Drum Roasters - when do you change air; your theory? - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#11: Post by Peppersass »

Airflow is more problematic in my Quest M3. Generally speaking, when airflow increases so does RoR and when airflow decreases so does RoR. I have yet to see a situation where adding more airflow, even with max fan, causes RoR to decrease -- i.e., cools ET. If I start a roast with no fan, RoR declines very steeply after peak and gets way too low to carry the roast to/through FC. The result is usually baked beans or worse. Compensating with more heat usually requires pushing MET above 600F, a level that's too high for the M3, and makes it much harder to pull heat down to avoid a massive flick in FC.

Usually I start a roast at 30% fan, which is where it first starts to push some air, then increase to 40% when RoR peaks in order to prevent an otherwise steep decline. Then I'll increase to 50% about a minute before DE and leave it there. At the end of the roast I'll push it to 100% to get rid of chaff, though I've not seen an appreciable difference in the amount of chaff in the collector when I forget to do that. I've tried to control RoR with fan instead of heat, but that doesn't work as well as leaving fan at 50% from a minute before DE to close to drop and reducing heat 60-120 seconds before FC.

I believe the issue is due to the small, thin drum and relatively poor airflow in the Quest M3 (I can't use the tryer because removing it it has significant effect on airflow.) My drum has been modified with holes drilled around the circumference of the back end, and I've added the copper pipe mod. I'm sure these help airflow a lot, but can't fully compensate for the design of the roaster. I think it's a convection roaster with little or no conduction. I've been considering getting an M3s drum to improve airflow -- it appears to have a lot more holes in the drum.

Would other M3 or M3s owners agree?


#12: Post by false1001 »

Every time I roast a new bean I keep airflow constant on the first roast. On the second roast I try and fix my curves with just heat changes. If that proves difficult, I will throw in an airflow change or two, but I rarely get to that point, and when I do I rarely go above two changes to the airflow.

My general theory is you should be utilizing convection as much as possible from the very start of the roast. I have (very generally) found that when I find myself increasing fan speed during a roast I can get better results by just using the higher speed as my constant and decreasing heat input on the next roast, if that makes sense.


#13: Post by Vince_in_Montreal »

Last few roasts I have tried MCR's 30-50-70% air idea. One thing I "think" I am noticing is with the higher air flow at the end the crash and flick is far less peaky. (Although can also be due to the fact that I am running the roast hotter and hotter every batch trying to find my perfect gas setting (For ROR), maybe I'm getting to first crack with more momentum? Grain of salt with anything I have to say lol)

Have you watched this airflow video from MCR?

http://www.youtube.com/watch?v=QMygTpssuxE (Especially where they discuss the bell curve, using airflow to either heat or cool)


#14: Post by EddyQ »

Almico wrote:I adjust heat pretty much just as MCR suggests: 25% to DE, 50% to FC and 75% after FC. This seems to be working well.
I've pretty much followed the lower air first approach for quite some time with very good results. But recently, I wanted to shake up the theory a bit by reversing the order. Basically fast air first. The reason for doing this stemmed from some drum temp along with input air temp measurements. The thought was I could lower the input air (MET) peak temperatures while maintaining the same BT profile. This in theory would allow faster profiles with beans that normally would tip if pushed with high heat (pulp natual Brazil). The second reason for this is to have more stable temperatures, heat driven mostly by drum, during development. The risk is more smoke flavors.

So, I created a profile that would do this. It required a LOT more gas during dry times and then more drastic cuts of gas as you approach FC with lower air. It is tricky to nail the right heat at FC since air/gas is a less significant heat source, but with practice isn't too bad. During development my gas is almost off completely. So far, no smoke flavors and the coffee still tastes great ( I usually end roasts a bit past FC and never into second crack). I did several roasts which followed identical BT profiles and I could not tell the difference in the cup or with multiple espressos.

As for reduction of input air temperature. Yes, I think it came down at least 40 deg F at the peak spots during the roast, while maintaining the same BT profile. My drum temps seem to stay around the same temperature which I thought would would be higher. So I think the added air during ramp must be helping with heating the beans. I have not notice a difference in my exhaust air temperatures.

There is still a lot of experimenting to do here. I still have not run my Brazils really fast yet. But I will report back if this technique helps or not.

I am very hesitant to recommend this to folks. I may have had too low of airflow on my reference roasts all along and this technique may just conclude I needed more air at the beginning. But it is an interesting experiment if you are bored with normal routines.


#15: Post by Roasty »

Peppersass wrote: Would other M3 or M3s owners agree?
Interesting, I have the opposite experience with my Quest M3. I leave the hatch open (cutting off airflow) until DE and then shut the hatch and have 100% airflow until the end of the roast. Once I shut the hatch and airflow kicks in, my ROR begins to decrease faster.

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#16: Post by Marcelnl »

Brewzologist wrote:

While just a proxy, based on these test results I generally start off with no/low fan thru TP, then increase to medium thru FC, and then increase again later in FC to max cooling effect to clear chaff/smoke and help avoid flick.
I do basically the same as posted above and also without much theory behind it other than that I know I have to clear chaff around DE and smoke and chaff after FC. I up the fan to 50%(? of what) a minute or 2 prior to FC, the fact that my Huky is a perforated drum machine makes comparisons difficult iMO.
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#17: Post by CarefreeBuzzBuzz »

EddyQ wrote: But recently, I wanted to shake up the theory a bit by reversing the order.

One of the LA Kings lived on my street when I was growing up. His nickname was Eddie the Entertainer. @EddieQ, you now have that title.
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#18: Post by CarefreeBuzzBuzz »

Vince_in_Montreal wrote:Last few roasts I have tried MCR's 30-50-70% air idea. ....

Have you watched this airflow video from MCR?

http://www.youtube.com/watch?v=QMygTpssuxE (Especially where they discuss the bell curve, using airflow to either heat or cool)
I had not seen this follow up video to the one they did two years ago. The response on 16:10 gives a theory on why low air at the start. Allows the bean to warm and heat more evenly, so less tipping etc.

MCR units have powerful fans. At 23, Joe says there is no right answer but he only makes two changes. He starts at 30 (same as me, but goes to 70 at the start of yellow; these are MCR dial numbers). I start at 30 but don't increase until after FC usually to 55-60, so I think I will experiment with increasing air at start of yellow. I think that this will result in me dropping charge temps in the long run since I am happy with many of my roasts hitting FC at 8 to 8:30 min and dropping around 2 min later (sometimes 1:30 or up to 2:30). Testing will tell.

Also remember that more dense beans they transfer heat quicker so less heat or convective air, and the opposite for less dense beans.
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#19: Post by crunchybean »

I think playing with the fan has its benefits, it certainly can improve or worsen a roast. My real concern is knowing what the air is actually doing, and how when to use it. How hot is the air introduced, and what causal effect that will have on the beans?

We talk about air being a better mechanism to transfer heat to the beans, but is it? It may cover more area of a single bean but does the air transfer that energy to the bean. And how does the transference of heat from a metal plate differ from that of air. And more importantly when should that heat or brake be applied? When do the beans need it, is the real question. I think knowing the behavior of beans from different origins is the most important, when do they start running away in the roast? And when/where/what amount of heat do I need to apply when to get to Flavor City? Who has the map?

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#20: Post by hankua »

I think conventional thinking says the majority of heat transfer in a "Probat style" roaster is convection and a small percentage is conduction. What happens when the air is reduced to a minimum and heat is increased to a high/higher setting? Wouldn't the conduction/convection ratio change? Is that a significant or insignificant aspect of the charge to drying end segment?