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If the airflow becomes too low at any time during the roast, the beans will stop circulating. This is called bean lock.

Symptoms of bean lock

During bean lock the temperature will usually increase steeply. This can cause wild fluctuations in the temperature line of the roast log. These can vary in appearance, please see the example log attached for an example of bean lock early in the roast cycle.

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Bean lock might not happen with one origin, and start happening with a different origin. This is because density and size of the beans affects bean lock.

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Solutions

1. Ensure that your roaster fan speed is calibrated correctly. This is especially relevant if you have upgraded from a mesh chaff collector to a glass chaff collector: your roaster will need re-calibrating by adding 0.06 to the fan speed calibration number.

2. If fan speed is correctly calibrated the simplest and quickest solution is to reduce the batch size. For example, if you have loaded 120g into the roaster and experience bean lock, try loading 100g or 80g until you are roasting successfully.

3. If you have BOOST increase the entered batch size. For example, if you have loaded 120g into the roaster and experience bean lock, try entering the load size as 140g or 160g. This will deliver more air to the same amount of beans.

4. If you are creating your own profile you should consider editing the fan speed profile to deliver more air in the parts of the roast where beans are locking up.