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Roasting 102
Rate of Rise, Roasting 102
Now that you have fully mastered Roasting 101, let’s move on to roasting with attention to rate of rise. We will use Fahrenheit throughout the discussion.
Rate of rise, you say? Don’t make it more difficult than it is. Rate of rise is merely tracking and roasting with an eye on the amount of degrees the bean (BT) is rising in any particular time frame. Some roasters use 30 intervals; we will use 60 seconds — or how much is BT going up in one minute. Delta BT = Bean’s current temp minus bean’s temp one minute ago.
Why bother? Lots of ways to roast but I favor a declining rate of rise (ROR). I find that by using this approach, it will give you the best development and sweetness the bean has to offer without baking out those flavors. So on with the show.
Remember from Roasting 101:
- Drop temp around 400, amount equal to roaster capacity
- Do not turn the burners off on 3K and above roasters. With 1K and 2K roasters, you may have to turn off the burners for 60 or so seconds.
- Air initially set for lowest airflow which keeps fan engaged. What is low? Use a cigarette lighter at the trier throat. A setting of low should have a slight bend in the flame direction, into the roaster.
- You want to have the roast with a ROR between 32-35 degrees for about 1.5 minutes and then let the ROR slope downwards.
- At end of drying ~ 5 min (yellow/no green hues), turn up your air to medium. At medium, the flame should lay right down into the throat.
- Your milestone for first crack (FC) is 8-10 min. Roasters at 3K and above, target 9-11 min for FC.
- Gas turned down 10-15% at about 45 seconds prior to anticipated 1st crack. Remember, this is general guidance. Learn your roaster’s approach. Keep the descending ROR on its natural slope downwards.
- Turn air speed up to high at 30 seconds prior to anticipated first crack, when the beans in the trier indicate smoke. High? The lighter will extinguish or come close to extinguishing the air flow. Don’t go higher than this setting.
- Drop when you achieve level or roast desired
A picture is worth a 1000 words so let’s look at a profile which I did on the TJ-067 gas – a Tanzanian peaberry. I ran the ROR a bit above the desired 35 degrees but it cupped well.
- Top green one is incoming air temp
- Middle one is red and is the exhaust temp
- Dark blue line is the bean temp
- Bottom bright blue line is the rate of rise in the bean temp (Δ BT).
Bars at the top? Phases of the roast
- Green bar represents drying phase
- Orange bar is the caramelization phase (Maillard)
- Brown bar is the FC and Beyond phase
Notice the initial spike (blue line) in the Rate of Rise (ROR) at the left of the graph.This is the amount of degrees which the beans absorbed in one minute (ROR). As an example, in this graph, it spiked to 46° at 2 min (too high) and at 4 min, it is at 34,° as read on the right side of the graph.
This is the ROR curve we seek — declining. This kind of roast profile is called a “declining rate of rise.”
As one way to roast, I target a 1st crack between 8-10 minutes (my general guidance on 1K and 2K) and this roast had first crack at 9:33. I was after a city roast, which generally comes at 2:00 after 1st crack. Note that the roast was dropped at 11:37 or a 2:04 in the FC and Beyond phase.
Cupping results? The flavors were a bit muted and it needs more development with more roasting flavor. The next roast, I topped out the ROR at 35*, stretched the roast to 2:20, a city plus roast. Flavors were more developed and more pronounced.
Try the guidance above and tell us about your success!
Dave Borton
2 Comments
Jassen Bluto
you say your drop temp is 400 but your artisan graph shows a drop temp of about 320. If 320 is a better drop temp this could explain why I get to first crack really early on my North 500 gram roaster. If I drop at 400 I can get 5.5 min drying phase and 8 minute crack only by slowing raising the ET back up to 400, this however does not give me a good ROR. Is the graph correct with regard to the drop temp?
Jonathan Smith
Hi Dave,
Thanks for all the great info on roasting. I’ve been loving the videos. I’m from New Zealand and I’ve just started a “3rd Wave” coffee shop in Thailand on the island of Koh Samui. I’m roasting Thai coffee from Doi Chang. It’s going pretty well. I first started roasting coffee about 8 years ago on a small electronic hottop but this is the first time I’ve roasted commercially and there’s a lot to learn.
I have a Dongyi roaster (2kg gas). It looks almost identical to the North Roaster machines but the control panel is different, do you know if there’s a relationship there?
My main question is this… I’m struggling with the 20-25% development stage rule of thumb with diminishing RoR, for me the numbers don’t seem to work out like your graph here. I always end up with more like 35% and I’m not getting to second crack, I think it’s about full city or full city plus. I notice in this artisan profile your 1st crack is at 395F but I understand the normal temp for 1C is 355F … and I usually get that, but then I drop at the same temp as you or slightly under. If that were changed, I think you’d have the same problem I have. I usually wait for quite a few cracks before pushing the button… Any ideas what I’m missing here?
Thanks, Jonathan