One of the things discussed at the cuptober fest event that sweet marias hosted was that larger batches should be roasted longer(this wasnt a discussion topic, but rather something that came up in the side conversations) It was something that both Schooly, and Blue bottles head roaster (Jen) believed.

This was a weird and foreign concept to me... and still is. It didn't make any sense to me, and still doesn't. Maybe this is one of those things that only apply on really big machines? Like maybe roasting 20 kilos shouldn't take as long as 60?

If I wanted to cook a cup of macaroni, or 10 cups of macaroni it would take the same time? Right?

Anyone roasting larger batches longer, so it tastes the same as your smaller ones?

Not me. The only thing that I sometimes encounter is accidental really short times on a small batch of a bean I'm not familiar with, e.g. new 150gm samples in my IR-1. But I'm getting those under control now, too.

But my 1lb profiles are the same as my 5lb profiles, obviously I've never roasted on anything bigger, though.

Are the bigger roasters harder to control at faster roast profiles? Are they concerned about uneven roasting on faster profiles?

I think this is an airflow thing. The more airflow you have, the shorter the roast should be and vice versa. This is what allows Diedrich roasters to have 17min roasts that don't taste baked, and air roasts as low as 6min.

I've recently been dropping my airflow for dark and espresso roasts, and turning it up for light roasts. I had been keeping a "sweet spot" of airflow previously, but the darker roasts were tasting baked and the lighter roasts weren't performing as well. Now I'm getting more of what I want from each.

Interesting idea. Perhaps this can be extrapolated to heat transfer efficiency, i.e. less efficient roasters can stretch longer roasts without baking or other ill effects.

That said, I've found that consistent times, regardless of batch size, produce better results on my gear. Scale is quite different though, I roast 200g on the low end and 455g on the high end.

I think with larger batches, you get shorter heat exposure for a bean, on most roasters. By that I mean the beans don't get agitated into hot spots as often as they do with smaller batches, due to larger mass of beans being agitated, so it takes longer for a single bean to go around the drum or fluid bed. One way to counter that is to raise the heat, to obtain equal profile times, which maybe responsible for baking, or go for a longer time, to ensure equal exposure.

The larger the variance between small and large batches, the more obvious this will need to be dealt with and taken into account. You can test this by monitoring ETBTA function in Artisan.

Increased time is to be expected unless the roaster/stove/oven can ramp up heat delivery. If you cook ten cups of macaroni, the water temp will take a lot longer to come back to a boil than for one cup. The burner can't deliver heat fast enough to make the times equivalent.

I was inside Peet's Roasting Plant yesterday where I watched them roast a 600lb batch of high altitude Ethiopia Yirge Cheffe to a full city + roast in 14 minutes. The airflow sounds like a turbocharger spooling up at times.

It was also surprisingly delicious, much, much sweeter than what a lot of lemonade Ethiopia coffees have been. The acidity and the great fruitiness was still intact. It was one of their Medium Roast SO offerings that they do for 3 weeks that are only offered online.

They also have the coolest damn cupping room I've ever seen.

That would be an awesome experience. Too bad we won't be getting any pictures or more info from that part of your class....

Actually I have plenty of pictures and stuff I could share. The program director shared the wrong information, it wasn't a non-disclosure agreement at all. It was a hygiene waiver that we had to sign agreeing not to wear perfume, loose jewelry, open toed shoes, that sort of thing. The only part of the plant that was off limits to cameras was the encapsulation area. There's an insane amount of money invested into proprietary pod technology in that place. They made no subtle points about it, it's the fastest growing segment of the coffee market and they couldn't risk not getting in. We couldn't even get within 100 feet of the pod area.

I'll share more on the appropriate thread. I just wanted to comment that they're using four 1000 pound capacity Probat's, and their longest roast is like 16.5-17 minutes, which was relevant to the OP question. They vary drum and ET temp by bean moisture content and bean size/density only, not batch size. The rest they control with air flow.

endlesscycles wrote:I think this is an airflow thing. The more airflow you have, the shorter the roast should be and vice versa. This is what allows Diedrich roasters to have 17min roasts that don't taste baked, and air roasts as low as 6min.

I've recently been dropping my airflow for dark and espresso roasts, and turning it up for light roasts. I had been keeping a "sweet spot" of airflow previously, but the darker roasts were tasting baked and the lighter roasts weren't performing as well. Now I'm getting more of what I want from each.

Thanks Marshall,
This has helped me understand a lot of what's going on with my roaster..
It has a very high air flow at the lowest speed..
I need to turn dial to 30 before the fan starts turning and has a fair amount of flow..
I think I have been baking the beans with high air flow and 10-11 min. roasts..

I'll have to try no airflow during drying and see how those work for me..