Buying a Coffee Roaster

Buying a Coffee Roaster

When I look back on the past when I was shopping for a coffee roaster these are the things I wish I had known. Yea your welcome.

This can be quite scary considering the price some roasters are, can compare them to buying a nice truck or boat! You don’t want to get it wrong once you have it that's it there is no going back. Most roasters are manufactured overseas unless you are lucky enough to live in the country of manufacture. This means considerable risk buying such a large piece of metal without even seeing it in person. I would not recommend buying a roaster from overseas that you haven't seen before in person and had experience using. Would you buy a car from another country without seeing it… maybe you would but it is high risk.

If you are keen you could fly to the manufacture and ask for a tour of their showroom and ask for a demonstration. This would give you the chance to ask all the questions in person and plus you'll get a feel for how the company will be in after sale support also. For many of us this is not an option.

What can we do to ensure we are making a wise purchase/business decision?


There are a handful of very well known coffee roaster brands around the world. Loring, Probat, Diedrich, Geisen and many more but these guys are the big dogs in terms of reputation and there is a good reason for it. You are not only buying a machine you are buying a part of history. You will see these brand roasters all over the world in specialty coffee roasters, some vintage. But! But! These roasters come at a huge price tag that some can’t think to afford. Sticking to the brands that have a good reputation I think is a pretty safe approach when choosing but you neede deep pockets.


I will list out below all the features that I think a good coffee roasting machine should have.


Now don’t ask me exactly what size the drum should be I am no engineer. I can tell you though use your sense of scale. Compare coffee roasters on in the size category that you are shopping for let's say 5kg. If one brand of coffee roaster looks significantly smaller to all the competition it's a good chance that it's not going to be able to really roast 5kg successfully. There are no rules and regulations as to what a 5kg machine should look like so companies can choose whatever they like. Because of this many roasters, I have talked to never roast at full capacity. When I roasted on a 12 kg Probat I was charging 10kg no more. Yes, Probat is probably one of the few that can actually roast at full capacity but with my roasting approach, I like to be able to roast faster with more tumble space for the beans to receive a higher dose of convective heat energy. I felt it made it easier to control the ROR in the later stages of the roast. (Rate of Rise will discuss in another blog post) 

Here is a video through the sight glass of a roaster that potentially has an overloaded drum

Here is a video through the sight glass of a roaster that is roasting close to the correct load size.

It's similar to a front loader clothes washing machine if you overload it the clothes are not going to mix properly and have the chance to get a tumble action going. This leads to an uneven wash, potentially clothes are not washed properly. The same goes for an overloaded coffee roaster, yes they all go from green to brown but are they evenly cooked? Maybe not, If you roast dark this is less likely. Only God can help you if you roast “Dark” Near and during the Second Crack.

Most good quality roasters now come standard with double walled drums I am a huge advocate for this, less chance for scorching the beans outside and normally you are gaining a bit more thermal mass. Carbon Steel, Stainless Steel and Cast Iron I couldn't comment on I don’t think one is better than the other.

Mixing paddles: If the mixing paddles are not well engineering it is unlikely the beans are going to be roasted evenly especially near full capacity. Please be aware of this with cheaper coffee roasters. On my old toper beans would get stuck somewhere in the roaster in between batches and go for a second ride. Lots of fun having to pick out the Charcoal beans out of the cooling tray! Not!

Perforations at the rear of drum: I have seen some coffee roasters that are completely perforated at the rear of drum and some with maybe 2 dozen holes. More Holes = higher air volume potentially through the drum. Be aware of this because it does affect the air pressure in the drum. Use the lighter test to test your airflow between a drum that has many holes V’s a drum with fewer holes you are going to have completely different airflow dynamics even if the lighter test is where you want it. Think of it as a car with the stock air intake V’s an aftermarket performance high flow air intake. Your car will be able to receive the airflow in higher volume easier / work less. Then gaining higher performance or using less fuel.


Most high-end coffee roasters I have seen don’t have this feature stock, you have to buy the addon of controllable drum speed. I Think this is critical if you want to roast various batch sizes in your roaster. Roast 3 Kg in a 12 kg roaster of some expensive coffee is going to be easier if you can reduce the drum RPM. Please refer to “The Coffee Roasters Companion” as to what the recommended RPM should be for each size roaster. You want your Thermocouple probe to always be in the densest part of the bean pile as the drum is spinning. This can change dramatically when you mess around with your charge size. (amount of coffee in roaster). I have seen some cool videos on Youtube of people doing a clear plastic test on the front of the roaster to see where the best place to install the thermocouple is. Funny thing is some roaster manufacturers get it wrong. Say that again … “Not correct for the customer's requirements”. Do yourself a favor and get a roaster with a variable speed drum.


I this video you can also see the drum is spinning too slowly as the beans are not able to be tossed in air enough. This test is good to figure out what RPM you should use at different load sizes and to figure out where to best place the thermocouple.


Again please refer to “The Coffee Roasters Companion” for accurate information the recommended power rating is per Kg of coffee, I don’t understand the science behind it but I do know it works. If a roaster says its a 5kg roaster use the formula in the book to see if the burner is actually powerful enough to roast that much coffee. On my old Toper 10kg, the burner only had enough power to roast 3.5kg of coffee with a decent declining ROR in an acceptable time frame. I personally don’t like coffee that has been roasted any longer than 13 mins. In my tests, I have always noticed the coffee became baked  (Baked = killing the flavour in the coffee) at times longer than 13 mins. For others this might not be true I respect that. Ask the machine manufacture what the output of the burner is. They should know!


I say ability because the motor connected to the cooling tray Impeller is not a sign of how well it can cool coffee. There are a few main designs I’ve seen, 1: Large wide cooling tray which cools fast buy spreading the coffee out wide and agitating well with mixing arms. 2: Narrow cooling tray which has a extremely powerful fan and fast agitation. Neither is better than the other just make sure the coffee is cooled to room temperature in 3-4mins. I am certain that the cooling tray needs its own fan. The older roasters which share the cooling traying fan with the drum are no good, so stay away from these. These old roasters you could divert the airflow using a adjustable baffle plate move air from drum to the cooling tray. This means you have to wait in between batches for the beans to completely cool down before you could commence the next roast, Bad for production and your sanity. Roast cooled to room temperature in less than 4 mins max … Thumbs up!


Air is pulled over the heat source powering your roaster then drawn through perforations at the rear of the drum, pulled through bean pile, through tubing that connects to fan/impeller then out the chimney. That's the simple way of looking at it but it can be rather complicated also if you want it to be. I think to roast specialty coffee well you must have at minimum a way of controlling the velocity of the air flow through. Most roasters have a adjustable baffle system in place to control the velocity of the air. One step better is a machine with a variable speed fan that you can control at any in point in the roast. Why? Controlling the speed of the fan controls the volume of air travelling through the roaster as opposed to a baffle controlling just air velocity. Its similar to pinching a garden hose to reduce the flow of water compared to installing a external pump with rpm control. When the volume is changed, so is the heat energy which is transferred to the coffee. Now is in the nice to haves basket but I would definitely have this feature because it's much easier to control a fan motor during a roast accurately than fumbling around with a damper at the back of the machine.

To achieve the desired airflow use the lighter technique in this video link and make fine adjustments from here as to what works best for you. Personally, I keep my airflow in 2 to 3 stages depending on how the roast is performing.

Low airflow: Start of roast to “Dry End” coffee has no green hues anymore

Medium Airflow: From “Dry End” to “End of Roast” or “Drop”

High Airflow: Sometimes I will increase the air to high during First Crack if I feel the ROR wants to gain and cutting the burner to zero is too risky.

If you want to know more about why and increasing airflow can benefit your roasts Mill City has a good explanation in one of their videos with Joe Morocco & Derek DaLaPaz ( awesome guys ). otherwise please email me I will do my best to explain.



A thermocouple is basically a metal probe which can read temperature which is relayed back to an electronic device which displays this temperature or connected to a computer and illustrated in a roasting software via a profile.

In most cases, the thermocouples provided by the manufacturer will not be accurate enough and tend to be slow reading and thick sheathed. I have worked on coffee roasters which have worked with probe diameters of 5mm 3mm and 1.5mm. First-hand experience has taught me the thick probe is less than ideal for a specialty roaster. My best advice is to install the thinnest probe possible in your roaster which isn't damaged by the beans moving around it. “K Type” Thermocouples seem to be the goto for most coffee roasters go a little further make sure it's of the ungrounded variety. Compare a thick probe to having on thick winter gloves and putting your hand into the snow, it's going to take a while for you to feel the temperature change as opposed to you having on thin lightweight gloves. The same goes for thermocouples you want to see that temperature change as quickly as possible especially at the end of the roast. In another blog post, I will discuss my journey from a 5mm probe down to a 1.5mm probe.

Image second image credit to Scott Rao


With today's technology buying a roaster with a electronic controller is a no brainer. At minimum a gas valve with a needle valve near the front of the roaster so you don't need to go behind the roaster to make gas adjustments. My old Toper had a Ball valve similar to what you would find on a gas isolating tap. It was terrible I had at most 6 reference points I could use as gas input referring to the pressure manometer down the line. A needle valve is far more accurate and less sensitive to adjustments. Having close to 100 points of adjustment from 0 - 100 gas input is going to help you alot. My small 2 kg gas roaster has a range from 0 to 6kpa with 10 points I can adjust between each kpa. When I worked on the Probat it had a scale from 0 - 100 but I did realise that at 50% gas setting it wasn't actually delivering ½ the gas to the roaster it was more around 30% heat transfer... but it worked well once you figured it out. Having electronic gas valves that can connect to your roasting software is super convenient for larger machines. It means you can control the gas inputs using the roasting software. It can then memorize these settings in a reference profile which can be loaded up and act almost like an autopilot. You can jump in at any point on the roast and make alterations if needed.   


If you want to roast dark coffee please stop reading this is not for you. There is a time and a place for dark roasted coffee I know but I don’t like it sorry. Roasting full developed (Properly cooked coffee) at a light to medium roast degree dropped during the first crack or not long after requires a certain roasting style where the beans receive enough heat energy to penetrate the centre of the bean without burning the exterior. From talking to other reputable roasters when they want to roast a very light single origin filters style coffee they are charging the roaster well underspecification. 1.5kg in a 5kg roaster, 4kg in a 12 kg roaster, 10kg in a 22 kg roaster or in my case 600g in a 2kg roaster. There is a good reason behind this we could discuss further. So if you are planning to do a lot of filter roasts keep this in mind. Some people will disagree with this, I am ok with that but I figured this out the hard way roasting plenty of underdeveloped filter coffee going straight to the compost before I managed consistently roast well developed light coffee. Roasting for a darker / medium roast level you can be closer to the roasters charge specification since the beans are experiencing typically longer roast times and higher temperatures the coffee is less likely to be underdeveloped (undercooked) if you roast it correctly that is. I have also roasted underdeveloped darker coffee before it's not pretty! Learn from your mistakes take notes along the way if you have shit memory like me.

(Image credit to BaristaHustle)


Cleaning your coffee roasters ducting system is required regularly. The inside of all the ducting working will build up with a thick layer of baked on coffee dust and a black tar-like substance. It will continue to build up and break off into pieces which can ignite. The piece of ignited coffee dust will travel into the cyclone/chaff collector and light up the bed of chaff. This is no fun! The saying goes around that your not a coffee roaster until you've had a fire. I’ve had multiple due to slacking off on my cleaning schedule. On my roaster, I have now installed a probe inside the chaff collector which has a temperature alarm to warn me of a potential fire starting. With a water spray bottle, I can then push a small burst of water vapor into the chaff collector. Once the roast is finished I can then open the chaff bin up to inspect for burnt chaff. Have a plan for roast fires they will happen.

So cleaning a coffee roaster can be a bastard when they are difficult to disassemble. Some roasters all the pipework can be easily up clipped or unbolted with basic tools. Where some of the cheaper roasters cannot be difficult to disassemble or cannot be fully pulled apart since the ducting is welded together inside. This means you will need special equipment to do a deep clean. When I first got my old Toper I spent a week cleaning it because the previous owner hasn't in years what a nightmare. The ducting was all internal and welded so had to make my own tools for cleaning these pipes. Before buying a coffee roaster consider are you good with taking things apart and putting them back together?

These are all the main things I wish I had known when I entered the industry. There are plenty of other things also but I will cover those in Part 2 at a later date.