Why do we roast coffee?

Coffee Part 2! So before we brew coffee, it gets roasted. What is roasting you might ask? Well it's pretty much the stage where all the magic is happening, everything that turns a little fruit seed into a delicious drink. Grab a cup of coffee, and listen to find out what chemistry processes created it.

124 Coffee 02

Melissa: Hey, I'm Melissa.

Jam: I'm Jam.

Melissa: And I'm a chemist

Jam: and I'm not.

Melissa: and welcome to chemistry for your life.

Jam: The podcast helps you understand the chemistry of your everyday life.

Melissa: Of your coffee life

Jam: of your coffee life.

And if this is one of your first time listening to our podcast. Thanks for coming.

Melissa: Glad to have you here.

Jam: When we say that melissa's a chemist, she really is a chemist. She has her bachelor's and master's in chemistry. She currently teaches chemistry and she's getting closer and closer every day to finishing her PhD in chemistry.

Melissa: So exciting.

Jam: And I really am not a chemist and I don't have

Melissa: It's true.

Jam: any, Uh,

chemist degrees

Melissa: Uh, that's also true.

Jam: And we are learning chemistry together. You and me are learning it from Melissa at the same time.

Melissa: Sometimes I'm learning it too. Sometimes I learn it to teach it, but it's usually I'm learning a new application of principles that I've already learned about in the past.

Jam: Yes. Yes.

Melissa: Well, that was a good introduction. And also, if this is your first episode, you might want to go check out part one

Jam: Oh yeah. Yeah.

Melissa: coffee, part one, the brew, because this is coffee part two, the roast.

Jam: the roast.

Melissa: So we are in the middle of a series of coffee that's been often requested and it's pretty fun because who knew there was so much chemistry in coffee,

Jam: Yeah, seriously. I mean, I always suspected, but now I'm getting to learn the chemistry behind something. I already love so much, which is so exciting.

Melissa: And I think you're going to feel excited about all the chemical reactions you do on a regular basis because you roast your own coffee.

Jam: I do. Yeah. Um, I've sort of a perfect. Sort of lay person for this because I do all these things. Everybody, everybody brews coffee in some way, most people do. But then when we talk about, you know, roasting, I guess there's some parts of coffee. I definitely don't do. I don't grow it, so I don't have experience there, but it is so nice to get that like extra, you know, deep layer of what's happening.

But I have a lay person's understanding of just like, why watch the coffee going around in a thing and it's heating up.

Melissa: You know, more than a lot of other laypeople would about this. In fact, I'm the lay person when it comes to coffee, but not the lay person when it comes to chemistry,

Jam: Right. Absolutely.

Melissa: Well, this works out really well, because I think you'll be able to talk some about what you've observed when I talk about the chemistry behind the roast of coffee.

Jam: Right. Me too. Yeah.

Melissa: Okay. So here's the thing that many people don't know and that, I wouldn't know.

Jam: Uh huh.

Melissa: if it weren't for you.

Jam: Okay.

Melissa: Coffee beans. Quote-unquote beans are actually the pit of coffee cherries. So the fruit that coffee trees. Yeah. Coffee grows on trees, which is kind of, you know, who knew the coffee trees, fruit, the seed of the coffee trees fruit the coffee. Cherry is what coffee beans come from.

Jam: Yes.

Melissa: Many people don't know. I think that coffee starts out as a green hard bean,

Jam: Yeah,

Melissa: more like a fruit seed than a coffee

Jam: totally. Yeah, It's very, very seed like in every way. And it's like, oh, that makes total sense.

Melissa: because it is a seed.

Jam: Yeah. It's like, oh yeah. And I also didn't think about it a little bit. You think? Oh yeah. It doesn't make sense for it to be a bean,

Melissa: No,

Jam: you know?

Melissa: but I don't think I would've ever thought about that before I'd met you. I would have just been like coffee. Is this drink? That smells good. And that's how much I care about. And it comes from beans in the end.

Jam: Yeah. I have a group chat with some other coffee nerds and for a while, we would just call them coffee seeds and just to try, see if we could get that to catch on.

And it really is, feels so weird. So

Melissa: Coffee seeds. I could see that that's a lot more accurate.

Jam: yeah.

Melissa: So when coffee beans come from the roasters, after they've been dried and quote unquote processed, which there's not a lot of chemistry about the processing of seeds, but I think it's just basically taking them from their fruity state to their isolated dried state.

Is that your understanding too jam?

Jam: Yeah. There's lots of ways to do that, but yeah, basically they're trying to dry them out. Yeah.

Melissa: Great. So once they're dried out, they come to the roasters and they are these hard little green beans, just like a seed. And then there is a. Plethora of chemistry that happens as they're being roasted and all this chemistry transforms these little green coffee beans into the delightful smelling, dark brown coffee beans that we know and love.

And I also think something that people might not know, is there something called coffee, bean cracking in this process? That's also part of what happens in the roasting process. And we're going to talk about that too.

Jam: Okay, nice.

Melissa: So very exciting. I am so happy to know about all the chemistry and it if it's in well with our purification episode from part one.

We talked about how all you can do all these chemistry reactions, but you ultimately need to purify to get just what you want. So we did the purification step in part one, and now I'm telling everyone you and everyone, how we make the chemistry or the chemical reaction is okay.

The chemistry is pretty complicated, not surprisingly and not everything is known about it, but a lot is known about it. One paper said it's complex. and poorly defined chemical reactions. Another paper described it as lots of chemical reactions over a range of temperatures. I think both of those are pretty accurate.

So when the beans come to the roasters in their green state, they have a lot of different molecules. Some have more caffeine than others. Some have different types of flavor molecules than. But all of them pretty much have carbohydrates in the form of sugar, other carbohydrates, proteins and some acids.

And those acids actually usually break down into the molecules that give flavor. There's also fats. And then of course, caffeine, although that comes in varying amounts. So all those are present in pretty much every green coffee bean.

Jam: Okay.

Melissa: But if you imagine you have all these molecules in a tiny little pod and you put that pod into heat, these molecules are going to start getting energy.

And when they get energy, what happens, they start to move around and they'll start to run into each other and chemical reactions happen.

Jam: Uh, yes, I see.

Melissa: So there's all kinds of chemical reactions that happen. One that happens pretty quickly is what's known as a maillard reaction

Jam: throwback.

Melissa: throw back. So if you don't remember this, you can go back to one of our very early episodes that was called what makes toast toasty?

I believe.

Jam: Oh yeah.

Melissa: And mired reactions is just a quick overview. It's what happens when a sugar and protein react to form a polymer

Jam: Hmm.

Melissa: and what's a polymer.

Jam: It is a large molecule made up of small molecules.

Melissa: That's right. Small repeating units. They just go over and over. So you could imagine it would be sugar, protein, sugar, protein, sugar, protein. To make this big, large brown polymer.

Jam: Nice. That tastes good.

Melissa: It tastes good. And it also is starting to turn the green coffee bean from greenish yellow, to a tannish brown as more and more of this polyamorous for.

Jam: Right, right.

Melissa: That's partially responsible for the color changing in a coffee bean. The other thing that's happening is caramelization. We haven't talked about that much, but caramelization occurs at high temperatures between just sugar. It's two sugar molecules, but it does also end up in a nice brown polymer.

Jam: Okay.

Melissa: Okay.

else is happening also.

Jam: Okay.

Melissa: Even though coffee beans seem hard and dried. There is some water in the beans still.

Jam: Okay.

Melissa: So while these reactions are going on, water is also heating up. And I think this is, we kind of already touched on it, but the best chemistry lesson of this episode is as molecules heat, they start to move around.

And as they go from their liquid state to their gaseous state, they move around even more. So they're spreading apart from one another. Right.

Jam: Right. right.

Melissa: as they're moving around that much, they start to put pressure on the walls of whatever space they're in. And as that pressure builds and builds it physically expands the coffee bean.

Jam: Okay, this is sounding very familiar to what I've experienced.

Melissa: Yes. As you roast coffee beans, oftentimes they will expand and it expands and put so much pressure on the bean up until the point that the bean physically cannot handle the pressure anymore. And what happens under pressure?

Jam: Things explode or pop or


Melissa: explode, pop or crack.

So the coffee bean actually cracks open to give an out to all of the vapor pressure that's building up in there.

Jam: that makes so much sense.

Melissa: So that's why they call when you hear coffee roasting, there's a first crack that, uh, that is the result of water vapor that has built up to the pressure point that the bean can't take anymore.

Jam: Nice.

Melissa: So usually the first crack is supposed to happen around 2 0 5 Celsius, which is interesting because water begins to vaporize, I mean, water boils at about a hundred Celsius.

So that is double the temperature of water's boiling point when the crack finally happens.

Jam: Yeah. Interesting.

Melissa: is that what you've seen in your roasting? Is it usually around 200 Celsius? I think that would be close to 400 in fahrenheit.

Jam: Yeah, it is. It is probably so the temperatures I have, or like, I have a reading of what the roaster is set to kind of like an oven. You know, you set your oven to 400 in the case of my roaster, I set it to that 480.

Melissa: Wow.

That's hot.

Jam: it's very hot, but I bet that finally the beans are getting to around, um, that temperature inside because it takes a while I would guess.

And then that's when they crack. So Yeah. that makes sense that sounds right.

Melissa: Well, there's also another reaction that continues to happen, but I'm going to stop right there and say light roasts are typically stopped after the first crack. Once that first crack occurs, then the roasting process shuts down.

Jam: Yes. And that's almost all I do. So my experience of the process, unless I mess up something stops right around there. I would try to make sure all the beans have reached first crack. And then I take them out and try to cool them off as fast as I can.

Melissa: So they're not continuing to

Jam: Yeah.

Melissa: Well, the other reaction that happens, or one other reaction, I guess there's probably lots of others making side products that smell really amazing, and everything is something known as pyrolysis

and pyrolysis is kind of a fancy term for molecules breaking down and releasing gas like CO2.

So there, they sometimes refer to paralysis as degrading, but basically molecules are still reacting with each other and they're releasing CO2. And this is happening within the coffee bean and within the coffee bean, there are strong cellular walls made of cellulose.

Jam: Okay.

Melissa: And so again, this reaction is happening and these gases are being released.

And now pressure is being put on the cell walls within the coffee bean, not the overall bean itself, but on the cell walls. And actually that pressure will build up again to the point that this cell walls will crack.

Jam: Oh, I see.

Melissa: And that is what we call the second crack

Jam: Yes.

Melissa: and something interesting that happens on the second crack, actually.

The cell walls have now cracked. So the oils and fats within the walls are able to get out of the cells and dark roasts that have gone to this point often have an oily appearance.

Jam: Yeah. Dang. That's interesting. I've definitely noticed that. And it's always bad news in my book because. I'm like, it means I forgot to take the roast out or I didn't hear my timer or I was too busy prepping the next thing or something like that.

And then I'm like, no.

Melissa: something interesting about that, that I think really speaks to how you love the flavor of coffee itself.

Is that they say that dark roast means that we are mostly tasting is the flavor of the roast of the side products.

And most of the coffee itself flavor is overshadowed by the, all of the pyrolysis products, the maillard reaction and the caramelization.

And you are tasting more of the roast itself rather than the coffee itself.

Jam: Got it. That makes sense.

Melissa: Yeah. So it almost overshadows the original flavor. You love the flavor of coffee.

Jam: Yeah,

Melissa: So it makes sense that you wouldn't want that, but I've heard they do use those dark roasts for lattes. I love lattes. So what does that say about me?

Jam: Well, I guess it's, I think one thing too, is that like all the flavors I don't like are severely curved when you have a latte. So like,

Melissa: That's true.

Jam: kind of nice. I bet you would. If you had to drink a black cup of coffee, you'd probably prefer light rose to, I would bet.

Melissa: In the past that's been true yet.

Jam: I think most people, I would, not everybody, obviously there's people who like the taste of ashes and stuff, but that's how I feel like it tastes sometimes it's like yikes.


Melissa: And as his reactions proceed, the coffee gets darker and darker, and that's why as it roasts longer, it's called a medium roast and then a dark

Jam: yeah. Okay. Dang. Interesting.

Melissa: And I will say when the coffee bean cracks and even in the second crack, oftentimes that's when the aromatic molecules are released giving the classic coffee flavor.

Jam: Uh,

Melissa: And there are actually hundreds of different molecules in coffee, but only around 30 have been identified that contribute significantly to the flavor of coffee.

Jam: Okay.

Melissa: Although that kind of surprises me. I think they may be mean classes of molecules, like 30 types of molecules,

Jam: I see. Yeah.

Melissa: because I know that maillard reactions themselves can give a lot of side products that also usually smell and taste. Great.

Jam: right.

Melissa: And that's it, that's the chemistry behind coffee roast.

You've got a lot of different reactions causing molecules to do a lot of different things and that results in your delicious coffee.

Jam: Nice. Very cool.

Melissa: Jam would you like to try to give a chemistry lesson recap

Jam: Yes. I'd love to.

Melissa: and then maybe we can do our coffee corner with Jam and you can tell us all about your roasting process.

Jam: Absolutely. I'd love to do that. As a quick disclaimer, due to some parenting overlaps, there are, and some schedule changes. There are some toddler sounds in the background.

of this section of the episode.

And so we're very sorry.

Melissa: Sometimes life happens, you know,

Jam: So we start out with this, we already have received this dried out seed of the coffee, plant coffee, cherry. And we've got a lot of them. They're this small little green dried seed and we

Melissa: Oh, I did forget to say that depending on the region that the coffee bean slash seed is from, it will have variety. It will have a variety of different molecules that may be present in it.

Jam: that makes sense.

Melissa: So that's why some have different amounts of caffeine and some, maybe have slightly different flavors depending on the region.

Jam: Yeah, that makes total sense. So we take that and obviously we put it in a lot of heat, no matter what kind of roaster you got, hopefully it's a heating, I think that's a requirement for roasting. So as these coffee seeds are being heated up, all the different kinds of molecules, which there's tons including some like water and stuff like that,

Melissa: water, sugar, proteins.

Jam: proteins.

and that you said that the sugar is carbohydrates or whatever, it's

Melissa: Yeah,

sugar is a type of carbohydrate and there's often other carbohydrates as well.

Jam: And as we know, when things heat up the atoms and molecules and them start to get excited and they expand and move around and interact and all that kind of stuff.

Melissa: Yup.

Jam: And we get all kinds of things to start happening. Like polymers can start being formed with the maillard reaction,

Melissa: That's right. The tastiest reaction.

Jam: Where sugars And proteins.

Turning into creating this, this polymer as they get hot enough and react together. And then.

also the water that's in the. Coffee seeds at a certain point starts to expand and turn into steam,

Melissa: Yes.

Jam: And as that happens, the beans get a little larger. And a certain point to be able to release that steam that pressure's being put on the beans, they crack open

Melissa: They literally explode.

Jam: and we can hear it. I hear it. Every time I roast coffee, like a little, it's like a little sort of faint popcorn pop kind of thing. And that lets me know that they are ready to come out of the roaster because they've reached the point that I want it to be roasted

Melissa: Which that's typically the light roast stage. Correct?

Jam: If I were to do something that I don't normally do and what a dark roast, I would leave them in longer

Melissa: Right.

Jam: And a lot of those reactions would continue happening.

Melissa: And in addition to the maillard we talked about what other reactions do you remember?

Jam: I remember?

at least the one where it starts putting pressure on. Cell walls,

Melissa: that's called pyrolysis

Jam: And that starts to break the cell walls open. Cause they have to release that pressure,

Melissa: right?

Jam: which releases oils. We see that like shininess and the outside of the coffee beans.

Melissa: Yeah. And you actually had a dark rose that I looked at and it really does have that oily. I was amazed to see


Jam: It's kinda crazy how quickly it.

happens. I've I was an accident, so I've just kept it and use it for lattes for my wife, because she likes to have this some times. Um, but That happens. Oil starts to come out. It gets a lot darker. Oh, I, I guess I should say that causes that second crack. We hear

Melissa: right?

Jam: pyrolysis the second crack is the cell walls and the coffee bean turned to crack and break open and release that pressure, Right.

Melissa: Exactly. I think the only thing you missed is something else that contributes to the dark color of the coffee is caramelization,

Jam: caramelization.

Melissa: which is sugars reacting with themselves.

And I do think it's really cool and important thing to know is a similar thing that causes sea level rising in climate change.

Is thermal expansion. And that also is what puts the pressure on the coffee beans they causes. The first crack is the water is expanding as it heats up to. That's kind of cool.

Jam: Yeah.

Melissa: The same thing that causes sea level rise also brings you, coffee

brings the delicious flavor of

Jam: It's great when it's on this tiny scale and one little coffee seed.. It's not great when it's the entire ocean.

Melissa: Right.

Exactly. Exactly.

So that's about it. In terms of the chemistry lesson for today, you did a great job of recovering it. I'm really impressed. And I love the idea of a lot of chemical reactions over a range of temperatures. I think that describes it really well,

Jam: Hm.

Melissa: but I did want to jump into coffee corner with jam and ask you how you roast your own coffee.

I mean, do you do it in the oven or do you have a roaster? What is your roaster even look like? What is that process like? Because I think our listeners also want to know, I've heard them also ask questions about that.

Jam: Yes, I'd be glad to tell you guys. Thanks for asking. Thanks for giving me an excuse to have to tell you about coffee so I have used a lot different things to roast coffee. The first thing I ever used was a wok. It's not a bad option. If you ever wanna just try it out, you just gotta stir it the entire time and keep all the, keep the beans moving and stuff like that. But

Melissa: Is it hard to get it up to the right temperature,

Jam: it's, it can be, I mean, wok's can to get, if you have one, that's not coated or anything, you can get them pretty hot.

Um, it's just, it's just really easy for it to be super inconsistent from time to time. Like stoves are normally not trying to be very super precise and every stoves, a little different. So you don't have the ability to necessarily know like, oh, when I turn it to five on my stove, it gets it to up to 480 degrees, you know, it's hard to like, know that stuff about your own

Melissa: It's not as consistent as some other instruments would be,

Jam: Especially the electric stoves, that kind of pulse, how much the, you know, stuff

like that.

Melissa: Yeah.

Jam: But, um, so I've used a wok. I've never used the oven. People usually say that that's not a great way for some reason. I'm not sure exactly why. So I've never tried that I've used a little stove top.

Melissa: it sounds like your son also wants to share his coffee resting experiences.

Jam: very excited about, he's like, oh, I've watched my dad do that. And here I'll tell you my version.

Melissa: I'm not sure how well people can hear, but he is. Chiming in.

Jam: I've used that a little stove, top popcorn popper thing that has a crank with it,

Melissa: Yeah.

Jam: It's really nice because as lid

Melissa: Yeah.

Jam: inside helps things be much more. Even

Melissa: usually lightweight too. So it probably conducts the heat pretty well.

Jam: Often they're made of aluminum, sometimes stainless steel. And so those are great options. If you're ever curious, those are available, lots of places and you don't

have to

Melissa: I got one at a thrift shop once.

Jam: Yeah. And at one point I, even my friend and I both had those, we, um, dremeled off the crank and attached a tiny little motor instead. And so then we had these motorized little, um, pop stove, top popcorn, poppers. I have a YouTube video that shows showcases mine

Melissa: That's

Jam: working. And, um, it's one of my most viewed YouTube videos on my very, pretty much nonexistent YouTube channel. And then I had this tiny little countertop roaster that could roast only like around a third of a pound at a time. So like about 150 grams or

Melissa: So

how many cups is that for the layman like me

Jam: So about 20 grams per mug of coffee. So you could do

Melissa: six or so? Six or seven?

Jam: yeah, so it was roasting around, you know, seven or eight mugs of coffee at a time. So not a lot.

Melissa: Right.

Jam: The finally, eventually I was able to upgrade to a little roaster that roasts half a pound. So Not a huge difference

Melissa: Not a huge difference at all.

Jam: what I currently use at roasts around 220 grams per

Melissa: Okay. All right.

Jam: And so I use that now it's called a Gene or Genie cafe.

Melissa: And about how much does the, one of those costs? Like how much have you invested in your coffee roasting experience?

Jam: if you were to buy one of those new, I think there's somewhere north of $500. For one of those

Melissa: but you bought it used

Jam: used from some friends of ours who used to roast and then abandoned it. And, um, it takes about, I have to preheat it, which helps a lot speed of the process. It's an it's kinda nice because then when you put the beans in, you're trying to get them up to temperature, to reach first crack the sooner, the better, um, for a lot of those little small roasters, you don't want the outside to get super reacting and really dark before the inside has reached temperature.

Melissa: right before the crack.

Jam: So what a lot of these, these little small roasters, the name of the game is to get it really hot, really fast, and then get them out of there. And you cool them externally. So That's what I do. It takes about nine or 10 minutes to do a roast after I've already preheated

Melissa: That's fast.

Jam: It's pretty fast.

And I will say that that's, I think some of the basics of how I roast coffee. Um, and then I store them in an airtight jar, keep them in a

Melissa: To try to keep the air aroma locked in there. Okay.

Jam: and I could definitely go on and go into lots of other details, but that's the sort of, I think most important elements of what it's like to roast coffee.

Melissa: Well, I will say, although I'm not involved in much of the coffee drinking in my home, coffee that is drunk in my home comes from jams, roaster.

Jam: That's true,

Melissa: And I think don't, you provide a few other people with coffee, roasted coffee, but you're not selling it right now to people that you'd have to ship it to.

Jam: correct. It is some neighbors. Um, it's like one of those things where, you know, if you are an avid baker or an avid, anything you. Often tend to just have extra around. So a few neighbors and friends of ours, um, get coffee from me, but it's not something that I can, I mean, I'm only posting half pound at a time.


Melissa: Right,

Jam: that is not really the kind of thing you want to scale for trying to have a business or anything like

Melissa: right. right. I know some people have asked.

Jam: Yeah, people have asked.

I would love to someday, but at the moment you guys can do the math and realize how hard it would be to only be able to roast half pound at a time and try to do that as a service for people.

It's just not, if I had an abundance of time, then I actually would, should probably do it because it's really fun. But at the moment, being able to move at a snail's pace on the roasting coffee makes it impossible. So.

Melissa: Yeah. That totally makes sense. Well, thank you so much for sharing about how you do your coffee jam. That was really fun.. And normally at this point we would share something fun. That's happened to us this week, but Jam's son is really interested in our stopping this podcast and hanging out with him instead, so perhaps you can hear him voicing his displeasure with us.

So we're going to wrap it up here. And next week is our Q and R. So you can hear all of the fun stuff going on in our week. In that episode.

Jam: Well Melissa, thank you so much for teaching me and all of us about the chemistry of roasting coffee. Super interesting. I've always wanted to know more. I know just enough to get the job done in term of. Actually doing the thing, but knowing the detailed chemistry behind it is awesome.

And you guys thank y'all for sending in your ideas and your questions about chemistry, please don't hesitate to do that things like what ha what's the chemistry of roasting coffee. We love to hear questions. They are such great ideas. So send them to us on Gmail, Twitter, Instagram, or Facebook at Kim for your life.

That's Kim for your life to share your thoughts and ideas. If you'd like to help us keep our show going or contribute to cover the cost of making it go to ko-fi.com/chemforyourlife and donate the cost of a cup of coffee. If you're not able to donate, you can still help us by subscribing on your favorite podcast, app and rating and writing a review on apple podcasts.

That also helps us to share chemistry with even more people.

Melissa: This episode of chemistry for your life was created by Melissa Collini and Jam Robinson references for this episode can be found in our show notes or on our website. Jam Robinson is our producer, and we'd like to give a special thanks to A Collini who reviewed this episode.

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