Coffee Roasting Explained

Summary

This video script offers an in-depth exploration of coffee roasting, from the basics of how the process affects flavor to the complexities of bean chemistry. It delves into roast levels, the distinction between specialty and commercial roasts, and the importance of roast profiles. The script also discusses different roasting machines, quality control methods, and the unique challenges of roasting for espresso versus filter coffee, providing viewers with a comprehensive understanding of the art and science of coffee roasting.

Takeaways

• 🌱 Raw coffee beans have little flavor and undergo a significant transformation during roasting to develop their characteristic taste.
• 🔥 The roasting process is what creates the familiar flavors of coffee, with three main characteristics affected: bitterness, acidity, and origin characteristics.
• 📈 Bitterness increases with the duration of roasting, while acidity initially increases and then decreases as the roast gets darker.
• 🏔 Lighter roasts tend to highlight the unique origin characteristics of the coffee beans, whereas darker roasts result in more generic roast tastes.
• 🔑 The 'first crack' during roasting is a key moment when pressure from built-up gases causes the beans to crack open, allowing the release of flavors.
• 📊 Roasters use terms like 'light', 'medium', and 'dark' to describe the roast level, with specialty roasters typically favoring lighter roasts to preserve origin flavors.
• 🛠 Different types of roasting machines, such as drum roasters and hot air roasters, are used in the coffee industry, each with its own method of heating and agitation.
• 📈 Roasting machines utilize temperature probes to monitor the roast profile, which is essential for achieving a consistent flavor in the final product.
• 🔍 Quality control in coffee roasting involves checking the roast profile, measuring roast loss, and using color testing to ensure the coffee meets desired standards.
• ☕️ Roasters may label coffee as 'espresso' or 'filter coffee' to indicate the roast profile that is best suited for those brewing methods, affecting extraction and flavor.
• 🌡 After roasting, coffee beans must be cooled rapidly to halt the roasting process, with methods including air cooling or quenching with a small amount of water.

Q & A

What is the main topic of the video script?

The main topic of the video script is the process of roasting coffee, including its impact on taste, the chemistry involved, and the different types of roasting machines used in the industry.

Why does the flavor of raw coffee seeds change significantly during roasting?

The flavor of raw coffee seeds changes significantly during roasting due to the chemical transformations that occur, including the Maillard reaction and caramelization, which create the familiar flavors we associate with coffee.

What are the three characteristics of coffee that change during the roasting process?

The three characteristics that change during the roasting process are bitterness, acidity, and origin characteristics. Bitterness increases with longer roast times, acidity initially increases and then decreases, and origin characteristics become less distinct as the roast gets darker.

Why do specialty coffee companies tend to prefer lighter roasts?

Specialty coffee companies tend to prefer lighter roasts because they retain more of the unique origin characteristics of the coffee beans, which is important for showcasing the distinct flavors and complexities of the coffee.

What is the 'first crack' in the roasting process and why is it significant?

The 'first crack' is a key moment in the roasting process when the pressure from the gases formed inside the coffee bean becomes too much, causing the bean to crack open. It is significant because it marks the beginning of the rapid browning reactions that greatly affect the flavor of the coffee.

What is a 'roast profile' and why is it important for coffee roasters?

A 'roast profile' is a record of the temperature changes that the coffee beans undergo during the roasting process. It is important for coffee roasters because it helps them to achieve consistency in the flavor and quality of the coffee they produce.

How do roasters ensure the quality of their coffee after roasting?

Roasters ensure the quality of their coffee after roasting by tasting the coffee, monitoring the roast profile for consistency, checking the roast loss percentage, and using color testing methods like the Agtron meter to measure the brownness of the coffee.

What is the difference between a drum roaster and a hot air roaster?

A drum roaster uses a spinning drum that is heated by a gas burner, primarily using convection, conduction, and radiant heat to roast the coffee. A hot air roaster, on the other hand, has a separate heat source that produces hot air which both roasts and agitates the coffee beans, without any moving parts inside the machine.

Why is the cooling process after roasting important and how is it typically done?

The cooling process after roasting is important to stop the roasting process as quickly as possible to maintain the desired flavor profile. It is typically done using air to cool the coffee beans rapidly, either through a cooling tray with stirring arms or by quenching with a small amount of water that evaporates quickly.

What does the term 'espresso roast' imply about the way the coffee is roasted and why?

The term 'espresso roast' implies that the coffee has been roasted in a way that makes it easier to extract, often with a slightly darker color and possibly a longer roast profile. This is because espresso brewing requires a more soluble coffee due to the intense and quick extraction process.

What is the purpose of the comments section at the end of the video script and what does the speaker hope to achieve by asking for feedback?

The purpose of the comments section is to engage viewers in a discussion about the video content. The speaker hopes to gain insights into what aspects of coffee roasting the audience is interested in learning more about, to help guide future content creation and ensure the information provided is relevant and helpful.

Outlines

00:00

🔥 Introduction to Coffee Roasting

The video script begins with an introduction to the art of coffee roasting, emphasizing its transformative impact on the flavor profile of coffee beans. The host promises to explore the basics of how roasting affects taste, delve into the chemical reactions within the beans, and clarify the terminology used by roasters such as 'light', 'medium', and 'dark'. The script also mentions the variety of roasting machines and the processes employed to ensure consistent flavor. The raw coffee is described as having little aroma or flavor, highlighting the importance of the roasting process in developing the coffee's complexity and taste.

05:01

🌱 The Journey from Raw to Roasted Beans

This paragraph delves into the initial stages of the roasting process, explaining how raw coffee beans, which are the dried seeds of the coffee tree, undergo a significant transformation. The roasting process is described as beginning with the drying out of the beans, followed by color changes from green to pale yellow, indicating the start of browning reactions. The script discusses the 'first crack', a key moment when pressure from built-up gases causes the beans to crack open, releasing steam and CO2. The host also touches on the importance of origin characteristics and how they are affected by the roasting duration, with longer roasts leading to a loss of unique flavors and an increase in bitterness.

10:04

📊 Understanding the Roasting Process and Profiles

The script continues with a deeper look at the roasting process, highlighting the importance of monitoring color changes, flavor shifts, and the 'second crack' which signifies a more advanced roast. It discusses the concept of a roast profile, which involves adjusting the heat and airflow to control the rate of browning and achieve a desired flavor outcome. The host explains that roast profiles are not universal and must be tailored to the specific coffee and roasting machine. The paragraph also addresses the practical challenges of quality control in coffee roasting, such as managing roast loss and using color testing to ensure consistency.

15:05

🛠 Exploring Different Coffee Roasting Machines

The final paragraph of the script focuses on the different types of coffee roasting machines, starting with the drum roaster, which uses a spinning drum to tumble the beans and relies on convection, conduction, and radiant heat for roasting. The host explains the process of cooling the beans post-roasting, either through air cooling or quenching with water. The script also introduces hot air roasters, which use a separate heat source to generate hot air for roasting and agitation, and hybrid air roasters that combine elements of both drum and hot air roasting techniques. The host concludes by inviting viewer feedback and expressing interest in future topics, including home coffee roasting.

Keywords

💡Roasting coffee

Roasting coffee refers to the process of transforming raw coffee beans into the roasted beans used for brewing coffee. It is central to the video's theme as it impacts the flavor and characteristics of the final product. The script discusses how the roasting process changes the beans' taste from the initial lack of flavor to the complex flavors developed during roasting.

💡Roasting process

The roasting process involves heating coffee beans to specific temperatures to alter their chemical composition, resulting in the flavors and aromas associated with coffee. The video emphasizes this process as it explains how different roast levels affect the taste, with terms like 'light', 'medium', and 'dark' indicating the degree of roast.

💡Bitterness

Bitterness is a taste characteristic that increases with the duration of the coffee roasting process. The script explains that darker roasts tend to be more bitter, akin to the bitterness in caramel as it darkens, which is a key factor in determining a coffee's flavor profile.

💡Acidity

Acidity in coffee refers to the tangy or sharp flavor notes that are present in the taste. The script describes how acidity initially increases during roasting but then decreases as the roast gets darker, affecting the overall flavor balance in coffee.

💡Origin characteristics

Origin characteristics are the unique flavors imparted by the coffee's growing conditions, such as soil type, climate, and altitude. The video script mentions that these characteristics are initially enhanced during roasting but can be diminished in darker roasts, leading to a more generic roast taste.

💡Roast levels

Roast levels categorize coffee based on the degree of roast, typically described as 'light', 'medium', or 'dark'. The script uses these terms to explain how different roast levels affect the taste, with lighter roasts highlighting origin characteristics and acidity, while darker roasts are more bitter and have less origin character.

💡Roasting machine

A roasting machine is the equipment used to roast coffee beans. The video script describes different types of machines, such as drum roasters and hot air roasters, and how they contribute to the roast profile and final flavor of the coffee.

💡Roast profile

A roast profile is a detailed record of the temperature changes during the roasting process. The script explains that roasters use these profiles to achieve consistency in the coffee's flavor by adjusting the heat and airflow to control the rate of browning.

💡Roast loss

Roast loss refers to the weight reduction of coffee beans during roasting, primarily due to the loss of water and other volatile compounds. The script mentions that roast loss is one of the quality control measures used by roasters to ensure the coffee meets their flavor standards.

💡Agtron

Agtron is a measure used by coffee roasters to assess the color of roasted coffee, which can indicate the roast level. The video script notes that while Agtron numbers can be used internally for quality control, they may not be as useful to consumers for determining flavor.

💡Drum roaster

A drum roaster is a type of roasting machine that uses a rotating drum to tumble the coffee beans while hot air is blown through them. The script describes how drum roasters combine convection, conduction, and radiant heat to roast the coffee and create a specific flavor profile.

💡Hot air roaster

A hot air roaster is a machine that uses a separate heat source to generate hot air, which both roasts the coffee and agitates it within the machine. The script explains that this type of roaster can produce a different flavor profile compared to drum roasters, as it relies solely on the hot air for roasting and agitation.

Highlights

The roasting process is crucial for developing the flavors in coffee beans, which are initially flavorless.

Roasting coffee involves three main characteristics: bitterness, acidity, and origin characteristics, each affected differently by the roast level.

Bitterness increases with longer roast times, similar to the bitterness in darker caramel.

Acidity in coffee initially increases then decreases with darker roasts, influencing preferences for dark roasts.

Origin characteristics, influenced by factors like soil, climate, and processing, contribute to unique coffee flavors that diminish with darker roasts.

Specialty coffee often prefers lighter roasts to preserve the unique origin characteristics of the coffee.

The roasting process includes stages like drying out the beans, color changes from green to yellow, and the development of browning flavors.

The 'first crack' in roasting is a key moment where internal pressure causes the beans to crack open, releasing gases and changing flavor profiles.

Roasters pay close attention to the roast profile, which includes temperature changes and color developments over time.

Roast profiles are not universal and must be tailored to the specific coffee and roasting machine.

Quality control in coffee roasting includes tasting, monitoring roast loss, and using color testing like the Agtron meter.

Different roast levels are categorized differently in specialty and commercial coffee, with specialty coffee rarely reaching very dark roasts.

Roasters may roast coffee 'for filter coffee' or 'espresso', adjusting the roast profile for easier extraction in different brewing methods.

Drum roasters are common in specialty coffee and use a combination of convection, conduction, and radiant heat to roast coffee.

Hot air roasters and hybrid air roasters offer different roasting methods, focusing solely on hot air for both heating and agitation.

The choice of roasting machine is a tool for the roaster to achieve the desired flavor profile in the coffee.

After roasting, coffee beans must be cooled quickly to stop the roasting process, using methods like air cooling or quenching.

The presenter expresses interest in making future videos about roasting coffee at home, indicating it's part of the plan but without a set timeline.

Transcripts

(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.