I ordered from a specialty roaster not to long ago down from Stockholm. (Stockholm and Umeå are actually quite far away from each other) anyway, I like to try different brands of specialty roasters in order to compare and improve my own roasting. To be perfectly honest, I was completely flabbergasted at how awful the coffee was.
I bought several packs and different origins at different roast levels. The roaster I bought from is a well known and established company. So it took me by complete surprise at how awful the roasts were. I will have to buy again in a month or so and see if it's still just as awful. The roasts taste baked, grassy, under developed and just all around awful, I couldn't make it through a full cup. I wasn't expecting this at all. Most roasters I buy from, even if I think the roast could be better, was still usually a delightful experience. I buy from Costas here in Umeå often, while I don't like all the roasts, I still enjoy the experience. Maybe not all the coffees are too my tastes, but they are complete and finished roasts and did exactly as the label stated them to do.
So this brought me back to the specialty roaster from Stockholm, and how awful it was. I started to think, it's either the taste profile they are looking for, or they don't have consistency in their roasting. Meaning, maybe they have a recipe that at one time tasted great, but very inconsistent in roasting that profile. So out of 10 roasts maybe 3 of them are great, 4 so-so, 2 bad, and 1 awful. I happened to get that 1 that was awful.
There are many different aspects that define roast quality and consistency. Many roasters just stare at the ROR (rate of rise) and DV% (development time as a percentage of overall roasts). But there are many factors that affect the overall quality of the roasts and consistency between roasts is usually overlooked. For example at what temperature is the roaster pre-heated at? Most roasters wait until the pre-heat gets to charged roast, then, they throw in the beans and go. However, this usually makes the first roast considerably different than the later roasts. Why? because the charge temp is only measuring the air temperature inside the drum, but not the actual drum itself. Obviously, if your machine has been sitting all night at room temperature, and them you just pop it on and wait for it to get to charge temp, that temp is going to be lower than after a few roasts when the drum itself gets nice and threat.
How to do a proper pre-heat
This is my own protocol, so take it for what it is, but I find that this really helps with overall consistency.
First, if for example I want to start my charge temp at 260 celcius, I will pre-heat my drum at around 280, wait for it to say "charge" meaning my temp has been reached, then I let it sit there at that temp for about an extra 20 minutes. Then I restart the pre-heat program down to 260 and wait for it to reach that temp, then I toss in my coffee beans.
Between batches
On the Aillio bullet you can easily have one batch cooling while the machine starts the pre-heat protocol. This allows for a consistent routine between batches. I find that the cooling of a 1kg batch usually takes about four to five minutes, which in turn is about a minute after the change temp has been reached. Which is perfect. Once that one minute charge time has been reached, I put my next batch into the machine. Usually around 900g each roast. While the Aillio bullet does well with 1kg roasts, I think it's a little more consistent with 900g. But for ease of discussion I usually just write 1kg here.
Cleaning the machine
The Aillio bullet collects a lot of Chaff in the chaff collector, great obviously, but it does hurt consistency if that chaff collector is not emptied about every 3 1kg roasts. The chaff collector gets so full that it affects airflow out of the machine and in turn makes perfect consistency difficult by definition.
My cleaning protocol for the Bullet:
- After every roast I vacuum out the cooling tray
- After every 3 roasts I clean out the chaff collector and vacuum the metal filter there
- After a full day of roasting say 10-15kg roasts I will clean the machine completely. I usually put the metal chaff filter and fan blade in the dish washer. This cleaning routine even includes popping of the front and cleaning the IBTS probe.
- Once a week I clean out the chimney and ventilation pipes where possible.
Other factors
Other important factors to consider when roasting is how the Green coffee is stored. Dark, cool and low humidity are to be prioritized. If your storing smaller batches, use a vacuum sealing unit to store the green beans. Otherwise try to control humidity - I use a de-humiditizer (No idea what that's called in English.)
Last - the room temperature where your roaster is used also has an effect. I find that roasting in the winter always takes longer to get to roast charge, and a little longer throughout. But this has been mitigated for the most part by having a constant room temperature and a ventilation fan that pushes that hot air of the roaster out and doesn't let the cold air come in.