Hello!

The extension in the dry phase is to be expected anytime you increase batch size and do not increase your initial fuel. Just like how a roast goes faster through dry phase as you decrease batch size. Below would be my initial thinking before working with charge temp so as to not change too many variables.

First option is to raise initial fuel and see if you can steer the roast in a similar time to landmarks. 2200-2400 oughta do it. This would act like you were increasing charge temp wtihout having to move it.

Second option is to use 1800 and allow the drying phase to be longer than your mid phase time for a profile closer to 42/38/20. Your goal for mid phase should still be 4.5, and development still 2.0.

Hope this gives you some ideas. Happy roasting!

Thanks for your insight. We did get a 41|39|20 on our Colombia but it definitely cupped different than when we charge 5.4 lb. Like you mentioned, I think we need to continue honing and making small adjustments until we get it the way we want it. We will test a higher charge temp next. Mahalo!

While there are probably some real math formulas that would be applicable to batch scaling, it can still be a bit more trial-and-error to get the results you want when scaling batches.

Issue is, there's inertia in the bean mass that changes in a (relatively) exponential way as you scale up/down. Larger batches spend more time in conductive heating (beans touching the drum because it's full) versus smaller batches that have more open air mass in the drum, and therefore more convective heating (beans tumbling through the air).

Related/unrelated....have you considered doing full size batches in your 3kg roaster? We learned that unlike our previous experience roasting on equipment from Dietrich and Probat, we can get 100% capacity out of the Mill City roasters. We can actually do better than 100% but rarely do that. For the most part, we only roast 2kg (4.4lb) on our MCR-2D. And without exception, we only roast 10kg (22lb) on our MCR-10. I've found that this eliminates variability (and too much over/under-thinking on our part).

That may not be an option depending on your volume and workflow, but it's my recommendation to anyone roasting on Mill City equipment to ignore the default advice out there that says you should only roast at 80% of rated capacity.

Thanks for your response! Great insight. We haven't tried a full capacity roast yet. I think we would if demand drove it but we're okay with the 80% throughput at the moment - but it's quickly becoming an issue and why we tested with 90oz.

I think part of our hesitation is the unknown, and we don't necessarily want to burn through a few batches while we figure it out. I tried to find a new full capacity example profiles in the library but didn't notice any. Roasting preference aside, it would be helpful for us to see how the numbers play out on another 3G machine with a full charge.

I'll let you know how it goes when we do try. Thanks again for your time and insight! 🤙🏼

Mahalo!

@theroastery said:

While there are probably some real math formulas that would be applicable to batch scaling, it can still be a bit more trial-and-error to get the results you want when scaling batches.

Issue is, there's inertia in the bean mass that changes in a (relatively) exponential way as you scale up/down. Larger batches spend more time in conductive heating (beans touching the drum because it's full) versus smaller batches that have more open air mass in the drum, and therefore more convective heating (beans tumbling through the air).

Related/unrelated....have you considered doing full size batches in your 3kg roaster? We learned that unlike our previous experience roasting on equipment from Dietrich and Probat, we can get 100% capacity out of the Mill City roasters. We can actually do better than 100% but rarely do that. For the most part, we only roast 2kg (4.4lb) on our MCR-2D. And without exception, we only roast 10kg (22lb) on our MCR-10. I've found that this eliminates variability (and too much over/under-thinking on our part).

That may not be an option depending on your volume and workflow, but it's my recommendation to anyone roasting on Mill City equipment to ignore the default advice out there that says you should only roast at 80% of rated capacity.

Are you on LP or Natural gas on your 2D?
At full batch size what's your average time to first crack and what's a normal charge temp for you? Just as a curiosity
I seem to be having trouble getting roasts to go quick enough when doing full batches for certain beans. I've scaled down to 1.5,1.6 or 1.8 kg for a lot of my roasts. For a lot of beans I get tipping if I charge over 440 F, I was advised to try charging at temps up to 465 but was unsuccessful. So far the best way I've personally found is to reduce batch size for a lot of the beans I work with.