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Handling Unique Situations When Roasting Ethiopian Natural Coffee

Sungbin Cho
February 8, 2024
min read
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This post continues the series on roasting Ethiopian natural coffee, following "Roasting Profile Design for Ethiopian Natural Coffee Part 1" and "Part 2".

Previously, I discussed various indicators observed in the roasting profiling chart. Through numerous roasts in my setup, I've identified indicators that yield positive results for Ethiopian natural coffee. Naturally, having more roasting profiling data makes it easier to find these indicators. However, if the coffee has physical exceptions, there can be factors that cause the main indicators to deviate from the average.

A roasting expert who deeply considers the process can quickly identify and resolve issues caused by unique conditions in green coffee during roasting. However, roasters who have not collected or properly analyzed roasting profiling data may attribute these issues to coffee quality problems or may not be able to discover the positive flavors in the coffee.

In this poast, we will not design the profile based on sensory evaluation, marking them as positive or negative. Instead, we explain the roasting profiling chart changes due to exceptional coffee characteristics and focus on roasting techniques that guide it back to a standard roasting progression. Thus, we ask for your understanding as we won't detail the sensory evaluation results of each profiles.

The baseline profile represents a typical roast for Ethiopian natural coffee, where various indicators are close to the average, and the coffee's positive flavors have been developed. This profile serves as the background for comparison with the example profiling charts that are presented later.

<Baseline Profile>

  • Roasting Machine: Easyster1.8 (2021)
  • Charge Weight: 1,000 g (2.2 lbs)
  • Discharge Weight: 866 g (1.9 lbs)
  • Weight Loss Rate: 13.4%
  • Roasting Discharge Point: About 6°C (10.8°F) temperature increase after the start of first crack
Ethiopia Gelana Abaya G1 Roasting Profiling Chart
Ethiopia Gelana Abaya G1

We will discuss the following four example cases:

  1. The green coffee's screen size is smaller than the average size.
  2. The first crack starts at a temperature 3°C(5.4°F) higher than usual.
  3. The first crack starts at a temperature 3°C(5.4°F) lower than usual.
  4. ET and ET RoR significantly decrease between 2-3 minutes into the roast.
  5. Smaller Than Average Screen Size of Green Coffee
  • The temperature increase at the beginning of the charge can be faster compared to the baseline profile.
  • Thus, the BT and ET graphs may plot at higher temperatures, or the BT RoR's peak value may increase.
  • Shorter roasting time and lower discharge temperature can lead to underdevelopment.
  • Additionally, the BT RoR value might form lower around the start of the first crack, potentially leading to a baked result.
  • If roasting proceeds with these points, it's advisable to keep the airflow setting unchanged and slightly reduce the charge temperature.

The following green coffee corresponds to the case of smaller than average screen size: Ethiopia Guji Uraga Goro Muda Natural, from Uraga Woreda, Guji, Oromia, by Goro Muda, Welichu Wachu W.S. It's an heirloom variety grown at an altitude of 2,228 meters (7,310 feet) and naturally processed.

<Profile 1>

  • Roasting Machine Info: Easyster1.8 (2021)
  • Charge Weight: 1,000 g (2.2 lbs)
  • Discharge Weight: 865 g (1.9 lbs)
  • Weight Loss Rate: 13.5%
  • Roasting Discharge Point: About 7°C (12.6°F) temperature increase after the start of first crack

Comparing <Profile 1> to the <Baseline Profile>, <Profile 1> shows a generally higher BT and ET temperature during the same time frame. In my environment, a positive BT RoR (60s) peak value is targeted between 23.0-24.9, but it reached a higher value (26.0), indicating a faster temperature rise in the early part of the roast. This often results in a lower BT RoR value around the start and after the first crack, affecting other indicators to deviate from the positive average.

To bring the unique indicators back to the positive average, <Profile 2> was conducted as follows:

<Profile 2>

  • Roasting Machine Info: Easyster1.8 (2021)
  • Charge Weight: 1,000 g (2.2 lbs)
  • Discharge Weight: 870 g (1.9 lbs)
  • Weight Loss Rate: 13.0%
  • Roasting Discharge Point: About 7°C (12.6°F) temperature increase after the start of first crack

In the progression from <Profile 1>, the airflow speed was almost unchanged, and the charge temperature was slightly reduced (by 10°C or 18°F). The BT RoR's peak value decreased, and most of the main indicators proceeded similarly to the <Baseline Profile>, leading to a positively predicted profile.

In the next part, we will continue with "2. The first crack starts at a temperature 3°C (5.4°F) higher than usual."

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Sungbin Cho
CMG Coffee Bar Head Roaster, Wecoffee Education Manager
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