Ep #2 – Drying/Yellowing

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<Joe> Hello everybody Joe Marrocco Here from Cafe Imports broadcasting from Mill City Roasters in Minneapolis,Minnesota and as you can see I’m all by myself today my co-host Dave Borton unfortunately is at home.Fortunately with a new knee and hopefully he’s got that knee propped up high with a nice beverage with a little umbrella in it or something like –well maybe not because he’s probably on some pain medication so maybe stick to the ice ice coffee, Dave and we’ll see you next month but for now you all are stuck with just me so it may get a little bit bipolar, I may start talking, you know asking myself some questions and going back and forth we’ll see how this pans out. Today I have a second part to the study that we’ve been going into on the profile on the curve as you can see and I’ve already done some artistic rendering so i hope you enjoy the art throughout today’s program.I’m starting to consider myself–oh what’s his name?Nick, you might have to help me thepainter my happy little, my happy little, profile right here

<Nick>Bob Ross.

<Joe> I’m the Bob Ross of coffee so I hope you all enjoy that.So today we’re going to talk about the drying stage.Last month we talked about the turn around or turning point, as they like to call it in these parts of the world and so today we’re going to talk about what happens between this turning point and when the coffee actually starts to change in color.We’re going to talk about not only what is physically happening to the coffee itself, but also how you should respond to its happening with the coffee and how you can decide whether or not what’s happening with the coffee is correct or incorrect. And I do want to give that disclaimer that on each roster it’s going to be different, so especially as you are getting deeper into the roast you may have a turning point that’s going to be similar from one roaster to another roaster. However, once you start moving past that point our roaster begins to separate: one roaster will go one direction another roaster will go another direction. Ok. And I also want to say that we are specifically talking generally on these shows about a drum roaster, not necessarily your air roasters or fluid bed roasters although the science is still the same as far as what is happening during yellow.So here you have the turning point, just in review if you did not get to watch last month’s maybe go ahead and pause this, watch last months and then come back to this. But I’ll quickly review a couple of things.The turning point itself is actually a myth.It’s a make-believe point of where we see coffee go from hot to then moving back up because this is actually not what’s actually happening. What’s Happening is coffee is down here,the drum is up here, and the probe has been steadily reading the temperature of the drum and now we’ve added coffee so as coffee is pulling against what the probe is reading it takes a little while for the drum in the coffee to reach a point of equilibrium. And that’s really what this is showing–so the coffee is not turning around, the coffee has been steadily increasing in its temperature since the moment that we introduced it to the drum Oak. As coffee is absorbing heat, that heat,which is energy, is going to start changing the state of the coffee.The first indication of change is color. When it comes to our eyes,visually we will see the color of the coffee change, and we’ll also smell the aroma of the coffee changing. Now a lot of people will start getting very carried away during this stage with looking at instruments. You’ll look at that that temperature probe and you’ll get drawn into that temperature probe and I Want to tell you you’ve got to stay in tune with the coffee.That doesn’t mean just sit there and keep trying and trying and trying and trying that means that you need to balance trying the coffee, smelling the aroma,looking at the color, look at the timer,look at your temperature, and make sure that all of these indications are in tune. Ok, so what’s happening with the coffee here? So we have a seed and that seed has has a particular amount of compounds within it. Those compounds are drawing in heat. Now Physicists tell us that things that are dense absorb energy more quickly. Things that are less dense absorb energy more slowly.So like for instance, right now I’m in a room if I’m cold in this room I can put a heater in the room. If i put the heater in the corner of the room,it’s going to take a long time for that heat to move its way over to where I’m standing because this room is not very dense. Now If i fill this room with water and I put a heater in the corner of the room that heat is going to move more quickly through the water because water is far more dense.Now, if this room–now of course i couldn’t survive in this scenario–but, if this room were nothing but metal and I Put a heating element in the corner the heat would move through this room very quickly because metal is a conductor. When you have something that is dense it generally will conduct energy. Ok, so a very dense coffee wants to conduct energy very quickly.Now you may be saying to yourself, “but wait, I thought that you’ve always said that are more dense coffee needs more time to absorb energy?”This is true. Since that dense coffee wants to absorb energy very quickly,during that process the outside part of that coffee will want to change due to energy being absorbed at a much more quick pace than the interior of the coffee.So for a more dense coffee, we want to have the time during this stage to kind of slow down. Ok, so let’s put on the board a coffee seed. I’m going to get rid of some of this stuff, ok. Here’s your coffee seed.All right. Now this coffee seed, let’s say it’s very dense, has these very tightly packed cells. On a very dense coffee energy will start to move in and what happens now is that moisture will start to move out off of the coffee. And as that’s happening there is a cooling that will start taking place on the surface of the coffee. During that initial stage of heat being absorbed into the coffee you were still losing moisture through the act of evaporation, and that evaporative movement will cool the outside of the coffee and then you will protect the inside of the coffee from that heat.So Even though density will absorb heat more quickly that reaction to that heat that it absorbs will also happen more quickly so we want to space that out. Ok, so for more dense coffee as you come around that that turning point,we want to make sure that that turning point then results in a little bit of a slope to the curve, a little bit less speed coming out of that turning point for more dense coffee. A less dense coffee is not going to have the absorbent ability that a higher dense coffee will have and so we have to enforce some more energy onto that coffee in order to get it to start moving.So for a less dense coffee we can have a tighter and sharper turn. Now, a lot of people want a very clear-cut answer as to how fast their rate of rise should be from the time that you have turn around until the time that you see yellow.There’s no cut and dry answer. I will say I like to measure every 30 seconds. I like thirty-second increments because if you have a roast that’s only10 minutes long and you’re only measuring every minute, from the time that you reach yellow to the time that you’re done, you’re really only getting about three to four, maybe five measurements.Whereas 30 seconds doubles that. So 30 second increment,I really like to see somewhere in the neighborhood between 14 and 18 degrees per 30 seconds.But, again that is really going to depend on your roster, on your instrument, on your coffee and all of that.If you’re roasting in a sample roaster, a very small roaster,you may see that that number is very high or you may see that that number is very low.Usually on the smaller equipment we see a larger divided on how their probes are reading. Ok, so what is happening physically to that coffee right now is what we call an endothermic reaction.The ability for the coffee to absorb energy, or the state of absorbing that energy. While the coffee is absorbing that energy however there is still reactions that are taking place.The reactions that are taking place at this point are not chemical reactions,where you have molecules that are breaking down, they are more physical reaction that’s taking place.The physical moisture that is in the coffee is beginning to leave that coffee.It’s beginning to be evaporated off the coffee. Don’t be confused with boiling point of water,ok, because we’re still not quite going to be at the boiling point of water.This is more of a drying action–so a lot of people call this to drying phase or the r drying stage and that is that endothermic reaction that is forcing the water to evaporate out of the coffee and then getting the compounds that are in the coffee ready for chemical reactions are what we would call EXOthermic reactions or the release of energy through change brought on by heat. Ok, I hope that is very clear. So as we move it actually starts way down herewith the coffee because, once again, this does not exist.So, as you’re moving from the temperature that you put the coffee into the drum at,room temperature let’s say 72 degrees, as you’re moving through the coffee is actually doing this. When you get to that stage where you see yellow, now you can know that that coffee has dried to the point where it’s ready for chemical reactions to start taking place. Ok, you’ll smell the difference in the coffee.So, as you put the coffee in it will smell like green coffee. If you want to know what green coffee smells like when you open that green coffee bag and you smell that aroma that’s what I’m talking about.It smells grassy, it smells kind of like green peppers sometimes it has a muskiness to it. That aroma will change to being more like hay or straw or oats, something of that nature. Now if you think about that in a botanical sense if you make a correlation to other grains or grasses,which coffee is not a greener grass, given, but it responds just like one.If you make a correlation to that and you smell grass and as grass gets cut,which were doing to the chlorophyll that’s in that green coffee seed, as we begin to heat it, as it gets cut you really start smelling that aroma.So as you get past turn around and star theating that coffee, that green coffee aroma will in intensify and then we’ll change. It will change to being like dried grass, which is your straw your hay your oats your wheat things like that it’s just dried grass.Now you’re getting down to the carbohydrates, then later you’re going to change as you move further through your browning reactions.So this stage is all about preparation. Ok,there’s been a lot of study that’s gone into this stage and one of the coolest parts of the research that I’ve seen is that for if you have one single seed and you’re in a lab scenario to where you can inflict upon the seed a curve that you want at any point,so for instance you could hold the seated at a yellow for an hour and then all of a sudden jump that curve up because you can inflict heat on it that way.Well, they found that the amount of time that it takes from green to yellow has no determinable result on flavor. It does not affect the flavor of the coffee because at this stage you’re not going through any kind of change as far as the chemistry of the coffee is concerned that will result in a flavor change. However in our drum we are preparing that coffee for those changes.So, as we nearer to those browning reactions, if we’re moving into browning at a very fast speed then we can move through browning without achieving all of the reactions that we want. If we move through browning at a very slow speed,then we will not be able to break down the coffee to have all of the reactions that we want.So we need to move into browning at a speed that equivocates to a browning reaction that takes the amount of time that we needed to take.So this is preparation–everything leading up two yellow is preparing the coffee to move through the browning stage.So you want to see that generally in about four to six minutes on most drums if you’re moving much slower than that,then as you approach browning you’re not going to have the energy to get those reactions. If you move too quickly then you’re going to move through browning so quickly that you’re going to have some singing to the coffee, some scorching to the coffee. Coffee scorching will also occur during this time.If you see little spots of darkening on the outside of your coffee as it turns yellow, those spots are scorches. If You’re seeing browning on the coffee during the endothermic stage, where that browning is happening is no longer endothermic. Now it’s starting to have an exothermic reaction on that spot. That Exothermic reaction will then continue as you move through the roast and it will over roast on that part of the seed.Once you start seeing that you really cannot reverse it. So at that point that coffee is going to,you know it’s going to have cherry flavor to it. I think that’s a good start to this conversation.Nick, do we have any questions?

<Nick> We had a question earlier that you started to touch on, I’m just gonna ask the question so that we get a nice sound bite for the new segment.What aromas should they be smelling from the start to the end of this phase?

<Joe> So,what aromas should you be smelling?You should be smelling grassiness, green pepper ness, those green chlorophyll-filled aromas to breadiness, the aromas of carbohydrates: pancake, waffles,biscuits, wheat, those kinds of things.

<Nick> Joe, would you be interested in doing a larger format Q&A session to let these guys just spew you stuff at you? At some point?

<Nick> Sure, I have the question of would I be willing to do some kind of a Q&A.I’m absolutely willing to do a Q&A.

<Nick> And the next thing is, and I know the answer to this but I’m hoping you can expand on this a little bit more:Why can’t we fix someone’s roast when they send us a profile?

<Joe> So the question is why can’t we fix someone’s roast when they send us a profile I would say that there are a lot of layers to that question.It’s kind of like, let me let me come up with a good analogy for this.While my brain is working on the analogy,I want to talk about the physical ability of our machines.So all of our machines are different. Your probe is going to be different than somebody else’s probe,even if you have the same probe, even if those probes are calibrated, the metal around the drum is going to allow for a different amount of ambient temperature to hit your probe, the beans going into your drum may be at a different ratio,may be at a different temperature going into the drum.There are so many factors involved,that’s why we have to go back to paying attention to the coffee.What is the physical coffee doing? And then retro fixing your curve. Ok- to what the coffee is doing. So if your probe is reading one number,like for instance if I tell you that yellowing happens at six minutes at 300 degrees Fahrenheit, and you go to your roster and you get to 300 degrees Fahrenheit in six minutes and you’re at brown and you come to me and say your profile is wrong,I’ll say, “no, my profile is right, you should have slowed down your roast.Your temperature is different than my temperature. So we can’t really just look at the numbers and figure it out.I can’t teach somebody how to paint with color by number chart. The only way that I can teach somebody to paint–well I can’t teach someone to paint it all–but the only way that I could teach somebody to paint is through helping them see how adding this color will cause the effect of seeing how that color corresponds with another color in those things coming together now start painting a portrait.And then you have to go and actually practice. You actually have to have the the physical ability and the interaction with the medium in order to adjust yourself to that medium and then start to artistically express yourself.So, coffee is artistically expressing yourself. Now we have science that we can go back on, but our tools for measuring that science are going to be different.So, if you are able to send you know–parts of your roast all the way through your roast along with the profile of your roast then that could start narrowing in on how somebody may be able to help you, because then they can smell and say, “oh wow, at yellow your scorching,” even though you say this is 300 degrees at six minutes. It’s still moved too quickly for this particular drum.We have to taste it and see it.

<Nick> Ding! Send some coffee with your profile. We’ll all appreciate it.Mike is wondering, if your aromas in drying always follow the same order?That’s very sensory, that’s very perspective of the individual roaster,and what he can smell out of it.Your experience? Do you find that the different stages in drying of yellowing phase follow the same aroma kind of curve with the temperature?

<Joe> This is a really good question, and interesting question: does the aroma of coffee always change in the same general direction?Yes, yes it does. Once you have gotten all of the chlorophyll out of the coffee,once you have achieved drying the coffee,it will not then smell like grass. Once you get past that wheaty stage, that really hay-like stage and start moving deeper into bread, and then into baked bread, and then like darker baked bread,and then into cookies, and other things we’ll talk about in the future, you won’t go back to just smelling that straw. Ok, because what’s happening is that molecule is now gone and now it’s different molecules, and then those molecules are gone,and then they’re different molecules.So you’re changing the coffee in a chain.So, the further you get down that chain,the more you’re going to not be able to go back. Ok. The maillard reaction, caramelization, you cannot undo what you’ve already done.And, the same is true for the very initial reaction.Even if you were to soak that coffee in water, you’re not going to get chlorophyll back into that coffee. Ok–Cool.Any other questions for us?

<Nick> We have escaped from the gauntlet of questions.

<Joe> Ok, so we have no other questions coming in, I did want to make another point that i’m going to try to recall. One thing that I was talking to Steve about, here at Mill City, is a lot of people are calling in about their temperature probe profile, or their profile software has got a lot of noise in it. You’ll see like a zigging line that’ll occur, especially you know, it’ll be like really intensely seen on your rate of rise. And so people get really caught up in looking at that crazy, you know, zigzag motion when really that’s again why you need to go back to the coffee.Those lines are there to help you,they’re there to go back to later and try to repeat a similar roast profile. But Just because you have a lot of noise through the electronic equipment doesn’t mean that you’re ruining your roast,or that you’re going to be able to taste that in your in your end product.All of these roasts are going to be kind of on a bell curve like, i’ll say over and over, of acceptability and even though your profile may have little zigzags,it’s still going to be in a situation on that bell curve to where you’re not going to be able to taste the difference if your rate of rise is you know a couple of degrees different on this little zigzag pattern. Ok, so take yourself out of your profile material and try to stay with the coffee as much as you can. When you start getting with the coffee too much take yourself out of the coffee and put yourself into the profile material. Until You can start using them in a really natural way, to where you flow and you’re comfortable with them and then at that point try a new coffee and just continue to grow, continue to build, and continue to look for things that make your coffee tastes good.If you are exchanging those profiles with each other,there’s going to be a lot of peer pressure for your profile to look polished.And while trying to polish your profile,you’re going to lose sight of what you’re actually doing which is roasting coffee.What you’re doing is cooking coffee,you’re cooking coffee.Don’t try to dress your profile to impress, try to dress your cook coffee in a way that actually tastes good to you,represents where the coffee came from,etc. That’s not coming at you as a reprimand but as an encouragement, and hopefully liberating you a little bit from worrying about that profile. Ok, another thing that I wanted to talk to you about is once your coffee does begin to reach that boiling point, where water is going to start boiling out, that is going to be where you’ll see that coffee dry out. And the drying of that coffee is actually, and I’m gonna erase this whole thing.Your coffee is going to start at about,let’s say well– I don’t know the quality of coffee that you’re getting it could be very different,so we’ll just say 9.5% moisture to 14% moisture somewhere in that range is where coffee is. We really really really like to see coffee at 10.5%moisture to 11.5% moisture.I’m going to go down a little bit of a rabbit trail here in a moment,if we have time, as your drying the coffee out this moisture drops,ok, this moisture drops to about 0.5%moisture to 1.5% moisture. Ok, during the rest of the stages of roasting your percentage of moisture is going to reside around this number.Generally closer to this number as you get later into your roast. Ok, so this is about where coffee is going to be at its final roasted product and the reason for this is as you start breaking those molecular chains down,even though this 0.5% is still evacuating your coffee you’re creating new moisture that’s going to replace that by breaking down your molecules. They’ll break off H2O molecules off of larger carbohydrates and other such molecules. Ok, so you’re you’re releasing moisture but you’re also replacing that moisture and so you reach the status,this like– what’s the word I’m looking for–homeostasis almost in the state of where your moisture lies because every time you really some you’re creating more,so you get kind of a cycle there. Ok,now this is my rabbit trail. Ok, are you ready? This number, this initial number–and this is, you know, something that is very controversial among a lot of roasters–this number does not matter this is not discussing density. Ok, this number does not matter as to how you apply heat to your coffee. Ok, if you’re reading 14%don’t say, “well, then i need to roast it in this way.” If you’re reading 9.5% don’t say, “well, then i need to roast that in this way.”Ok, because those those things are percentages of moisture in relationship to density of the coffee and the density of the coffee’s what you really need to look at. The density of the coffee in correspondence with the moisture of the coffee, and in correspondence with the size of the coffee will tell you how your coffee seed is going to absorb energy. Whether or not it’s going to absorb very quickly– too quickly or too slowly and how you can apply energy from there.I hope that is clear, I know I harp on that a lot.One of these days maybe I’ll write a really good concise article on all of that we’ll see if I have the time.

<Nick> Somebody asked you to draw more beans, just thought you could show us all a quick–

<Joe> Oh yeah so my friend–

<Nick> It’s like a perfect math circle for coffee beans.

<Joe> My friend Ian Pico Down at Tulsa, at Topeka Coffee,drew this lovely coffee seed and I’ve Been practicing it ever since.It’s kind of something like that–that looks more like a tongue or a butt–let me try that again. Ok, so he just kind of comes around and then makes a little curve that–

<Nick> A wave?

<Joe> Yep, the little wave, the reverse wave. So I’ve adopted that into my repertoire of artistic abilities, thank you Ian.Any other questions?

<Nick> How is the density of a bean measured? Oh we have a video that.

<Joe> Mass over volume. Get Yourself a pipette, fill that pipette to a certain level with all of the different coffees that you have–

<Nick> Not together.

<Joe> Not together, separately and then weigh that out. If you fill it up to 200 milliliters and it weighs ‘x’ grams,and then you fill another one up and it’s ‘x+1’ grams, then you know the ‘x+1’ is more dense than the ‘x’ grams.

<Nick> Do you remember which video that’s in?

<Joe> I don’t–

<Nick> Perfect.

<Joe> I’ll do something, actually let me–

<Nick> You want to draw it?

<Joe> I’m going to draw something, how much more time do we have?

<Nick> We have as much time as you want.

<Joe> Ok, let’s get into this a little bit.This may be worth all all of your money that you paid for the show.Ok, so give me a second i’m going to turn my back to the camera and draw a couple things.You’re welcome.Ok.Ok, this way is…

<Nick> Steve’s probably at his desk watching us right now just like, shaking his head.

<Joe> Ok, you have 2 pipettes.We are going to get hypothetical here and say these pipettes are both 200 milligrams and they’re both filled with coffee.To 200 milligrams. Ok, hopefully you are with me so far. This Pipette weighs 100 grams .Ok, this pipette weighs 125 grams. So, mass over volume is going to give you your density. Density equals mass over volume. Ok, so I’ve done this so that it’s very easy for you to see.Now, which one you– don’t have to answer because I won’t hear you–of these is more dense?You’re right, this one. I heard you.This one is more dense than this one, ok?Now let’s pretend together, shall we,that each one of these grams is actually one seed. Ok, so if each one of these graphs represents one seed, which it would not in real life would be closer to seven to ten,but if each one of these seeds represents one gram, or each one of these grams represents one seed then this pipette would be filled with 100 seeds.Following?That would mean that for the same amount of space there would be 100 seed filling this, but each seed would have to weigh 1.25 grams.1.25 grams, ok, so 25% more than the sister seed over here.Now, what if I then took a moisture measurement on these two coffees and both of these coffees read 10%.Let me put that in a different place.What if both of these are 10%moisture?Now, if i measure of just moisture and I go off of that then i’m going to assume that i’m going to need to roast both of these coffees the same way. But, I don’t need to assume that because I’ve Measured the density of the coffee, ok, and the density of the coffee tells me that these are different.Now, moisture can be a component of density. Ok, so i’m not saying that the moisture within the coffee is irrelevant but i’m saying it’s only partly relevant. It’s part of a whole picture and the whole picture can be seen much more clearly when we have mass over volume, when we have that density reading. Ok, if you have a really nice density meter generally there should be some kind of component, if it has a volumetric component which a lot of them will have a tube that comes with it, that volumetric component can be used to give you a density reading which is usually bushels over pounds or something like that so that you can start charting your density on your coffees as well as your moisture in your coffee.So now, if this is 10% and this says 10%, we know that this one by nature of being more dense, 10% of 125 is more than 10% of 100 grams.So I know that here I have 12.5 grams of water and here I have 10 grams of water.So even though my percentage is reading the same, my percentage then I can use mathematically do some algebra and you can look at exactly how much water you have in that particular coffee .Ok. So that’s why the percentage of moisture can be very misleading. Ok. Furthermore, furthermore, as you are going through yellow and this is where we’re coming back to reality here for our drying stage. As you’re coming back through yellow, pretend like this is our graph, remember it falsely has the turnaround, as you’re coming through yellow whether or not you have 12.5 grams or 10 grams you’re going to drop down to about 0.5% to 1.5% moisture during that stage.You’re going to dry out enough, hopefully if you go through the stage correctly and then start moving through your browning reactions correctly enough to where this moisture is going to be out of the way. If this moisture is present you cannot have a browning reaction, of?Browning reactions, by definition, are dehydration reactions. That is when you’re molecules are losing H20 components off of the molecule and your molecules are breaking down.So, if there is H20 present at that time you cannot have the maillard reaction and you cannot have caramelization, ok? So that’s why drying is so important. We need to get that moisture out of the way,use the moisture while it’s there to pull energy into the seed. Once that energy is there we release the moisture,we have more airflow, and we can move through the next reactions, which–comeback next month and we’ll talk about those. Any questions? I’m sure we’ve sparked some more.

<Nick> Milliliters. Not milligrams.

<Joe> Milligrams…exactly, this should be milliliters. So sorry.

<Nick> That one’s for you, Rob. There ya go.

<Joe> And just a point of clarification:milligrams and milliliters are virtually the same with water, but with coffee obviously coffee is a lot less dense than water so you’ll have a lot fewer grams per milliliter with something less dense than water.But yes, sorry about the milligrams. I don’t know what I’m thinking.

<Nick> We often don’t either, bud. Anybody else have anything else?Now we have to wait for the delay.

<Joe> It’s okay.We’re gonna hang out for a second and wait for the delay. This is gonna be awkward because you will have already been through the delay by the time you hear me talking about the delay. But it should pay off in case we have any other questions.

<Nick> It’s only gonna be like another five seconds.Youtubes. What we give them 20 seconds to type?

<Joe> Yeah.

<Nick> It should be like right around now.And we’re calling it!

<Joe> All right–that’t it.

<Nick> Roaster’s School, Episode 2.

<Joe> Episode 2 of Roaster School is out.Please hit us with your questions for Episode 3 which is going to be on your browning reactions, as we’re moving from yellow to first crack.I’m not quite sure where the first crack is going to get its own episode or whether that’s going to be included in next week we’ll just see how next week goes.Thank you, please come again. Get better,Dave.

<Nick> Bye Dave!



Addicted to coffee at a young age, Nick has turned his caffeinated attention towards coffee roasting education. Behind the scenes, Nick produces, directs, and edits all video series for Mill City Roasters.