Achieving the desired flavor in green coffee requires finding the optimal airflow during the roasting process. Once a comprehensive understanding of a wide range of roasting points is established, exploring the changes in the roasting profile resulting from minor variations in exhaust temperature becomes essential. In this blog post, we delve into the nuances of roasting profile adjustments with a focus on the exhaust temperature, using Guatemalan-washed coffee as an example.

Finding the right airflow: To express the flavor of Guatemalan-washed coffee, it is crucial to identify the appropriate airflow during the roasting process. Referencing the principles discussed in "Roasting Profile Design for Colombian Washed Coffee 1," two test batches were roasted to determine the suitable airflow for Guatemalan-washed coffee.

In summary, roasting Guatemalan-washed coffee requires a similar airflow to Colombian-washed coffee. By applying the principles outlined in "Roasting Profile Design for Colombian Washed Coffee 1," a roasting profile can be designed following the same principles.

Considerations for airflow and roasting points: Considering the characteristics of green coffee and roasting points, it is imperative to establish the airflow during roasting. Merely extending or shortening the profile without adjusting airflow, heat input, and exhaust temperatures can lead to unfavorable outcomes.

Positive adjustments: Extending the profile in a positive direction while increasing exhaust temperature can result in a "baked" flavor, leading to roasty, smoky notes, decreased body, and a rise in bitterness due to burnt elements.

Negative adjustments: Conversely, shortening the profile while decreasing exhaust temperature can result in an "underdeveloped" flavor, leading to grassy, astringent, and sour notes.

Recommendations for roasting profile adjustments: To modify the roasting profile based on changes in exhaust temperature, consider the following methods:

1. Formulate the airflow considering roasting points, adjusting airflow settings according to changes in exhaust temperature.
2. Gradually slow down the airflow as the exhaust temperature increases proportionally. Increase heat input and shorten roasting time.
3. Gradually increase the airflow as the exhaust temperature decreases proportionally. Decrease heat input and extend roasting time.

Example roasting profiles: Compare and contrast the changes in heat input, exhaust, and input temperatures for small increments (2°C) in exhaust temperature across four roasting profiles.

The following profiles illustrate the adjustments made for each variation.

Example roasting profile information: Coffee: Guatemala Antigua Finca Medina Washed Region: Antigua Farm: Finca Medina Varieties: Bourbon, Caturra Altitude: 1,433 m ~ 1,555 m Processing: Washed

Profile 1: Machine: Easyster 1.8 (2021) Input: 1,000 g Exhaust: 872 g Weight loss: 12.8% Roasting exit point: Approximately 8°C temperature increase after the start of the first crack

Airflow settings: Max gas pressure 5.8 hPa, damper 4, input temperature 170 °C, exhaust temperature 213 °C.

Profile 2: Machine: Easyster 1.8 (2021) Input: 1,000 g Exhaust: 870 g Weight loss: 13.0% Roasting exit point: Approximately 10°C temperature increase after the start of the first crack

Airflow settings: Max gas pressure 5.3 hPa, damper 4, input temperature 190 °C, exhaust temperature 215 °C.

Profile 3: Machine: Easyster 1.8 (2021) Input: 1,000 g Exhaust: 867 g Weight loss: 13.3% Roasting exit point: Approximately 11°C temperature increase after the start of the first crack

Air Flow Settings: Max gas pressure 5.0 hPa, damper 4, input temperature 210 °C, exhaust temperature 217 °C.

Profile 4: Machine: Easyster 1.8 (2021) Input: 1,000 g Exhaust: 863 g Weight loss: 13.7% Roasting exit point: Approximately 13°C temperature increase after the start of the first crack

Airflow settings: Max gas pressure 4.6 hPa, damper 3, input temperature 220 °C, exhaust temperature 219 °C.

Profile comparison: The comparison of the four profiles provides insights into the changes and shapes of the profiles. Additional details on mass loss, color values, and regular changes in the roasting stage can be observed in the detailed profile comparison.

Adjusting roasting profiles based on changes in exhaust temperature requires careful consideration of airflow. Gradual adjustments to airflow, heat input, and roasting time are essential for achieving the desired results in the flavor profile of the coffee. Observing and analyzing the changes in multiple profiles can provide valuable insights into the roasting process.

Detailed profile comparison:

By following these recommendations and closely monitoring the roasting profiles, roasters can optimize the flavor expression of Guatemalan-washed coffee and achieve consistent, positive results in their roasting endeavors.