Problems

To make the energy consumption and emissions across different roasting machines comparable, any standardized roast process has to tackle a number of problems.

• P1: Beans
  energy consumption on roasting depends on the type of beans (density, size,..) and their state (moisture, temperature,..)
• P2: Batch size, drum speed, air flow
  batch size, drum speed and especially air flow influence the energy consumption considerable
• P3: Accuracy of temperature measurements
  temperature measures taken are not easily comparable across machines due to different probes and their placements
• P4: Pre-heating
  the thermic state of the roasting machine before starting a roast influences largely the additional energy that has to be added during the roast to follow a certain profile
• P5: Exhaust air treatment
  for larger machines an afterburner is mandatory and its consumption needs to be accounted for (especially since some machines have an “integrated” afterburner). The degree of purity to be reached needs to be either fixed or measured and documented.
• P6: Roasting capacity
  roast times are not consistent across roasting machines due to differing capacity and heater rating
• P7: Roasting location
  ambient air (temperature, pressure, humidity,..) and elevation of the roasting location can have effects on the roast parameters as well as consumption
• P8: In-between batches protocol
  different machines require different in-between batches protocols that needs to be accounted for on computing the total energy required
• P9: Sampling
  sampling during the roasting process will change the heat in the drum during roasting and thus also the energy consumption result
• P10: Roast color
  if the roasting target is determined by the resulting roast color there are many different methods and scales to obtain those which might lead to different results. Further, research showed (eg. Münchow et al.: Roasting Conditions and Coffee Flavor: A Multi-Study Empirical Investigation, Beverages 2020 Vol.6/2) that the same target color can be achieved by roasting profiles of varying length on a machine using the same beans, each of those roasts consuming a different amount of energy. Thus roast color is a weak marker to verify a standard profile