Thanks for the follow-up Ed. I'd have more numbers but I only track the MET in the grill and use sounds (and more importantly) smells to gage the roast.

I assume your roaster is an air roaster of some kind? With that amount of beans and you're low MET (compared to me) I assume you're using a more efficient air roasting set-up.

In my grill I have to compensate for lower air flow with a slightly higher MET (never above 520F) and slightly lower bean weight (I like one-pound maximum).

Again thanks for the follow up.

Tim
Yes, I have some convection air circulation in my hybrid home-built(see my www/blog site for pictures). Also my 200rpm(adjustable) bean bats keep the beans moving around for good heat exposure and transfer.
Ed

Now I recall Ed and I must say that's one decked out machine. Interesting use of a hybrid set-up. Nicely done!

Tim, the beans become exothermic.

The roaster temperature should not fall if the heat input / loss is constant. If the flame becomes short of oxygen due to smoke, the temperature could drop. Any chance of a draft or dropping gas pressure?

Do you inspect the beans during the roast?

Have you logged the temperature above the middle burner right below the drum? This maybe higher than 520°F. Flame tip temperature for propane can be 400°C / 750°F

Have you tried using just the end burners so there is no direct flame on the beans?

cafeIKE wrote:Tim, the beans become exothermic.

Thanks for the clarification Ian, I was referencing what I read on sweetmarias.com:

Sweet Maria's wrote: Since first crack is an exothermic reaction, the beans are giving off heat in first crack, but the quickly become endothermic, meaning that a roaster that is not adding enough heat to the process will stall the roast at this point ...not a good thing. --Sweet Maria's "A Rough Pictoral Guide to the Coffee Roast Process" (In the First Crack paragraph)

cafeIKE wrote:The roaster temperature should not fall if the heat input / loss is constant. If the flame becomes short of oxygen due to smoke, the temperature could drop. Any chance of a draft or dropping gas pressure?

No I don't think there was any draft. The others maybe, but again the temp readout only dropped 2F (is that really enough to worry about)? I reacted by a slightly higher burner setting.

cafeIKE wrote:Do you inspect the beans during the roast?

No, I don't open the grill during the roast and I'm using the stock RK Drum (no trier setup).

cafeIKE wrote:Have you logged the temperature above the middle burner right below the drum? This maybe higher than 520°F. Flame tip temperature for propane can be 400°C / 750°F

Have you tried using just the end burners so there is no direct flame on the beans?

I have not logged the temps from any other location than the current one (just below center of the drum on the side that the beans rotate to). I'm real close to center of the tumbling mass.

I have roasted with just the outside burners and it went well. I don't notice any drastic difference when using only the outer two or all three. Obviously with only two I have to roast on medium rather than low.

I don't see any tipping and colors are very even, am I missing something else? Again thanks for all the input, I find it very helpful.

Thanks for the response. I know a couple of people with RK drums and they sometimes ask questions I can't answer.

farmroast wrote:Tim

Min.....BT......ET......Degree rise/min....Variac voltage
........................................................
5.......297.....397......22.....................107
6.......318.....411......21.....................102
7.......335.....419......17.....................101.3
8.......350.....420......15....................100.5
9.......365.....430......15.....................99.5
10......376....435......11.....................99
11......388....435......12.....................99
......................................................
16:30.433.....465......14...dump
still will do some more adjusting, but think I'm getting closer. Suggestions welcome.
Ed B.

I like to run about 3 to 4 minutes in this phase. On my set up I'd be worried that so long in the early roast uses up a lot of the sweetness to create woody/toasty Maillard compounds. Have you ever tried speeding this phase up a bit?

Thanks Jim,
Will give it a try. I won't cut back the variac at min.4 but will still try to go through first crack at about 440-45ET, so I will try to cut 2.5min from 297-388f BT. The rest staying the same it will be about a 14min. roast vs. 16.5.
Ed
Edited

another_jim wrote:I like to run about 3 to 4 minutes in this phase. On my set up I'd be worried that so long in the early roast uses up a lot of the sweetness to create woody/toasty Maillard compounds. Have you ever tried speeding this phase up a bit?

follow-up I tried cutting almost 2 mins off this phase with improved results! thanks Jim. 5min. was 305f and 9mins was 389f. ET was 463f at first crack and keep level until dump at 13:40 433f.
This weekend I will give it another try.
farm

Sounds like your roaster is running very sweet, since you are getting fast roasts with low ETs.