No big. Dial back your preheat temp and drum speed and everything will be reasonably normal. If you've got a reasonable amount of control, you won't notice any glaring difference in the cup.

I can confirm what Steve said. While I don't have any experience with the 1kg, I did roast on the 500g and 20kg for classes and found they behaved similarly despite the size difference. Having gone from an Ambex to a Mill City, I can attest that it is a remarkably flexible roaster in terms of output. I've done everything from 8lb to 20lb charges in our 15kg and cupped all but 8 of 140 of the results because I don't trust myself to get it right every time. The results have been reasonably consistent between batch sizes.

Drum speed has clearly felt like the most arcane of all the variables for me, but in my experience it seems to make the biggest difference over the course of the roast when changing charge sizes sizes. If you haven't watched it yet, "Drum Speed Bingo" on the Mill City Youtube is a solid primer for experimentation. The general rule of thumb I've heard is to set your drum speed so the beans are tumbling at a 45 degree angle when viewed from the sightglass. I've stuck to that and it's worked for me.

For the sake of repeatability, I determined the actual RPM on our roaster by drawing reference marks on the outer lip of the drum and faceplate with a chalk marker, counted the rotations at certain settings (I have the knobs for controls, so I went in increments of 10), noted the exact frequency (Hz), and wrote it all down so I have a chart handy. Based on that, the 45 degree rule, monitoring things like scorching or tipping, and cross referencing roast charts, I've figured out my preferred settings for various batch sizes. After getting that sorted, the rest has been managing heat input, airflow, and following the curves.

Great input, Mark. Soon you'll be publishing a book on the roast control variables for Mill City Roasters!

Could you recommend some starting points for a 100g sample in my 1kg?

I've done some research, and based off the things here:

I pre-heat to a lower temp

Maybe charge at 225F - got that from sweet maria's using his 1kg electric roasting 150g sample

Slow down the drum speed - by how much? I don't know

still aim for a typical First crack

Low airflow throughout?

Try to change one thing at time

rely on visual and aroma mostly

Maybe shoot for 6-9 mins roasts depending on the coffee.

Any other tips you can give me? I was going to test my own green at 100g batches and see if I can get a good base from that first before I try the samples I got from the potential supplier.

Thank you!! 🙏

Hi Meg.

Charge at about 300-320F and "soak" by leaving the burners off for the first minute.

If you are doing tiny charges to decide which greens to purchase (grading roast) it's not a bad idea to use a static medium low airflow.

I visualize drum speed for small batch sizes as the best speed to cascade the green coffee on the BT thermocouple. This works for me and it gets me a slightly more stable BT reading.

I've done 100 gram charges in the 1kg with a longer 2mm BT probe bent down and to the left, but I was also much more comfortable with 200 grams in the 1kg.

You will have a tough time roast profiling 150 grams without the thermocouple change, but you can get very consistent simple grading roasts as I've described.

Steve