Roast and Learn Together - November/December 2015

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

Postby TomC » Oct 27, 2015, 9:46 pm

Mark ( [creative_nickname] ) is going to head up a two month run focusing on airflow on the roast, using two quite different coffees, sourced thru Mill City.

With the holidays upon us, it's easier to lay things out now and give plenty of time for folks to participate, schedule willing. I'll let Mark link the specific coffees here shortly.

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[creative nickname]

Postby [creative nickname] » Oct 28, 2015, 10:14 am

Hey everybody, I'm thrilled to be hosting this R&L. Just to give you a heads up, here are the coffees we will be using to explore the effects of different airflow settings on flavor:

Kenyan, Gichugu Division, Kirinyaga East District

Brazil Natural, Carmo de Minas, Minas Gerais

My plan is to focus the discussion on the Kenyan during November, and then switch to the Brazilian for December. The coffees should provide a nice contrast, and will let us explore whether airflow settings need to be adapted when we switch from high to low-density beans. Those who are in a hurry, or plan to go through a lot, can go ahead and order now, but those who want to roast fewer or smaller batches might want to wait, as Mill City Roasters will be offering a bundled offering of 2.5 lbs of each coffee to facilitate this thread.

My own greens are en route. Once they get here and I can take them for a spin I'll post my first few profiles for the Kenyan.
LMWDP #435

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[creative nickname]

Postby [creative nickname] » Oct 28, 2015, 3:22 pm

And here is the combo offering, for those who would prefer to start with 2.5 lbs of each coffee: ROAST AND LEARN BUNDLE - BRAZIL MINAS GERAIS & KENYA GICHUGU.
LMWDP #435

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Boldjava

Postby Boldjava » Oct 29, 2015, 8:26 am

Gents, the Brazil sold out. I am going after another Brazil, grown at relatively the same elevation. Stay tuned for cupping and available notes/buying opportunity. Will hustle.

DB
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LMWDP #339

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Boldjava

Postby Boldjava » Nov 04, 2015, 1:03 pm


My plan is to focus the discussion on the Kenyan during November, and then switch to the Brazilian for December...


Good timing. Importer has a Carmo de Minas which he recommends. I reserved two bags pending cupping and evaluating next week. Plenty of time for Dec delivery. Lots of Kenyan remains.

As soon as cupping evaluation is done, new buy icon will be up and I will post back here. Sorry for any inconvenience.
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LMWDP #339

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[creative nickname]

Postby [creative nickname] » Nov 04, 2015, 7:24 pm

OK, here is the first set of three roasts I've done. I didn't isolate airflow as much as I would have liked, but I think there are still some things of interest to be gleaned from my failure, in terms of the interaction between different airflow settings and the profile curve. In all three roasts, starting conditions were identical, and heat was kept constant up until first cracks started. At that point, I shifted into manually reducing the heat in stages to try to keep the ROR in a steady decline. As you will see, that was much easier at some airflow settings than others (at least on my solid drum roaster).


FYI, the evaluations below are based on a blinded cupping after one day of rest.

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Roast 1: Airflow = 25% of max fan power

Roasting Info:

Bean: Kenya Gichugu - Kirinyaga E. Dist.
Roaster: USRC Sample Roaster
Charge Mass: 333g
Charge Temp: 390F
Dry/Ramp/Development: 3:20/3/1:55
FC-start temp: 371F
Finish Temp: 390F
Overall Roast Time: 8:11
Moisture Loss: 13.6%

Profile Plot:

Image

[BT=Red, Exhaust=Green, Gas=Blue, Fan=Yellow]

As you can see, the ROR cratered pretty quickly, more so than I'm used to, as I never roast with airflow this low. I did my best to keep things controlled but there was a modest flick at the end.

Cupping Notes:

I cupped this with the other two coffees after one day of rest. It had the best dry fragrance of the three, mingling classic Kenya smells with rich vanilla and hazelnut notes. The flavors, especially the floral notes, were a bit more muted compared with the best roast (the one with 75% airflow), but it was a very drinkable cup.

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Roast 2: Airflow = 50% of max fan power

Roasting Info:

Bean: Kenya Gichugu - Kirinyaga E. Dist.
Roaster: USRC Sample Roaster
Charge Mass: 333g
Charge Temp: 390F
Dry/Ramp/Development: 3:15/3:10/2
FC-start temp: 372F
Finish Temp: 390F
Overall Roast Time: 8:24
Moisture Loss: 13.9%

Profile Plot:

Image

[BT=Red, Exhaust=Green, Gas=Blue, Fan=Yellow]

I had expected this one to be more manageable, but I was still surprised at how dramatic the flick was, and I failed to anticipate it or respond quickly enough. Obviously the added airflow has slowed the whole roast down slightly, and it made the decline of ROR during the beginning of first crack more moderate (although still steeper than I would like).

Cupping Notes:

This was, by far, the worst cup of the three. It had a striking astringency flaw in the finish, which I attribute to the pronounced flick. On a scoring sheet it fell almost four full points behind the best roast. Given that the 25% airflow roast was better, I don't attribute this to the airflow setting alone, but rather to the excessive dip/flick. But as will become clearer looking at the third roast, the airflow setting and the flick are related to one another.

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Roast 3: Airflow = 75% of max fan power

Roasting Info:

Bean: Kenya Gichugu - Kirinyaga E. Dist.
Roaster: USRC Sample Roaster
Charge Mass: 333g
Charge Temp: 390F
Dry/Ramp/Development: 3:25/3:25/2:20
FC-start temp: 370F
Finish Temp: 390F
Overall Roast Time: 9:10
Moisture Loss: 13.9%

Profile Plot:

Image

[BT=Red, Exhaust=Green, Gas=Blue, Fan=Yellow]

As you can see, with otherwise identical inputs this roast was much easier to manage. It was the slowest of the three, but it was still within the range I think of as a sweet spot (7:30-10m), and it had a nice, gradual decline of ROR during first cracks, with almost no flick at all.

Cupping Notes:

This one was by far the best tasting of the three roasts. It had a nice, hibiscus/rose fragrance and aroma, plenty of juicy tropical fruit, and a smooth, sweet finish.

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Overall takeaways: The effect of a stronger flick seems, in this evaluation, to be much larger than moving from 25% to 75% airflow. But to the extent that airflow made a difference, a higher setting seemed to be beneficial for this coffee. Also, lower airflow settings seemed to lead to more pronounced "dip and flick" behavior during first cracks, requiring more active temperature management at that stage, and thus making roasting results more fickle.

Soon I will try another round of three roasts, this time trying to anticipate the stronger dip/flick associated with lower airflow so that I can get more comparable profile results to compare.
LMWDP #435

9Sbeans

Postby 9Sbeans » Nov 10, 2015, 4:27 pm

I've been playing with various airflow settings for a while. IMO, airflow controls could be as important as the power applications. However, each roaster has distinct airflow design. The length/diameter of exhausting hose and the number/angle of turns may also impact the airflow on the same machine.

I would like to briefly describe the features of my roaster so that it could be compared to other machines in the same context. My gas roaster is dual-wall solid drum design, with sufficient heat mass in the drum. I assign 500 mmAq as arbitrary 100% gas pressure (P100) in my roaster, and in reality I seldom use more than 40% of the full power. At 0% of fan (F0), the airflow of my roaster at the bean tryer opening can already bend the flame of a lighter. The lighter is blown off at around F57. The typical range of my airflow (F30 ~ F45) pulls off heat and it can drag the RoR. When I study roasting profiles generated from other roasters, I feel that my KapoK sample roaster is very similar to a USRC sample roaster (as Mark's). When compared to a TJ-067 (from Dave's video clips), I suspect my usual airflow settings is always in the medium-high range. But it's merely my speculation though, since I don't have hands on experience on other machines.

Anyhow, I received my bundle pack last week and did an aggressive sorting to remove about 10% of the bean. I decided to divide the Kenyan into 4 batches, and drove two batches first. I pulled out a Kenyan profile from last February as a reference point.

Image

As can be seen, I charged at 356F, and did a fast roast (3:45/3:36/2:33). I simply decreased the gas and increased the fan during the roast, and as the result created a declining RoR profile. The fan speed was further increased half-way during the first crack in the hope to tame the flick. This batch was used as drip in the first few days and then SO espresso when rested longer than one week.

In the above batch, there was minor woody/cardboard/roasty notes when aged and I had to reduce the extraction temperature. In the new batches, I wanted to repeat the Dry/MAI phase, but to decrease the RoR in development phase. In addition, I wanted to cut the development/total time ratio to 22-23%. My questions are, 1. Can I repeat a roast profile in Dry/MAI phase, but manipulate the Development phase by changing gas-airflow settings? 2. Can I smooth out the post-1st-crack dip & flick by manipulating gas-airflow? And assuming I can minimize the dip & flick on the plot, can I actually taste the difference in the cup?

9Sbeans

Postby 9Sbeans » Nov 10, 2015, 4:29 pm

Here is my first batch. Note that the charge mass was 250g (instead of my routine 227g), and I adjusted gas-fan in small incremental steps. In my Feb. roast, I made less gas-fan adjustment during a roast. The drum mass provided sufficient buffering capacity to smooth out sudden change and the operation were simple. However, when I wanted to repeat a certain roasting profile, big step adjustment became hit-or-miss. After reading Hoos' book, I wanted to have better traction on the curve and had to use small step adjustment. I brought up gas before the dry end, and only decrease the gas afterward.

I increased the fan at the dry end (in two small steps); if I adjust the fan speed in a step greater than 3 notches, the BT probe seems to register the (unwanted) change. It also seems to me that, on my machine, increasing fan speed could transiently bump up RoR for about 10sec, and then it pulls the heat away. The first crack start time was a bit subjective, because I waited for denser crack sounds. The RoR dip concurrent with my marked 1st-Crack-Start. Since I expected the increasing of fan from F37 to F39 may transiently bump up RoR, I increased the fan only after the 1st-Crack-Start, in the hope to slightly compensate the dip. During the first crack, I gradually increased fan from 39, 41, 43, and 45 to 47. The increased airflow dragged the RoR, and the bean was dropped before the flick showing up. I didn't note the first crack end time in this batch.

Image

Roasting Info:

Bean: Kenyan Gichugu Division
Roaster: KapoK 500 sample roaster (dual-wall solid drum gas roaster)
Charge Mass: 250.0 g in; 215.5 g out.
Charge Temp: 357.0F
Dry/MAI/Development: 3:47/3:33/2:10
FC-start temp: 375.6F
Finish Temp: 390.6F (1C+15F)
Overall Roast Time: 9:31
Weight Loss: 13.4%

9Sbeans

Postby 9Sbeans » Nov 10, 2015, 4:32 pm

I did a second batch. My idea was that to repeat the Dry/MAI in the first batch, and play with the airflow during the Development phase. Since the airflow pulls off the heat, and I wanted a little bit more heat in the first half of the first crack, I expected the reduced airflow may counter the dip in the first half of the dip. I therefore kept the F37 into the first crack, and quickly reduced fan speed from 37, 35, 33, to 30 in the first minute of the 1C, and quickly brought back the airflow from 30, 33, 35, and 37 to 39 in the hope to compensate the flick. Since the heat wouldn't be dissipated as fast as the first batch, during the development phase I also reduced the gas at earlier time.

In my batch #1, the slowest RoR was 4-5 F/min. In my batch #2, the slowest RoR was 5-6 F/min. It seems that manipulating airflow is an effective way to control RoR. In theory, if I can know the airflow & gas combination balances of my machine, I can set it up and the roast should approach my target RoR and drop temperature.

I missed the mark and dropped the bean few seconds later than my batch #1. As the result, the flick showed up and the drop temperature was higher. The tastes in the cup of the two batches were virtually indistinguishable. The batch #1 may have an edge on dry fragrance, and the slightly more acidity (when hot) of batch #1 stand out more in the side-by-side comparison. Thin body; no unpleasant taste when cool. It was not a blind test though.

Image

Roasting Info:

Bean: Kenyan Gichugu Division
Roaster: KapoK 500 sample roaster (dual-wall solid drum gas roaster)
Charge Mass: 250.0 g in; 216.4 g out.
Charge Temp: 356.4F
Dry/MAI/Development: 3:45/3:34/2:18
FC-start temp: 378.1F
Finish Temp: 395.6F (1C+17.5F)
Overall Roast Time: 9:37
Weight Loss: 13.8%

9Sbeans

Postby 9Sbeans » Nov 10, 2015, 4:56 pm

I exported the roast log files, averaged my two batches during the Dry/MAI phases (black line), and zoomed in the development phase: Green dotted-line, archived Feb. profile; Blue, batch #1 increasing airflow; Red, batch #2 variable airflow.
Image

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Ps. Will be traveling next week, and be back after thanksgiving. I still have two batches of Kenyan to run, please feel free for questions/comments, or suggestions of certain roasting profiles for me to try. :)