April 2021 Roasts

Bean: Colombia Sergio Cocha Cauca FW from Sucafino (see link for specs)

Machine: Giesen W15A (at Settlement Roasting Collective)

1st batch
When comparing this roast to the others we need to keep in mind that this batch was the first batch of the day for the roaster (can be different in a co-roasting space) so even though we gave the machine plenty of time to warm up, the front plate doesn't get fully heated until after the first roast because it needs beans roasting against it (airflow alone isn't enough).

Roast weight 12 kg / 9.9 kg (-17.5%)
First crack: 09:44 - 193.1°C
Duration: 12:32
Dev. time: 02:48
Dev. time ratio: 22.3%
Start temp: 210.7°C
End temp: 205.5°C

Cropster Roast Curve and Gas Changes for Colombian Bean

Download the CRC file here

2nd batch

Roast weight 12 kg / 9.9 kg (-17.5%)
First crack: 09:15 - 193.4°C
Duration: 12:09
Dev. time: 02:54
Dev. time ratio: 23.9%
Start temp: 213.5°C
End temp: 205.4°C

 Cropster graphs of Colombian Coffee Roast

Download the CRC file here.

Comparison of batch 1 and 2

Blue is the 1st batch, red is the 2nd

Comparing 2 Cropster Coffee Roast Profiles of SIngle Origin Colombian Coffee

So firstly, both were 12kg charges and had the same 17.5% moisture loss. The 2nd batch started a bit higher but both end temperatures are the same. Difference in the roasters thermal energy given first batch was the first of the day for this machine.

In the second batch the gas goes to 100% a bit earlier but then steps down way faster to try to push the ROR down before first crack. The finish temp is hit a full 30 seconds before the first batch.

In blind cupping soon after the roast, the second batch had more body and sweetness than the first.

The modulation chart from Cropster shows pretty modest differences in Maillard and Development phases:

Cropster Modulation Chart Comparison of batch 1 and 2 

Very happy with the result in the cup for that second batch.

3rd batch 

Roast weight: 12 kg / 10.2 kg (-15%)
First crack: 09:21 - 193.2°C
Duration: 12:04
Dev. time: 02:43
Dev. time ratio: 22.5%
Start temp. 214.9°C
End temp. 206.1°C

Cropster graph of batch 3
Download the CRC file here.


Comparison of batch 2 and 3 (3 is blue):

Comparing Cropster Graphs of batch 2 and 3

Looking at this comparison, while I reduced the gas earlier on the 3rd batch, I did it in smaller steps and so hit first crack later. Roast time was the same so the 3rd batch spent less time in development, which you can see in the modulation chart comparison (3rd batch is the top bar):

Cropster bar chart for modulation comparing batch 2 and 3

4th batch

Roast weight: 12 kg / 10.2 kg (-15%)
First crack: 09:02
Duration: 11:32
Dev. time: 02:30
Dev. time ratio: 21.7%
Start temp. 213°C
End temp. 206.1°C

Cropster profile curves and gas control for batch 4
Download the CRC file here.
We were going to pull the gas down sooner and faster than the 3rd batch but were discussing the 2nd batch and missed the window of opportunity. 
Comparison between batch 2 and 4
I'm going to be interested in the flavour differences in the cup over the next couple of weeks between batch 2 and 4. The profiles track pretty close up until first crack but then the 4th batch has more momentum (presumably from the later gas changes) and so reaches end temp much faster. Total roast time difference of 37 seconds and the modulation chart shows the difference in development. Theoretically, the 2nd batch should be sweeter and with more body, just like it was when comparing to the 1st batch.
4th batch is the top bar in the modulation chart below:
Cropster modulation chart comparison of batch 2 and 4
So 6 days after roasting I cupped everything again and 2 and 4 were actually pretty similar despite such different profiles. Here they are next to each other, batch 2 is green and batch 4 is red.
Comparing Cropster roast profiles of batch 2 and batch 4
Batch 2 had a bit more body and sweetness.
However, the big difference in flavour was when those two were compared to batch 3, which had nowhere near the body of 2 and 4. Batch 3 is added in below in orange:
Comparing batch 2 3 and 4 Cropster roast profiles
So I'm now looking for the key differences in profile and gas control between 2/4 and 3. Firstly, the gas turned up to 100 sooner in 2 & 4. This meant that batch 3 was never keeping up with them until after first crack. Next month I want to do a batch where it just starts at 100 and see if that enhances body further. Then I can go to 50% gas at 6 min, 20% at 6:30, 10% at 7:30, 5% at 8:00 and 1% at 8:30 with the potential to turn the gas off at 11:00 depending on, you know, what the temp is.
Really looking forward to trying out this plan! Will repeat batch 2 so I can compare them side by side from the same days roast.  
More to come.

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