Yes I agree, but that would be the same regardless of "rates of change." They would need the same amount of time if you cycled the temperature up and down with dramatic and wonderful rates of change, or held it steady for a few minutes with no rates of change. You could even add acceleration and jerk and unnamed higher time differentials to the temperature's dance, without impressing the chlorogenic acid.

To me, it just sounds misleading to apply the term "rate of change" to any part of this discussion.

I would say that the rate of change has a secondary effect, not primary, which would be to build pressure. So maybe both theories (one and two) are true. If you were to take theory two without taking in account pressure, then it is sounds reasonable. But with the added factor of pressure in the mix, theory one sounds also reasonable.

There is also the issue of linearity. It could be that the conditions for maximum aroma are not linear across the profile but centered around the critical point of maximum pressure. In my opinion, the point would peak at around 30 seconds before the first crack pop to about a minute and a half after. This is so because the first cracks cannot be heard but with a humidity meter, you can see the humidity jumping at about 30 seconds before the first audible pop. I think that in this brief time of high pressure (~ 2+ minutes), a lot of non linear magic happens depending on the conditions. Then the issue of reducing acidity sounds linear and easier to control with exposure to high temperature and time.

Another issue is humidity. It seems that humidity is dried during the Dry Phase, but then is again created as a by product of the mid phase reactions. I am not sure if initial humidity should be left aiming at arriving at First Crack with enough pressure, or if the created mid phase humidity is enough.

Maybe I'll try different "profiles of the first crack" next weekend to see if I fish anything interesting.

Cheers

I recall from reading the chapter on Illy that during roasting two factors are important: the heat and vapor front. Generally the heat and vapor progress in the same direction, from the outside to the inside of the bean, and until all extracellular water becomes vapor, it then moves from inside to outside. I think this is what we hobbyists call the "drying phase". The intracellular water then becomes vapor, and this is what we hear as "first crack". My understanding after reading the chapter is, if heat is applied too quickly, the heat and vapor front will move in opposite direction, therefore undesirable.

Arpi wrote:It could be that the conditions for maximum aroma are not linear across the profile but centered around the critical point of maximum pressure. In my opinion, the point would peak at around 30 seconds before the first crack pop to about a minute and a half after. This is so because the first cracks cannot be heard but with a humidity meter, you can see the humidity jumping at about 30 seconds before the first audible pop. I think that in this brief time of high pressure (~ 2+ minutes), a lot of non linear magic happens depending on the conditions.

That is a good point

My experience is that I can't really control what is happening in those few minutes. On the PIDed P1, I've had to detune the controller, so it always runs a few degrees behind, in order for it not to go nuts in this period and rocket the ETs up an down in response to every pop. For a while, I even gave up on BT based control and just had the PID controller ramp up the ET. But this was somewhat annoying since it created up to two minute different roasts times for higher and lower density, or wet and dry beans. On the M3, I just back off the heat at 385F and hope it slows down in time.

So my practical experience is that if you are not backing off the heat, and holding the ET steady, or even bringing it down a tad, before the first crack starts, you'll end up finishing the roast much too fast. This advice is prepeated by every roaster I've ever known. If it turns out that an increased heat flux makes the beans happier during the first crack, you'll have a very tricky problem, unsolved as of now, designing a way to brake the roast subsequently without catastrophic temperature drops.

I've tasted the results of braking the roast after the first crack by using big ET drops, and it wasn't pretty. Whatever benefits more available energy during the first crack created were wiped away by the bad effect of the subsequent ET drop.

I have a custom 15lb rotating fluidized bed roaster, ala Neohaus Neotec /sivetz /etc. Regardless of coffee, I find that I absolutely must increase heat at 385F in order to maintain a steady increase in bean temperature, this increase in heat must be applied until about 410F before "putting on the brakes". I suspect moisture explains both yours and my own experiences here. Increased convection in a closed environment, and massive energy loss in my open environment.

As to differing flavors given the same time vs. bean surface temperature profile, in retrospect I actually have experienced that via adjusting airflow. "My bad." In the cup, I get harsh bitter notes at the lowest airflow required to maintain fluidity, increased clarity at "medium" airflow, then ultimately a flatter cup at the greatest airflow possible.

I agree on a proper decent of RoR coming into first. Since I have live RoR I can aim for a touch down speed at start of first while factoring my ET. For me stretching is most important pre and during 1st crack. Really as Jim mentioned my considerations for the finish start about 385f BT, 10-15 degrees before first.

I just did two trial roasts

El Salvador Santa Rita. 250 grams. SweetMarias. Roast 1



I tried to do a "power" First crack. The first crack was OK. It wasn't like machine gun but it was vivid. Other times I've done "machine gun" first crack but not this time.

El Salvador Santa Rita. 250 grams. SweetMarias. Roast 2



The first crack came out with the about the same sound intensity and speed as before, probably a little faster but it is hard to tell. I tried to see if reducing the dry end time made a difference (carrying more humidity to the first crack). I also increase the rate of change of BT towards the first crack for the purpose of building internal pressure. I could make the finish phase longer (and flatter) in future roasts.

I'll cup roast 1 and roast 2 tomorrow. In a previous roast, with semi flat first crack, these beans came out boring. Hope they gained some life.

Roast 2



Personal thoughts: In my most successful roasts, I set the power before reaching the first crack and then I let it adjust naturally by it itself (BT slowly curving down). That is, I don't touch the power after or at the first crack. I'll try that technique tomorrow and see if I get an improvement. The goal would be to find a balanced rate of change for BT before reaching the first crack and let it go solo till drop. I suspect that the big dips in deltaBT at first crack (by cutting back the power) may be sinking some important chemical reaction

Rafael
On the to graph, are you adding the heat gun to get the 40+ BT/min. between 8-9 mins, just before first? That's really fast for that point.

farmroast wrote:On the to graph, are you adding the heat gun to get the 40+ BT/min. between 8-9 mins, just before first? That's really fast for that point.

Yes. I was trying to do a "power first crack".

Just cupped both roast using the clever dripper. No defects of any kind. The characteristic that stands out at the firs sip is sweetness at the tip of the tongue. The second roast is sweeter but less savory. Little acidity on both (drip). The first roast tasted more coffeed than the first. That does not make it better.

The finish phase is about balancing chemical decomposition to fix the roast. My though about the length on the finish phase is that people use it to "kill" the bad acidity or remaining green notes. That is, it is used as a kind of fix. But at 2.5 minutes I don't see much of that here. So it would seen counter productive to me to use a longer finish phase for this particular mellow coffee.

I can feel a little more acidity in the second roast (faster), which is good for this coffee (drip). I also tried in espresso. But at this time, it has a pungent acidity that throws it off. It would probably get better with time but this coffee does not have the right notes for espresso. It is best for drip.

I cannot say that the first crack made much of a difference between these two roasts. I think the flavor difference here is more from a time exposure than a difference of the pressure. I did not feel that the original theory about building pressure manifested here. They were better roasts than before and I feel I added more value to the beans roasting them this way, but I did not discover the pressure jack pot, not yet

I'll try a different method next time around.

Cheers