TomC wrote:I've long since advocated that the most important part of roasting coffee is the first third of the profile. I can speak only anecdotally, but I strongly believe it has the greatest influence.

While I generally agree - I have found the initial stage of the roast to be extremely important for later stages, even make or break - in my experience, on my machine, it's slightly more complex. Our recent R&L in December demonstrated the importance of air flow, and I performed many experiments with various air settings. Mark found he could use one setting the whole way through, while on my perforated Huky, best results come from low air flow to start, moving to high air flow later on in the roast (for high/hard beans only).

This means that both A) setting the first-third heat transfer up properly, and B) getting the air flow right later in the roast, are both critical for me, on my roaster in particular. Either that or I have a grandiose sense of the importance of turning my air flow knob just so, which is entirely possible.

Those two learnings in particular have taken my roasting many, many steps ahead over the past year, and I owe a huge debt of gratitude to everyone who hosted and posted to a R&L in 2015, as well as to Dave and Joe at Mill City.

9Sbeans wrote:There are many possible reasons.

Two of professional roasters I know of using the same machine as mine don't turn off the gas completely after the charge.

Ask them why next time you see them and see if they respond as Joe did.

I would then turn the gas full on in a big single step instead of breaking it into many small increments so that I would have time packaging the previous batch of bean on the cooling tray.

Single setting vs many small increments. I turned a corner on my roasting when I realized that the initial correct setting permitted me to replicate a roast, time and time again. I always felt I could improve by tweaking (perfectionism can get you...). I now try to focus on that initial setting and leave it alone Dave! Continually adjusting the gas leads to sheer frustration if you nail a roast and then try to achieve that profile again.

Interesting discussion. I generally only turn gas way down but never off (like Joe I worry about relighting I guess) when doing a very small charge with a really hot drum. If it's one of the first 2 or 3 roasts I wouldn't necessarily turn it off. With large charge weights in my 5k (say 8-9 lbs) gas is wide open during charge and only gets turned down if needed.

TomC wrote:Pretty accurate summary of heat moving into beans, if I might say.

... I've long since advocated that the most important part of roasting coffee is the first third of the profile. I can speak only anecdotally, but I strongly believe it has the greatest influence. . .

Amen and amen. If drying phase is done incorrectly, you have pooched the roast. You may finish at same time and temp by catching up/slowing down but it won't produce the same quality cup as if the first 1/3 is spot-on. Data at min 3 is critical and then it is quick to adjust to bring it into line immediately if you are ahead/behind.

I use a mental formula at each minute tick time. I do it every roast, virtually every minute beginning at min 3:
a. 393* (-) current bean temp
b. Result of (a) above divided by Delta BT
c. Add that to current time to get projected first crack, realizing that Delta BT as a denominator is constantly decreasing, not remaining constant. Need to project out a couple of additional minutes for that variable.
d. As a secondary check, further into the roast, I look at end of drying time (mine are usually at 340*, not the 320* many use) and double check the projected time to first crack.

Metrics are great but (and it is a big but) the real check is eyes, nose and ears on the front of the roaster.

Joe Marocco talks a bit about this in an early "Coffee of the Month" video (from MillCityRoasters). It's the episode with the Huky500 roaster.
I'm following this thread with great interest, as every little piece of info builds in the coffee roasting puzzle.

I turn the the gas off or charge lower for the same reason; to have a consistent turning point using the equipment at hand. If the turning point is too low or too high, managing the roast profile becomes difficult.

Boldjava wrote:Amen and amen. If drying phase is done incorrectly, you have pooched the roast. You may finish at same time and temp by catching up/slowing down but it won't produce the same quality cup as if the first 1/3 is spot-on. Data at min 3 is critical and then it is quick to adjust to bring it into line immediately if you are ahead/behind.

I use a mental formula at each minute tick time. I do it every roast, virtually every minute beginning at min 3:
a. 393* (-) current bean temp
b. Result of (a) above divided by Delta BT
c. Add that to current time to get projected first crack, realizing that Delta BT as a denominator is constantly decreasing, not remaining constant. Need to project out a couple of additional minutes for that variable.
d. As a secondary check, further into the roast, I look at end of drying time (mine are usually at 340*, not the 320* many use) and double check the projected time to first crack.

Metrics are great but (and it is a big but) the real check is eyes, nose and ears on the front of the roaster.

You call end of dry at 340? Would that be at the onset of true tan rather than end of green/beginning of yellow? I have been under the impression it falls more in the 300-310 range?

It's all probe dependent, probe placement dependent, coffee density dependent, length of time in the drying phase dependent, etc. It's not something that can be nailed down with scientific accuracy. There's always moisture in the coffee, even at the end. And the surface can be tan/yellow and smell like it's "dry" with the centers still lagging behind.

TomC wrote:It's all probe dependent, probe placement dependent, coffee density dependent, length of time in the drying phase dependent, etc. It's not something that can be nailed down with scientific accuracy. There's always moisture in the coffee, even at the end. And the surface can be tan/yellow and smell like it's "dry" with the centers still lagging behind.

I hear what your saying, but he also stated that fc happens at 398ish for him, so if we are thinking rao percentages that is a pretty big difference from 300-340 with fc at 398 on his probe

See my earlier post. I want all green hues out of the coffee. It is not tan on my machine at 340*; it is all yellow. It doesn't matter if you call it at 320 or 340* so long as you call it consistently.

As Tom pointed out, probes are approximate, not lab precise. As those beans tumble, the readings are an approximation as bean mass, expelling gases, and air spacing are being measured. We can discuss 320* as academic point; I focus on my eye preference/practical consistency/no green hues and mark, probably later than most of you do. Roaster's preference.