Diedrich Roasting Insights from Founder Stephen Diedrich

If you’ve ever wondered why your roast curves don’t match up, why some beans taste flat despite careful timing, or how professional roasters develop and maintain consistent roast profiles year after year, this deep dive into the methods of Diedrich Roasters’ founder, Stephen Diedrich, offers concrete technical answers. This isn’t theory — it’s decades of hands-on engineering, testing, and refinement focused entirely on making better coffee through better roasting.

Stephen Diedrich recommends using Fahrenheit for roast temperature readings due to its finer degree increments, suggests aiming for a roast weight loss of 13.5–15% for most coffees, and emphasizes following—rather than merely recording—your roast curve to achieve optimal results.

Why Diedrich Uses Infrared Heating in Their Roasters

Stephen Diedrich explained that Diedrich Roasters use infrared heating elements instead of traditional gas burners for several key reasons: cleaner air during roasting, higher energy efficiency, improved health and environmental standards, and greater temperature stability. His father, Carl Diedrich, originally designed roasters with water curtain dust collection in the 1960s. But Stephen observed that traditional open flame roasting made exhaust gases visibly dirty—like “roasting with car exhaust.” That led him to develop an infrared-based system.

The design draws inspiration from Stephen’s background in aircraft and luxury automotive repair. He adapted the principle of air-cooled aircraft engines by reversing the heat absorption method to create radiant infrared heat, which then warms clean ambient air used to roast the coffee. Traditional gas roasters rely mostly on heated air (primary) and some radiation (secondary), resulting in less stable hot air temperatures. In contrast, infrared heating provides primarily radiant heat with secondary convection, resulting in more stable air temperatures throughout the roast.

Key Roast Metrics and Development Philosophy

According to Stephen, the ideal first crack temperature on a Diedrich roaster is consistently around 197°C (387°F), while second crack varies depending on bean density. He also emphasized recording not just temperatures but the rate of temperature change (the “rise ratio”) between readings, and doing a quick cupping immediately after roasting—even if the coffee is only 20–30% developed—to inform immediate adjustments.

He shared that higher green bean moisture content tends to produce sweeter roasted results. For roast weight loss, his preferred range is 13.5–15%, while deeper roasts often exceed 18%. He avoids the 15–17% range, as it often sacrifices sweetness and other positive attributes without fully developing deeper roast characteristics. Every batch should have its weight measured before and after roasting to determine the loss ratio.

Changes in weight loss can indicate alterations in roast time, depth, or airflow settings. Longer roasts, darker roasts, or stronger airflow typically increase weight loss, while shorter roasts, lighter roasts, or weaker airflow decrease it.

How to Develop and Follow a Proper Roast Curve

Diedrich roasters are engineered for 70% convective heat and 30% conductive heat, with airflow adjustments allowing roasters to shift that balance. Poor maintenance—like a clogged exhaust pipe—reduces airflow, lowers convective heat, and forces increased flame use, raising conductive heat and altering the roast profile.

Stephen stated that effective roast curves usually follow an S-shape or inverted M, not a straight line. He broke down curve development into six key steps:

1. Decide the target roast depth
2. Determine the optimal time to reach that depth
3. Develop the ideal temperature rise slope
4. Set airflow based on the above
5. Recheck the temperature curve with the chosen airflow
6. Reassess whether the roast depth needs adjustment based on all prior variables

Rather than simply documenting the roast, Stephen stressed the importance of actively following your roast curve in real-time, making constant small adjustments to stay on profile. He noted that the optimal roast curve should be updated at least three to four times per year, and anytime you change green bean batches.

Cleanliness is also paramount—dirty roasters and ducts render your carefully developed curves ineffective. For determining roast end point, Stephen advised watching bean color closely, pulling sample spoons repeatedly, confirming the desired hue, and dropping the batch within 10 seconds. Waiting too long or releasing beans the moment color looks right often leads to lighter-than-intended roasts.

Recommended FrontStreet Beans for Roast Development

Explore FrontStreet Coffee’s Ethiopia Humbera for bright, complex acidity to test your first crack timing, or Yirgacheffe for floral and citrus notes that respond distinctly to infrared roasting profiles. For deeper development, try FrontStreet’s Classic Blend to observe how weight loss and roast curve affect body and sweetness. All beans are freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.