kPa throughout the roast

[alejandrooo]

Hi everyone, anxiously awaiting my first green beans to arrive today and thought I'd double check on one area still not clear to me as I get started.

When you hit your ideal charge temp and drop in the beans to start roast, at that point, what do people do as far as kPa until the TP?  Do they keep it low at 2-3kPa or off completely?  Mr. Li suggested waiting until around 100c/212f before then cranking up the heat to start the ascent towards first crack. 

Any tips on what people have seen work well on a perforated drum as far as what changes they make throughout roast to kPa would be much appreciated!  I'm sure there are many theories and would love to hear them all =)

[edtbjon]

For me (on a solid drum), I usually have the roaster slowly soar down to my intended charge temp with the burner closed. For a 350g charge I usually aim for 300F/150C charge temp and after charging the beans I put the exhaust back on (J model). At the 60sec mark I add a minimum exhaust fan and at 70sec I hit the burner "full charge" at 3.0-4.0kPa. I usually get my TP around 90-100sec. I stay at this "full blast" until about 3 min and I then gradually lower the heat throughout the roast, either by lowering the heat or speeding up the fan.
I do try to reduce the number of changes made during the roast. This makes it much more easy to repeat or fine-tune a roast. 3-5 changes of heat is acceptable, but if there are more changes, some of them could probably be condensed into single (larger) changes. Airflow more or less always follows a standard "low til DE, mid til FC, then high" pattern".
That basic receipe is about the same for a perforated drum, except that the charge temp would probably be about 190C/375F.

[harlancoffee]

Hey man! I've taken the liberty to copy a couple of your questions over our e-mail chain to answer them over here.

When you hit your ideal charge temp and drop in the beans to start roast, at that point, what do people do as far as kPa until the TP?

I typically raise my gas at 1:00 to about 75% of my max gas that I'll be using during the roast, and then 100% at TP.

What variables are you most closely watching/modifying during roast - the kPa with blue needle and then increasing airflow in second half especially? 

I closely watch my BT & ET rate of rises. I want to make sure I hit my ideal peak BT RoR and make sure it doesn't flatline or dip too low once maillard reactions begin happening. I also watch for spikes in my ET because that is a surefire indicator that my BT will respond the same way very shortly.

What is max kPa you get to and at what point during roast?

I'm not sure my gauge will correspond well with yours (Marshall and I have different readouts). However, I do look for around a 30 degrees F RoR/min (or 15F/30s) as my peak rate of rise. You can use that figure to roughly see where your gas settings will create solid thermal momentum that works for you. Nothing too fast, nothing too slow!

-Neil (Tweed Coffee)

[hankua]

Seems like the OP is using a perforated drum, maybe change the profile setting?

Good advice so far, I experimented early with maximum heat; scorching/tipping was not an issue with the solid drum.

If the goal is to have say @5:00 to end of drying using high heat; a lower turning point is one solution. High heat combined with longer EOD give the beans more time to absorb heat.

To accomplish this the charge temperature combined with gas/air settings should get one to an estimated target TP. TP too high, charge lower; TP too low charge higher. Turning off the gas should only be a last resort; say at the very end of the roast. Huky has little mass and uninsulated, if someone was turning the gas off after charge then it should be a regular practice.

Why is turning point important? That's the first indication where the roaster, thermocouple, and beans are in equilibrium. That's why I think it's good to have a target in mind, and work on getting close.