Level: Apprentice
Read Time: 10 minutes
I’ve heard broken beans are a sign that the beans are too dry and that I need to adjust my roast profile. What is the minimum moisture that is acceptable, how do I measure it and what do I have to adjust in my profile?
I both love and hate this type of question. Well, I guess I don’t hate the question but I dislike the semi-nebulous answer I’m working on giving.
Here are the answers and then I’ll dive into my thoughts.
I have found little correlation between breakage and moisture.
I don’t know what a minimum moisture is and also don’t care. Average moisture is 6-8%.
Because I don’t care, I don’t measure it. If I did I would use ASTM D2216 – 19 and NOT a moisture meter. This is my chemist roots showing.
You don’t have to change the way you roast if you roast in a way the eliminates the need for that piece of data and true profile roasting does this.
First off your questions make an assumption that beans can be too dry. I guess technically that could be correct….but in 18 years doing this I have not come across it so it is sort of a moot point. But I have come across beans that have quite a few broken beans in their raw bagged state….and they roasted up just fine with no issues and I didn’t have to do anything particularly special.
With that laid out it seems like the answer is that you don’t have to adjust the roasting profile….and that is true…but not fully true either.
Let’s pull out my favorite roasting analogy and relate it to driving and rework the question.
I’ve heard that when going down hill I will use less gas or I will speed up and that I need to adjust my driving style. How would I go about that?.
Ok, so that isn’t a perfect analogy but I think it gets the point across if I ramble a bit. Yes, of course you will have to adjust your driving a bit when going down a hill. Gravity is helping and if you are unaware you can easily get going to fast, it can be dangerous, you could crash and die. But really, slowing down based on the speed you want to go and how fast you are going is basic driving and going down hill is nothing special at all. What do you do? You apply the break or coast.
If you happen to be driving a known course for a while, and have mastered doing it on muscle memory and can even do it blind, then if suddenly the same course is laid out on a slope then you are basically screwed and yes, you need to adjust your driving or you will fail, but I also can’t tell you with any detail other than “go slower, or use less gas” and that is basically useless. You know that.
My point here is if you are drum roasting, and you are monitoring your bean temperatures and paying attention to the profile curve, then you will find that when you have less moisture in a bean (which again, may or may not correlate to broken beans) the roast profile will proceed quicker given the same conditions (load, ambient temperature, roaster temperature, charge temperature, etc). In other words, a roast can go too fast and you have to reduce the fuel or the profile will get out of control….but that is just the basic technique for roasting in a drum roaster where you are monitoring the roast. It is no more complicated than that.
But why doesn’t the starting moisture matter? Well, it is because moisture in the beans normalizes as it approaches 212 F/100 C and comes out of that temperature zone pretty much at the same moisture content regardless of the starting content. All that changes is the amount of time and energy it will take to get there. A drier bean will require less energy or you can scorch it…but scorched beans or beans in danger of scorching will announce that with a sharp (non-vinegar) acrid aroma and you as a seasoned roaster, will note that aroma and back off the heat….naturally slowing the roast and keeping it in control. On the flip side, if they are too wet (ignoring mold issues in beans that are delivered too wet) the Drying phase will simply take longer but as I’ve outlined in Ask the Alchemist 201 how long it takes really does not matter nor does it affect the final flavor.
Now, you don’t mention how you are roasting and I’ve only addressed roasting in a drum roaster with bean temperatures available. If you are roasting in any other way, you are effectively on the driving course that you know, but are blindfolded and where they have laid it out on a slope. Sure, you intellectually know you need to apply less gas but that is literally all you know. It is down to trial and error until you can work out the new driving pattern without crashing. I can’t help you any more than that if you are in the Behmor or an oven (convection or not).
In short, if you are not directly measuring the bean temperature at all times and adjusting your profile according to a preset plan (which includes roasting by smell the first time) then there are just too many variables for ‘turn the heat down’ to be useful.
At the end of the day, this is just another reason I don’t care for roasting in anything but a temperature monitored drum roaster as all other methods are unique to one bean, of one load and/or one moisture content. Those methods are just too fragile for my tastes.
Alright, there is one more thing that can give you a little bit of something to experiment with. During roasting, there are characteristic aromas that come off are various stages and to some degree you can train yourself to correlate those aromas to certain temperature events.
Personally I’ve only found this useful in drum roasters like the Behmor where you don’t know the temperature but do know the power input (roughly) and we are all working with the same standardized procedure. When I do my sample roasting in the Behmor, I monitor the temperature (I’ve modified it with a probe that I’ve outlined here. ). When I roast in the Behmor I do the following to minimize variables.
Pre-heat until the “A” temperature is 130 F with 1 kg of beans in the roaster.
Let the beans set 3 minutes and start the roast again with the drum speed on high with the 1 lb 18 minute P1 automated profile.
Around 4 minutes left (14 minutes elapsed) I’ve found the beans will be at approximately 212 F. The great thing is that you can train yourself to note at the point it actually hits 212 F (plus or minus about 5 F) you will start to smell the roasting beans. This is more than vinegar or burning dust smell you will have noticed before. The key here is that because you are at the roaster (you’d never think of walking away, right? RIGHT!) if you find that aroma has started earlier than normal, then you can be pretty assured you are at 212 F and the beans were at a lower moisture content. What do you do because of that? Nothing. I’m just giving you a benchmark for what I do next.
At 212 (around the 14 minute mark) or whenever I start getting yummy smells I reduce the power input by going into manual mode and hitting P4. This is 75% power. Two minutes later (the rough time it takes to get through the Development phase) I lower the power again to P3/50% and let the roast finish. How do I know when it is finished? That same back of the throat acrid aroma. It is usually around 19-20 minutes but can be longer or shorted depending on what the particular bean needs.
I hope that little Behmor tip helps roast not quite 100% blind.
One final note about breaking beans. If you can’t roast without massive breakage then don’t use those beans. I’ve rejected beans for just that reason. NOT because they were too dry but because the breakage caused poor roasting and nibs roast very different from whole beans. Make you decisions on actionable items (breakage) not theory (the moisture seems low).
Stay safe out there eveyone.