Relative batch size and why - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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millcityroasters
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#11: Post by millcityroasters »

vilseiprairien wrote:Here's a closely related question: how do the people making the roasters decide what the nominal capacity will be?
This has been answered several times on H-B and usually quoted from a post on Homeroasters.org.

Roast size (ounces) = Drum Volume (cubic inches)/10

Bodka Coffee
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#12: Post by Bodka Coffee »

I find that to hit the profile that I like I can't do full batches either. It is partially dependent on gas pressure. After the pressure falls off of my tank I usually won't charge more than enough greens for around 8 lbs of coffee in my 5k roaster. If you like or need a longer roast profile you can charge more. I have charged up to 12 lbs. As Neil said it needs to be well into the roast batches so it's heated up good.

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vilseiprairien
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#13: Post by vilseiprairien »

millcityroasters wrote:This has been answered several times on H-B and usually quoted from a post on Homeroasters.org.

Roast size (ounces) = Drum Volume (cubic inches)/10
So that's the general guideline? Reading further, I see that it can vary quite a lot from roaster to roaster. If my calculations are not way off, the North 1kg roaster has a drum of about four times the volume of the 500 gram? Sounds way off..maybe I plugged the wrong numbers in? I had 5x5x6.3 for the 500g and about 8.6x8.6x9 for the 1kg (converted from mm from the North site). Looks like that makes the tj-066 a 350g roaster, and the tj-067 a 1.4kg roaster?

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[creative nickname]
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#14: Post by [creative nickname] »

I generally do about 75% of rated capacity on my USRC sample roaster, which amounts to 333g batches based on the rated 450g. It has the power to do full loads with adequate control, but I like variety, and so prefer to roast more batches and have more available options to hand at any particular time. I can also roast smaller batches, but I find that my bean mass temperature measurements become less reliable below 300g (66% batch size), and so I rarely do that except by necessity (such as when I have only obtained a small sample of a particular coffee to try out).
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9Sbeans
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#15: Post by 9Sbeans »

I use a KapoK 500 commercial sample roaster, and the manufacturer's rated capacity is (from 150g to) 550g. My general charge mass varies from 227g (40%, most common batch size), 160g (30%, leftover beans of a 10-pound bag after culling), 450g (80%, if I occasionally need more capacity) to anywhere in between.
Here are two of my recent roasting profiles with different charge sizes (227g vs. 450g) but similar 5-min Dry/4-min Ramp time segments. Note that I only used maximum of 48% gas in the 450g batch and this sampler has sufficient power and agility for profile shaping. A sampler should do what a sampler does: precision, consistent and agility.





I prefer variety (origins of beans, roasting profiles), and only roast for my own family consumption. When I made my purchase decision, I calculated my preferred utilization capacity (40%) and conserved enough head room for future growth (visitors, gift, etc.).

As Neal and others pointed out, if you are roasting in a commercial setting, you'll have many other factors to consider. I would routinely charge 80% (or the maximum allowable size as long as it maintains profile shaping agility) on a production roaster to reduce the labor/machine time.

wearashirt (original poster)
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#16: Post by wearashirt (original poster) »

vilseiprairien wrote:Here's a closely related question: how do the people making the roasters decide what the nominal capacity will be?
A quick 2pir*length comparison of drum sizes don't show a direct proportion between rated capacity. Then again, maybe it's supposed to be compared to some other geometric index whatever...

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millcityroasters
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#17: Post by millcityroasters replying to wearashirt »

A roaster is a system, not just a drum. There's broad variations in materials, construction, heating modalities, airflow, etc, etc. Beyond that, there's broad variation in how people use the machine. Most commercial coffee roasters will eventually turn a full (stated capacity) charge of green coffee brown. If you're roasting commodity, gas station coffee into submission, I'm guessing most 10 or 12 kg roasters will get that done in 18-20 minutes, but that's rarely the coffee we aspire to.

Obviously, speciality coffee requires a little more rigor. Behold: the ubiquitous and mysterious 70% (more or less and highly subjective) sweetspot.

This isn't a commandment, just a technique to get the headroom you need to do what you want to do.

wearashirt (original poster)
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#18: Post by wearashirt (original poster) »

Hi all, posting an update on my original post.

In my four-coffee roasting session today, I decreased batch size from a usual 1.500kg to 1.200kg. I found that I was able to roast to the same end-temperature while conserving bean mass. For example, what used to be end at 365F (BT) & 17% moisture loss, it is now 365F & 15.7% moisture loss. This particular example is the one that has the biggest difference, however the observation was uniform across all 4 coffees.

While maintaining the same roast procedure between 1.5kg and 1.2kg roast batches, I also observed higher ROR (e.g., 15F/min vs 19F/min) and a "sexier" S-curve on each roast profile. The procedure is as follows:

400F ET drop temp, gas turned off for 90-s during which the bottom-out temperature was observed and allowed to climb 1-2F, before the gas was turned back on to 1.5 kPa. The gas was boosted to 2.5 kPa on the 4:00 mark. 1C was reached by around the range of 8:00 - 9:30 for the four coffees. Convection was minimized at the initial part of the roast to conserve moisture loss (citing a Mill city video for this one). Prior to the known 1C temp, gas pressure was decreased to 1 kPa, while maintaining final fan and drumspeed (i.e., relatively high convection), towards bean dump

With the smaller batch size, the coffees were rolling and bouncing through the sight glass, which I've long held to be a negative thing, since I discovered better roasts when I overloaded my Gene Cafe -- the coffees were compacted together, thereby uniformitizing the heat gain throughout each bean. I maintained this same belief, thereby roasting in the 1.5kg - 1.8kg ranges on my North 2kg gas.

Just 2 hours since roasting, I brewed one of the coffees from the 1.2kg batch and feel that I have better cup results than the 1.5kg batch. Thoughts?

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#19: Post by Boldjava »

wearashirt wrote:Hi all, posting an update on my original post.y four-coffee roasting session today, I decreased batch size from a usual 1.500kg to 1.200kg... the gas was turned back on to 1.5 kPa

Just 2 hours since roasting, I brewed one of the coffees from the 1.2kg batch and feel that I have better cup results than the 1.5kg batch. Thoughts?
On your North 2K, are you heating with propane or natural gas? If working with propane, a high pressure regulator will double your pressure to the roaster. Your kPa readings strike me as low compared to our former set-up on propane. I used to work with about 4.1 kPA, though our gauges are not necessarily calibrated one to another.
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wearashirt (original poster)
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#20: Post by wearashirt (original poster) »

Boldjava wrote:On your North 2K, are you heating with propane or natural gas?
I do use LPG tanks. I actually CAN make the pressure reach 4 kPa, but the flames seem violent, or I'm just not used to it.

Do you mean to say, I should swap out North's regulator? The 1 stage regulator on my tank?