Bean temp Vs Probe temp

[fnq]

This question is related to the development time thread below, but i added here rather than subvert it.

I am a very inexperienced KL roaster ( up to about log 60, so 6 kgs under my belt) and i am now dabbling with trying to record (button push) first crack and then get into some Development Time Ratio driven roast parameters.

Over a small trial period i have been hearing and marking my first crack between 208-210 degrees celsius.

In theory, the bean temp for most beans to achieve first crack is 196.

So i am postulating a 12-14 degree difference in prob temp to internal temp @ FC. (or alternatively i am a terrible listener)

Again in theory the bean temp of 224 -226 achieves second crack. My highest ending temp has been a 228-229 in a 4.4 roast depth, I have not heard second crack noises.

So , are there some probe numbers we could be looking for for First and second crack?

I include a log of a successful and tasty 4.4 depth roast

log GTTT 4.4.klog

(80.79 KiB) Downloaded 223 times

If i use 210 degrees as FC then my DTR is approx -27 ( which is just a number but one i can now say produced a tasty cup of espresso)
but i would also like to get a feeling for roasting just into second crack-----


Cheers Darryl

[Angela]

Slightly tongue in cheek may I say if you get a sensible answer I will eat my hat.

I've asked it before; I'm still confused.

I will say with Wayne's profiles I'm getting a fairly consistent FC starting around 205/6. Whereas with some other profiles my FC was as late as 214/5.

I think it isn't really too helpful to look to drum roasters for comparison. This machine needs a body of experience and understanding; it is coming, it appears; it is just taking time to be developed. Accept, as early adopters, we are the guinea pigs.

[Howard W]

Hi Darryl, I've tried to get better at roasting by tackling numbers like FC temp / end temp / DT / DTR etc and scouring the forums and books for an answer. But at the end, everyone's preference is different and there's no end of the generic type of advice. To answer your question it may be easier if some sort of objectives are better defined, as in what qualities in the roast / cup are you trying to improve?

[fnq]

thanks for the quick replies Angela and Howard.
It looks like i will keep trialing ( along with Resting times, grind fineness etc).

I suppose I am trying to nail down a couple of variables in search for a better consistent taste in the cup.

Angela - i am getting very good profile Vs log results using the official core profiles and so i think i will keep checking but if in doubt stick with 206@FC

Howard- what exactly am I chasing> it changes just about every roast/ blend /!!!!! .
Currently i am trying to get a consistent good KJM blend, and am wondering if i push the indonesian coffee into a darker roast will it produce more cocoa on the finish. I can do this through trial and error, but looking on other forums it would seem home drum roasters try to get an Indonesian roast to just on second crack for this to occur - without getting into ashy/ smoky tastes).

So to be a bit more specific, i am seeing whether i can improve on a 1200-1500 REST profile for 4.4 depth- for this bean (Sulawesi Blue ) or at least get some feedback to inform which way i could jump next.


Sorry if i am going over old territory, I quite like playing around and in doing so, i lose a bit of diligence in testing out some theories as my blends evolve.
Cheers Darryl

[Geronimo]

If i use 210 degrees as FC then my DTR is approx -27 ( which is just a number but one i can now say produced a tasty cup of espresso)
but i would also like to get a feeling for roasting just into second crack-----

Hi Darryl

I’m still trying to get my head around things, but if you are aiming for second crack, do you manipulate the profile in anyway to still aim for around 25% DTR? Or does this DTR of between 20 and 25% go out the window with the dish water when roasting a little darker?

Hi Geronimo

I hope you are well .. 2nd crack can be tricky at times . I have found 2nd crack occur at around 34 - 36% DTM .
So you an extend the roast and reach 2nd crack .

We also have to be mindful , sometimes 2nd crack isn't as audible as FC .. Also , it differs coffee to coffee .

The bigger question here is , What is your purpose for roasting to 2nd Crack ? If a 26 , 28 , 32 % DTR is tasting really good. Why do we need 2nd Crack .

Wayne

[Wayne]

Hi Darryl

Thank you for the post . this is much appreciated .

I just want to start off by addressing the log . This is the first thing I always ask for . This is just to allow me to check the KL and make sure we are looking at the same info . Thank you for this . Besides the lower mains voltage , The log looks great . I can see why you are happy with the taste .

My advise on the Indonesian . The Sulawesi Blue is typically grown in 1400 - 1900 m . I see you are using the 1200-1500 GTTT . Be very careful not too push the coffee too far . The likelihood of more cocoa is low purely because your are not adapting the development phase between yellowing and 1st crack . Maybe try the 1500-2000 GTTT . New name : 1500-2000 REST .

The Development phase is more pronounced and probably more likely to develop more of what you are looking for . The balancing act is really to push the flavour development without developing too much ashy , roasty taste . The level of your end roast (4.4 ) will probably remain . Maybe work on not achieving level but achieving the same 26% DTR you roasted on the previous profile .

There are also lil tips and tricks you can apply to your brewing method / extraction method to bring out more of what you want . I can assist you with this if you let me know what brew/ extraction method you use and what your typical brew ratio is and you take me through your extraction plan .

On the probes of the KL , the difference between drum and air probes . Why you are not getting a 196 but a 206 .

There are a couple of reasons why .

1st we have to look at what the probe is measuring and how much information it is measuring . Probes will never measure direct heat transfer that occurs in the bean in roaster . Whether there are 1 ,2 or 3 probes .

In drum roasting , they will have a probe in the local area of the tumbling mass ( This is always made up of beans and air) , If you are luck , in the bean mass .
Using 2 probes here , gives us an average of the heat of the bean mass . In drum roasting however , these probes are not as effected by fan or extraction than in air roasters . So you get a more bean orientated result . However , This is also not exact because the bean mass is forever tumbling and moving toward the front of the roaster and then being pushed to the back . So the game continues . There are points in a drum roasters cycle where the probe measures direct drum heat ( air) but this shouldn't cause a huge fluctuation because , the air in the drum and bean temp effectively are now the same . Thats what a turn around point is .

The exit or Environment probes are positioned at the top and close to the exit of the roaster . Their temperature is higher than the bean mass temp . This makes sense . Hot hair being exhausted .

Remember this HOT AIR later in Air roasting .

Lets not forget about the drum casing and in fact the drums structure .. They absorb heat and there is a huge percentage of latent heat that is sitting there , helping us maintain consistency through roast . A perfect ecosystem or Convection oven .

Remember the latent build up of energy prevents the drum from loosing heat . It aids the roasting process. We don't need to max out our burners to roast . The environment will do it for us .

So beans in this situation only need 195 deg to reach FC BUT if there was not enough latent heat in the drum and casing + there is not enough hot art being pulled from the roaster . We will only achieve FC at 200 - 204 deg . Depending on the batch size of course .

If we look at an air roaster and directly at the KL . The single bean probe is sitting just above the bean mass at start and loading . It needs to be because as we dry out our coffee , it rises and the goal in the development stage of the roast is to measure as accurate as we can , the change in the bean mass . Bean mass is beans and air .
With air roasting , because we don't have preheat and latent heat . A focus on driving heat into the bean is critical .

How do we do this . We build profiles with intense - but regulated - starts . We speed up our drying phase as much as we can and try and push as much raw energy into our bean in early development phase . This is why the logging of colour change is so important . On your log , you will see a development % between this and FC .

We push the probe slightly further away from the main bean mass to give us a more accurate average . Pointed out above .
Remember that the probe is still closer to the heat source ( The bottom of the KL ) but it needs to be for the accurate reading ( This is immediately going to give us a higher probe reading ).
Then we force hot air through the coffee bed , It has to be aggressive because we want the coffee to tumble and be effected by heat evenly ( prevent scorched and tipping ) . We have to be careful not to lower the air flow too much and at the same time , maximise heat transfer to the bean with the goal here of bringing on exothermic process in the bean quicker .. There is a higher chance of baking coffee roasted in an air roaster .

The probe fundamentally is measuring both air and bean . Its trying to average out the temp and give us a lot more accurate bean data BUT it cant ...

The FC degree temp you see at FC is a combination of Bean Mass and Air temp . with the probe in the middle of the ROASTING bean mass , not the rested green bean mass , and constant streaming of air creating that drum like turn similar to drum roasting .

It's only logical that the tamp will be higher .

Remember it's a bean mass measurement . never an individual bean temp .

I hope this has answered your question on this Darryl . Id be more than happy to help you with your extraction .

To add to Angelas point on the consistent FC through the Core profiles . This is achieved by roasting multiple origins on the same profile , adjusting each profile and fine adjusting the tools to give us better flavour in the EARLY DEVELOPMENT pre FC . Taking these multiple roasts and averaging : Colour change , yellowing , early browning , mid browning , FC , DTR and End time .

Putting all the above into each Core Profile . Including the RTD profiles . The golden thread through these profiles are : how do me maximise the development phase pre FC .

I am so happy you have noticed the consistency . I would love some more feedback .

I hope this has helped .

Happy roasting and Darryl , please try a higher altitude on that Indonesian . Please let us know .

Wayne

[Geronimo]

If i use 210 degrees as FC then my DTR is approx -27 ( which is just a number but one i can now say produced a tasty cup of espresso)
but i would also like to get a feeling for roasting just into second crack-----

Hi Darryl

I’m still trying to get my head around things, but if you are aiming for second crack, do you manipulate the profile in anyway to still aim for around 25% DTR? Or does this DTR of between 20 and 25% go out the window with the dish water when roasting a little darker?

Hi Geronimo

The bigger question here is , What is your purpose for roasting to 2nd Crack ? If a 26 , 28 , 32 % DTR is tasting really good. Why do we need 2nd Crack .

Wayne

Thanks Wayne, good answers and question.

I guess I used second crack as a marker more so. A known point in the roast (if it can be heard) and do you have to try and aim for this narrow band of 20 to 25%. And as you’ve answered, no if it tastes nice. Which makes sense.

I guess the confusion for me, is that you read so many people aiming for this Scott Rao DTR. And I just followed like a sheep without engaging any reasoning. I’ve only just gone into second crack on your profiles, thus the question. I’ve typically aimed for around 25% On previous profiles. But didn’t know any better so to speak.

Cheers

[Wayne]

Yes

I guess that is the problem with reading up on these issues .. SR states that out of the thousands of roasts he has done . His best have been in that 22- 25% .. He has not discounted the other DTR . He hasn't told us ONLY that range is good .

He goes on to say that taste is the override and that if you roast a coffee and it tastes great BUT is not in that range . Enjoy it . Mark it and if you want , make it your norm ..

Now the above I agree with .

Lets say for example , You are roasting and log your FC but you log it too early .. The DTR now will be skewed . What is usually great for you on your normal 26 % is now suddenly 30% ..

Should you discard the coffee - Its still your 26% .

I guess what I am trying to say is . Use DTR as a mark . Its not your definitive on the roast . Use as many marks as you can ... FC , Time , Time and temp at a specific point .. They are all important .

Its like an espresso extraction - Try it at a 1:2 ratio , Then a 1:2.2 , 1:2.4 .. Try adding in just a bit more coffee for intensity boost . You have to experiment in order to determine the range of the coffee - Then find your sweet spot ..

Same with the KL in my opinion .

I hope this assists

[Geronimo]

I guess what I am trying to say is . Use DTR as a mark . Its not your definitive on the roast . Use as many marks as you can ... FC , Time , Time and temp at a specific point .. They are all important .

Nicely said Wayne. Very good points.

Many Thanks

[fnq]

Thanks Wayne for the extended reply. It will take me a couple of morning coffees to glean all of the info.

I do appreciate the effort for going over air roasting 101 for a KL newbie.

I will be contacting you shortly re some extraction ideas.

Hi Geronimo, Do i manipulate roasts around DTR and roast levels - heck No i am lucky if i remember to log First Crack

Seriously though, i am trying to get some trend info about my tasting of coffee and where it fits in the coffee culture knowledge base.

So far i have noticed that roasts that run to about 27-30 DTR i much prefer to those that have DTR nearer 35.
None of my roasts that i have checked against have run lower than 25 DTR as yet,, but i may be mislogging FC marker.- i am not going to chase the magic 20-25DTR as such, and i haven't really manipulated away from a profile yet, i spend my time trying to emulate the profile as best i can.

in a similar way I am trying to get a feel for the espresso extraction. With my current medium roasts ,i approximate 20 gm in / 45-50 gm out over approx 35-40 seconds,,, BUT on darker roasts, i think i will try a bit shorter extraction 1:2 .

Cheers Darryl