[Question] Constant vs Declining RoR


Hi everyone :slight_smile:

I am really new to roasting world, and aillio bullet v2 is my first ever roast machine. I am currently learning to roast by reading books like the coffee roaster’s companion by Scott Rao and modulating the flavor profile of coffee by Rob Hoos.

For me both books are incredibly informative. But I find Rob’s book is more applicable as he explains clearly about the variables on the profile and how those affect the outcome. As he explained that playing with the length of MAI and Development will yield different results, I am more comfortable to plan the time lenght by targeting a constant RoR to reach FC from yellow point in MAI phase, or to reach end temperature from FC in development phase.
But as Scott rao mention in his book, that RoR needs to steadily declining from yellow point to the end of the roast. That makes me confuse on planning the profile. Do I have to calculate the declining RoR with derivative formula so I could get RoR targets on my time interval? Or I’m just too busy with math? :smile:

I found an article (I forgot which one) says that the declining RoR happened naturally only with bigger machine. What do you guys think about it? Does it really matter if I roast with aillio bullet v2?

As far as I try with straight RoR, I couldn’t detect any baked or flat flavor (I could find it on too long dev. phase though) . But I couldn’t just believe my tounge now as my cupping skill is not that good.

I’m more than pleased if you could share your experience and thoughts here…


*sorry for my English :wink:


I’ll take a stab at this. It’s hard to get where you want to go if you don’t know where your destination is.

You are approaching this in what I think is the wrong way, and the wrong order. First, you need to develop a palate for coffee; you need to know what you like, then what you want to accomplish in your roasting efforts. Probably the best way to do this is to taste coffee that has been properly roasted by other people, for example, in good cafes.

Once you know what you like, you can learn about roasting, either by doing it yourself (although I would probably start out on a simpler device than the Bullet, something like a popcorn popper or air roaster), learning some of the basics of roasting, observing what happens during the different phases of roasting, the color changes, the expansion of the beans, the cracks, etc. You can correlate these things with how the coffee tastes.

You can also spend some time with people who roast professionally; I did that a number of times years ago when I was starting. I have encountered a number of professionals who were more than willing to let me watch them roast a few batches, complete with their editorial comments along the way. Not everything that they said was useful or even correct, but it was a starting point.

You could participate on a coffee forum on roasting related threads and try to learn some basic things from other people participating. For that matter, you could just go to roasting forums and read a bunch of threads related to roasting.

I don’t personally think that you can start with what appears to be your current knowledge base and tasting ability, then learn how to roast by reading a couple of books then trying to apply what you read to roasting on the Bullet.

The Bullet is (in my view) a roasting appliance without an innate profile built in. This is very different than, for example, a bigger gas roaster with a massive roasting drum. Those sorts of roasters tend to have what amounts to a profile built into them, that they want to or will reproduce because of the thermal properties of all that metal and how it takes on heat from the heat source. In contrast, the Bullet will just do whatever it is you tell it that you want it to do, by adjusting the heat input and the fan speed. So, it can do everything and nothing. But you have to know what you want it to do, in order to give it the commands/instructions to do what you want.

You may have started with the wrong roaster, given what sounds like no prior roasting experience and no firm idea of what you want to accomplish. You can overcome these things, but it won’t be as simple as picking up a couple of books, no matter how good the authors may be, then discussing concepts in the abstract with no firm ideas about where you want this to go. Perhaps you could take some canned profile for the roaster and use it, then tinker with it, and see how that goes. I guess that would be one way to approach it.


Hi @yvroes, welcome!
I think it’s great that you are studying about roasting. Sounds like you are really getting into it. I haven’t read the well known books that you mention, but I do have Scott’s latest Coffee Roasting Best Practices. There he describes techniques for adjusting your machine to obtain a smoothly declining RoR and eliminate “crashes” and “flicks”. In my (limited) experience these techniques work well on our machines. But I’ve also roasted great tasting batches that didn’t follow Scott’s guidelines, so don’t throw away a roast with a bumpy RoR before trying it.
In answer to your question, yes it does seem very challenging to hit a target drop time and drop temperature with a linearly declining RoR, and even tougher if you want the final RoR value to be zero. I use Overlay during every roast to provide some reference, selecting a nice old profile from a similar bean. I also roast smaller batches (325g) to get more tries out of each 5# bag. If you are very careful to preheat the same way, you can get amazing repeatability from the Bullet, so you can see the effects of small profile changes.
I also think it is great you are getting started on a Bullet, where you have instrumentation to see what the coffee and machine are doing. Do lots of testing and let us know how it goes!


I agree with BradM. Bullet is a great machine, especially if you are a ‘data person’ as it provides lots of info and control. The secret then, IMO, is to be methodical on making limited changes between batches to see what results. I’m far from an expert cupper but I’ve been roasting for several years and have converged on coffee I really like. And I still learn new things each batch.

I subscribe to Rao’s declining ROR rule. While I have not removed every sawtooth bump, I primarily look to avoid an ROR increase as the beans go exothermic at FC. So I anticipate FC, start to reduce power, and try to keep the ROR steadily declining. As FC reaches peak, I then often add just a little power back in to compensate for the lack of heat from the beans.

Like BradM describes, doing small batches of a larger bag allows you to test variables while using the same beans. As you see different results from each, after a while you’ll know what generates coffee that you like and start tweaking to get that every time. Also, with small batches, you won’t be afraid to try something that you’re pretty sure won’t be good - but sometimes trying extremes provide information to help you learn and develop your roasting intuition.