Managing the heat in the roaster effectively between batches is just as important as warming up the machine correctly before the first roast of the day. The between-batch protocol (BBP) is a way of ‘resetting’ the thermal energy contained within the different parts of your roaster, so that you start successive roasts with the identical amount of energy.
The body of a roaster can absorb and store a large amount of thermal energy as it heats up over the course of a roasting day. An effective BBP manages this heat to ensure consistent results.
The goal of the BBP is to ensure that when you roast multiple batches of coffee back to back, the results are identical each time. In the absence of an adequate BBP, most machines get hotter when you roast successive batches, causing roasts to run more quickly as the day progresses. The BBP must therefore allow the drum to cool between batches before it gently brings the roaster back up to charge temperature.
Here are Scott’s recommendations for an effective BBP:
- At the end of the roast, set the gas to zero and drop the batch into the cooling tray.
- For maximum consistency, hold the drop door open for a set number of seconds each time you drop a batch.
- After you close the door, the BT probe measurement will rebound and then begin to drift downward as the roaster cools.
- Allow the roaster to cool for 3.5–4.5 minutes, and then record the BT reading. This is your ‘bottoming temperature’. Before you begin to roast any future batches, allow the machine to cool until it reaches the bottoming temperature.
- As soon as the roaster reaches the bottoming temperature, turn the gas to a setting that will bring the BT up to charge temperature within 60–90 seconds.
- Charge the batch when the BT reaches your chosen charge temperature.
These recommendations apply primarily to conventional, directly heated drum roasters.