Uneven roasting

Owned by Sean Ellis
Last updated: Jun 19, 2023 by Chris Hilder
2 min read

If you are concerned about uneven roasting of beans the first thing to consider is the coffee you are roasting. Sometimes green beans are themselves very inconsistent, consisting of a wide range of bean sizes, ripeness at picking, and processing variations. Do not spend time trying to get inconsistent coffee to roast consistently.

However, if you know that your coffee is well graded and should roast consistently, but it is not, or if you are seeing a small number of obviously burnt beans in among otherwise well roasted coffee, your fan speed is most likely too low for the coffee you are roasting. This could indicate a need for re-calibration, but it could equally well indicate an unusual coffee for which you need to make some adaptations.

See Bean circulation calibration for how to check if re-calibration is needed.

Note

When roasting on BOOST at lower sized batches we find that sometimes the auto adjusted fan speed might still be too high with some coffees. Lowering the entered load size or altering the fan profile can resolve this issue.

Adaptations

If you need to make adaptations to accommodate specific beans, do not do this by altering calibration. Do one of:

  1. Use the BOOST feature to adjust the entered load size setting until you have the correct circulation. Best practice is to do this during fan preview.

  2. Alter the size of the load you are roasting; less beans means more circulation. Use fan preview to check.

  3. Alter the fan profile in Kaffelogic Studio. This is the preferred method, especially if you plan on sharing your adaptations with other Kaffelogic users.

How to alter the fan profile in Kaffelogic Studio

  1. In KL Studio, click on the ‘Fan profile curve’ tab, here you can make manual adjustments to the curve.

  2. In the same tab, click on ‘Tools’, ‘Transform profile’, and in the second RPM block on the right you can enter a value to move the profile up, or a negative value to move it down. 

The default fan speed for the unit is 14,700 RPM and the input is multiplied by 10. Inputting a value of 25 will raise the fan profile by 250 RPM. A good starting point is inputting a value of 10 (100 RPM) and going from there.

The above instructions will move the entire fan profile up to higher values. If you know that the problems are in specific stages of the roast you can take a more nuanced approach by dragging the blue control points of the fan profile curve to increase specific parts of the curve.

Each coffee is unique and you may need to spend some time dialling this value in to achieve the perfect roast for that particular coffee.

See also

Bean lock

Upgrading to new glass-walled chaff collector

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