Roasting times inconsistent

[Kiwi]

Hi all
Any ideas to achieve consistent roast times?
I am roasting on a 30 kg Toper with bean and environment temperature probes. Each roast is 25 kg. The burner is controlled by set temperatures through the bean probe. What we have noticed is that our roast times progressively get longer as each roast is completed. We are dropping our green into the roaster at 200 deg C and running the burners to a set temperature of 202 deg C. When the burner stops we get the bean temperature rising to around 212 Deg C where second crack occurs.

First crack is consistently being achieved at around 15.5 mins at 193 deg C. We are finishing our roast at the start of the second crack. Our roast time between first and second crack progressively gets longer where our first roast is reaching second crack at 19 mins and by the time we get to the 10th roast that day we are reaching second crack at about 23 mins.

ANY IDEAS PLEASE. Should we run the burner on half heat from 202 deg C?

Cheers
Chrissy

 

[topher]

We drop our batches around 205 and have our set point at 234, it coasts up to anywhere from that point to 243. One question, are you roasting the same coffee for all 10 batches? The later batches could be taking longer due to the fact that you are opening the door to dump the coffee into the cooling bin.

 

[Kiwi]

I have been researching different roasting styles. A number of roasters take the heat through to around 202 deg C and either turn off or cut back to half heat. Using this principle the bean temperature continues to increase up to around 212 deg C where second crack is starting to occur.

What we have noticed is that to achieve consistent roast times of around 19 to 20 minutes we have to continue to adjust the burner temperature up by a few Degrees each roast. Our Topher burners are either on or off as we don't have a modulator to cut back to half heat.

Is this normal with coffee roaster out there? Or do we need to study more on the exothermic and endothermic reactions as this may explain more? Any thoughts?

 

[marko53219]

Is this a new roaster you are using or used? If used is it clean? The roast times seem long to me. I would think you have lost too much of the flavor roasting 19-20 minutes and just hitting second crack. If things are clean then I would try to lighten the load some. Maybe try a 20 kilo load doing all else the same. See if you can achieve a 10-11 minute first crack. If you can do that then see if the roast times are more consistant.

Please let us know,

Mark

 

[Kiwi]

Thanks Mark for your thoughts.
Using a secondhand but reconditioned 30kg Topher, 5 years old. I am told that Tophers traditionally don't roast to there weight capacity. Have tried reducing roast size by 10% with a reduction in roast time of 1.5 minutes. I will keep you up to date with our cupping results. Also trying an option of dropping in the green at 190 deg C and running the burner longer.

Cheers

 

[ElPugDiablo]

We are dropping our green into the roaster at 200 deg C and running the burners to a set temperature of 202 deg C. When the burner stops we get the bean temperature rising to around 212 Deg C where second crack occurs.

First crack is consistently being achieved at around 15.5 mins at 193 deg C. We are finishing our roast at the start of the second crack. Our roast time between first and second crack progressively gets longer where our first roast is reaching second crack at 19 mins and by the time we get to the 10th roast that day we are reaching second crack at about 23 mins.

What was your environment probe reading in each batch? How is your airflow controlled? What was your air flow setting in each batch right around first crack until 212 deg C?