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(upbeat music)
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- Today we're gonna talk
about roasting coffee.
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I'm gonna cover what you,
someone who buys drinks
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and enjoys great coffee,
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needs or maybe even wants to know,
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about what is a fascinating process.
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There's a lot to cover today.
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We'll start with the basics
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of how the roasting process impacts taste
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and then we'll go deeper
into some of the chemistry
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going on inside the coffee
bean during the process.
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We'll cover what roasters
are really trying to say
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when they use 'light', 'medium',
and 'dark' on their bags.
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We'll get into the
different kinds of machines
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that specialty coffee companies
use to roast their coffee.
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And we'll also talk
about the processes they
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go through to keep it tasting
great every single day.
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Before we get into that,
we should begin where
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this whole journey begins with raw coffee.
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So this is raw coffee.
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This is the seeds, the dried
seeds of the coffee tree.
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And right now it smells and
tastes, well, pretty terrible.
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It doesn't smell of much at all.
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It smells kind of like,
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[Sniffs]
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well plant seeds a little
bit, 'cause that's what it is.
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All of the flavor happens in that process
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of transformation inside
the roasting machine
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and it is an astonishing
process of transformation.
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You would never think looking at these,
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potentially tasting these,
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that they were capable
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of so much flavor and so much complexity.
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But as we're gonna explore
today, they absolutely are.
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Now, it's the roasting process
that creates those kind
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of familiar coffee
flavors that we all enjoy.
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And when we talk about
the roasting process,
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we often simplify it down
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to three characteristics that change
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in the process, as we roast the coffee.
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And the first one is bitterness.
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The longer we roast the coffee,
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the darker the color of it will be.
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And a little bit like caramel,
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a darker caramel will also
taste much more bitter.
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So there's an increase
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in bitterness during the roasting process.
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The second characteristic we
often simplify is acidity.
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Now that actually increases initially,
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and then has a little bit of a bell curve,
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and then begins to decrease
the darker the roast gets.
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For this reason, a lot of people prefer
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darker roasted coffee.
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It doesn't have the acidity
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that they don't particularly enjoy.
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However, it's rare to
find dark roasted coffees
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in the specialty coffee world.
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And that's because
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of the third characteristic
we need to talk about,
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which is difficult to talk about,
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without sounding a little bit pretentious.
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And that is origin characteristics.
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Where you grow coffee,
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be it soil type, climate, altitude,
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or even how you process
it after harvesting,
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well, all of that will have an impact
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on the kind of chemistry inside the seed.
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And when you roast it,
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well, different coffees will
produce different flavors.
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We'll call this origin characteristic.
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And initially when you roast a coffee,
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you do create those flavors.
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You can only create them
based on what's there,
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but there's a process
of creation initially.
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Then, however, the longer
you roast the coffee,
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the less of those distinct
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unique characteristics that belong
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to that particular coffee remain.
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And you get more and more
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of what we call a kind
of generic roast taste.
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Put another way, darker
roasted coffees ultimately end
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up tasting much more similar.
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And because specialty
coffee is so interested
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in unique characteristics,
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that's why you tend to see lighter roasts
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that also happen to have
more acidity in them.
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But this is a simplification
of the process.
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Let's go a layer deeper.
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What we'll do now is we'll just follow
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along the roasting process,
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from raw all the way through
to a pretty dark roast.
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So what we're gonna show you is a couple
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of angles of the roasting machine running
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and what we'll also do is
pull out a sample every minute
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or so initially for the
first five or six minutes,
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and then every 30 seconds
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after that, as the roast progresses,
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so that we can see the
color changes happening.
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Now, initially, not a lot happens.
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You'll see that the green
coffee remains green
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for a little while.
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Green coffee has quite
a lot of moisture in it
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and what the roasting
machine needs to do first,
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is essentially dry it out.
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It's really hard to have
those browning reactions
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take place with moisture present.
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It kind of limits your temperatures.
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Once that coffee has gotten dried out,
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you'll see the color changes from green,
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it gets kind of paler,
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and then relatively quickly
will begin to yellow.
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And we're at the very beginnings
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of those kind of browning flavors.
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Now, this roasting
chemistry, as it progresses,
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does some really interesting stuff.
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Firstly, all of that water
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that hasn't escaped is turning to steam
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and is building up pressure.
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And then other roasting chemistry
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is causing gases to form, gases like CO2.
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But we'll see a lot more of that later.
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And you build up pressure
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inside the coffee bean,
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and a really key moment
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in the roasting process
is called first crack,
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because at some point relatively early on,
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that pressure becomes too
much and the gas escapes
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from the coffee bean
causing it to crack open
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and you can literally see those cracks.
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But more interestingly, you can hear them,
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it sounds a little bit like popcorn.
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(machine whirring)
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But it isn't like popcorn.
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It doesn't swell in size.
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It just lets the gas out.
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As a roaster, you're paying attention
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to when this happens in
your roasting process.
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And from this point onwards,
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the browning reactions are really underway
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and those are so complex and
so rapid that this is a point
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from now on where you are really
paying a lot of attention.
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Those color changes are relatively minor,
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but the flavor changes happening now
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are actually surprisingly large.
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Historically, roasters just looked
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at the color of the coffee beans.
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We'll talk about why they
don't do that anymore.
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But ultimately these
shifts aren't very visible,
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but they are big changes in flavor.
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Big changes in acidity and sweetness
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and bitterness are happening right now.
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At this point, you could
probably take the coffee
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out and drink it and enjoy it,
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depending on your vision as a roaster,
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on how you like coffee to taste.
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The coffee may roast a little bit longer.
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This point, everything
is drinkable and good.
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So as the roast progresses,
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those beans will begin to
get a little bit darker.
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They'll also get a little less wrinkly
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and a little bit more even looking.
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As they get darker,
they'll kind of smooth out.
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But as we continue to progress,
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well we get towards dark roasts
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and what'll happen is
there'll be another release
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of gases later on and
that's called second crack.
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Here you you'll see that the
beans are really pretty smooth,
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a much darker brown and the beginnings
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of oil on the surface of the bean,
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that's happening because
of those pressures
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inside the bean forcing
the the oil to the surface.
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And the coffee bean itself
is much more porous.
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It's actually swelling
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and growing in volume,
decreasing in density.
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Now, you can keep roasting
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and you can keep roasting,
you can keep roasting.
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You'll generate more and
more of that bitterness.
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At this point, acidity
is really pretty low.
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Origin characteristics
is really pretty low
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and bitterness is going up and up and up.
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You might also see an increase in texture
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and kind of body and mouth
feel when you brew that coffee.
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But after, in this case, I
think 17, 18 minutes of roasting
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we're gonna call it a day here,
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However, people do roast darker than this.
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For me though, this was dark enough
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to show you what I wanted to show you.
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So what we've done is we've laid out some
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of the coffee from each of
the samples here on the table,
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so we can talk about roast
levels and really what they mean.
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Now we'll talk about specialty first,
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because I would say,
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the the kind of categorization
of light medium dark
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is a little different between
specialty and commercial.
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Specialty would start,
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I would say around here,
really pretty light
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and it would run probably to around here.
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So anything within this,
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could be classified as a light roast.
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Medium would run
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from this point up until maybe here.
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The minute I see any sort of
oil of any kind on the surface,
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I would say you've
crossed into a dark roast.
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And from here onwards it's a dark roast.
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It's rare for special to be
at this end of dark roasting,
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but it's not unusual to see
coffees roasted this way.
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Commercial's a little bit different.
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I would say the light
starts about the same,
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but probably runs a little bit further in.
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Then medium would start here
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and run again a little bit further in.
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And then after that, dark roasted.
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They'll also roast darker
than we have done here.
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I don't think it tastes great
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from a specialty perspective,
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but some people still do enjoy
very darkly roasted coffee.
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At some point,
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it just turns to carbon
and then catches fire.
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I don't recommend that.
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But darker roasts are certainly possible,
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but the color alone does
not tell you everything.
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To understand that a bit more deeply,
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we need to talk about what's
called a roast profile.
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Now, if you wanted to
roast coffee at home,
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you could certainly get a sheet tray
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and pour out some raw coffee on it,
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pop it in an oven at 200 degrees Celsius
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and it will roast in
there, it will go brown.
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If you look at the roast profile,
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you'll see that the temperature
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of the coffee would increase
and it would begin to slow,
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the closer it gets to
the target temperature.
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When you take it out though,
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that's not going to be
the best tasting coffee,
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for a couple of different reasons.
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Firstly, where the coffee beans have been
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touching the metal the whole time,
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well they'll have had a lot
more conduction heat transfer
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and they're probably gonna
be a little bit burnt
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around those spots.
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And secondly, you don't
necessarily want to have
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one constant temperature that
the coffee is trying to reach.
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What we've learned through
coffee roasting is actually
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you wanna vary the amount of heat coming
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into the roaster and change
it to change the rate
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at which the coffee is turning brown.
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So this brings us to
what roasters are talking
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about when they talk about
a coffee roast profile.
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Now, machines themselves
can often be very old.
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They can be sometimes very new.
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Regardless, they're all
using multiple temperature
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probes positioned around
the roaster to collect data
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and feed it into some
sort of computer software.
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What that's ultimately gonna track,
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is the temperature of the bean probe.
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That's our closest
guess to the temperature
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of the beans themselves during the roast.
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Now, the journey of the beans in terms
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of how quickly they get hot,
it will change depending
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on the coffee and what
you want it to taste like.
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It might be that this phase here
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in the middle is it's heating
up if it heats up quicker
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or if it heats up slower.
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Well that would change the flavor
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and through a period of trial and error,
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and ultimately then knowledge
that's passed around
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within the industry, you learn
to create a roast profile
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for a particular coffee,
usually on a particular machine.
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So it's not something you can take
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from one person's roaster and apply
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to another person's roaster,
which is kind of confusing.
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Now here on the screen you
can see a few things going
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on and quite a lot of data,
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and for most people it's
kind of overwhelming.
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But ultimately, this probe here
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is the beam temperature probe
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and you can see the journey
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that it goes through and you'll see,
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that generally it's heating
up pretty quickly here.
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It slows and continues to slow
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and towards the end slows even more.
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That's not absolutely universal,
but it is extremely common.
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And during the roast, roasters
are making small changes
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to the amount of heat coming out
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of the burner or in some cases the amount,
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of air flowing through the drum,
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to change how much heat
is being transferred
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to the coffee itself.
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And that's how you create a roast profile.
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Roasters aren't aiming
for one perfect profile,
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but they are aiming for
consistency in their roasts.
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And I wanna talk just briefly
about how they approach that.
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Now, the first most obvious thing to do
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is to taste the coffee that you roast.
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And most roasters will
be tasting everything
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that they roast, but there is a problem.
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Modern expectations say
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that the consumer wants
their coffee roasted,
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bagged and shipped the same day,
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so that it is as fresh as possible.
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And this means really functional
tasting is difficult to do
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before the coffee goes out the door.
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So they're looking for other ways,
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other checks that the the
coffee can pass or fail to hit,
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to make sure that what
they bag up and ship
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is tasting the way that they want it to.
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There's really three ways
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and the first way we've
kind of touched upon,
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that's the roast profile.
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The coffee should have
followed the desired lines
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during the roast in order
to pass that at the start.
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But some roasters will
have higher tolerances
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than others there.
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And there are still other ways to check
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if things have gone as planned.
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Another common thing is
what's called roast loss.
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Now when you roast
coffee, it loses weight.
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You might start with 10 kilos
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of coffee and anywhere from
maybe 13% through to 22%,
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23% of it may be lost
during the roasting process.
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Most of that is water, but
the darker you roast coffee,
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the more stuff breaks down and disappears.
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It doesn't tell you that much.
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But if you're expecting 14.5%
roast loss and you get 15%,
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that should be a red
flag that things haven't
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gone as expected.
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And the third one that, again,
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is very common is color testing.
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This is using some sort
of machine that kind
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of measures brownness, how
light, how dark the coffee is.
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Most roasters will grind
a sample after roasting
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of every single batch and
test the color using one
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of a variety of meters that do this.
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The most popular one
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or the most commonly talked
about one is one called Agtron.
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And sometimes you'll even see companies
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publishing the Agtron
numbers of their coffees
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to give you some indication
of how light or dark that is.
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I'm not sure that's very useful.
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It's really a good solid
internal measurement.
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As we talked about with roast profiling,
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the color alone doesn't
tell you all that much,
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but it's definitely gonna be a problem
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if that color is too dark or too light.
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And again, roasters
will have some variance,
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some allowance within
that color measurement,
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a kind of window of tasty.
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Those are the primary ways
in which roasters QC coffee.
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Now one thing I wanna talk about here
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is what roasters mean when they talk
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about a coffee being
'roasted for filter coffee'
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or having the word
'espresso' on the label,
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implying that it's roasted
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in a way that should
be brewed as espresso.
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Espresso is difficult brew method,
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it doesn't use much water.
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It's very intense.
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It's very quick and and
what roasters typically try
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and do is roast the coffee
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in a way that it's easier to extract.
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That might be they roasted
a touch darker in color.
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It might be that the whole profile
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takes a little bit longer.
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They slow the roast down and
there's variations within that.
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But that's what espresso
on the label means.
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It it's typically a more
soluble roast than it would be
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for a filter coffee,
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'cause it's easier to properly
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brew coffee when you brew
it as a filter coffee.
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You've got a lot more
time and you've actually
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got a lot more water to do
the extraction work with.
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Now, you don't have to brew
espresso labeled coffees
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in an espresso machine.
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You can brew it in a moka pot,
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you could make it in a pourover
and probably enjoy it still,
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but that's what roasters
are trying to communicate
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with that language on the label.
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Let's talk now about how these
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roasting machines actually work.
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So first up, I wanna talk about a type
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of machine called a drum
roaster, and it's called that
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because in the middle of this
thing is a big spinning drum.
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It's like a kind of giant tumble dryer.
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Now the way that these
work is that you have
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underneath here a heat source,
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typically it's a gas burner
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and that's gonna heat two things.
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By proximity, it's actually gonna heat
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the big metal drum
typically made of cast iron,
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but primarily it's gonna heat air.
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Now that air is being
pulled through the back
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of the drum through the coffee and out,
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and it'll run from here through this fan
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that's doing all of that work.
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And it'll be pushed out
of the exhaust and away,
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typically in larger roasters to be burnt,
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to get rid of any smoke in
what's called an afterburner.
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Drum roasters are interesting.
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They're probably the most common type
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of roaster used in
specialty coffee companies.
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And they heat coffee slightly differently.
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They heat coffee three ways.
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Primarily it's convection,
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it's the hot air flowing
through the coffee beans.
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But because the drum is hot,
there is some conduction heat,
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a little bit like a steak in a frying pan.
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That that touch of the bean
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onto a hot surface does
have some heat transfer.
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In addition, because that drum is hot,
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there's also radiant
heat kind of emanating
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from the metal into the coffee.
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But primarily it's gonna be the convection
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of the air going through it.
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It does produce a
different kind of flavor,
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conventional wisdom says,
to other kinds of roasters
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but I don't know how true
that really, really is.
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There's a lot of different
ways to use a drum roaster
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and you can get a lot of very
different results from it.
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Now the roaster operating
the machine is gonna be
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paying a lot of attention
to the probe data coming
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from it to decide when to
make changes to the gas going
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to the burners, but at a
very specific endpoint,
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a combination of time,
temperature, and color,
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the coffee very quickly
needs to stop roasting
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and to be cooled down
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and pretty much every
roaster will use some sort
00:15:40
of cooling tray.
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Now, when the coffee leaves
the roasting machine,
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it's often in excess
of 200 degrees Celsius.
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And I dunno what that is in Fahrenheit,
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but it's very hot and we
need to make it as close
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to room temperature as possible,
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as quickly as possible to
stop the roasting process.
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Now, most machines will
use air to do that.
00:15:58
The coffee will tumble into a tray
00:16:00
like this one, arms will stir it,
00:16:02
and mix it as a very large fan pulls air
00:16:05
from the room down through it,
to cool it down very quickly.
00:16:08
Now, larger machines or machines
00:16:10
with slightly smaller cooling trays,
00:16:12
sometimes need to use a different
process called quenching.
00:16:15
Here, a very, very small amount
00:16:17
of water is sprayed onto the coffee beans.
00:16:19
That water instantly evaporates
because the beans are so hot
00:16:22
and the evaporative
cooling really very quickly
00:16:24
cools the beans down.
00:16:26
Now, there's no real
downsides to quenching,
00:16:28
except that that coffee will
need a little bit less rest
00:16:31
before cooling and it will
stale slightly quicker.
00:16:34
But quenching does not impact the quality
00:16:37
of the coffee whatsoever.
00:16:40
Cooling done.
00:16:40
Let's talk about a different
sort of roasting machine.
00:16:43
There is another type of roasting machine.
00:16:44
It's called a hot air roaster,
00:16:46
a little bit different to a drum machine.
00:16:48
Here you've got a big heat
source and that's separate
00:16:50
to the machine and it
produces one side a blower,
00:16:53
vast amounts of hot air
that flow into the machine
00:16:56
and the hot air is not only
gonna roast the coffee,
00:16:59
but it's gonna do all of
the agitation as well.
00:17:01
So when you look inside these,
00:17:03
you can see the coffee
being thrown around,
00:17:05
churned and moved just by the volume
00:17:07
of air flowing through it.
00:17:10
That means there's no real
moving parts in the roaster.
00:17:12
The way there are inside a drum roaster.
00:17:14
but just the same,
00:17:15
you're gonna vary the
intensity of the heat,
00:17:18
but here you can also vary the volume
00:17:20
of air flowing through it.
00:17:21
There's no better roaster out there
00:17:22
in the world than any other.
00:17:24
There's simply a tool
00:17:25
for a roaster to create the
flavor profile that they like.
00:17:28
And for some roasters,
they prefer the style
00:17:30
of coffee you get from an air roaster,
00:17:32
that is a little bit
different to drum roasters.
00:17:33
And then there's a third type of roaster,
00:17:35
a kind of hybrid air roaster.
00:17:37
Here, you still have a drum
00:17:39
that rotates to tumble the coffee,
00:17:41
but like an air roaster the
heat source is separate.
00:17:44
So it's really just heating the air.
00:17:45
The drum itself does not get hot.
00:17:48
Some people say these can
be much more efficient.
00:17:51
Others like the fact that
the drum doesn't kind
00:17:52
of have any conduction
heat into the coffee.
00:17:56
Again, roasters are just tools
00:17:58
to make the coffee that you wanna make.
00:18:00
And that is the basics of coffee roasting.
00:18:02
And now I want to hear from
you down in the comments below.
00:18:04
What aspect of this do
you wanna know more about,
00:18:07
should we go deeper into in the future?
00:18:09
Has this been helpful in
how you think about coffee?
00:18:11
Has it been eye-opening?
00:18:13
Let me know your thoughts.
00:18:14
I'd really appreciate it.
00:18:15
Now, I will say, some of
you are gonna ask a question
00:18:17
and that question is, when
are you gonna make a bunch
00:18:19
of videos about roasting coffee at home?
00:18:21
I don't know.
00:18:22
But I will tell you that I definitely,
00:18:23
definitely want to make those videos.
00:18:25
They are in the master plan,
00:18:27
the big what we will do in the future.
00:18:29
I just don't know when.
00:18:31
All right, enough caveats from me.
00:18:33
I'll say thank you so much
00:18:34
for watching and I hope
you have a great day.
