Different roast profiles while Playback roasting

Roasting on the Bullet
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Hi everyone,

I really hope someone can help me, feels like i’m on a dead end.

Most of the times I playback my Kenyan or Ethiopian Light Roast. They are amazing.

However, since June I cannot get my Playback roasts done the exact same way as it used to be. Mostly they’re nowhere done yet and very underdeveloped so i extent the roast. It mostly results in a lot of weight loss % (+16%) from what i believe a long drying period (but i am not sure?)

Before the playback roasts (with same bean, same amount) literally was a copy of the previous roast. For a while this hasn’t been the case anymore. And I hope someone can explain me why, or know how to fix this.

Ethiopian LR comparison
Ethiopian LR comparison1887×1016 502 KB

What you can see here is a playback roast I did today. The ‘current’ is the old one I tried to Playback, the overlay is the result of todays ‘playback’. What you can see is that the IBTS temperature is lacking and moving behind, resulting in the bean temperature doing the same. also B-ror is behind and i wonder why?

Weight Loss comparison
Weight Loss comparison1578×734 78.5 KB

Also my weight loss is really high since june (since the playback is not as good anymore). I think because if the long drying fase and me extending the roast because it is underdeveloped otherwise.

does anyone has tips? Or been in a similar situation?

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Does anyone has some idea? ^^ I will be very happy

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I’d recommend making a recipe instead of doing playback - playback will literally replay P/D/F settings from the reference roast based on time. A recipe will set the intervals based on temperature and I’ve found to be much more accurate.

I’ve had some success with playback when doing back-to-back roasts from the same day and the drum is fully warmed up, but things like ambient / raw bean temp can greatly change the resulting profile.

Looking strictly at time/moisture loss, it looks like your first roast of the day is ending at a lower temp than your second - probably because your drum hasn’t warmed up enough.

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Sorry, only just noticed. What you’re describing should be attributed to a dirty IBTS. Clean it and it should go back to normal. I don’t want to sound arrogant claiming this is 100% the right cause, but you only have 47 roasts on your record, and the problems started once you went through some 15-20kg of coffee, so that’s what my first guess would be, since you did not share any information other than experiencing higher weight loss, which also could be caused by a dirty IBTS.

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