ambient temp and bean temp

[Jazz]

I would like to maybe get a discussion on ambient temps and bean temps. How important is the ambient temp when roasting. Isnt the actual importance really on bean temp?

 

[eldub]

There are folks here with a lot more experience in the than me, but I'll give it a shot....

The ambient temp is important when considering how quickly you want to raise the bean temps. The closer the ambient temp to the bean temp, the slower the roast will proceed. If your ambient temp falls below the bean temp, your roast will stall out. If you raise your bean temp too quickly, you risk "tipping" the beans, or putting small pits in the surface.

 

[Jazz]

Hi eldubI try to run a 12 to 13 min. Roast, charging at 390 bean temp (bt)and 480 ambient temp (at)When Im ready to dump (finish), my temps at 1st crack are500 at375 btI dont know but the ambient seems high doesnt it?Your thought or concerns are appreciatedThank you

 

[eldub]

How large of batches are you roasting?

So far, I have rarely let my ambient temp get up past my finishing temp. (420* to 450*)

Are you seeing any tipping (pitting) on the surface of the beans after the roast is completed?

 

[Jazz]

I am roasting 20 lbs green

 

[topher]

On what size and make of roaster? 500 degrees seems a bit high. Thirteen minutes is really fast. How does it taste? My roasts are around 18 to 20 minutes.

 

[eldub]

Thanks for chiming in Topher. I really appreciate your input.

What difference in the beans' flavor profile would you expect to see between a 15 and 20 minute roast?

 

[topher]

I've found that if you roast too quickly you don't develop the coffee. You end up with a "grassy" taste. With the 12 to 13 minute roasts...are you getting and even color on the bean? I would imagine that it isn't even..possibly scorched or tipped?

 

[eldub]

Interesting.....

From this conversation I'm going to slow my darker roasts down a bit and shoot for 16-17 minutes.

For my medium/medium dark roasts, the only bean that has a bit of variation in the color after a 15 minute roast (medium dark/ 440*) is the natural processed Ethiopian Sidamo.

On the other hand, the one attempt I made to take a roast to 460* in 15 minutes ended up tasting scorched. However, brazilian roasted to 450* in the same amount of time tastes great.

 

[topher]

What brand coffee roaster are you using? What is your drop temp?

 

[eldub]

I'm using a US Roaster Corp 12kg unit. For 1/2 load batches, I'm dropping the beans into the roaster @ 380* and looking to get down to 250* before raising the temps back up. However, for small sample batches (2-3 lbs.) I've been dropping at 320*.

scott

 

[Jazz]

Thanks to those chiming in. Im sorry that I havent posted replies in a timely manner.I am roasting 20 lbs green Honduran on an L12I charge at 390 bean probe/ 480 ambientMy rate of climb is about 30 degrees pmFirst crack is around 9 to 10 min.Temp at that time is 395 bean temp/470 ambientWater column at 4"I like to pul 3 to 4 min after first crack, no laterMy question is How do I achieve a lower ambient temp without compromising the bean temp.Thank you so much for any input

 

[eldub]

How long does your roast take?

It sounds like you are climbing too fast. I shoot for 20*/min until first crack. The goal is to stretch the time between the first crack and finish so I ease off the gas at first crack.

Keep in mind that its possible to get the bean temp above the ambient temp toward the end of the roast. If I'm shooting for a 440* roast, my ambient temp never gets above that number. In fact, I shut the gas down after the first crack and let the beans coast to final temps. (I'll have the ambient temp running about 430* and the bean temps will slowly climb past that level to finish.)

I can post the scheduled temps rate of our roasts if you would like. There are specific marks I like to hit at specific times in the process to let me ease up on the gas at first crack and still finish up in around 15 minutes.

The analogy I'd use is grilling a steak. After you remove the meat from the grill, the meat's temp will continue to rise for a few minutes.

 

[farmroast]

is How do I achieve a lower ambient temp without compromising the bean temp.Thank you so much for any input

increase convection. more air flow at a lower ET vs lower air flow higher ET to keep the same heat transfer rate or rate of rise of the beans.

 

[Jazz]

Thank you for the reply. I am sure that not only I but others too could benefit if you could post your scheduled times. I would find this info very helpful