What batch size, in %, do you do, and why?

Asking because: I don't know if it's just me, but I've seen one photo too many of large roasters spewing out so few coffee. This is opposed to the beautiful coffee-valanche that's so nice for food photography. For the low capacity % roasting that I see, there's barely enough coffee to spread over the cooling bin.

In another post here, the OP mentioned that in a roasting workshop he attended, the pros told him "don't roast anywhere near the rated capacity", for the sake of control.

And another question: In spite of being able to control BT ROR, conceptually, with any batch size, are there scale-based interactions between relative batch size, heat throughput, fan throughput, drum size?

wearashirt wrote:What batch size, in %, do you do, and why?...

In another post here, the OP mentioned that in a roasting workshop he attended, the pros told him "don't roast anywhere near the rated capacity", for the sake of control.

You mentioned you roast on a North 2K roaster purchased directly from North. You can roast full stated capacity on a North, which I have found achieves the best roast. Each machine has its own sweet spot.

And another question: In spite of being able to control BT ROR, conceptually, with any batch size, are there scale-based interactions between relative batch size, heat throughput, fan throughput, drum size?

Absolutely. With decreased batch size on your North, lower your BTU input, fan staging in the 3 phases of roasting slows just a bit, and slow the RPMs. For RPMs, look into your porthole for some bean congregation and a 45* angle of descent. You can go down to a 20-25% capacity with practice. Batches that small are a just a bit inconsistent but cup worthy.

I do roast some full capacity batches on my IR-12, but only because I have a good idea of what my roaster is capable of, what coffees I'm likely to need that much of, and can design profiles with that in mind. There are other roasters who have exactly the same model of machine as I do who can only go up to 80% capacity because for whatever reason they just can't get enough heat transfer to the beans going beyond that. There can certainly be limitations in the design of a roaster beyond the size of the roasting vessel that affect what you can really achieve with it. As the mass of the coffee goes up, the energy needed to move it along its profile increases and it's harder to make rapid adjustments, either pushing things faster or slower so you really do need to read ahead more on those larger batches if it's a profile that can be matched at that capacity. On the other hand, with the larger batches if you don't want those rapid changes and know how to read ahead you can just get the momentum you want and I find the control easier on those, so there are trade offs and those control trade offs change during the day, so I usually need to roast a number of smaller batches before the roaster is hot enough to do those full capacity batches. That can be mitigated somewhat with extensive pre-heating, but I think it's a better use of time and fuel to just roast some small batches at the start of the shift. There are two other good reasons for going to smaller batch sizes. Faster cooling times can definitely have a beneficial effect with some coffees and if the coffee or the roaster is unpopular, doing more smaller batches results in fresher coffee on average. In a commercial environment, larger batches reduce the per pound cost of labor of roasting the coffee which is definitely (hopefully) significant for shop roasters. So you can see there are a lot of conflicting concerns that need to be balanced when picking batch sizes to run through a large roaster.

Boldjava wrote:You mentioned you roast on a North 2K roaster purchased directly from North. You can roast full stated capacity on a North, which I have found achieves the best roast. Each machine has its own sweet spot.



Absolutely. With decreased batch size on your North, lower your BTU input, fan staging in the 3 phases of roasting slows just a bit, and slow the RPMs. For RPMs, look into your porthole for some bean congregation and a 45* angle of descent. You can go down to a 20-25% capacity with practice. Batches that small are a just a bit inconsistent but cup worthy.

I guess I have to pay my dues first and learn. I still hearken back to this one time when I hit 1C in 7:00 on an 800g batch, and the coffee tasted really great afterwards -- the blackcurrant and tropical fruit coming out. But then it faded pretty quickly, which I thought must have been the underdone-ness of the beans. Since then, I've retreated to hitting 1C at minute 9-11.

Somehow I think cooling takes a while with full batch sizes. Unlike in German roasters, the bins are wide and the hot coffee beans lay out nicely flat to cool quickly.

N3Roaster wrote: On the other hand, with the larger batches if you don't want those rapid changes and know how to read ahead you can just get the momentum you want and I find the control easier on those

Hi Neal. An honor to read your reply on my post. Quick question: where would you likely put a filter coffee through, a high relative batch size or low relative batch size?

Because you mentioned better momentum control with large batch sizes, and I agree. With the large crowd of beans inside, the heat gain is more distributed and unform -- but is this the right frame of thinking for filter coffees, or coffee in general? Would there be issues with the needed convection effects?

I guess what I mean to ask is: is there a notable, artisanal reason as to why a lower batch size would be good for acidity, flavor longevity, aroma in the bag, aroma when ground, etc..? Does BT profile account for a majority of coffee quality as opposed to whether it was in a high batch roast size or a low batch roast size? Could the heated-air tech of Vittoria and Loring be on-point with their claim for a "better roast"? Hope these questions make sense.

wearashirt wrote:where would you likely put a filter coffee through, a high relative batch size or low relative batch size?

I don't really think about things in those terms. The last check I do on any profile is a drip brew. If I do run into something where there's a quality reason aside from managing freshness to push batch sizes smaller, that comes out later when a batch fails a QA check. I haven't found it a real issue for most coffees with what I like, but YMMV.

In what I think was the first of the Mill City Roaster videos, Joe mentioned that a roaster (I don't know if he meant just the one he was using, but I took it to be a generic comment) performs best at about 75% of its stated capacity. That works well in my HUKY.

SJM wrote:In what I think was the first of the Mill City Roaster videos, Joe mentioned that a roaster (I don't know if he meant just the one he was using, but I took it to be a generic comment) performs best at about 75% of its stated capacity. . .

He said that in a generic sense and is roaster dependent.

Here's a closely related question: how do the people making the roasters decide what the nominal capacity will be?

Steve should weigh in. I saw him doing the geometry on his scratch pad when he was looking at drum size needed for the 500g sample roaster.