For most roasts in a typical drum roaster, the optimal gas changes follow this pattern: Start at a high gas setting. Gradually reduce the gas throughout the roast, except for 45 seconds on either side of first crack.
In an air roaster, it is usually optimal to start at a lower gas setting. Increase the gas during the first few minutes of the roast and gradually lower the gas settings thereafter.
To prevent a crash, it’s important to prevent the ‘plateau’ by lowering the gas setting around 45 seconds before first crack. Choose a setting low enough to prevent the plateau but not so low that the roast stalls after first crack.
At around 45 seconds after the onset of first crack, resume decreasing the gas setting, reaching a very low gas setting by 16% development time ratio in order to prevent a flick.
Try to limit the total number of gas changes in order to make it easy to follow a roast curve consistently.
When you are deciding when to drop a batch, the total roast time is not the most important factor. Instead, focus on bean colour, bean temperature, and the progression through first crack to determine when to drop a batch.
Be aware of the limitations of each method for determining when to end a roast, and use a combination of all three methods. Don’t drop batches based solely on the development time ratio.
Avoid making airflow changes mid-roast. Airflow changes have different effects on the roast depending on the gas setting, which can make designing a roast curve more complicated.
Increasing airflow can prevent a crash or a flick, but it reduces the amount of heat available to future batches.
Mark first crack based on the trough in the ETRoR, if possible, rather than by sound. If that’s not possible and you can’t hear first crack over the sound of your machine, mark first crack at a set temperature instead.
You can easily avoid certain common mistakes in roasting.