Changes in roast profile by batch size

Hello all,

Since beginning my roasting on the Bullet, I have developed my roast profiles at around a 1.15lb green input weight, yielder 1lb roasted coffee.

I am sort of scared to try roasting a max-capacity roast in fear I’ll screw up 2+ lbs coffee :frowning:

In general, what key differences do you find when varying your batch sizes? How do the graphs compare, and what changes would you suggest for achieving a similar roast profile when, say, roasting at max capacity vs half capacity? Thank you for any input!

-David

For me when going from 600g to 900g…

On average I do the following:

  1. increase the preheat by 10-20’c.

  2. All power settings get increased by +1

  3. Everything else I leave it as is and just modify the fan speed.

P.S. Overlay the old roast during roasting. Help immensely in troubleshooting modifications.

Lower initial heat? Increase preheat by 10.
Roast curve seems to climb faster? Reduce the power.

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With that sort of increase, is the timing of the milestones relatively consistent with the overlay?
I would expect the larger batch to still take longer.

I have been having the opposite problem in that I find recipes for 800g but I only want to roast 400g until I “get my eye in” for a new bean. I have discovered that I have to drop the Power by 1-3, and the charge temperature by up to 40C.

It would be a nice feature to have the overlay “scaled” up or down based on batch size… even it’s a scale factor we manually specify.

I wouldn’t say that the milestones will be the same. If you’re doubling your batch size but hitting the same milestones (and assuming the half capacity roast is your target profile) the larger batch will likely be more unevenly developed as you are using way more power - which increases the temperature gradient between drum and beans. This causes too much conductive heating and results in scorching or uneven development.

The reverse applies if you’re decreasing batch size but hitting the same milestones, you’re not supplying sufficient heat to provide that temperature gradient to drive development - giving you baked roasts devoid of acidity.

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Scaling the overlay wouldn’t work because the turning points will also shift (both in time & temp) depending on batch size… Everything else follows from there so you’ll be trying to also follow an ROR that isn’t realistic

You might want to try the search function for profiles that uses 400-500g. I think many of us don’t create and save recipes. I don’t create recipes as I jot my roast plans in a notebook (yes old school) but I search for profiles for ideas to scale up to 1kg from my current 500g, which I scaled to from 300-350g when I started on the Bullet.

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