Home coffee roasting. Basic knowledge for home roasters

Coffee roasting is not an art, but a craft. And that's why you can also easily roast your own coffee at home. But to make sure it tastes good and isn't too dangerous, we've compiled these tips for you.

If you've ever been to a coffee roastery, you know how much space roasting machines can take up. We roast on a 12kg roaster, but it also weighs a good 500kg and is the size of a small car.

Our 1kg Probatino roaster is also well over 100kg heavy, but still quite large. If you've ever been to a large roastery and seen a 250kg roaster, you'll find that these machines, with all the trimmings, come close to the size of a small house.

But it can also be much smaller. There are devices that are no bigger than a shoebox, with which you can roast 50g or several hundred grams at home. And it's really fun. Rarely are you as close to the product as when you roast coffee on the smallest possible scale.

A little adventure

We've tried various home roasting machines and present them on our YouTube channel. One thing upfront – I had a blast. I normally roast on a 12kg roaster and advise other roasteries that have 5kg – 60kg roasters. Those are sizes I'm used to.

But roasting just a few grams is somehow very exciting. A lot of things are trickier, less controllable, faster and – yes – sometimes just more random. The background knowledge I've acquired over years on larger roasters is being put to the test here. So if you have contrary experiences with the machines discussed or anything else, please write to us in the comments section.

Roasting coffee yourself is initially a little adventure. It smokes, it crackles, it gets hot, maybe things happen a bit out of control, but you will like your coffee. Even if it might not taste as good as from elsewhere, the work that goes into it tastes really good.

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

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

First, we have to disappoint you – we can't give you exact specifications for time and temperature. Not because we don't want to, but because we can't.

Temperature

Just as my grind size isn't your grind size, my temperature isn't your temperature. I recently roasted on two different roasters with two identical machines. But the temperature was always somewhat cooler on Roaster A than on Roaster B.

This was mainly because Roaster A had a different temperature probe installed in the roaster. 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 for that.

So what was the correct temperature? I would say neither. Honestly, I don't really care what the temperature is "exactly" – the main thing is that we stick to a temperature and think from there on.

The 180° in a popcorn roaster* are probably different from 180° in a drum roaster. It always depends on what and where is being measured. That's why temperatures are irrelevant. If you're already roasting at home, you've already gathered experience values and can orient yourself by them. If you're starting from zero, then we recommend setting the temperature suggested by the manufacturer.

Time of roasting

Time and temperature are mutually dependent during roasting.

The hotter the temperature, the faster the roasting.

The cooler the temperature, the slower the roasting.

Giving exact times doesn't help much here, since different roasting machines transfer heat to the bean differently.

Generally:

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

20 minutes is quite long, especially for very small quantities – we're just baking the coffee and essentially hollowing out its flavor.

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

What is the right amount?

One of the big advantages of roasting is that many steps are simply explainable and logical. So too the question of how much quantity 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's hardly any energy stored in the system (roaster walls, floor, lid, etc.). Most of the energy input comes via hot air or direct contact heat.

When you put green coffee into the roaster (=roasting system), the system first loses energy. Green coffee at 20° C ambient temperature comes into a hot environment and first absorbs heat.

When you bake lasagna, preheat the oven, then open the door and put the cold lasagna in, the temperature in the oven drops first. The same thing happens when roasting.

So if you put a large quantity into any roaster, roasting takes longer because you're removing energy from the system.

If you put a small amount of coffee into the roast, you remove 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. Everything is system-dependent. Definitely stick to the specifications the manufacturer provides. Then you see how long the roasting takes and orient yourself by the points mentioned above.

When you make adjustments to batch size, then make them definitely clear. If you roast the 1st batch at 100g and the 2nd batch at 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 somewhat more extreme tests, exploring the strengths and weaknesses of the system by choosing larger differences in batches or temperature. That's how you get to the goal faster.

The first crack and the development time

Over several minutes you approach the first crack, the first pop, or simply the crackling. Then, when the pressure in the coffee bean is so great that it must escape, you hear, depending on the roasting system, distinctly quieter or louder crackling.

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

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

It's fun to hear this crackling and assign it to coffees. Pay attention to this crackling and you'll understand your coffees even better.

When does the 1st crack begin?

Have I mentioned that it's really fun to listen for the 1st crack? Depending on the flavor you're aiming for, your crack comes earlier (lighter coffees, because faster roasting) or later (more developed coffees, espresso, for example)

The 1st crack comes 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 joins in (first mark from the left). Then it gets more intense. As soon as you hear the first triplet, that is, a closely spaced crack-crack-crack, that's when we mark the 1st crack (second mark from the left).

The crackling (1st crack) resembles a normal distribution

That way we can be sure the whole batch is starting to crack. It takes some practice, nerves, and patience not to mark the 1st crack right at the first crackling.

Shortly after the 1st crack, the whole batch takes off and it crackles more evenly, the majority of the beans (third mark from the left) now crack simultaneously.

After that the curve drops off until there's no more crackling to be heard. If you continue roasting even longer and especially hotter at this point, you're approaching the 2nd crack, which is much quieter and more like crackling. For our guide here, we'll 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 only roast strictly by time, e.g., all filter coffees 10, all espressos 14, and all dark roasts 18 minutes, then I'm doing the coffee a disservice. Because many coffees behave differently during roasting.

Since we roast many coffees for others, we gather experience with all sorts of different coffees. The more different coffees we roast, the more we can make predictions about an unknown green coffee.

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 completely differently and taste like it. The 10 minutes for the Kenyan coffee might show it in the best light – fruity, balanced, well-integrated acidity – while the Brazilian coffee might already be charred because it's much softer.

If we instead get used to marking the 1st crack with each coffee and not roasting by total roasting time, the coffees taste much better pretty 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 when 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 be 90 seconds, in relation to 480 seconds. This way we can calculate the percentage development time, which in this case would be 15.8% (90sec of 570sec).

And what does that mean now?

A shorter development time of about 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 about 8-10% can mean that I

• get such a coffee with lots of aromas,
• more acidity, tea-like texture, and
• little roast notes.

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

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

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

• achieve many roast notes, fewer light, floral, and fruity aromas,
• less acidity, less texture,
• but lots of body and dark sugar notes

All these specifications are so often "without warranty" because they depend on the respective roasting system. But I've tried to treat them as generally as possible so that it's more universal than very specific.

The roasting curve

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

Years ago – just a few years back – this software was rarely widespread. Programs like Cropster or Artisan, however, have experienced immense growth in recent years. More and more roasteries are relying not only on their gut feeling, but want to convert their data into information, display it graphically, and learn even more.

We read roasting profiles from left to right. The x-axis shows time, the y-axis on the left shows bean temperature, the y-axis on the right shows rate of rise (RoR) – the energy increase per 30 seconds.

Three roasting curves from the Kaffeemacher roastery

Temperature probes at various locations 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 light roasted filter coffee.

The yellow curve is our Feingeist, a specialty espresso.

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

The roasting language of the three profiles couldn't be more different. In time, the coffees differ between 9:10 and 17:30 minutes. The final temperature is also different each time. But what becomes very clear is the rate of temperature increase – very steep with the Ichamama, somewhat flatter with the Feingeist, and noticeably slower with the automatic coffee.

How you can draw such a curve yourself, without complicated roasting software, we'll look at in another place. What's important so far is to understand that differences in time and temperature have a massive impact on the final product.

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

Which beans for which taste?

It's probably one of the most beautiful tasks that happens in a roastery: selecting green coffee. At the same time, it's one with many consequences. Depending on your choice of green coffee, you either open up or limit the application range of the chosen coffee.

Green coffees differ in density, size, and shape. They all roast somewhat differently.

Highly acidic coffees are delicious for filter coffees because we dilute them there with lots of water and create a light beverage. But these green coffees are probably not everyone's cup of tea when it comes to espresso.

But also the other way around – simpler, tends to be nutty-sweet coffees can make a great espresso, but perhaps a somewhat monotonous filter coffee.

Now it's your turn. Because every roasting style is individual. Everyone who roasts has their own interpretation of how the coffee should taste in the end.

Green coffee selection – we open our warehouse

You have to start somewhere, and buying a whole 60kg bag right away probably isn't the way to go. So we now also sell 1.5kg and 3kg bags of green coffee. They're the same ones we use in our assortment. So if you want, you can, for example, re-roast our classic Dreispitz blend.

Which of our coffees do we use for what:

Which coffee best suits you, you already know – if you need a little inspiration, we've compiled a little guide here for you.

After roasting: cooling and storage

We recommend roasting standardly with a stopwatch, marking the 1st crack, and writing down the data. This way you can create references and always compare again.

You determine the end of roasting. Then, when you've reached your desired development time, you remove the coffee from the roasting system.

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

a) pull the smoke away

b) cool the coffee quickly

You can also just use a pasta strainer and cool the coffee in it. Important: always keep it in motion and blow on it to cool the coffee down.

This stops the physical and chemical processes of roasting and prevents uncontrolled further roasting.

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

How long must the coffee degas after roasting?

For our coffees we recommend:

• minimum 7 days for a filter coffee
• minimum 14 days for an espresso

However, we usually do a cupping for quality assurance after 24-76 hours. We pour 12g of coffee with 200g of hot water, wait 4 minutes, break the crust, and sip the coffee.

As a guideline, you can use this here:

long roast = long degassing time

short roast = short degassing time

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

That's how you'll quickly find the time that works for you.

What coffee scientist Chahan Yeretzian says about freshness, we discussed in this video.

How can I improve?

Another fascinating aspect of roasting is this total analog. Unlike a digital camera, where you can simply delete a bad photo, you have to master the analog camera, otherwise you've used up space on the film roll. That's roasting.

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

Green in, brown out. If you've done everything right, the result tastes good. If not, well then, do it again. Learning by doing, or as a colleague once said: learning by burning. So there's always a bit of adrenaline involved in roasting, and that's probably why it has such a fascination for many people.

Recording data in the roasting log

To really understand how you're improving, you need to write down your data. By hand, in an Excel spreadsheet, whatever, the important thing is that you record this data:

• which green coffee
• amount of green coffee
• starting temperature (if possible, otherwise doesn't matter)
• time until 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 roasting, you determine how much roasting loss there was. Calculate about 14-20%, depending on the type of roasting. Especially with simple roasters without a temperature display, it's worth measuring the weight. This way you get a feel for how much material you roast away.

Taste, taste, taste

Now all numbers might look great, but if the coffee doesn't taste good, all the beautiful numbers don't help. So challenge yourself and taste every batch, and do it standardized.

How can you proceed?

• always taste after x hours
  • that way you compare equally old coffees

• grind 12g of coffee and pour with 200ml water
  • approx. 96°C
  • use your own water, whether it's hard or soft
  • in this case, it's about you developing a sense for your craft
  • it's best to balance it out by not changing the basic constants (for now)
  • let steep for 4 minutes, skim the crust, start slurping after about 8 minutes

• or you have your own ritual, e.g. you pour a French press or a filter coffee. It's all the same, the important thing is that you do it the same way every time. Consistency, consistency, consistency.

We are your coaches

Now that you've read it all, learned a roasting technique, and want our feedback, just send us a sample of your skills. 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 for you and will think through with you how you can do it all even better.

Tips, tricks, safety

• Green coffee selection
  • in our Kaffeemacher shop we offer most of the green coffees that we roast ourselves
  • You'll also find green coffees at Ingo from Roast Rebels
  • Kafischmitte also offers green coffees for sale

• where to roast?
  • if you roast in the apartment, in the house – then definitely under a range hood with the window open
  • roasting produces a lot of smoke and the silver skins detach from the green 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're still holding back on recommendations because we're also still in test mode
  • best to subscribe to our YT channel, where we'll feature the tested machines
  • Ingo from roast rebels sells home roasters in the mid-price range and tests them for you
  • we ourselves don't sell machines, but we have fun testing everything that works
  • if you give us tips on what we should check out, feel free to recommend in the comments
  • the popcorn pot used can be found here at Amazon*

*We bought the popcorn pot. This is a principle for us in all tests. Because we want to evaluate all devices neutrally and without external influence. The link is an affiliate link to Amazon. If you order something via the link, it won't cost you any more – but our machine testing fund gets a little fuller.