The Kaffelogic is a transitional fluidisation roaster. This means that most roast profiles have been created to work just on the threshold of fluidisation, that is, with a minimal amount of air. There is a delicate balance between the bean mass, density, and size, and the air flow required to circulate the beans.
This balance will change during the roast cycle.
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.
If bean lock happens early in the roast some beans will receive excess heat. This results in the affected beans cracking early. You might hear one or two beans crack loudly at a temperature of between 190 deg C and 200 deg C. In extreme cases these ‘early’ beans will be obvious in the final appearance of the roast as half a dozen or more very black beans among the brown beans.
If bean lock happens late in the roast the roaster is likely to detect it as thermal runaway, and terminate the roast by entering cool down with a warning message.
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.
Solutions
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. See Fan speed calibration .
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.
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.
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.
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