Your Roasting Temperatures Don't Make Sense To Me

[expat]

I keep reading different threads about the temperature of the coffee you're roasting and we are roasting much cooler, maybe 100 degrees F cooler than some of you. I see final roast temperatures mentioned of 450F, 475F, even 500F. For us that is crazy hot.

Granted we are a fairly new roaster so don't have near the experience of most of you but here's what we're seeing from our roaster. It, by the way, is an Ozturk with a CAST IRON drum, not a STEEL drum, so maybe that is were the difference is.

Our drop temp for the green beans is 175C (about 350F). The beans will then drive the temp down to, sometimes, about 90C (close to 200F). Then we'll go through our roast, each type of bean finishing at a different final temperature but usually somewhere between 190C-200C (375F to 390F) and occasionally running up to 205C (400F).

We get (what we think are) beautiful roasts, tasty and flavor-full. Even getting very dark roasts. And our roasts average about 20min (some 16 or 17 minutes, some 22 to 24 minutes).

Are we doing something wrong to be roasting at these "lower" temperatures? Somehow I can't think we are because the proof is in the cup and we like what is in the cup quite a lot. Maybe it is the cast iron versus the steel roaster? I don't know but there sure is a BIG difference in my roast temps and many of yours.

Any thoughts?

 

[chast]

Temps

I Use US Roaster Corp roasters and was given roasting instruction from someone who uses Ambex. Did not work at all as far as quality roasts. Every machine is different as far as time, temp ( bean & ambient ). I drop at 350 and average 15 - 17 minutes for roasts that range from 425 degrees to 435. My POE is around 200 and it takes about 9 minutes to climb back up to 350. When it reaches 350 I crank the gas up to my desired temp and that has been working for me. I try to get hints from roasters who are using the same brand and close to the same size. I also have a dampner that I use and some roasting units do not.
If the coffee is coming out great, why change your procedure?
Charlie

 

[Josh]

I think the roasters read differently. At 400 what kind of roast are you getting? 400 for me is right before 2nd crack and we dump between 392 and 402 depending on the coffee. 405 is almost always 2nd crack. 365-375 1st crack.

 

[eldub]

Expat: I think your roaster's temp readings are off.

In our machine, we hit first crack at about 385*. (According to my reference guide, first crack should be reached at between 380 and 400*)

Second crack doesn't occur until between 435 and 445* according to my guide, and when I dump beans at 440*, they are usually still cracking in the cooling tray.

 

[eldub]

Here's a roasting guide from Sweet Maria's. (Not the guide I use, but appears ot give similar reference points of bean development.

https://www.sweetmarias.com/library/content/using-sight-determine-degree-roast

 

[expat]

Chast, I agree. The roasts are coming out great so we aren't going to change, I was just wondering why my numbers differed so much from many others in this forum. But looking at Josh's post I see I'm getting close to the same numbers as he is so he's probably right, all roasters are different. Also I've got to think my cast iron drum makes a difference over steel drum roasters. We've got a lot more metal to heat up -- wall thickness on the drum sees about 5mm or so, so we'd have quite different heat transfer rates as opposed to a faster heating steel roaster of a similar size but with a thinner wall thickness. At least that seems logical to me but I'm not a heat dynamics physicist. Heck, I didn't even know I could spell 'dynamics' or 'physicist'.

And Eldub, as to your 385F first crack we are often, depending on the bean, done with our roast, all the way to 2nd crack and beyond before we see 195C (385F). Sumatras and Kenyas may run up to 200C-205C (390F-400F) but our Ethiopians, Brazils, and Colombians are done well before that. I have checked the temps using a handheld Omega logger and get similar temps so don't think my temp probes are out of whack. Of course my temp probes could be in a different place than yours which could easily yield the temperature variations I'm seeing between my roasts and so many others on this forum.

 

[eldub]

Temps should be consistent regardless of barrel materials, imo. However, it might take longer to get a cast iron barrel up to temp as it could maybe absorb more heat.

And I'm pretty sure the temps at which coffee beans reach certain points in the roasting process have been well documented and are universal.

That said, I see no reason to change anything you are doing.

 

[eldub]

Btw, our roaster has a probe giving bean temps and another for air temps in the barrel.

 

[Josh]

My feeling is that, it doesn't matter what the readout says, as long as it is consistent.

You can't expect to read numbers off the internet and assume your machine will read the same temps.

 

[eldub]

Josh: I agree that it doesn't matter what the read out says, as long as its consistent.

However, are you claiming that there isn't a specific range of temps where coffee beans reach certain stages in the roasting process?

 

[farmroast]

As we're starting to have some handy computer roast softwares to hook probes up to, better probe placement becomes more important. If your readings are too far off from bad bean mass contact with the probe they will also likely be effected nonlinear from different batch sizes, different heat or air profiles. But when all is the same in repeated roasts there should be some decent consistency.

 

[Jazz]

I had a post a month or so ago about ambient temp and bean temp. I am wondering if the differences of opinions are because when describing the roasting processs, maybe we should be more clear on whether we are talking ambient or true bean temp. Also my question is, does it make a largr difference where the probe is? Great topic, lets keep it Rollin. There are no dumb questions

 

[expat]

My roaster measures the drum temperature and the exhaust temp. So possibly that is where the discrepancy lies. Some folks are talking drum temp, others are talking bean temp?

 

[eldub]

Our drum temp tends to run 40 to 80* above the bean temp until I get up to 370* or so. At that point, I shut down the gas and extend the time between cracks. Its common for our bean temp probe to reach 440* while the drum temp is 10* or so lower than that. However, if I let the bean temp get higher than the drum temp early in the roast, the process will stall out.

 

[eldub]

Jazz: In the earlier discussion, I was talking about bean temps.