Part 3: Putting it All Together During the Roast.

Before diving into this article, please have a read of the previous two prerequisite sections:

So much like in the 1st part of this article, understanding heat vs mass, is critical to understanding how to properly roast.  Roasting coffee is exactly like boiling a pot of water, except instead of a pot, we have a drum and instead of water, we have beans with water in them.  If you understand the pot-water-boiling experiments in the 1st article, then you can understand easily what is happening inside the bean.  

The key difference here, is that instead of us setting the heat, then waiting for the water to boil at “X” minutes, we are going to flip those two variables. This is the most critical part to roasting well. We are now with the coffee going to adjust the heat up to speed up the roast, or adjust the heat down to slow down the roast, just like increasing heat boils the water faster, vs. lowering the heat boils the water slower. This is the most critical part to understand.

Instead of targeting your temperature and waiting for the roast to finish (a common approach for some people) we are instead going to attempt to “fix” the time as your fixed variable and use temperature to speed up or slow down the roast (your adjustable variable) so that the roast finishes on time per the roast profile chart for your drum and volume.  See this article for more on this subject.

So let’s look at a specific example:

Let’s use the following reference charts for our roast.

2LB Drum

Finished Roast Volume Green Load %Load Temp Est. 1st Crack Est. 2nd Crack
1/2LB
9.6 OZ
25%
470
6 mins
10 mins
1LB
1LB 3.2 OZ
50%
500-525
9 mins
12 mins
1.5LB
1LB 4.8 OZ
75%
525-550
14 mins
16 mins
2LB
2LB 6.4 OZ
100%
550-600
16 mins
18 mins

4LB Drum

Finished Roast Volume Green Load %Load Temp Est. 1st Crack Est. 2nd Crack
1LB
1LB 3.2 OZ
25%
470
8 mins
12 mins
2LB
2LB 6.4 OZ
50%
500-525
11 mins
14 mins
3LB
3LB 9.6 OZ
75%
525-550
16 mins
18 mins
4LB
4LB 12.8 OZ
100%
550-600
18 mins
20 – 21 mins

6LB Drum

Finished Roast Volume Green Load %Load Temp Est. 1st Crack Est. 2nd Crack
1LB
1LB 3.2 OZ
16.6%
450-470
8 mins
10 mins
2LB
2LB 6.4 OZ
33.3%
470-500
12 mins
14 mins
3LB
3LB 9.6 OZ
50%
500-525
14 mins
16 mins
4LB
4LB 12.8 OZ
66.6%
525-550
16 mins
18 mins
5LB
6LB
83.3%
550-575
18 mins
19 mins
6LB
7LB 3.2 OZ
100%
575-625
19 mins
21 mins

8LB Drum

Finished Roast Volume Green Load %Load Temp Est. 1st Crack Est. 2nd Crack
1LB
1LB 3.2 OZ
12.5%
450-470
8 mins
10 mins
2LB
2LB 6.4 OZ
25%
470-480
10 mins
12 mins
3LB
3LB 9.6 OZ
37.5%
490-500
12 mins
14 mins
4LB
4LB 12.8 OZ
50%
500-525
14 mins
15.5 mins
5LB
6LB
62.5%
525-535
16 mins
17.5 mins
6LB
7LB 3.2 OZ
75%
535-565
17 mins
19 mins
7LB
8Lb 6.4 OZ
87.5%
565-585
19 mins
20.5 mins
8LB
9Lb 9.6 OZ
100%
600-625
19 mins
21 mins

12LB Drum

Finished Roast Volume Green Load %Load Temp Est. 1st Crack Est. 2nd Crack
1LB
1LB 3.2 OZ
8.3%
450-470
8 mins
10 mins
2LB
2LB 6.4 OZ
17%
470-480
9 mins
11 mins
3LB
3LB 9.6 OZ
25%
490-500
9 mins
11 mins
4LB
4LB 12.8 OZ
33%
500-525
10 mins
12 mins
5LB
6LB
42%
525-535
12 mins
14 mins
6LB
7LB 3.2 OZ
50%
535-565
12 mins
14 mins
7LB
8Lb 6.4 OZ
58.3%
565-585
16 mins
17.5 mins
8LB
9Lb 9.6 OZ
66%
600-625
16 mins
17.5 mins
9LB
10LB 12.8 OZ
75%
625-650
17 min
19 min
10LB
12LB
83%
625-650
17 min
19 min
11LB
13LB 3.2 OZ
92%
650-675
19 min
21 min
12LB
14LB
100%
650-675
19 min
21 min

5.  During the roast, set the temperature to the suggested temperature to start and then adjust the temperature up or down while you roast to keep the roast progressing so that 1st crack occurs ON TIME for your drum and volume and ON TIME for 2nd crack.  Keep in mind that things happen VERY quickly during the onset of 2nd crack.  You can go from a medium roast to charcoal in 60 seconds after 2nd crack.  During the lull between 1st and 2nd, be sure to have your gloves on and cooler running, and be on your toes from this point on. 

6.  If you’re new to roasting, pull the coffee when you hear 10 cracks in 10 seconds (10-in-10).  This is a safe point to pull your coffee at with almost any coffee, and will all but guarantee happy customers and happy coffee drinkers, though there is always rooom for improvement in your roast profile.  Sweet Marias is a great resource to perfect your profile for both the roast and the bean.  If you would like to go a bit darker, then go to 10-in-10 and then add just 20 more seconds.  At this point we will be at or around what is called “Rolling 2nd crack” where the beans are firing as fast as they can and could be equated to what sounds like machine gun fire, and is accompanied by tremendous smoke.  Most coffee’s aren’t great past this point, so be very careful past this point as it’s likely in another 60 seconds your roast might be on fire.

That’s the basic concept.  If you’re still having issues, give us a call and we can go through things on the phone, or do a roasting session together.

Author: Shane Lewis

Shane is the founder of the green coffee exporter Old Spanish Main, Ltda. in Bogotá, Colombia, having practiced under the renowned grader & cupper Lelly Espitia. He is a cultivator of a #14 Colombian Cup of Excellence coffee. Shane currently designs & manufactures coffee, cacao & grain roasters with RK Drums.