Coffee-Tech Solar Roaster after 3 years commercial use.

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#1: Post by frustrated_uk »

I feel compelled to write a comprehensive overview of my experience with the Solar, as I feel that the machine is a bit of a mystery to those looking in, given its unconventional control system. There are lots of great threads about specific issues but I wanted to share what I've learned throughout my use.

My Background

I trained in roasting full time for 5 years in a well regarded London speciality coffee company using 60kg and 20kg Petroncini convection roasters, I moved to a new startup roastery in 2014 which took on the dealership of Coffee-Tech roasters in the UK. I was responsible for sales and training of the equipment as well as coffee roasting. I used a Ghibli 15kg as well as a Solar and FZ94. 2 years later I started my own roastery-café, Yellow Bourbon Coffee Roasters, equipped with a second hand Solar. The business is growing well and I now use 2 Solars simultaneously, so you can tell my thoughts about the machine are favourable. I am no longer connected with Coffee Tech or its sales agents, I just want to share my experience.

What you Should know about the Solar.

The best roaster in the world is the one you're really familiar with, whatever that may be. Understand how the machine works, what it was designed to do, work within those parameters and don't try to overcomplicate things and you'll get great results. The machine is capable of delicate, complex light roasted dense coffees, right through to perfectly developed espresso roasts. We'll get to that.

The Solar is primarily designed to operate within a high volume serving café to supply the demand of that shop, plus some retail, and a small amount of wholesale. To be safe in this environment the machine must be automated to kill the heat at a certain point and for a cold air cooling cycle to begin in the drum. These functions are very well designed and contribute to excellent development of the coffee.

The machine is electrically heated. 3 x 1kw heating elements surround the bottom half of the perforated drum. Heat is transferred by convection, conduction and infra-red. At programmed intervals a blower sends a pulse of accelerated air into the roasting chamber causing a climb in the environment temperature which keeps the bean pile temperature climbing at an even rate of rise.

The user controls are limited to setting the charge temperature and the temperature of the final stage. The final stage is the temperature (set just prior to first crack for a medium roast) at which power is cut to the heating elements. From this point the machine continues for 3 minutes in the Final Stage before Cooling Stage begins and fans blow cold air through the drum. Sounds limiting? No way, electric elements fading down are just great for a declining rate of rise. Just before first crack when the coffee starts to throw heat back out into the drum the element is switched off, but unlike gas, that doesn't mean a sudden and complete loss of energy. The heating elements fade down slowly, continuing to add heat but ever more gently, corresponding with the rate at which the coffee is heating the drum, and they do it naturally without the need for complicated controllers. The set 3 minutes time works, it's the time it takes for the elements to run out of useful energy, you've just got to get comfortable with it. After the 3 minutes the cooling fan sparks up. Use it. Let the coffee remain in the drum for 1-2 minutes. The coffee is still developing at this stage, plus if you let the coffee out too early you get blasted with sparks and ash. (chaff falls through the perforations in the drum and burns to ash on the heating elements, then gets blown through by the fans. It needs a minute to clear the drum.) At this point I should point out that the optional external cooling fan is a must. Even equipped with it, the coffee takes 10 minutes+ to fully cool, I find this one of the shortcomings.

But it doesn't have a sample trier

No, it doesn't, you'll have to get over yourself with that one. Trust the systems in the machine. If you keep a good between-roast routine the machine will deliver a roast the same colour, in a time within 10 seconds of the previous roast. Its consistency is remarkable.

Why the Solar works for my business

That automated thing. When I started the business I was keenly aware that there would be a lengthy quiet period as we built custom. The shop had to be operable by 1 person otherwise the wage bill would be unsustainable. The Solar was located at the back of the shop within reach of the espresso machine. Before I go on - Don't leave your roaster unattended, ever, ok? That being said, I had to be able to serve lattes while roasting was going on. This would be impossible with a fully manually controlled machine, you'd never hit all the points and you'd set the place on fire. So the Solar could take care of ending the roast, reliably and safely producing great tasting coffee, without an additional member of staff.



Add to that my shop is tiny, there is no gas and bottled gas is prohibited by the landlord. The machine is now located upstairs, in fact there are 2 Solars upstairs and happy to say we now have a team of 4 so there is always a fully trained operator supervising the roasting.


We are now roasting between 150-200kg of green coffee each week. The 2kg size is perfect for our turnover of retail single origin coffees - they move more slowly so the small batch keeps them fresh on the shelves. For espresso blend I've got to say it's slightly onerous now with several good size wholesale accounts, but what I have not touched on is that customers love it. Love it. To be roasting in the shop in view of the customers all the time because you have to do repetitive small batches is the best promo you could ever want. Locals will talk about 'that place where you see them roasting the coffee' and you gain a lot of impulse buys of roasted coffee in addition to their flat white. Most of those will go on to be repeat customers, they've taken away a piece of ownership with them. We have no way to house a larger gas machine within our premises. The alternative is to rent an industrial unit to house a big machine and move from pushing the limits of our capacity to having expensive redundant capability. The overheads involved don't make sense for us right now, I'm holding out until we regularly can't fulfill demand within the 48 hours the shop is open each week.

Roasting on the Solar

The Solar roasts pretty slowly, and that's OK. If you've been reading about 7 minute roasts and such, well good for those guys, but don't worry about trying to force your Solar to do that. For a 2kg batch expect 10 minutes to drying end, 14-15 minutes to 1C and 16-17 minutes to enter cooling stage, then a minute or 2 after that. For denser coffees you can drop the charge down to 1.5kg for greater definition in the acidity, with a roast entering cooling stage at around 14 minutes.
When setting your temperature controls note that the drop-in temperature basically dictates the length of the roast and the final stage temperature decides the colour. Adjusting the final stage temperature by 1 degree does not necessarily mean that the end temperature will increase by 1 degree, its that taking your foot off the accelerator and rolling to a stop thing. The faster you're going the further you'll roll.

I'm going to give you a couple of example roasts, but note that the numbers might not work for you. On our 2 machines the red one drops in an indicated 25 deg higher and reaches final stage 5 deg higher than the black one for the same roast colour and time. Your numbers are your numbers, they're not a lot of use to anyone else.

Ok so a roast of espresso blend: 2kg batch, pre roast blended. 50% washed Colombia, 30% natural Brasil, 20% honey Honduras. Drop-in temp 145, final stage temp 172. 16.5 minute roast. Flavour profile rich body, dark choc, caramel, orange aftertaste.

We recently reduced the drop in temp by 1deg as we wanted to slow down the roast to get easier extraction in espresso. It had started getting a little tart and nippy, so we lengthened the roast by a few seconds to get more body and sweetness down low and subdue the acidity a touch. The final stage was decided upon by pushing it up until the first hint of carbon was tasted in the cupping bowl, then coming down one. Two degrees lower and there was a faint hint of under development, one degree lower and it just was lacking a little caramelised sweetness.

Example single origin: 1.5kg batch, Ethiopia Beloya washed Yirgacheffe. Drop-in temp 148, final stage temp 167, 13.5 minute roast.

Reducing the batch and increasing the charge temp gets the rate of rise up and boosts convection. 2kg batches are very sweet and soft but are muted in the citrus complexity and florals, I'm aiming for a juicy bright lemon finish. Lighter overall colour but first crack all finished before dropping it out. I rasied the charge temp until I started to see scorching and uneven cooking then came down a bit. The final stage temp I kept lowering until it got grassy then nudged it up a notch, you get the idea.

The most important part of your input takes place between roasts. Keep a good routine and you'll get consistency. Listen carefully for cooling to begin. Take note of the temperature displayed at this point and get the coffee out when you start to see it fall. Quit the cooling cycle on the controller before opening the door. This will give the machine enough time to clear the debris and prevents the coffee cooling very slowly in the drum, harming definition. TBH with roasts developed for body and smoothness this is not an issue. If you leave the coffee in there for the full 10 minutes of cooling its not a disaster, but complex juicy coffees want a quick exit. Once the coffee is out let the machine cool naturally to 1 deg below the next roast's drop-in temperature. Hit the start button. This ensures that the roaster is always in the upswing when you charge and at a predictable energy level. The alarm will sound when drop-in temp is reached so drop it in promptly and you're on your way again. If your final stage temp is very close to the drop-in temp then temporarily put the final stage temp up 10 deg. This ensures that as the temp over-runs during charge it doesn't trick the roaster into thinking the coffee has reached final-stage temp and kill heat to the elements. Remember to put the final stage temp back down when the indicated temp is lower than it.

A note about exhaust extraction. The Solar doesn't like forced airflow through the exhaust. The ideal situation I have found is the shortest run of 100mm semiflex possible straight out of a window. If you need a booster fan leave a gap between the top of the Solar's chimney and the inlet of your exhaust duct. This allows the Solar to operate at its natural airflow, whilst the extractor vacuums the ambient air.

Modifying the Solar

It's a very well designed machine for its purpose, you don't need to do anything and I would recommend that for at least the first year's use you don't touch it. Learn to get the best from it using its basic functions. You will develop an intuitive understanding of the machine and that's the most important skill you have. That said, I've messed with mine. The black machine I cut a hole in the bodywork by the side of the cooling tray to fit a duct to a booster fan to shift more cooling air through the tray. We would find during summer that the batch in the tray was not adequately cool by the time we wanted to drop the next batch. This has solved the problem, cutting cooling time to about 6 mins. Practically speaking it has been a success but repeated blind cuppings have shown no improvement in flavour, favourites picked from the table were pretty much 50/50 with and without the additional cooling.


Then we added probes and started logging roasts using Artisan. It's been very illuminating. I'm not going to go into too much detail but it has asked 1000 questions of us and made us very keen to explore a whole new world of options. However, I feel that I can only exploit these because I understand what the machine is trying to do. Please don't rush in to this, especially if you are a beginner.


Maintenance and reliability

The most common thing you will encounter is failed heating elements. This can be greatly reduced by removing the left hand triangular plate on the front cover and getting in there with a bit of hose on a hoover. The ash from the fallen chaff collects around the bottom element and chokes it. Removing this before each session gives much better lifespan. Be careful though, the ceramic board insulation on the roaster floor is very soft and breaks up if you stab at it with the hose. I replaced my insulation after 4 years of service, was a straightforward job. I have replaced the temperature controller as the display showed signs of failure. I replaced the drum bearings but they were not in bad shape at all. I have had to replace the sight glass as I knocked it out accidentally, that wasn't a big deal either. I have not lost a day of production to mechanical breakdown. This is all routine stuff with a hard working machine.


Routine maintenance consists of the vacuuming described above, emptying the chaff collector every third roast and dismantling the exhaust and giving it a bash and a scrape once a week, get all that carbon out of there, you want to maximise smoke extraction for the sake of clarity in the cup.

In conclusion then, I have had a very happy few years with my Solar. Understand it, get to know it and you will be unlimited in the flavours you can achieve with it. It is reliable, dependable and functional. If you're starting out or need a small machine for slower moving coffees its for you.​



Kind regards
Steve Peel, owner, Yellow Bourbon Coffee Roasters Ltd (UK)
★ Helpful


#2: Post by false1001 »

Two unrelated things: I really like your branding and holy crap are your prices low. Are those normal prices for your area? Even in relative backwaters here in the US 300g of specialty coffee will run you $14-20 (£12-16ish)

On topic, I'm very interested in your roast curves (and specifically the AUC/integral of them) and some clarification on what you mean by "final-stage" and "cooling" stage. It sounds like you're essentially applying a lot more heat but over 1.5-2.5x the amount of time compared to your average drum roaster. Is this due to the mechanics of the electric heating elements as you explained or are there other factors? As you say, charge temp/charge size ratio is the largest variable for drum roasters. Could you not just preheat to a higher temp?


#3: Post by frustrated_uk »

Thanks, glad you like the branding. Prices are pretty standard for UK, but I do keep overheads tight and margins keen.

WRT roast times it's largely down to conduction being a big part of the heating here and the slower times that tends to achieve compared to primarily convective heat. If we push the charge temp too high we risk scorching, and even when we avoid that it tastes less developed when we try to speed up the roast. It's just happy at those kind of roast times. The relationship between convection, conduction and IR is a big gap in my understanding but we're getting closer now that we're graphing the roasts in Artisan.

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#4: Post by Chert »

Great write-up and quite intriguing. I also like the branding very well. Congratulations, too!

The pulses of air that you describe sound like convection heating, but your roast times and low temperatures sound more like conduction as you say. Perhaps the air pulses really just convect air onto the drum and not directly on the bean mass.
LMWDP #198

now more than ever


#5: Post by frustrated_uk »

Hi Chert thanks for the kind words. I think you're right about the air pulses. Basically I think 3kW to roast 2kg is not enough on its own. The air pulses boost the ET to keep the BT RoR moving, without this it looks like the roast would stall. On the graph you can see the ET goes up in steps whilst the BT stays smooth. The steps directly correspond with the automatic air pulses. It causes an unorthodox RoR pattern in the BT but it works, the overall trend is downward between the spikes.



#6: Post by frustrated_uk »

Update: Now we have a FZ94 on the fleet as we needed to increase capacity but also because I wanted a fully manual machine so I don't lose my skills for roasting using my senses. It gives us loads more options for tweaking, and looks bloody great. Happy times. Oh and I painted the red one black for uniformity too. Image


#7: Post by BeachWatcher »

Steve, thanks for an excellent review a piece of coffee tech roasting equipment (the Solar). I have been roasting on an FZ-94 for almost two years and it is incredible. It will do magic when coupled with Artisan. It produces easily over 15 pounds of roasted to medium beans an hour. I have done some simple modifications to increase throughput. I have been looking at the solar recently as an addition to the FZ for it's more "hands off" capability . Should be able to train someone else to roast easily given your input. Your thoughts have given me a lot more information in the decision making process. Thank you.

Best regards,
Bob in Virginia Beach, VA USA

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#8: Post by redbone »

Good to hear of your positive experience with C-T roasters. Local owner \ acquaintance with a 12kg Diedrich roaster was looking to add another machine and attempted to contact C-T roasters no less than 3 times using different methods with no response. He then asked if I could try and also no response with email and voice message. Machines may be great but based on the lack of response for potential sales I could only imagine what support would be like. He has decided to save up for a Loring instead. Support should be a huge factor when purchasing any commercial machine, ymmd.
Between order and chaos there is espresso.
Semper discens.

LMWDP #549


#9: Post by Séb »

redbone wrote:Good to hear of your positive experience with C-T roasters. A local friend with a 12kg Diedrich roaster was looking to add another machine and attempted to contact C-T roasters no less than 3 times using different methods with no response. He then asked if I could try and also no response with email and voice message. Machines may be great but based on the lack of response for potential sales I could only imagine what support would be like. He has decided to save up for a Loring instead. Support should be a huge factor when purchasing any commercial machine.
I am very surprised by this. I did own a Solar roaster with Avirnaki for about three years and i always got very fast response by Ram the owner or any of their technician guys. I met Ram at the last SCA in Boston, they produce great equipment (loved the Solar and the Silon roaster) and for me they have been very professional and fast to reply to any question I had. I now roast on a fluid bed roaster but next summer i will open my first Cafe and i am still contemplating buying an other Solar roaster to roast in front of the customer (my fluid bed is WAY too loud).

That was a fantastic review BTW. Thanks for taking the time to write this nice detailed experience you have with the Solar roaster.


#10: Post by BeachWatcher »

RE: Response from Coffee Tech to questions/Issues: I always get a quick response from the coffee tech folks. On the one time I needed a part it came in quickly. I use both the online technical support at their site and in some cases a direct email contqct. Bob