Coffee roasting at home: Basics for home roasters

Coffee roasting isn't an art, it's a craft. And that's why you can easily roast your own coffee at home. To ensure it's delicious and not too dangerous, we've compiled these tips for you.

Anyone who's ever been to a coffee roastery knows how much space roasting machines can take up. We roast on a 12kg roaster, which weighs a good 500kg and is the size of a small car.

Our 1kg Probatino roaster weighs well over 100kg, but it's still quite large. Anyone who's ever been to a large roastery and seen a 250kg roaster will know that these machines, with all the trimmings, are almost the size of a small house.

But now things are also much smaller. There are machines as small as a shoebox, allowing you to roast 50g or even several hundred grams at home. And it's really fun. There's hardly anywhere else where you can get as close to the product as when you roast coffee on the smallest possible scale.

A little adventure

We've tried out various home roasting machines and are presenting them on our YouTube channel . First of all, I had a blast. I normally roast on a 12kg roaster and advise other roasters who have 5kg-60kg roasters. These are sizes I'm used to.

But roasting just a few grams is somehow very exciting. Many things are more delicate, less controllable, faster, and—yes—sometimes simply more random. The background knowledge I've acquired over years working on larger roasters is put to the test here. So if you have any contrary experiences with the machines discussed, or otherwise, please let us know in the comments.

Roasting your own coffee is a bit of an adventure. It'll smoke, crackle, get hot, and things might happen a bit uncontrollably, but you'll love your coffee. Even if it might not be as tasty as from elsewhere, the work that goes into it tastes really good.

With our little guide, we'll show you how to roast a solid coffee at home right from the start.

Time and temperature – how long and how hot should you roast?

First of all, we have to disappoint you – we can't give you precise information about time and temperature. Not because we don't want to, but because we can't.

temperature

Just as my grind is not your grind , my temperature is not your temperature. I recently roasted at two different roasters on two identical machines. However, the temperature at roaster A was always slightly cooler than at roaster B.

This was mainly due to the fact that Roaster A had installed a different temperature probe in the roaster. One that was thinner and therefore more sensitive. Roaster B had installed a thicker and therefore less sensitive probe.

If we want to measure the temperature in the manual popcorn roaster, we need a temperature probe.

So which was the right temperature? I'd say neither. Honestly, I don't care what the "exact" temperature is—the main thing is that we stick to one temperature and think from there.

The 180°C in a popcorn roaster * is probably a different 180°C in a drum roaster. It always depends on what and where it's measured. Therefore, temperatures are irrelevant. If you're already roasting at home, you've already gained experience and can use that as a guide. If you're starting from scratch, we recommend setting the manufacturer's suggested temperature.

Roasting time

Time and temperature are interdependent during roasting.

The hotter the temperature, the faster the roasting.

The cooler the temperature, the slower the roasting.

Specifying exact times doesn't help much here, since different roasting machines apply heat to the beans in different ways.

Generally :

Four minutes would probably be too short; the taste would be quite harsh because the coffee hasn't undergone enough sugar conversion yet.

20 minutes is quite a long time, especially for small batches – we're just baking the coffee and literally hollowing out its flavor.

Everything in between seems to be delicious. Shorter roasts for filter coffees and lighter coffees, slightly longer roasts for espresso. That would be universal—but unfortunately, there are no time or temperature specifications.

What is the right amount?

One of the great advantages of roasting is that many steps are easy to explain and logical. This includes the question of how much coffee should be added to the roasting drum.

Small quantities heat up faster – large quantities heat up slower.

Makes sense.

Especially with small roasters, popcorn roasters, etc., there is hardly any energy stored in the system (roaster walls, base, lid, etc.). Most of the energy is supplied via hot air or direct contact heat.

When you put green coffee into the roaster (=roasting system), the system initially loses energy. Green coffee at an ambient temperature of 20°C is placed in a hot environment and initially absorbs heat.

When you bake lasagna, preheat the oven, then open the door and add the cold lasagna, the temperature in the oven will initially drop. The same thing happens when roasting.

So if you put a large amount into any roaster, the roasting will take longer because you are taking energy away from the system.

If you add a small amount of coffee during roasting, you will use less energy from the system and you can roast faster.

Is there a right amount of coffee?

You already know the answer – no, there isn't. It all depends on the system. Make sure you follow the manufacturer's instructions. Then check how long the roasting takes and use the points mentioned above as a guide.

If you make adjustments to the batch size, be sure to make them clear. If you roast the first batch with 100g and the second batch with 110g, the difference will be significantly smaller than if you roast, say, 100g and 150g.

When I come across a new roasting machine during roasting consultations, I always conduct somewhat more extreme tests, exploring the system's strengths and weaknesses by choosing larger variations in batches or temperatures. This way, you can reach your goal faster.

The first crack and the development time

Over several minutes, you'll approach the first crack, the first pop, or simply the first crack. Then, when the pressure in the coffee bean is so great that it needs to escape, you'll hear a significantly quieter or louder crack, depending on the roasting system.

Softer coffees tend to crack, like when you crush peanuts. We often hear this crack in Brazilian coffees.

With harder, denser coffees , such as those from Kenya, the cracking is much louder and more explosive, as if a firework were going off.

It's fun to hear this cracking sound and identify it with the coffees. Pay attention to this cracking sound, and you'll understand your coffees much better.

When does the 1st crack start?

Did I mention that it's really fun to listen for the first crack? Depending on your taste, your crack will come earlier (lighter coffees, due to faster roasting) or later (more developed coffees, espresso, for example).

The first crack occurs in increasing intensity, similar to a normal distribution in this image. At first, it's just a single bean that starts and cracks (far left in the image). Then a second, a third, and a fourth join it (first line from the left). After that, it gets more intense. As soon as you hear the first triplet, a crack-crack-crack in quick succession, that means we're marking the first crack (second line from the left).

The cracking (1st crack) resembles a normal distribution

This way, we can be sure that the entire batch will start cracking. It takes some practice, nerve, and patience to avoid marking the first crack on the first attempt.

Shortly after the 1st crack, the whole batch goes off and the cracking becomes more and more even, the majority of the beans (third line from the left) now crack at the same time.

After that, the curve drops until the crackling is no longer audible. If you continue roasting longer and, above all, at a higher temperature, you'll approach the second crack, which is significantly quieter and more reminiscent of a crackling sound. For this guide, we'll leave the second crack out.

Why is the 1st crack important?

Because it gives us a simple and precise way to roast coffees individually. If I roast strictly according to time, for example, all filter coffees take 10 minutes, all espressos 14, and all dark roasts 18, I'm doing the coffee an injustice. Because many coffees behave differently when roasted.

Because we roast many coffees for others, we gain experience with very different coffees. The more different coffees we roast, the more predictable we can make about a green coffee we're still unfamiliar with.

Example:

I take a pulped natural from Brazil and roast it for 10 minutes, as this is my "filter recipe." Then I roast a coffee from Kenya for 10 minutes.

The two coffees behave and taste completely different. The 10 minutes for the Kenyan coffee perhaps shows it off at its best—fruity, balanced, with well-integrated acidity, while the Brazilian coffee may already be charred, as it is much softer.

So if we instead get used to marking the 1st crack on each coffee and not roasting according to the total roasting time, the coffees will taste much better pretty quickly.

And what happens next?

After the first crack, the so-called development time begins. This is the time the coffee spends from the beginning of the first crack until the moment it is removed from the roaster.

An example:

I roast a coffee that cracks after 8 minutes. I mark the first crack. Now I roast for another 90 seconds and then remove the coffee from the system. The development time would therefore be 90 seconds, relative to 480 seconds. This allows us to calculate the percentage development time, which in this case would be 15.8% (90 seconds out of 570 seconds).

And what does that mean now?

A shorter development time of about 5% can mean that I

• the coffee is almost certainly under-roasted
• create few aromas,
• the coffee still tastes green and unpleasantly nutty to corny

An average development time of about 8-10% can mean that I

• such a coffee with a lot of aroma,
• more acidity, tea-like texture and
• I get little roasted notes.

A longer development time of about 12% plus can mean that I

• intense aroma,
• more body and roasted notes
• and reach a heavy sweetness

A long development time of about 18% plus can mean that I

• many roasted notes, less light, floral and fruity aromas,
• less acidity, less texture,
• but achieve a lot of body and dark sugar notes

All of these details are often "without guarantee" because they depend on the specific roasting system. However, I've tried to cover them as generally as possible, so that they're more universal than very specific.

The roasting curve

We can now measure everything that happens inside the system during roasting with temperature probes and digitally record it via an interface. This so-called roast log software helps us roast as precisely and consistently as possible.

In the past—just a few years ago—this software was hardly widespread. However, programs like Cropster and Artisan have experienced immense growth in recent years. More and more roasters aren't just relying on their gut feeling; they want to convert their data into information, display it graphically, and learn even more.

Roasting profiles are read from left to right. The x-axis represents time, the y-axis on the left represents bean temperature, and the y-axis on the right represents the rate of rise (RoR)—the energy increase per 30 seconds.

Three roasting curves from the Kaffeemacher roastery

Temperature probes at various locations in the roaster measure the temperature and record it in software. In the example above, you can see three curves from our roastery.

The blue curve is the Ichamama , a light roasted filter coffee.

The yellow curve is our fine spirit , a specialty espresso.

The red curve is an elongated fully automatic coffee that we roast on behalf of a private label customer.

The roasting language of the three profiles couldn't be more different. The roasting time for the coffees varies between 9:10 and 17:30 minutes. The final temperature also differs. What is quite clear, however, is the temperature rise – very steep for the Ichamama, somewhat flatter for the Feingeist, and significantly slower for the fully automatic coffee.

We'll look at how you can draw such a curve yourself, without complex roasting software, in another section. It's important to understand that time and temperature differences have a massive impact on the final product.

Wolfram Sorg from Backyard Coffee has written an enlightening article about profile creation: https://www.backyard-coffee.com/blogs/kaffeewissen/entwicklung-eines-kaffees .

Which beans for which taste?

Selecting green coffee is probably one of the most rewarding tasks in a roastery. But it also has many consequences. Depending on the green coffee selection, you can either expand or limit the range of uses for the selected coffee.

Green coffee beans vary in density, size, and shape. They all roast slightly differently.

Highly acidic coffees are delicious for filter coffees because we dilute them with plenty of water, resulting in a light drink. However, these green coffees are probably not everyone's cup of tea when it comes to espresso.

But the other way around is also true – simpler, nutty-sweet coffees can produce a great espresso, but perhaps a somewhat monotonous filter coffee.

This is your turn. Because every roasting language is unique. Everyone who roasts has their own interpretation of how the coffee should ultimately taste.

Green coffee selection – we open our warehouse

You have to start somewhere, and buying a whole 60kg bag probably isn't going to cut it. So, we're now also selling 1.5kg and 3kg bags of green coffee. These are the same ones we use in our product range. So, if you'd like, you can roast our classic Dreispitz blend , for example.

Which of our coffees do we use for what:

You already know which coffee suits you best – if you still need some inspiration, we've put together a little guide for you here .

After roasting: Cool and store

We recommend using a stopwatch as a standard method for roasting, marking the first crack, and recording the data. This way, you can create references and compare them repeatedly.

You decide when the roasting process will end. Once you've reached the desired development time, remove the coffee from the roasting system.

After that, it's important to cool the coffee as quickly as possible. Not with water, which is only done with large quantities, but with air. In our academy, we use these fans that suck air downwards and thus

a) pull the smoke away

b) cool the coffee quickly

You can also simply use a colander and chill the coffee in it. It's important to keep it moving and blowing to cool the coffee.

In this way, we stop the physical and chemical processes of roasting and prevent uncontrolled further roasting.

The silver skins on the green coffee bean (whitish), clinging to the coffee table after roasting. The airflow must remove the silver skins from the system so they don't catch fire.

How long does the coffee need to off-gas after roasting?

For our coffees we recommend:

• min. 7 days for a filter coffee
• min. 14 days for an espresso

However, we generally do a cupping after 24-76 hours for quality assurance. We pour 12g of coffee into 200g of hot water, wait four minutes, break the crust, and sip the coffee.

You can use this as a guideline:

long roasting = long degassing time

short roasting = short degassing time

It's best to taste the coffees regularly, every day after roasting, and taste the differences.

This way you can quickly find the time that suits you.

We discussed what coffee scientist Chahan Yeretzian says about freshness in this video .

How can I improve?

Another fascinating aspect of roasting is its completely analog nature. Unlike a digital camera, where you can simply delete a bad photo, you have to have control over an analog camera, otherwise you'll have used up space on the film roll. That's roasting.

You put green coffee into the system, roast it, and that's it. Once the coffee is roasted, you can't roast it again. You can, but it doesn't make sense. You'll burn the coffee, and that's no fun.

Green in, brown out. If you've done everything right, the result will be delicious. If not, well, then try it again. Learning by doing, or as a colleague once put it: learning by burning . So there's always a bit of adrenaline involved in roasting, which is probably why it holds such fascination for many people.

Register data in the roasting log

To truly understand how you're improving, you need to record your data. Whether by hand, in an Excel spreadsheet, it doesn't matter. The main thing is that you're recording this data:

• which green coffee
• Green coffee quantity
• Starting temperature (if possible, otherwise irrelevant)
• Time until the 1st crack
• Development time
• Final temperature (if possible, otherwise irrelevant)
• Weight of roasted coffee

Weighing the roasted coffee at the end of the roasting process will determine the amount of roasting loss. Expect 14-20%, depending on the roasting method. It's especially worthwhile to measure the weight with simple roasters without a temperature display. This will give you a sense of how much material you're losing during the roasting process.

Taste, taste, taste

Now, all the numbers may look great, but if the coffee doesn't taste good, even the prettiest numbers won't help. So – challenge yourself and taste every batch, in a standardized way.

How can you proceed?

• always taste after x hours
  • This is how you compare old coffees

• Grind 12g of coffee and add 200ml of water
  • approx. 96°C
  • take your own water, whether it is hard or soft
  • In this case, it's about getting a feel for your craft
  • The best way to adjust this is to not change the basic constants (for now)
  • Let it stand for 4 minutes, skim off the crust, after about 8 minutes start slurping

• Or you have your own ritual, like making a French press or filter coffee. It doesn't matter, as long as you do it the same way every time. Consistent, consistent, consistent.

We are your coaches

If you've read everything, learned a roasting technique, and now want our feedback, send us a sample of your roasting. We'll taste it and give you feedback. Our feedback is honest, because we want you to improve.

So: roast, practice, roast, and if you want, we're here to help you figure out how to do it all even better.

Tips, tricks, security

• Green coffee selection
  • In our coffee shop we offer most of the green coffees that we roast ourselves
  • At Ingo from Roast Rebels you will also find green coffees
  • The coffee shop also offers green coffee for sale

• where to roast?
  • If you roast in the apartment, in the house – then definitely under an extractor hood with the window open
  • During roasting, a lot of smoke is produced and the silver skins detach from the green coffee, which then swirl around
  • Always keep the coffee moving so it doesn't burn
  • If you have a terrace, balcony, or garage, we recommend roasting there, too. For the good of everyone.

• Which devices can you recommend?
  • We are still holding back on recommendations because we are still in test mode
  • the best thing to do is to subscribe to our YT channel , where we will present the tested machines
  • Ingo from roast Rebels sells home roasters in the mid-price segment and tests them for you
  • We do not sell machines ourselves, but we enjoy testing everything that works
  • So if you have any tips on what we should watch, please let us know in the comments.
  • The popcorn pot used can be found here on Amazon *

*We purchased the popcorn pot. This is a principle we follow in all our tests. We want to evaluate all appliances impartially and without outside influence. The link is a commission link to Amazon. If you order something through the link, it won't cost you any more – but our appliance test box will fill up a little.