Home coffee roasting. Basic knowledge for home roasters

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

Anyone who has 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 is also well over 100kg and still quite large. Anyone who has been to a large roastery and seen a 250kg roaster will know that these machines, with all the bells and whistles, can be the size of a small house.

But now, it can be done on a much smaller scale. There are devices no bigger than a shoebox with which you can roast 50g or even several hundred grams at home. And it’s really fun. You’re rarely as close to the product as you are when roasting coffee on the smallest possible scale.

A Little Adventure

We’ve tried out various home roasting machines and introduce them on our YouTube channel. First of all—I had a huge amount of fun. I usually roast on a 12kg roaster and advise other roasteries that have 5kg – 60kg roasters. Those are the sizes I’m used to.

But roasting just a few grams is somehow very exciting. A lot of it is trickier, more uncontrollable, faster, and—yes—sometimes simply more random. The background knowledge I’ve acquired over years of using larger roasters is put to the test here. So, if you have any conflicting experiences with the machines discussed or anything else, please write to us in the comments section.

Roasting coffee yourself is a bit of an adventure at first. It smokes, it cracks, it gets hot, maybe things happen a bit uncontrollably, but you will like your coffee. Even if it might not taste as good as it does from somewhere else, the work that goes into it tastes really good.

With our little guide, we show you how you can roast a solid cup of coffee at home right from the start.

Time and Temperature – how long and how hot to roast?

First off, we have to disappoint you—we cannot give you precise details on time and temperature. Not because we don't want to, but because we can't.

Temperature

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

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

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

So, which was the right temperature? I would say neither. To be honest, I don’t really care what the “exact” temperature is—the main thing is that we stick to one temperature and think from there.

The 180° in a popcorn roaster* is probably different from 180° in a drum roaster. It always depends on what is being measured and where. That is why temperatures are irrelevant. If you are already roasting at home, you have already gathered experience and can use that as a guide. If you are starting from scratch, we recommend setting the temperature suggested by the manufacturer.

Roasting Time

Time and temperature are mutually dependent when roasting.

The hotter the temperature, the faster the roast.

The cooler the temperature, the slower the roast.

Providing exact times doesn't help much here, because different roasting machines bring heat into the bean in different ways.

In general:

4 minutes would probably be too short, the taste would be quite harsh because the coffee hasn't gone through enough sugar transformations.

20 minutes is quite long, especially for tiny quantities—we just bake the coffee at that point and virtually hollow out its flavor.

Everything in between seems to be tasty. Shorter roasts for filter coffees and lighter coffees, slightly longer roasts for espresso. That would be universal—but unfortunately, time and temperature specifications are not.

What is the right amount?

One of the great advantages of roasting is that many steps are easily explained and logical. The same applies to the question of how much quantity should be put into the roasting drum.

Small amounts heat up faster—large amounts heat up more slowly.

Makes sense.

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

When you put raw coffee into the roaster (=roasting system), the system first loses energy. Raw coffee at an ambient temperature of 20°C enters a hot environment and first absorbs heat.

If you are baking lasagna, preheat the oven, then open the door and put the cold lasagna in, the temperature in the oven drops at first. The same thing happens during roasting.

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

If you add a small amount of coffee to the roast, you withdraw less energy from the system and you can roast faster.

Is there a correct amount of coffee?

You already know the answer—no, there isn't. Everything is system-dependent. Definitely stick to the specifications provided by the manufacturer. Then see how long the roast takes and use the points mentioned above as a guide.

If you make adjustments to the batch size, make sure to make those adjustments significant. If you roast the 1st batch with 100g and the 2nd batch with 110g, the difference is much smaller than if you roast, for example, 100g and 150g.

When I come across a new roasting machine during roasting consultations, I always do slightly more extreme tests, probing the strengths and weaknesses of the system by choosing larger differences in batch sizes or temperature. This helps you reach your goal faster.

The First Crack and Development Time

Over the course of several minutes, you approach the first crack, the first pop, or just simply the cracking sound. When the pressure inside the coffee bean is so great that it must escape, you will hear a clearly quieter or louder cracking sound, depending on the roasting system.

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

With harder, denser coffees, such as those from Kenya, the cracking is much louder and more explosive, like fireworks going off.

It’s fun to hear this cracking and attribute it to the coffees. Pay attention to this cracking and you will understand your coffees even better.

When does the 1st Crack begin?

Did I mention that it’s really fun to listen for the 1st Crack? Depending on the flavor you are aiming for, your crack will come earlier (lighter coffees, because of faster roasting), or later (more developed coffees, e.g., espresso).

The 1st Crack arrives with increasing intensity, similar to a normal distribution curve as seen in this image. At first, it’s just a single bean that starts and cracks (far left in the image). Then a second one comes, a third, and a fourth joins in (first line from the left). Then it becomes more intense. As soon as you hear the first triplet, i.e., a rapid crack-crack-crack, this means to us that we are marking the 1st Crack (second line from the left).

The cracking (1st Crack) resembles a normal distribution

This way, we can be sure that the whole batch is starting to crack. It takes some practice, nerves, and patience not to mark the 1st Crack at the very first crack.

Shortly after the 1st Crack, the entire batch goes off and it cracks more and more evenly; the majority of the beans (third line from the left) are now cracking at the same time.

After that, the curve drops until no more cracking can be heard. If you continue roasting even longer and, above all, hotter at this point, you will approach the 2nd Crack, which is significantly quieter and sounds more like crackling. For our guide here, we will leave the 2nd Crack out.

Why is the 1st Crack important?

Because it gives us a simple and precise means of roasting coffees individually. If I strictly roast only by time, e.g., all filter coffees for 10 minutes, all espressos for 14 minutes, and all dark roasts for 18 minutes, I am doing the coffee a disservice. Because many coffees behave differently during roasting.

Since we roast many coffees for others, we gain experience with very different coffees. The more different coffees we roast, the more we can make a prediction about a raw coffee that is still unknown to us.

Example:

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

The two coffees behave completely differently and taste that way, too. The 10 minutes for the Kenyan coffee might make it appear in the best light—fruity, balanced, well-integrated acidity—while the coffee from Brazil might already be charred because it is much softer.

So, if we get used to marking the 1st Crack for every coffee instead of roasting according to total roast time, the coffees will taste much better quite quickly.

And what happens after that?

After the 1st Crack, the so-called development time begins. This is the time the coffee spends from the beginning of the 1st Crack until the point at which the coffee is removed from the roaster.

An example:

I roast a coffee that cracks after 8 minutes. I mark the 1st Crack. Now I roast for another 90 seconds and then remove the coffee from the system. The development time would therefore be 90 seconds, in relation to 480 seconds. This allows us to calculate the percentage development time, which in this case would be 15.8% (90sec out of 570sec).

And what does that mean now?

A shorter development time of approx. 5% can mean that I

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

A medium development time of approx. 8-10% can mean that I

• get a coffee with a lot of aromatics,
• more acidity, tea-like texture, and
• few roast notes.

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

• achieve intense aromatics,
• more body and roast notes
• and a heavy sweetness

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

• get many roast notes, fewer light, floral, and fruity aromatics,
• less acidity, less texture,
• but instead a lot of body and dark sugar notes

All these details are very much “without warranty” because they are dependent on the respective roasting system. However, I have tried to treat them as generally as possible, so that it is more universal than very specific.

The Roast Curve

Everything that happens inside the system during roasting can now be measured with temperature probes and traced digitally via an interface. This so-called roast log software helps us to roast as precisely and consistently as possible.

In the past—that is, just a few years ago—this software was hardly widespread. However, programs like Cropster or Artisan have experienced immense growth in the last few years. More and more roasteries are not only relying on their intuition but want to convert their data into information, represent it graphically, and thus learn even more.

We read roast profiles from left to right. The x-axis shows the time, the y-axis on the left the bean temperature, and the y-axis on the right shows the Rate of Rise (RoR)—the energy gain per 30 seconds.

Three roast curves from the Kaffeemacher roastery

Temperature probes in different places in the roasting apparatus 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 lightly roasted filter coffee.

The yellow curve is our Feingeist, a specialty espresso.

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

The roasting language of the three profiles could not be more different. In terms of time, the coffees differ between 9:10 and 17:30 minutes. The final temperature is also different in each case. But what becomes very clear is the temperature rise—very steep for the Ichamama, somewhat flatter for the Feingeist, and significantly slower for the fully automatic coffee.

We will look at how you can draw such a curve yourself without expensive roasting software in another section. The important thing to understand up to this point is that time and temperature differences have a massive influence on the end product.

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

Which beans for which taste?

It is arguably one of the most beautiful tasks in a roastery: the selection of raw coffee. At the same time, it is also one with many consequences. Depending on your choice of raw coffee, you open or limit the range of use of the chosen coffee.

Raw coffees differ in density, size, and shape. They all roast slightly differently.

Coffees high in acidity are delicious for filter coffees because we dilute them with plenty of water and a light drink is created. However, these raw coffees are probably not for everyone when it comes to espresso.

But the other way around, too—simpler, tendentially nutty-sweet coffees can make a great espresso, but perhaps a somewhat monotonous filter coffee.

This is where it is your turn. Because every roasting language is individual. Everyone who roasts has their own interpretation of how the coffee should taste in the end.

Raw Coffee Selection—we open our warehouse

You have to start somewhere, and buying a whole 60kg sack right away is probably not the goal. So, we are now also selling 1.5kg and 3kg bags of raw coffee. They are the same ones we use in our assortment. So if you want, you can, for example, roast our classic Dreispitz Blend.

Which of our coffees do we use for what:

Which coffee suits you best, you already know—if you still need some inspiration, then we have put together a small guide for you here.

After roasting: Cooling and storage

As a standard procedure, we recommend roasting with a stopwatch, marking the 1st Crack, and writing down the data. This way, you can create references and compare again and again.

You determine the end of the roast. When you have reached the desired development time, remove the coffee from the roasting system.

After that, it is important to cool the coffee as quickly as possible. Not with water, that 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 just take a pasta colander and cool the coffee in it. Important here: always keep it in motion and blow on it to cool the coffee down.

This is how we stop the physical and chemical processes of roasting and prevent uncontrolled continued roasting.

The silverskin on the raw coffee bean (whitish), adhering, and on the table after roasting. The airflow must get the silverskin out of the system so that it does not catch fire.

How long does the coffee have to degas 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 for quality assurance after just 24-76h. We pour 12g of coffee with 200g of hot water, wait 4 minutes, break the crust, and slurp the coffee.

You can use this as a guideline:

long roast = long degassing time

short roast = short degassing time

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

This way, you will quickly find the time that is right for you.

We discussed what coffee scientist Chahan Yeretzian has to say about freshness in this video.

How can I improve?

Another fascinating aspect of roasting is this totally analog nature. Unlike a digital camera, where you can simply delete a bad photo, you have to have the analog camera under control, otherwise, you have used up space on the film roll. That is roasting.

You put raw coffee into the system, roast it, done. Once the coffee is roasted, you cannot roast it again. You could, but it makes no sense. You will then burn the coffee and that is no fun.

Green in, brown out. If you did everything right, the result tastes good. If not, well, then once more. Learning by doing, or as a colleague once said: learning by burning. So there is always a bit of adrenaline involved in roasting, and that is probably why it exerts such a fascination on many people.

Register data in the roast log

To really understand how you are improving, you must record your data. By hand, in an Excel table, it doesn't matter, just make sure you include this data:

• which raw coffee
• raw coffee quantity
• start temperature (if possible, otherwise doesn't matter)
• time to the 1st Crack
• development time
• final temperature (if possible, otherwise doesn't matter)
• weight of roasted coffee

By weighing the roasted coffee at the end of the roast, you determine what the roasting loss was. Expect 14-20%, depending on the type of roast. Especially with simple roasters without a temperature display, it is worth measuring the weight. This gives you a feeling of how much material you are roasting away.

Taste, taste, taste

Now all the numbers might look great, but if the coffee doesn't taste good, the most beautiful numbers won't help. Therefore—challenge yourself and taste every batch, and in a standardized way.

How can you proceed?

• always taste after x hours
  • that way you compare coffees of the same age

• grind 12g of coffee and pour over with 200ml of water
  • approx. 96°C
  • use your own water, whether it is hard or soft
  • in this case, it is about you getting a feel for your craft
  • it is best to calibrate this by not changing the basic constants (for now)
  • let steep for 4min, skim off the crust, start slurping after approx. 8min

• or you have your own ritual, e.g., you pour a French Press or a filter coffee. That is all irrelevant, the main thing is that you always do it the same way. Consistency, consistency, consistency.

We are your coaches

If you have now read everything, have learned a roasting technique, and now want our feedback, please send us a sample of your work. We will taste it and give you feedback. Our feedback is honest because we want you to be able to improve.

So: roast, practice, roast, and if you want, we are here for you and will think along with you on how to make it all even better.

Tips, tricks, safety

• Raw coffee selection
  • in our Kaffeemacher shop, we offer most of the raw coffees that we roast ourselves
  • You will also find raw coffees at Ingo from Roast Rebels
  • the Kafischmitte also offers raw coffees for sale

• where to roast?
  • if you roast in your apartment or house—then definitely under an extractor hood with an open window
  • when roasting, a lot of smoke is produced and the silverskin detaches from the raw coffee, which may then swirl around
  • always keep the coffee in motion, so it doesn't burn
  • if you have a terrace, a balcony, or a garage, we also recommend roasting there. For everyone's benefit.

• which devices can you recommend?
  • we are still holding back on recommendations because we are still in test mode
  • it is best to subscribe to our YT channel, where we will introduce the tested machines
  • Ingo from Roast Rebels sells home roasters in the medium price range and tests them for you
  • we ourselves do not sell machines, but have fun testing everything that works
  • so if you give us tips on what we should take a look at, then feel free to recommend it in the comments
  • you can find the popcorn pot used here on Amazon*

*We bought the popcorn pot ourselves. That is a principle for us in all tests. Because we want to evaluate all devices neutrally and without outside influence. The link is an affiliate link to Amazon. If you order something via the link, it costs you nothing more—but our machine testing piggy bank fills up a little.