Using batch size to manipulate roasts.

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Postby Stephanie Ratanas » Fri Dec 09, 2011 11:18 am

I'm wondering if anyone else out there uses batch size regularly as a way to manipulate roasts.

When I'm doing test batches, much smaller than a full batch (44-45 pounds, that is 80%) I'm able to have a lot more control over my heat transfer, of course, and when I want to place first crack. In a normal production day, if I have enough of a certain coffee to do a full batch, I can't necessarily reach first crack when I want to, even with a high charge, so I'll cut the batch in half to increase the proportion of airflow to my batch and therefore increase my control.

We've never had any issues with scorching, in fact, it's actually difficult for me to scorch coffee on our G25 even for training purposes, but hey--maybe I'm not pushing it hard enough?

Just wondering if anyone else does this. Obviously, it's not super efficient.
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Postby N3Roaster » Sat Dec 10, 2011 10:05 pm

We tend to go at that from the other direction, understanding what batch sizes we're likely to need for a coffee and for things we'll need full batches on controlling the test batches to produce target profiles that the roaster can reliably hit on full loads.
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Postby ChrisSchooley » Mon Dec 12, 2011 2:19 am

Super Awesome post! Using batch size to manipulate roasts is just as viable as using a gas control or an air damper. If the efficiency issue is just about that you're not using the roaster to it's "full capacity" than in my mind that poses a bigger question/problem which is that if a roaster is rated by the manufacturer as a 25 or 45 Kilo machine, why do you have to do an 80% or many times much lower size batch in order to have the control that you desire? If this is so consistently the case, shouldn't the drums just simply be rated lower? Why isn't this being addressed?
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Postby rojo » Mon Dec 12, 2011 9:04 am

That's why we have so many mods on our machine... our 60K can't do 60K with any real control. Even with the mods and the odd manipulations we've managed to develop to profile within our desired times and curves, we really only succeed at around 45-50K in the machine. So we only do more with coffees for which the longer profile that goes with it works. For a long time too we wasted a lot of energy trying to make it work at capacity. When we gave up on that is really when we started to get control of the roasts and it moved us into another realm.
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Postby Stephanie Ratanas » Mon Dec 12, 2011 1:13 pm

Schooley-- I agree! I always thought that was slightly confusing too for people starting out, and looking at their equipment needs. Another thought along those lines though-- presumably not everyone who roasts is trying to achieve what may be the best profile for the coffee-- in which case you could probably roast the "full" capacity the roaster is meant for, which is why the ratings are the way the are maybe? I suppose of it becomes common knowledge that 70-80% of the drum "capacity" is what will truly allow you to have the control you want over the roast if that's what you care about, then the ratings wouldn't need to be changed...

I don't think I would try to tailor my profiles to hit certain crack times etc. based on drum capacity if that's not what tastes best. I'd rather see what the coffee is capable of in several conditions before I come to some sort of conclusion on a basic profile, obviously keeping realistic profiles in mind.

:arrow: <--what a strange smiley....
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Postby pbarter » Fri Jun 07, 2013 12:17 pm

In our machine, batch size seems to have a more direct impact on the convection/conduction ratio than airflow adjustments within the range where chaff/exhaust still goes out the vent and not the tryer hole. We had a great example recently with a fancy microlot Columbia. We normally roast it as a ~3/4 batch, and it's great and very balanced. Following the same bean temp profile, that roast was over-dried and thin as a 1/2 batch. I was surprised to notice the difference, since the temp profiles were indistinguishable.
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