(upbeat music)
- Today we're gonna talk about roasting coffee.
I'm gonna cover what you, someone who buys drinks
and enjoys great coffee,
needs or maybe even wants to know,
about what is a fascinating process.
There's a lot to cover today.
We'll start with the basics
of how the roasting process impacts taste
and then we'll go deeper into some of the chemistry
going on inside the coffee bean during the process.
We'll cover what roasters are really trying to say
when they use 'light', 'medium', and 'dark' on their bags.
We'll get into the different kinds of machines
that specialty coffee companies use to roast their coffee.
And we'll also talk about the processes they
go through to keep it tasting great every single day.
Before we get into that, we should begin where
this whole journey begins with raw coffee.
So this is raw coffee.
This is the seeds, the dried seeds of the coffee tree.
And right now it smells and tastes, well, pretty terrible.
It doesn't smell of much at all.
It smells kind of like,
[Sniffs]
well plant seeds a little bit, 'cause that's what it is.
All of the flavor happens in that process
of transformation inside the roasting machine
and it is an astonishing process of transformation.
You would never think looking at these,
potentially tasting these,
that they were capable
of so much flavor and so much complexity.
But as we're gonna explore today, they absolutely are.
Now, it's the roasting process that creates those kind
of familiar coffee flavors that we all enjoy.
And when we talk about the roasting process,
we often simplify it down
to three characteristics that change
in the process, as we roast the coffee.
And the first one is bitterness.
The longer we roast the coffee,
the darker the color of it will be.
And a little bit like caramel,
a darker caramel will also taste much more bitter.
So there's an increase
in bitterness during the roasting process.
The second characteristic we often simplify is acidity.
Now that actually increases initially,
and then has a little bit of a bell curve,
and then begins to decrease the darker the roast gets.
For this reason, a lot of people prefer
darker roasted coffee.
It doesn't have the acidity
that they don't particularly enjoy.
However, it's rare to find dark roasted coffees
in the specialty coffee world.
And that's because
of the third characteristic we need to talk about,
which is difficult to talk about,
without sounding a little bit pretentious.
And that is origin characteristics.
Where you grow coffee,
be it soil type, climate, altitude,
or even how you process it after harvesting,
well, all of that will have an impact
on the kind of chemistry inside the seed.
And when you roast it,
well, different coffees will produce different flavors.
We'll call this origin characteristic.
And initially when you roast a coffee,
you do create those flavors.
You can only create them based on what's there,
but there's a process of creation initially.
Then, however, the longer you roast the coffee,
the less of those distinct
unique characteristics that belong
to that particular coffee remain.
And you get more and more
of what we call a kind of generic roast taste.
Put another way, darker roasted coffees ultimately end
up tasting much more similar.
And because specialty coffee is so interested
in unique characteristics,
that's why you tend to see lighter roasts
that also happen to have more acidity in them.
But this is a simplification of the process.
Let's go a layer deeper.
What we'll do now is we'll just follow
along the roasting process,
from raw all the way through to a pretty dark roast.
So what we're gonna show you is a couple
of angles of the roasting machine running
and what we'll also do is pull out a sample every minute
or so initially for the first five or six minutes,
and then every 30 seconds
after that, as the roast progresses,
so that we can see the color changes happening.
Now, initially, not a lot happens.
You'll see that the green coffee remains green
for a little while.
Green coffee has quite a lot of moisture in it
and what the roasting machine needs to do first,
is essentially dry it out.
It's really hard to have those browning reactions
take place with moisture present.
It kind of limits your temperatures.
Once that coffee has gotten dried out,
you'll see the color changes from green,
it gets kind of paler,
and then relatively quickly will begin to yellow.
And we're at the very beginnings
of those kind of browning flavors.
Now, this roasting chemistry, as it progresses,
does some really interesting stuff.
Firstly, all of that water
that hasn't escaped is turning to steam
and is building up pressure.
And then other roasting chemistry
is causing gases to form, gases like CO2.
But we'll see a lot more of that later.
And you build up pressure
inside the coffee bean,
and a really key moment
in the roasting process is called first crack,
because at some point relatively early on,
that pressure becomes too much and the gas escapes
from the coffee bean causing it to crack open
and you can literally see those cracks.
But more interestingly, you can hear them,
it sounds a little bit like popcorn.
(machine whirring)
But it isn't like popcorn.
It doesn't swell in size.
It just lets the gas out.
As a roaster, you're paying attention
to when this happens in your roasting process.
And from this point onwards,
the browning reactions are really underway
and those are so complex and so rapid that this is a point
from now on where you are really paying a lot of attention.
Those color changes are relatively minor,
but the flavor changes happening now
are actually surprisingly large.
Historically, roasters just looked
at the color of the coffee beans.
We'll talk about why they don't do that anymore.
But ultimately these shifts aren't very visible,
but they are big changes in flavor.
Big changes in acidity and sweetness
and bitterness are happening right now.
At this point, you could probably take the coffee
out and drink it and enjoy it,
depending on your vision as a roaster,
on how you like coffee to taste.
The coffee may roast a little bit longer.
This point, everything is drinkable and good.
So as the roast progresses,
those beans will begin to get a little bit darker.
They'll also get a little less wrinkly
and a little bit more even looking.
As they get darker, they'll kind of smooth out.
But as we continue to progress,
well we get towards dark roasts
and what'll happen is there'll be another release
of gases later on and that's called second crack.
Here you you'll see that the beans are really pretty smooth,
a much darker brown and the beginnings
of oil on the surface of the bean,
that's happening because of those pressures
inside the bean forcing the the oil to the surface.
And the coffee bean itself is much more porous.
It's actually swelling
and growing in volume, decreasing in density.
Now, you can keep roasting
and you can keep roasting, you can keep roasting.
You'll generate more and more of that bitterness.
At this point, acidity is really pretty low.
Origin characteristics is really pretty low
and bitterness is going up and up and up.
You might also see an increase in texture
and kind of body and mouth feel when you brew that coffee.
But after, in this case, I think 17, 18 minutes of roasting
we're gonna call it a day here,
However, people do roast darker than this.
For me though, this was dark enough
to show you what I wanted to show you.
So what we've done is we've laid out some
of the coffee from each of the samples here on the table,
so we can talk about roast levels and really what they mean.
Now we'll talk about specialty first,
because I would say,
the the kind of categorization of light medium dark
is a little different between specialty and commercial.
Specialty would start,
I would say around here, really pretty light
and it would run probably to around here.
So anything within this,
could be classified as a light roast.
Medium would run
from this point up until maybe here.
The minute I see any sort of oil of any kind on the surface,
I would say you've crossed into a dark roast.
And from here onwards it's a dark roast.
It's rare for special to be at this end of dark roasting,
but it's not unusual to see coffees roasted this way.
Commercial's a little bit different.
I would say the light starts about the same,
but probably runs a little bit further in.
Then medium would start here
and run again a little bit further in.
And then after that, dark roasted.
They'll also roast darker than we have done here.
I don't think it tastes great
from a specialty perspective,
but some people still do enjoy very darkly roasted coffee.
At some point,
it just turns to carbon and then catches fire.
I don't recommend that.
But darker roasts are certainly possible,
but the color alone does not tell you everything.
To understand that a bit more deeply,
we need to talk about what's called a roast profile.
Now, if you wanted to roast coffee at home,
you could certainly get a sheet tray
and pour out some raw coffee on it,
pop it in an oven at 200 degrees Celsius
and it will roast in there, it will go brown.
If you look at the roast profile,
you'll see that the temperature
of the coffee would increase and it would begin to slow,
the closer it gets to the target temperature.
When you take it out though,
that's not going to be the best tasting coffee,
for a couple of different reasons.
Firstly, where the coffee beans have been
touching the metal the whole time,
well they'll have had a lot more conduction heat transfer
and they're probably gonna be a little bit burnt
around those spots.
And secondly, you don't necessarily want to have
one constant temperature that the coffee is trying to reach.
What we've learned through coffee roasting is actually
you wanna vary the amount of heat coming
into the roaster and change it to change the rate
at which the coffee is turning brown.
So this brings us to what roasters are talking
about when they talk about a coffee roast profile.
Now, machines themselves can often be very old.
They can be sometimes very new.
Regardless, they're all using multiple temperature
probes positioned around the roaster to collect data
and feed it into some sort of computer software.
What that's ultimately gonna track,
is the temperature of the bean probe.
That's our closest guess to the temperature
of the beans themselves during the roast.
Now, the journey of the beans in terms
of how quickly they get hot, it will change depending
on the coffee and what you want it to taste like.
It might be that this phase here
in the middle is it's heating up if it heats up quicker
or if it heats up slower.
Well that would change the flavor
and through a period of trial and error,
and ultimately then knowledge that's passed around
within the industry, you learn to create a roast profile
for a particular coffee, usually on a particular machine.
So it's not something you can take
from one person's roaster and apply
to another person's roaster, which is kind of confusing.
Now here on the screen you can see a few things going
on and quite a lot of data,
and for most people it's kind of overwhelming.
But ultimately, this probe here
is the beam temperature probe
and you can see the journey
that it goes through and you'll see,
that generally it's heating up pretty quickly here.
It slows and continues to slow
and towards the end slows even more.
That's not absolutely universal, but it is extremely common.
And during the roast, roasters are making small changes
to the amount of heat coming out
of the burner or in some cases the amount,
of air flowing through the drum,
to change how much heat is being transferred
to the coffee itself.
And that's how you create a roast profile.
Roasters aren't aiming for one perfect profile,
but they are aiming for consistency in their roasts.
And I wanna talk just briefly about how they approach that.
Now, the first most obvious thing to do
is to taste the coffee that you roast.
And most roasters will be tasting everything
that they roast, but there is a problem.
Modern expectations say
that the consumer wants their coffee roasted,
bagged and shipped the same day,
so that it is as fresh as possible.
And this means really functional tasting is difficult to do
before the coffee goes out the door.
So they're looking for other ways,
other checks that the the coffee can pass or fail to hit,
to make sure that what they bag up and ship
is tasting the way that they want it to.
There's really three ways
and the first way we've kind of touched upon,
that's the roast profile.
The coffee should have followed the desired lines
during the roast in order to pass that at the start.
But some roasters will have higher tolerances
than others there.
And there are still other ways to check
if things have gone as planned.
Another common thing is what's called roast loss.
Now when you roast coffee, it loses weight.
You might start with 10 kilos
of coffee and anywhere from maybe 13% through to 22%,
23% of it may be lost during the roasting process.
Most of that is water, but the darker you roast coffee,
the more stuff breaks down and disappears.
It doesn't tell you that much.
But if you're expecting 14.5% roast loss and you get 15%,
that should be a red flag that things haven't
gone as expected.
And the third one that, again,
is very common is color testing.
This is using some sort of machine that kind
of measures brownness, how light, how dark the coffee is.
Most roasters will grind a sample after roasting
of every single batch and test the color using one
of a variety of meters that do this.
The most popular one
or the most commonly talked about one is one called Agtron.
And sometimes you'll even see companies
publishing the Agtron numbers of their coffees
to give you some indication of how light or dark that is.
I'm not sure that's very useful.
It's really a good solid internal measurement.
As we talked about with roast profiling,
the color alone doesn't tell you all that much,
but it's definitely gonna be a problem
if that color is too dark or too light.
And again, roasters will have some variance,
some allowance within that color measurement,
a kind of window of tasty.
Those are the primary ways in which roasters QC coffee.
Now one thing I wanna talk about here
is what roasters mean when they talk
about a coffee being 'roasted for filter coffee'
or having the word 'espresso' on the label,
implying that it's roasted
in a way that should be brewed as espresso.
Espresso is difficult brew method,
it doesn't use much water.
It's very intense.
It's very quick and and what roasters typically try
and do is roast the coffee
in a way that it's easier to extract.
That might be they roasted a touch darker in color.
It might be that the whole profile
takes a little bit longer.
They slow the roast down and there's variations within that.
But that's what espresso on the label means.
It it's typically a more soluble roast than it would be
for a filter coffee,
'cause it's easier to properly
brew coffee when you brew it as a filter coffee.
You've got a lot more time and you've actually
got a lot more water to do the extraction work with.
Now, you don't have to brew espresso labeled coffees
in an espresso machine.
You can brew it in a moka pot,
you could make it in a pourover and probably enjoy it still,
but that's what roasters are trying to communicate
with that language on the label.
Let's talk now about how these
roasting machines actually work.
So first up, I wanna talk about a type
of machine called a drum roaster, and it's called that
because in the middle of this thing is a big spinning drum.
It's like a kind of giant tumble dryer.
Now the way that these work is that you have
underneath here a heat source,
typically it's a gas burner
and that's gonna heat two things.
By proximity, it's actually gonna heat
the big metal drum typically made of cast iron,
but primarily it's gonna heat air.
Now that air is being pulled through the back
of the drum through the coffee and out,
and it'll run from here through this fan
that's doing all of that work.
And it'll be pushed out of the exhaust and away,
typically in larger roasters to be burnt,
to get rid of any smoke in what's called an afterburner.
Drum roasters are interesting.
They're probably the most common type
of roaster used in specialty coffee companies.
And they heat coffee slightly differently.
They heat coffee three ways.
Primarily it's convection,
it's the hot air flowing through the coffee beans.
But because the drum is hot, there is some conduction heat,
a little bit like a steak in a frying pan.
That that touch of the bean
onto a hot surface does have some heat transfer.
In addition, because that drum is hot,
there's also radiant heat kind of emanating
from the metal into the coffee.
But primarily it's gonna be the convection
of the air going through it.
It does produce a different kind of flavor,
conventional wisdom says, to other kinds of roasters
but I don't know how true that really, really is.
There's a lot of different ways to use a drum roaster
and you can get a lot of very different results from it.
Now the roaster operating the machine is gonna be
paying a lot of attention to the probe data coming
from it to decide when to make changes to the gas going
to the burners, but at a very specific endpoint,
a combination of time, temperature, and color,
the coffee very quickly needs to stop roasting
and to be cooled down
and pretty much every roaster will use some sort
of cooling tray.
Now, when the coffee leaves the roasting machine,
it's often in excess of 200 degrees Celsius.
And I dunno what that is in Fahrenheit,
but it's very hot and we need to make it as close
to room temperature as possible,
as quickly as possible to stop the roasting process.
Now, most machines will use air to do that.
The coffee will tumble into a tray
like this one, arms will stir it,
and mix it as a very large fan pulls air
from the room down through it, to cool it down very quickly.
Now, larger machines or machines
with slightly smaller cooling trays,
sometimes need to use a different process called quenching.
Here, a very, very small amount
of water is sprayed onto the coffee beans.
That water instantly evaporates because the beans are so hot
and the evaporative cooling really very quickly
cools the beans down.
Now, there's no real downsides to quenching,
except that that coffee will need a little bit less rest
before cooling and it will stale slightly quicker.
But quenching does not impact the quality
of the coffee whatsoever.
Cooling done.
Let's talk about a different sort of roasting machine.
There is another type of roasting machine.
It's called a hot air roaster,
a little bit different to a drum machine.
Here you've got a big heat source and that's separate
to the machine and it produces one side a blower,
vast amounts of hot air that flow into the machine
and the hot air is not only gonna roast the coffee,
but it's gonna do all of the agitation as well.
So when you look inside these,
you can see the coffee being thrown around,
churned and moved just by the volume
of air flowing through it.
That means there's no real moving parts in the roaster.
The way there are inside a drum roaster.
but just the same,
you're gonna vary the intensity of the heat,
but here you can also vary the volume
of air flowing through it.
There's no better roaster out there
in the world than any other.
There's simply a tool
for a roaster to create the flavor profile that they like.
And for some roasters, they prefer the style
of coffee you get from an air roaster,
that is a little bit different to drum roasters.
And then there's a third type of roaster,
a kind of hybrid air roaster.
Here, you still have a drum
that rotates to tumble the coffee,
but like an air roaster the heat source is separate.
So it's really just heating the air.
The drum itself does not get hot.
Some people say these can be much more efficient.
Others like the fact that the drum doesn't kind
of have any conduction heat into the coffee.
Again, roasters are just tools
to make the coffee that you wanna make.
And that is the basics of coffee roasting.
And now I want to hear from you down in the comments below.
What aspect of this do you wanna know more about,
should we go deeper into in the future?
Has this been helpful in how you think about coffee?
Has it been eye-opening?
Let me know your thoughts.
I'd really appreciate it.
Now, I will say, some of you are gonna ask a question
and that question is, when are you gonna make a bunch
of videos about roasting coffee at home?
I don't know.
But I will tell you that I definitely,
definitely want to make those videos.
They are in the master plan,
the big what we will do in the future.
I just don't know when.
All right, enough caveats from me.
I'll say thank you so much
for watching and I hope you have a great day.