments worth millions. Things that you would never be able to use in a more practitioner context. So, on one hand, we would like to measure freshness, at the same time we also ask ourselves can we do something that can be eventually be replicated at a cheaper level? So, and I think this is the challenge of science in the field that we are here, the specialty field. On the one hand you want to create data, inside impact in the coffee world but you hear a lot also from the people who are in the business that they also want to have a tool, go home and be able to become themselves, like people who do science, you know to participate in the in the process of measuring their coffee so, it’s kind of dual challenge.

We want to understand freshness at the same time. We would also like, in some point offer tools that you might be able to use at your place to say whether your coffee is fresh. So, I don’t think we are there yet, but it is somehow in the back of my head also that at some point that’s also ambition or also an expectation from the specialty coffee community that it’s not only insight that you’re you are expecting. So, we are somewhere in between. We are between inside and impact I would say.



12:00 How to measure the freshness of roasted coffee through CO2

Chahan Yeretzian: So, let’s go into it. Take a step back and say how could you eventually measure freshness and when I talk about freshness, I’m talking about freshness of roasted coffee, not of green coffee. That’s another world. It really only roasted coffee. So, the clock in our system starts when you finish roasting and that’s basically your original product which has its unpaired qualities and what we’re actually measuring as freshness is the difference between this zero point state as a function of time. So, something changes.

When you roast coffee have it fresh at time 0 and then coffee is a very labile product. I can say so. It really evolves very fast and what could you actually observe scientifically? What could you measure scientifically that gives you like a measure, like a thermometer of the changes happening which then you can translate as a loss of freshness? Essentially the approach taken here, what are the major changes relevant to the quality. Could you measure that and relate that to the time zero? And that difference is essentially the change in freshness. It’s the approach taken here. What are the parameters that change once you have roasted, and which are relevant to the quality and to freshness? There are really two different things one is the CO2 and the other one is the aroma. These are two very important attributes that affect your quality. So, what you need is techniques to monitor the changes of CO2 in your coffee which we call degassing if you want and the other one is changes of aroma as a function of time and translate that into something that we would call a freshest index.

So, we define things that we call a freshness index that is essentially loss of freshness, a function of time. Here on this graph it’s a schematic of what happens. So, when you roast your coffee, that’s the starting point. Green coffee doesn’t have any CO2 it’s zero CO2. All the CO2 but also the CO, carbon monoxide is generated during roasting. So, you can assume that these gases they alternate to chemical reactions. There are different processes caramelization, Maillard reaction, we don’t have to go into that. But there are some chemical processes that generate your CO2 during roasting. Most of that gas, nearly 90% is CO2 carbon dioxide so often I simplify and say the inorganic gases in coffee during roasting are CO2, but there are days of course, a little bit other things.

There’s a little bit of nitrogen and this number is too high, 7.2, 7.3% water. This is to our this is a mistake. It’s more around 4, 5% percent water, 3%, 2%. So, I think I know what is. It’s the CO content. That’s the CO content, That’s not the water content.  There is actually a little bit of carbon monoxide which is about 7% and then you have also the aroma. The aroma in percentage rate is below 0.1%. Aroma as a mass is nothing but it is of course very important. So, what we’re doing essentially is we’re following the content of CO2 and the aroma as a function of time and translate that into a change of freshness. That’s the approach that we have taken in order to have some handle on the concept of freshness and I will discuss both and show you first of all. First I will address the issue of CO2, how we measure it and how we can discuss some of the impact it has. How can we use that essentially and then, in the second part I will discuss the side the aspect of aroma. I won’t say too much about how you measure it. It’s nothing new, and then how we use it in order to monitor the loss of freshness in different conditions. So, dissect two different aspects, the aroma side, and the gas, the CO2 side as thermometers for freshness.

So, I’d like to start with carbon dioxide which is around 80%, 89, 87. Now, first of all, I go straight to measurements. How do we measure the amount of CO2and the loss of it in coffee as a function of time? We have essentially three methods right now that we can do it and the good thing is we can measure the CO2 content loss into different… The reason we have that is to validate methods with each other. They shouldn’t contradict each other but I’m going to show the one that is I will call the most original and that was developed by us in our lab. There is one developed by Probat that we also have in our lab which is an interesting one. I’m not going to show that and another one developed by Jacobs Douwe Egberts that we have also in our lab, we are testing. But in principle they are all giving the same information and I think this method here is the most original one that also we developed recently in our lab.

So, what do we do? We roast coffee and then you put the coffee into a small container, here whole bean, sometimes also ground bean. You can have both and then you put that onto a balance. This is a balance. Here’s the reservoir and there’s a small capillary. It’s a small hole in it, which allows the coffee to degas and the gas flows out here, out of the capillary. It’s a very thin capillary. While it’s degassing, it’s losing weight and we’re measuring weight loss. So, you have a given amount of coffee initially and you measure the weight loss. You have some techniques to avoid that water goes out, so you don’t want to measure that loss. Potentially, what we ‘re measuring is the weight loss of our coffee as a function of time and this weight loss is loss of CO2. Of course, there are a lot of tricks and things. You would have to measure quite precisely but that’s the way it is and just as a reference when you roast coffee, fresh coffee, you have, depending on roast, green road speed you will have approximately 1% of the weight of your coffee is CO2.

So, that’s the weight you’re losing while storing and that you can measure very precisely and you get information about the amount of CO2 in your coffee the weight, how much you lose and we use then that as a thermometer, as a measure of the freshness. A coffee that has no freshness has no CO2 in it basically and one that is very fresh has a lot and it’s degassing. So, the amount of CO2 is an indicator of freshness and within a month or two you will have very little CO2. You have very little freshness., essentially the starting point. So, what we do is this setup also a little bit mimics the bag with a valve where you have a little bit of pressure against it for degassing. It gives you a little bit the situation, it builds very, very small pressure inside, but it’s very small and you degas, and you have a thin capillary to avoid option to come in.

Always some kind of gas flowing out. So, that’s the technique and then we put it all into an oven. We do experiments generally at 35°. We have two balances to have duplicates and that’s the other thing. The basis of scientific research is to generate data that you can trust. So basically, our business assigned is to create reliable data. That’s the first thing people expect from us, so we do the repetitions and validation and so, the goal, of course, we started out with a company called Mettler, Mettler who does balances coming back to passing something to you. The goal, of course in the long term is to have this balance as a tool where everybody can use, put in the lab and use to measure the weight loss as of function of time for specific plans, for specific roast degrees, roast profiles and see a little bit how his coffee is degassing, how much is in there to do this experiment themselves. Right now, it’s not on the market, but that’s the direction we’re going and then you can measure the CO2 loss. So, understanding first of all, basically data, so getting some data on that.

The experiment that we did is we took one particular coffee in that case, Arabica and we roast it to three different roast degrees light, medium, dark and each one with different profiles.  Five minutes, 10 minutes, 13 minutes and got by that nine different profiles, three rows degrees, three roast times and the question here is how is degassing happening? How is it influenced by the roast degree, by the roast speed? How much gas is released? How much time does it take? How fast is it released?  Just to make things visible, you know, before we go further. So, here is a typical weight loss. So, the way it is plotted is it is plotted towards the top. It’s basically you have here time and here you have the loss of weight in milligram per gram 10 milligram per gram coffee is 1% of the weight of your coffee just as a reference.

So, we’re measuring here the weight loss. You might think perhaps you should plot it downwards, but it makes sense for us to plot upwards. So, after one day you lose two milligram, which is like a 1/4 of percent of weight and so you can really measure the weight loss as a function of time for this specific plan, for this specific coffee roast degree as a function of time and this is the kind of data we get. That’s kind of the raw data you get out and you get this curve. Now before I go further what we do of course is we fit this curve so we can we can do some mathematical fitting with the objective that for example you measure four, five days and you extrapolate to how much total gas is in your coffee because this curve will go on and will go on and then at some point it will plateau and so one of the fitting result is, how much is the total amount of gas you have in your coffee and how good can you predict that when you measure just four days for example? And actually, we realize you have to measure quite a long time.

I don’t go into the mechanism of release because they are different, the CO2 can be in different places in your coffee. It can be in the macropores, micropores or it can be absorbed or dissolved in the oil and each place where the CO2 is will have different release dynamics and they are all superimposed to each other. That’s why it’s not just one curve. There are mechanisms that are early on visible and others that are visible only at the later time like the release from the oil partitioning. This kind of CO2 will take much longer and that’s why you will see CO2 coming off your coffee forever and I can say that for example. You can let your CO2 degas forever then you put into water then suddenly more CO2 is coming.

There is some CO2 sitting in there that just doesn’t degas which is somehow absorbed on surfaces that will only be released when you extract it. That’s why you always will have a little bit crema even if your coffee is really, really old. You will always have a little bit crema when you extract with espresso and the crema is mainly coming from the CO2 in the coffee, but you release most of it, you know, and we can actually measure these different part for reaction. But this is essentially the curve, we try to simulate it. We can also for example, for an application say capsule systems. We want to know how; we want to have like a specific amount of CO2 left in the coffee to do the packing.  How long do we have to degas in order to have a specific level of CO2 in it before packing to create some internal pressure in the capsule? So, this kind of calculation can be done if you have a good simulation.

Now this, here you see 10 days. In 10 days, you have approximately lost 10 milligrams it’s 1% of the weight and then it goes on 18 days is 1%, about 0.1% more. Of course, it plateaus but it goes on, it goes on for 80, 90 days you still have release. You can measure, it’s not stopping. Now here is an experiment now where you roasted the same coffee. It’s a dark roast with different speeds and the question is does the speed of roasting affect the amount of CO2 you have in the coffee? And yeah, it does and the way it does you can just measure it, you can see it here. This one is the slowly roasted coffee, too dark roast, medium speed and fast. Fast means probably around five, six minutes, and this is around 14 minutes. So, it’s a big difference in time, but you can see that the speed of roasting has a significant impact on the CO2.

Fast roasting will generate more CO2 in your coffee, and it will also have different release behavior as a function of time. Once you see it, you might have explanations. From other experiments, we know that during roasting we already start to release of course. So, you generate your CO2, but you also release while you’re roasting towards the second part of your roasting. So, if you have a long roast the hypothesis is that you have already released quite a bit, but perhaps because of the lower temperature also generate less because perhaps the chemistry is different, but the fact is systematically, if you roast fast to give a roast degree you will have significantly more gas inside your coffee which will then degas also much more and if you have Robusta just an example you will have also more approximately 30% more. That has to do with the composition of the coffee.

So, this is the dark roast and if you do medium roast, the same phenomena, but of course as you see the total amount of CO2 now is less and that’s kind of logical, nothing really surprising. The darker your roast, the more you will have but we know from other experiments that there’s some kind of a plateau. If you go to dark roast and then you go darker and darker there’s not more CO2 coming in. That’s probably due to the fact that you already start to release them. At a given point your coffee has become too brittle but from a light to medium to dark roast you get more and more CO2 and then if you go more darker than just a regular dark, which is, in our case 80 color red. I don’t know in the US units, whatever you use. It doesn’t add more CO2 with some point.

It more or less plateaus in the amount of CO2. But here you see clearly and again the slow, medium, the fast roast, the order is the same. You will have more CO2 in it and the CO2 is then initially in the coffee and then released and you have less and less and here basically a summary. This is now even a lighter roast. There you don’t see really any more difference between fast and slow. Here you see and you see the darker you roast, the more you have, and this is the fast and this is the slow. This is kind of a phenomena and we can now put real numbers on it. We can say that degassing 20 days you will have lost about 1% of the weight of the coffee just from degassing. If it’s a medium roast, it’s about 1/2%, if it’s a light roast, in that case, it is about 1/4%. We can quantify that; we can extrapolate to endless time how much gas you would release.

These are the numbers. Now, the same thing for ground coffee, we did that particularly thinking of capsule systems which are essentially ground coffee and their degassing is also really, really important because it has to do with the pressure build-up inside the capsules and keeping the thing fresh inside. So, here is a release curve now of ground coffee, very light roast. The behavior is very different. You see that here it’s a very steep degassing very early on and kind of, you might say it’s expected, if you ground the coffee it will release. Within the day or two, you will have most of it released. It continues to release here and plateau slower, but it has a very different curve compared to the whole bean degassing. It’s much faster and also you see that the amount that is left here is much smaller than the…

Overall you can say, if you ground the fresh coffee the process of grinding releases approximately 60 to 70% of your gas. So, grinding is an abrupt and fast release of CO2. 60 to 70% percent if it’s a fresh coffee. If it’s an old coffee, then it’s a little bit less, the percentage because the CO2 it can be released easily, say it that way. It was released, so the grinding release perhaps 50%, if it’s old 40% only. So, the fraction that is released, but the overall amount of CO2 is also less the older your coffee is, but the fraction is released by grinding reduces as you wait, and the coffee gets older. At the fresh coffee level, it’s around 60, 70%. It just lost, just from grinding which is also an issue. Eventually, if you are somebody who is grinding big amount of coffee somewhere in a closed space because 7. 8% of that gas CO, carbon monoxide which is toxic. Yeah.

Attendee 1: Quick question. When you say 60 to 70% release, is that immediately or within a time frame?

Chahan Yeretzian: During roasting immediately. Immediately, during the two minutes of roasting or ten seconds of roasting. Yeah.  During grinding sorry. Sorry. Immediately. The other moment where you have immediate release is when you wet coffee. When water touches, you have an explosion of CO2 and when you grind you have like a huge release,. So, these are like the fast moments and then there is this release over time which is as ground or whole coffee.

So, this is a light roast and now we roast it a little bit darker and darker and you see that the curve now goes up and you see at the given roast level that it plateaus again. So, if you roast dark and darker you will not get more and actually we have the same curve for Robusta. Same thing Robusta also goes up, but it has significantly more CO2. Robusta has more. This has to do with the precursors in the coffee that generates more.  CO2 again this is your chemistry, this is another chapter. Where is the CO2 coming from? It’s not really relevant at this point but the precursor pull in a Robusta is such that you will have more CO2 being generated. Now, if I plot that as points now here is the amount.  The mass loss milligram per gram of CO2 lost after 90 hours and here is the roast degree. This is a light roast, and this is a dark roast. Here on top is Robusta. Here a point for Arabica. What we see is that initially when you go to darker roast it’s nearly a linear increase with the color rate value, whatever the color rate value is. Color rate value is also a mysterious thing, but you have here the roast degree.

You see that the Robusta systematically has more than when you reach something like a medium to dark roast degree it doesn’t decrease anymore. It more or less stays stable. Of course, perhaps you need more data, but this has been confirmed through other experiments also. Essentially you have 30, 40% more CO2 in a Robusta. People know that also. Probably people who do espresso see that the Robusta will have more crema which is basically a reflection of the amount of CO2 in your coffee and you get here kind of physical numbers on how much is CO2 in your coffee.


34:45 How does CO2 release affect processing and the cup

Chahan Yeretzian: Now, I’d like to give a few examples for implications. How does that affect processing? Where does it affect the cup? There are of course many, many instances. As I said, you have to be aware that when you grind coffee, you release a lot of coffee in a very short time period, 7, 8% of this gas is carbon monoxide. Carbon monoxide is toxic, and it is heavier than air which means that it will saturate to the floor and will fill the room that you are in. So, if you grind a lot of coffee somewhere and you don’t have proper aeration, it’s actually not safe because you release. We can calculate the amount of CO2 and CO that generates. A small grinding, just a small coffee shop will not be an issue but if you do it kind of a bigger scale you need aeration, it is a health issue and we can calculate that.

So, that’s the first point here during grinding and of course CO2 plays a significant role in the preservation of quality in your bag during storage and at least we believe and so, it will actually create an atmosphere because the coffee beans that are inside will degas and you can measure actually the function of time. I didn’t bring the data, but we measured when you put coffee into a bag, after a while, the atmosphere will change. If there was any oxygen in it, it will be pushed out and it will be mainly CO2 because of the CO2 being released from the coffee and you create a protective atmosphere inside the bags and if you have a fresh coffee that you put in you will have that faster and better. But there’s also a trade-off. If you do it too fast, it will create too much pressure and the valve might not be working properly but the CO2 here will create a nice atmosphere for protection. Another place where CO2 plays a role is extraction.

When you have most, some baristas might know when you extract coffee, you come with hot water on it you will immediately release the CO2 that is inside and if it’s too fresh it will affect the extraction. The same thing with filter coffee actually but in the espresso system what will happen is that it will create a pressure inside the coffee, inside the portafilter and it might prevent water flowing. So, if you have too fresh coffee or you don’t control the freshness of a coffee, you will have an impact on the way the water flows and that’s not having to do the amount of coffee. It has to do with the amount of CO2 that is released. When the water touches your coffee, it will release immediately the CO2 and if it’s very fresh, it will create a pressure against the flow of water because a lot of gas is there and you will not have a good flow and if somebody asks me, how long do I have to store my coffee before I prepare coffee, I do extraction for espresso the argument is that you have to wait a little bit for your coffee to calm down because the first, second, third day the amount of CO2 is very different. It changes so much that you have basically to readjust your coffee machine constantly after say a week or 8, 10 days.

The amount of CO2 is already coming to plateau a little bit. No more changing so much and you have a more stable coffee so you can actually prepare it better in your machine, you can adjust the amount of coffee, the grind in a better way. So, it’s a little bit and for me a coffee that is 10 days old is not old. So, as long as you store it on the CO2 but the only disadvantages of doing a coffee very early in the two, three or four days is basically the amount of CO2 that is so much that it’s kind of an unstable element in your extraction process and it varies fast. and then, of course, the crema. The crema is also a result of the CO2.

So, CO2 is a small molecule, but it plays a lot of roles. So, a coffee that has no CO2 in it will have essentially no crema and the crema is essentially the CO2 released while hot water gets in contact with your coffee. It is released and by other elements in the coffee by macromolecule, the bubbles are being stabilized. It forms a layer around the skin and so it’s not enough to release the gas. You need also some molecules in your coffee that stabilizes your bubbles in order to make a stable  crema or foam, whatever you call it and so, on one hand, you need the gas to generate some foam and then you need some molecules which are in the coffee that make a skin around these bubbles, macromolecule compounds to stabilize it and sometimes people say that the skin is fat. It’s not fat because fat is not good for the crema. So, if you have too much fat in your coffee, you will have a bad creamer.

So, the stabilizing things around the bubbles is not fat layer. You can do the test eventually if you have a finger where you have a hand cream, you touch your glass inside. You will see that at that are aware you have fat on your glass the crema will break down. Fat destroys crema. It’s not stabilizing crema. So, all these elements, so it has an impact during grinding for health issue. it’s important for the stability in the packaging. It’s very critical in the way you extract, it defines extraction. It creates the crema and then finally it also has, but there’s not enough scientific evidence, it has also some impact on the acidity feeling in your cup. It would be logical lot of people say it. I don’t think we have scientific data on that but because of the CO2, it transforms to H2CO3 which is an acid. You get a fresh coffee it will give you some kind of acidic note. But some people say they experience that very clearly. We don’t have a measurement on that, but it makes sense.

So, here’s another example now on cooling. Now we always get asked what does cooling do to your coffee. So, here are and here I am going to show it on CO2 and say something about aroma as well. Here we have a coffee. We roasted that coffee, whole beans and then the green curve here is the release of CO2 of the freshly roasted coffee. So, we measure how much CO2 is in the freshly roasted coffee. We take also some of this coffee, we store it at minus 25 Celsius. I think that’s minus 15 Fahrenheit and after one week storage we take it out and we measure the CO2 in that. So, the question is did you lose CO2 during this one week storage at minus 25 and another back two weeks and what you see here is that they are totally overlapping so storing coffee, roasted coffee at minus 25 leads to no loss of CO2. It’s basically stabilizing a system. It is important not to call that freezing because you’re not freezing your coffee. You just cooling it down. Sometimes people consider because we go below 0 degree people call that freezing but freezing is a notion only true for water.

Coffee bean has, roasted coffee bean has 2, 3% water and so there is really too little water inside a coffee bean to call it the freezing and so going to minus 25 is just cooling your bean. There is really no freezing going on in the coffee bean. In the green bean which has significantly more 12% then you can ask yourself what does that water do to your bean structure if you freeze it, you know, if you go below zero. But for roasted coffee, there’s no water in it. So, it’s just the cooling and it seems that if you cool it down to minus 25 degrees you basically stop the degassing. It’s not degassing but it’s not the true story. If you do it longer, 70 days not two days, not two weeks at minus 25 degrees here we have the freshly roasted coffee and here we have the same car that was stored for 70 days at minus 25. You see now that the degassing is slower. So, you lose something. You lose something.

The question is, how much do you lose for cooling? And what you actually can do here, it’s quite interesting is you can shift this blue curve into the red curve and then find out how many days you have to shift it forwards that you get to follow overlap. I don’t know if you understand. So, basically what we do, we shift that into it and then we have to shift it only two days towards longer times here to have a full overlap. So, the blue curve and the red overlap totally only by shifting the blue curve by two days which means interpretation that storing at minus 25 degrees during 70 days is the same thing as storing 2 days of 35 degrees because this is 35 degrees, and these are 70 days. So, you shift two days in front, you’ve overlapped totally so storing at minus 25 degrees 70 days is same as two days at 35 degrees and if you translate that into other numbers you see that by cooling it by 10 degrees you reduce the degassing by a factor of 2 or vice versa and that’s quite a known rule in chemistry, which basically says that a lot of processes go slower if you cool down and the rule is 10 degree cooling, factor of 2 and it seems that in degassing we have more or less the same. The real number here would be 1.8 but it’s very close to 2.

So, cooling by 10 degrees slows down everything by a factor of 2. 20 degrees factor of 4, 30 degrees factor of 8 and so that’s kind of the rule that we are observing here and some similar number a little bit similar for the aroma. It’s more difficult to see but that’s basically what cooling will do to your coffee. It will never stop things, but 10 degree will slow down everything or extend the shelf life by a factor of 2, say it that way. That’s what we see here on the CO2 side. Now here the crema, here are four coffees one was freshly roasted, the other one was 10 days old, two months and one year. We’re extracting these coffees.

Now you see that they flow differently. Here we have a thick flow, here a very thin flow and here you have much more crema, here you have much less crema, but you still have a little bit of crema after one year. It’s not like you don’t have any crema. But more or less you see these are just four different movies we put together. You see that the age or degassing has significant. Now, this one is already stabilized, there is nothing. Here crema is still segregating, building the thing. You have seen that the flow was thicker and essentially this is the other effect.

The amount of CO2 will affect directly your crema and of course, the extraction process and here after a while when you let it rest a little bit you end up with such a thing. That’s the other expression of the CO2 in your coffee. It will of course affect your crema. You also always have also to readjust your extraction. If you have less CO2 you cannot just use exactly the same conditions, but this is one other impact. So, that’s a little bit what I want to say about CO2. There is more in the booklet, you can read it there. But CO2 is a small molecule often neglected but it plays quite an important role in the coffee and so we’re trying to bring more rational data into it. We measure how much is released as function of roast, also of variety and different type of coffees and the work is going on in different projects.

Now, I’d like to go to the other side of freshness, which is perhaps more obvious, which is the aroma site. We know that coffee people in general now are aware that aroma is something very labile and coffee, when you extract the coffee of the five minutes it’s normally the same, after two hours normally the same. Aroma, that’s kind of the sensory world people are aware of. So, it is obvious to look for some freshness markers in the aroma site and aroma research is all we do since many, many years. Aroma research since 20, 40 years people do that. It’s quite complex. You need instruments, GCMS. So, it’s not that easy if people don’t do gas chromatography to have access to aroma analysis. It’s not that easy to do it with very simple tools.


49:00 How to measure the freshness of roasted coffee through volatile aroma compounds

Chahan Yeretzian: But here is the green coffee. The green coffee has all kind of constituents, you know sugars, amino acids, trigonelline, lipids and then you roast it and what you do is you generate all kinds of flavor compounds.

These are the key flavor, key compounds as we call them that has been identified in research. We know that there are different type of reactions. For example, some that you might know is the Maillard reaction. The Maillard reaction is a reaction between sugars, reducing sugars for the chemist and amino acids when they come together they react, and they generate all kinds of aroma compounds and we call these the Maillard reactions. One avenue which generates aroma, and these are some typical molecules. Often the sulfur containing molecules are in this group coming from amino acid with sulfur. They are very important for the aroma. Furfurylthiol as an example is a compound that is well known in the in the world of chemists as having some kind of coffee aroma like smell but it’s not really coffee aroma. The interesting fact with coffee aroma is that there are perhaps 30 molecules that are important for the coffee aroma, but there’s not a single molecule that smells coffee.

Individually, they all smell all kind of different things. It’s only when you put them all together that you end up with a coffee aroma. This is different for example in fruits in ananas or banana. In banana, there is one molecule that you can identify that smells banana. Vanilla, you have one molecule that smells like vanilla. In coffee that doesn’t exist. You have a range of compounds. People sometimes say, you know, you read even in scientific papers there are a thousand aroma compounds in coffee. This is not true. There are a thousand volatile compounds. Compounds that are volatile but most of these don’t smell. Really there are only about 30 flavor compounds or aroma compounds and you hear constantly people talking about a thousand aroma compounds. It’s just not true. These compounds are there but a lot of compounds are in the air here, but they have no smell so people can find they make a mistake between volatility and aroma impact. Most of them are at such low concentration that they are below threshold. You don’t get their aroma. So, really there are more like 30 aroma compounds in coffee that are relevant, and the rest are not relevant because they are below threshold or non-smelling. So, these are the compounds.

Now, if you want to study freshness, what you could do is you can monitor the concentration of these compounds as a function of time during aging, during storage for loss of freshness and somehow extract index that expresses your loss of freshness. Now this is done, but there has been now, it’s not new but we have a little bit pursued that in more detail. We look at very specific individual compounds and we don’t look here for compounds. You don’t have to worry too much this is this just four compounds here. They have other attributes, volatilities, and reactivities and here are two compounds, methanethiol is a compound that is present in freshly roasted coffee.

When you roast coffee, this is one of the compounds that you find in really fresh coffee, but this appears very fast for two reasons because it’s very reactive. It’s a very unstable molecule and it is volatile. So, methanethiol is actually a compound that is a very nice signature of freshness. So, this is something that you have to watch if you want to see whether your coffee’s fresh. Other compounds like dimethyl disulfide. you will not find in fresh coffee because it’s a compound that is generated during aging. It is a compound that its present signals the loss of freshness or aging. In fact, what’s special is that they are connected when methanethiol, two methanethiol molecules react they form dimethyl disulfide. So, it’s chemically connected.

So, the approach that is being taken and I’m going to show is we don’t look anymore at single compounds. How much is of that or that, but we look at the ratio. The relationship of two compounds and the ratio we call the freshness index and depending on whether this is growing or not we can say whether this coffee if fresh or not and so we can define many different ratios, but this is quite an important one that we use quite often because it is very sensitive to changes early on. It is something that you can measure, within few days you see changes of these compounds, so they are very sensitive to fast changes of freshness and here are typical ratios. So, here you have the compound. dimethyl disulfide I told you. Initially, in the fresh coffee, you wouldn’t have anything, here you have a little bit and then it increases. The content in your coffee increases just over three weeks whereas the other compound is methanethiol which is very present in freshly roasted coffee. It essentially goes away within three weeks and if you form the ratio of these two.

The concentration of dimethyl disulfide divided by methanethiol you get a ratio that increases and that’s what we call the freshness index and you can define with that different freshness indices which puts in relation two compounds to each other, the relationship and it’s an expression of a balance in a way if you want to call. The balance in your coffee is changing and you get this freshness index and by following this and looking at the number you have another way now, when I refer back to CO2, here’s an aroma signature of the loss of freshness and you can define these freshness indices that we apply to different situations and follow the loss and I’m going to show a few examples how we apply that now to follow the freshness.

I’m going to jump over the chemistry. This is how it going. It is an example. Here is a coffee. This is a whole bean that it’s an Ethiopian coffee that we roast ourselves on a Probatino. We put in a bag with a valve and we stored at two different temperatures and what we want is to use this ratio to see the impact of temperature during storage on the loss of freshness. So, it’s simple, we can expect the temperature will have an impact, but we’d like to see that our freshness index expresses that as well and we measure this fresh index here. Here at 22 degrees. We start at the very small value, the ratio and it goes up but if we store at 50 degrees, it goes also up but see this is a totally different scale. So, you have actually an acceleration of the increase of this fresh index. So, this fresh index really expresses the loss of freshness and it is in a way, it’s more or less also a doubling per 10 degrees Celsius of the speed of increase.

We don’t have much experience at that the doubling, but you see significant increase and you see that the temperature here on this index that is called dimethyl disulfide, methanethiol ratio freshness index, the temperature has an impact and so we have here ratio that shows you how the temperature will affect, for example, the storage. One simple application. Another application is to look at the impact of oxygen in the packaging. Now we didn’t do a packaging but what we did is we had here whole beans. We stored it like that and then we put, no what we did we grind it, we put it in here as ground coffee and we stored it as a ground coffee for a period of time and we varied the atmosphere, oxygen content in the vial and the temperature of storage and we looked again at this ratio. And so, we had heat reduction level 0, 10 and 20 and to temperature 1350 and we just didn’t see any impact of option content in the vial.

So, if you have actually oxygen, you have some oxygen. We talked about between 0 and 20 degrees oxygen in the vial. This difference in oxygen is probably not that significant compared to how much oxygen you have absorbed in your coffee and so even rinsing the ground coffee, you know, rinsing the headspace of the ground coffee and storing it with different oxygen content the change, and now we’re plotting it the other way around and is the methanethiol. It’s actually, the ratio is turned down. That’s why we have a decrease here. We can plot it in both ways actually. So, it increases or decreases depending on how you plot it. I don’t want to go into that discussion. But you see that the different oxygen levels doesn’t have any impact on the way the freshness is lost. The freshness is going away, storage a 30 degrees, at 5 degrees much faster. Basically here, this ratio is not usable if you store at 50 degrees because it’s a very sensitive ratio, but oxygen doesn’t have an impact if you store it. If you don’t it’s very difficult actually to get rid of the oxygen.

If you grind your coffee and then you rinse the headspace with oxygen at 0 degrees you somehow don’t see the difference between these two and we had seen that in the past. So, there must be either big reservoirs oxygen in the ground coffee or it’s just not a big impact. But temperature, of course, shows an impact and so we can basically test different conditions. Is that now a good way of rinsing with oxygen? Does it make a difference or not? And we can see in some cases it doesn’t make a difference, whatever the imputation is. Here’s a third example, which is we have a whole bean in a bag, and we pack it into four different packaging formats. Here one is a paper, the other one is a plastic composite film, these are these two and these here are packaging with aluminum inside. It’s aluminum packaging and we have here different ratio because I just want to show that you can have different ratios, not only methanethiol, dimethyl disulfide. There are different ratios you can use in order to express the freshness and what you see here is, that as soon as you have aluminum in your packaging this ratio doesn’t move and it’s really important to have aluminum in your whole bean packaging in order to change dynamics of freshness.

So, this is another fresh index and you see that this index doesn’t move really if you have aluminum, whereas if you have paper or plastic, it changes the ratio. The chemistry is moving on, the ratio is fresh. This is reducing and this is a way to show that aluminum actually, what most people might now, but you can actually show it here and you can also of course taste it if you want. But a very important element and the actually you see it even within a few days. This experiment we did it with the idea, we said that you know, so specialty coffee is something you’re going to consume anyway within three weeks, you know or say a month perhaps paper could be okay because aluminum is perhaps better, but the difference will only show up after one or two months, but the reality is that it shows very fast even after one week we see a significant difference between a paper packaging or a plastic versus aluminum packaging. Aluminum does make sense, you know, because you might all say why use such high-tech packaging if it’s consumed within a month. These results indicate that it makes a difference.

Another example are different capture systems. A lot of experiments has been going there. If you have the same coffee in different capsules which packaging protects your coffee the best? And here are four different packaging, these are both only plastic packaging. This is a full aluminum packaging, and this is a plastic packaging with a secondary aluminum foil around it. Secondary packaging where it is inside and so, we followed for this four different coffees the change, some of the fresh index and look how it evolves and here is the one that is only aluminum, fully aluminum this kind of packaging and here, this one here is the plastic but in a second aluminum coating and these two are only plastic and you see a significant difference. You see, of course a difference at time 0 which indicates some aging that has happened before you package. So, it’s also relevant how you treat your coffee. It will only age before you pack it into the packaging but then here you have hardly any change and here also, we have actually less change if you package it into a secondary aluminum, whereas the plastic packaging is going up and so you can have an indication of the impact of the packaging on capture systems for example and you can apply that to different things.

Let me jump over that. The last application is what I call secondary shelf life Once you open your pack you can put; you can store it differently and consume it while your packaging is open. That I call the secondary shelf life and now the question is you can store it in different packaging formats. Do you see any difference? Does this fresh index help you to see a difference? The first one is essentially we did a project with a company who introduced this is a whole beans with a screw cap opening where you screw open and you take out and then this typical clip that a lot of people use. Sometimes people cut it open and stick it with a scotch down and sometimes people use this kind of canister can where they put all the coffee in it and so the question is if I store the coffees in this four different formats do I see difference just by going back to this fresh index I introduced before and can I say if there’s any difference or it’s all the same?

Well, here is the is this ratio. this another ratio, 2-Butanone Methylfuran, and what you see is that if you put into a can the freshness as you’re consuming using it out here really goes away this here. The here, the reference is when you never. This is basically your coffee that you never open you open your roasted coffee after one two, three four weeks. So, this is the primary shelf life as I call without putting it into the secondary packaging it would have evolved like that, this ratio but what you see is that this here, the clip and this one are performing the best. Of course, it will age, the scotch tape the second and putting over into another can is the worst.

So, ideally you keep it in your original packaging and use a clip in order to have the stable. The reason is also not so complicated to understand if you have a bag, the coffee has degassed a lot already. The CO2 creates a protective atmosphere inside the bag. If you take it and you pour it over, you just lose the whole protective atmosphere. It starts to degas but has not so much gas. You essentially lost its protection by putting in here whereas if you leave it inside and just cut open, you will just leave the CO2 that’s protective and so, this is another way to look. So, this index also allows you to see these kind of differences on different secondary packaging, all the ratios don’t show.


1:06:00 Presentation conclusion

Chahan Yeretzian: So, I think I’d like to conclude here. I showed a lot of information. I hope not too much and those who want can go and read that or read publications that we have published. Essentially to summarize, take off message. I think freshness is becoming more and more something important people talk about, people claim the coffee’s fresh and so what we’re trying to do is develop some kind of systematic measurement, some kind of rational approach what is freshness, you know, so it doesn’t become a religion. So, you can essentially measure the aroma, the gas content and we can put numbers on how fresh is your coffee actually. So, it’s to take a little bit, the religious aspect away by making it measurable. and we do that by having one index that is related to the aroma and one to the CO2. These are the two major changes that happened during storage. You might have other changes like perhaps a little bit migration of all the surface. I don’t know really how to use that but the major, two major changes that happened during aging is the aroma change and the CO2 loss and so we’re taking these two and trying to monitor that as a function of time and to develop some tools, some understanding, some information out of that that can be related to freshness.

So that’s what we do, and we would like of course to develop tools that at some point can be passed over to you. For the aroma it’s really not that easy because you need to look at the compounds individually, you need gas chromatography. But today, you know, I mean gas chromatography if you buy a second-hand GC you can buy it for 5,000 but you have to learn how to use it. But I have I have seen people over the last five years who have learned a lot, you know, it’s not impossible. Perhaps we’ll see in five years a coffee shop with a GC in the back who knows. It’s not something. I see more and more people losing their fears towards technology so whereas the gravimetric I can imagine that will be something easier to bring to the market perhaps in a few years. So, that’s the way we’re going.

I’d like to thank the group, I’m running the Coffee Excellence Center.  I’m the head of this, I’m actually chemistry professor, but we do mainly coffee research and the people in my group the important people are Sebastian. He is mainly focusing so we have a Coffee Excellence Center where we have five pillars and people focus on different areas and Sebastian is mainly on origin, health, green coffee overall. Samo is responsible for project that we call Transformation, which is roasting and grinding, and he is the lead scientist on this freshness work we have presented. He’s not here today. Marco, he’s giving he’s here.  Marco gave yesterday a presentation on tracking extraction and he’s going to give a workshop on water and he’s also the main author or of this booklet. They say water handbook.

So, that’s a big subject that we have been developing on water. Marco is also a Q grader. He is a specialist on extraction, water and sensory. Then we have one person who is really a specialist on aroma, chemistry, contaminants. I don’t know if you know furan acrylamide. So, this issue, these are the process contaminants of the negatives but also the positive side of aroma and then we have Sabine who is responsible more for the sustainable social aspects of coffee and we have also some post-grad degree that we are offering, eLearning post-grad degrees that she is developing. So, our university is offering coffee degrees, you can study coffee and that is Sabine.

Okay, I think that’s what I want to say. Thank you very much for your attention. There is evaluation form and so I don’t know if there are any questions. Yeah, everybody’s forms are there to fill out? Thank you very much.


1:10:15 Is flushing freshly roasted coffee bags with nitrogen a waste of money?

Attendee 2: My compliments. Just a quick question. We are roaster/packager, we spend a lot of money flushing packaging with nitrogen to displace oxygen. If what I’m hearing you say today is correct. It’s a total waste of time and money.

Chahan Yeretzian: For ground coffee?

Attendee 2: For ground coffee yes.

Chahan Yeretzian: For whole bean I wouldn’t say that statement, we have to test that but actually we have just seen less impact on flushing. Yeah, but really on ground coffee. On a whole I would I would prefer to have more data because you cannot flush all you know, that’s the problem. What we will do next is we’re going to try with the gas that is really heavy like argon that will really displace the oxygen that is sitting there. Eventually, that could help but we don’t know really right now we haven’t seen the effect.


1:11:00 With different CO2 values from different roast values, which is more important:  the absolute CO2 concentration or the percentage loss?

Attendee 3: Excellent work. Thank you so much

Chahan Yeretzian: Thank you.

Attendee 3: Two questions. One is, they’re both related to sensory experience. One, all of this work as you mention anything about the sensory experience because it’s great to have chemistry but how practical is that? And the secondary part is the different roast levels and the CO2 values. Would you then suggest that the absolute CO2 concentration is important or that percentage loss is more important because the lighter roast had much less CO2 levels. Does that mean it’s going to be fresher tasting longer or?

Chahan Yeretzian: Yeah.

Attendee 3: Anyways, go for it.

Chahan Yeretzian: Yeah, so really the freshness is related to the amount of CO2 that is left inside, but you have to scale that with roast degree. So, if you have a light roast, A little bit of CO2 left inside means more than if it’s a dark roast. But really freshness, a coffee that has no CO2 left is less fresh than the one that has much. So, if you if you have a coffee that you don’t know you measure how much CO2 is in there. But of course, if it’s a very light roast you will have already initially in the beginning much less. So, we have to scale that with the roast degree. So, the loss is of course what makes it age but if you want to measure the freshness it’s how much is left there, is to find out. So, that’s more the measure of ratios here, but you can phrase it two ways, of course, but yeah and the sensory, sorry, the sensory. Yes. We haven’t done that much work. We have done some so for example the freshness index, the methanethiol dimethyl disulfide, what we have been trying but we haven’t been really successful is say once you are above one then you are going into an area where you are no more totally fresh, but it hasn’t been possible to do that. We need much more time and right now, we are, in our group we have one Q grader and two that are going to do it soon. So, we work with external panels. It just needs more work. But yeah, we taste a difference, but we don’t have scientific data. Yes.


1:13:15 During the CO2 experiments, what purging testing through a GCMS was done to see they were getting any of the VOCs out, or is the weight is solely CO2?

Attendee 4: I want to thank you; your work is really awesome. I was wondering, just some clarifications. In the beginning we were going over the first picture to review VOCs in CO2 and I was wondering as we progressed you were just measuring the CO2 and not the volatile organic compounds and during your degassing did you ever do any type of headspace testing or purging through a GCMS to see if you are getting any of the VOCs out or if the weight is solely CO2?

Chahan Yeretzian: Yes, this we have done. So, what basically the question there is, loss of CO2 does that correlate also with loss of aroma? So…

Attendee 4: Oh, and so just the way that you are getting, like the numbers that you are getting for the CO2 coming out. Do you know that solely CO2 coming out and not any of the VOCs coming out with it especially during the grinding? That was one thing that was really interesting because with that you’re applying a little bit of heat. so, you would be getting a little VOC out.

Chahan Yeretzian: Yeah.

Attendee 4: and so, I was wondering if that was looked into at all yet?

Chahan Yeretzian: We looked into that and we see that it doesn’t correlate totally. So, the CO2 loss is not it an identical with the VOC loss, there are differences. So, one of the strategies there is because CO2 actually, you could say I’d like to get rid of it. As long as I don’t lose volatiles. So, one possibility and that’s one thing we’re doing is how can I get to a situation where I lose preferentially CO2 and no aroma. So, I get rid of my CO2, which is a problem for many things. Actually, it’s not except for the crema. I know if you want the crema but really there are ways probably with temperature to promote CO2 loss without losing aroma. They are, of course connected, but they are not totally connected. There is a difference between both and so we are actually building new equipment to be able to measure the difference for that. Right now, we have indications that they are not totally connected, but we don’t have very solid data and right now we’re building equipment to measure both in parallel and to see how we can decouple these two to promote for example this degassing.

Attendee 4: I have one other question about the freezing. Just in coffee there are so many pros and cons of freezing. I was wondering if you know the water, you said 2 to 3% after roasting. Is that free water or is it bound? Does it have the ability to crystalize at this temperature?

Chahan Yeretzian: No, it doesn’t have.

Attendee 4: Okay. Thank you.


1:15:45 Once a coffee’s temperature was dropped to reduce the CO2 release in the freezing experiments, were experiments done studying the what happens when temperature is increased again? 

Attendee 5: Thank you again for your great course here. I was wondering if you did any studies over the effect of once you drop down the temperature of the freshly roasted coffee to reduce the CO2 release, if you did any studies of what happens once that temperature increases again, and if there’s any way to better the change?

Chahan Yeretzian: Well, you know when you freeze it you bring it back to room temperature before the experiment. So, it’s never just only freezing. So, all the experiments are done, you freeze it and you bring it back to room temperature and then, so that’s how the results are. It’s not like we don’t do the experiment with frozen coffee. We bring them back to room temperature. So, we have it always, the whole cycle and we don’t, in the CO2 I showed you we see a reduction of the released by factor of 2 by 10 degrees. So, my feeling is that it doesn’t do anything to the structure of the bean.  It’s just it slows down the synetics because the factor of 2 in the chemistry, it’s called the Arrhenius law. It is a pure kinetic rule. Chemical processes are slowed down by cooling by a factor of 2. If you go 10 degrees down and we see something similar here. So, it seems to be pure chemical, physical process but not like a cracking of the bean that would make it. That’s what I think.

Attendee 6: Hi. Thank you for your lecture. I just wanted to provide a quick story on kind of what you’ve done with your research and how we applied it in a practical sense using a third graders knowledge. So, we kind of encouraged our daughter to enter a coffee related science project and so, we were looking at coffee freshness and in order for us to assess how coffee was going to be fresh we gave her some balloons and some glass bottles, and we asked her to basically place coffee, you know that’s been aged for one day, 7 Days, 15 and 30 days.

Chahan Yeretzian: Oh.

Attendee 6: But a balloon if she was capturing the CO2 and so we gave her a kind of a graphical way, an empirical way to show coffee freshness and she like won her physical science fair project.

Chahan Yeretzian: Oh, she did that at school and what, did she see difference on the balloon?

Attendee 6: Yeah. We saw the difference actually after 21 days. We saw a significant reduction in the amount of CO2 that was being captured by the balloon and by 30 days, it was almost, it wouldn’t even go up.

Chahan Yeretzian: Yeah exactly. Oh great, great so happy for your daughter then.

Attendee 6: Thank you.

Chahan Yeretzian: Yeah. Okay. Thank you very much.


1:18:15 Outro

Heather Ward: That was Chahan Yeretzian at Expo in 2018. Remember to check our show notes for a full transcript of this lecture and visit worldofcoffee.org for tickets to our next run of lectures!

This has been an episode of the SCA Podcast. Thank you for joining us!

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