mkane wrote:How dark? Comparing this to SM's chart is FC+.

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Those are some good looking dark roast curves!

Yeah, but taste is king!

No arguments there!

Hello:

another_jim wrote: ... bean temperature has stopped rising ...
... beans are not getting darker.

Impossible to argue with that.

another_jim wrote: ... want to roast darker ...
Too high an ET may scorch the bans ...

This "too high an ET" you mention, where would it be with respect to an ET of 250°C?

I ask because I recall a post (here at HB?) where the OPs idea/concept was to arrive to adjust his power output so as to arrive at the vicinity of 1st. crack at an ET just below <250°C, all the other curves being additional information.

I think the OP said it was the only curve that he cared about and that doing it this way made roasts easier and very consistent.

Edit:
Found it ...
The post was at HomeRoasters by a chap called renatoa and he was citing a post here at HB by ... you. 8^ )

another_jim wrote: If there is one thing that somewhat works for all roasters, it's that a good roast requires that the ET follow a certain profile, and stay within certain limits, so the beans don't under dry, over dry, bake, scorch or tip.

Basically, this magic profile is a starting temperature of around 325F to 400F (163-204C), and a ramp up to around 450F to 480F(232-250C) in around 6 to 8 minutes, and holding it steady there to the end of the roast, whenever that may occur.

This ET part is basic roasting chemistry, and the same for all roasters and coffees. But the heat inputs required moment by moment to achieve this ET curve is based on the roaster's thermal characteristics, and is different for every roaster design.

https://forum.homeroasters.org/forum/vi ... post_62977

renatoa@homeroasters.org wrote: Why is this so important for me... because is about ET, not BT ! because I gave up to fight finding the method of accurate BT measurement... it simply don't exist !

And I say this as a computer/automatics engineer, since 1985...

The mix of beans and hot air is simply too chaotic to rely on any measurement method for predictable, repetitive and accurate results.
More, using this information (BT) to drive the process is simple lottery.

Conversely, measuring ET is so simple and precise, that the JS quote become a gem in this field.

TIA

CIV

That ET profile applies to air roasters. In drum roasters, there is usually so much heat storage (i.e. how long it takes for a change in the ET to show up in the beans), that you have to start with a high ET and keep it pretty flat line.

The problem is you can't really measure the ET, as it immediately affects the beans, inside the rotating drum. So the usual place to measure is upstream in the heat flow, and hotter. In an airroaster, you can measre the air exactly where it contacts the beans, and the transfer function from ET to BT has much smaller integral terms.

But all this nasty calculus stuff is now obsolete, since we have achieved the high-tech Babylonian science breakthrough of ROR

Hello:

another_jim wrote: ... applies to air roasters.

I see.

another_jim wrote: In drum roasters ...
... start with a high ET and keep it pretty flat line.
... usual place to measure is upstream in the heat flow ...

Yes, that's what I do.

I have a DIY gas fired drum roaster. (JB sample roaster type)
The only airflow I get is the one generated by the drum's inclination (~ 10°) and the motors' two speed rotation.
The back end of the drum is perforated to allow this to happen and I measure ET with a probe clear of the beans and as high as possible near the exit but inside the drum.

After a few changes to the gas supply, the burner train and the box's insulation, many roasts later I am slowly learning how the thing behaves.
In the past few roasts, I have been able to keep a reasonably flat line for ET, albeit a bit high for my liking.



The variation in the slope of ET curve you see at ~ 03:10 is due to a speed change in the drum.
The moment to do this makes for a tricky decision as if I do it too soon, the beans have not lost enough water and centrifugal force hampers their movement, risking an uneven roast and if I do it too late, I risk a scorched roast because they are not getting their heat from the surrounding hot air.

But like they say, the proof is in the taste and I really like how my espresso tastes lately, so I feel that I am on the right track.

another_jim wrote: ... we have achieved the high-tech Babylonian science breakthrough of ROR.

8^D!

Cheers,

CIV

250C max ET is pretty good for a drum roaster. There's a compromise between a decent roast speed, bean weight, and a low ET. If I need a really crystalline brewing roast, I keep the ET at about 240C-245C and the roast at around 10 minutes. But that only gets me 125 grams.

Hello:

another_jim wrote: 250C max ET is pretty good ...

Like most DIY experiences, it took me a good deal of trial and error to get that.

Direct flame below the drum, important mods to the burner train/regulator and ceramic wool insulation were necessary.
There's not much volume there, but the temperature around the drum/inside the insulated outer box can reach ~ 300+°C by the end of a 10' roast.

another_jim wrote: ... compromise between a decent roast speed, bean weight ...

I agree.
I wanted drum volume to be as large as possible, given the stuff I had to work with.
As things stand, I've managed to tune it to roast 750grs. to the edge of 2nd. crack in ~ 10'.

I still have to find the right gas modulation to be able to do it between 8' and 9' as the firepower is there.
I suspect that it may be a question preheating longer.

Thanks for your input.

Cheers,

CIV

Bottom roast I upped the charge weight + didn't compensate for the machine being hotter overall.