CarefreeBuzzBuzz wrote:Some of your questions are discussed by Joe Marrocco in the new air video linked above. His theory is beans needs less convection at the start so they heat evenly. He also discussed density near the end. I had not seen this video before and it was much more useful than the earlier one from a few years ago.

video

Yes I would like to use that video as a starting point but "new" it is not. It is also inaccurate. As much as I learned and bred familiarity of roasting through those (and others) videos, they don't pan out as well as they convey general roasting technique. Another stepping stone is the "Roast Along" by Derek DelaPaz (sp?) via MC's youtube. He conveys his ideas, and more importantly, the practice/and showing when to apply heat or when to back off the heat. How he roasts and for what purpose is more important (in this case). I don't care that he cannot tell me when lipid oxidation will yield a prime window for yada yada yada, blah blah blah. I understand thats well above the main home roasters "paygrade" and will loose more than gained. What I am asking is when do you apply air and for what purpose, for what bean, etc.

But going back to the inaccurate: how can a more uneven heating (conduction) heat beans more evenly than convection? It cant but conduction in a drum (without being fed accurately hot air) can add more energy into the beans, rather than the story which gets everyone to participate, which I guess is fine.

Again I will ask the question so it does not get lost:

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?

Roasty wrote: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.

Is your drum drilled. Any other mods? What diameter probe are you using and where is it placed?

hankua wrote: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?

I think that method (the soak?), would effect drying time/range but I do not know when to apply that method. Read: what bean do I use it on? Or is fan/air based on what type of flavor profile or mouthfeel I am trying to get?

-To All-

From what I've read its mainly three air adjustments. Is there any method to this madness. My questioning comes from my confusion. Do you make these heat adjustments for every bean, regardless of origin, altitude, density, varie-ty/tal? Or is it to follow Rao's BT declining ROR?

To reiterate that I thought the video was fine for conveying an idea, but I sit from a point of having to convert everything from a drum roaster to an air roaster so if it is not precise it makes it very confusing for me.

When I add more air it does not roast faster, I can get to a temperature faster, but speed of temperature (deltaT) becomes a critical variable than speed of air. How fast or slow temperature travels from ET into BT determines development. At different parts of the roast the same fan will end up doing different things. At the beginning of the roast it is penetrating, at the end it is buffering the beans from fluctuating too much in temp from its own chemical reactions. The largest sized bean that is the least dense will require the most air, and the lowest finish temp.

That is the main thrust of my Theory when it comes to air in roasting coffee.

P.s. I do not think you drum roasters consider 'loft' or drum speed enough when talking about air speed.

***for any confusion, I very much do like and appreciate all the Mill City/Cafe Imports Joe, Dave, et al., videos. I have learned a great deal from them and they are a must watch for a strong foundation in understanding the basic concepts.

However I am past the basics, I want to know more like how a yellow catuai feels vs a yellow bourbon vs pacamara vs SL##. And other things of the sort****

Yes, I apologize for the confusion but I don't think air should be talked about properly without the drum speed. Loft is a critical "variable" when it comes to convection/conduction ratio. Air wont effect the temp of the bean mass if it's only skimming the top of the mass and not through it...(y/n?)

I have been implementing some new ideas around airflow following on from this recent thread where I have been trying to imitate Alan's (Almico)
The Duke with a Brazil pulped natural. (Thanks Alan)
Roasting ain't easy - not even for Marshall Hance
For comparison, I posted some profiles shortly after Alan's which use a fixed fan setting.
Roasting ain't easy - not even for Marshall Hance

The following was 400g batch, drum speed is 64 RPM, highly modified Kaldi Classic - direct fire.
By starting with the fan OFF and hopper left open I am getting quite strong natural convection current out the top.
Depending on the bean, the sound of the tumbling changes as they start to swell and release some moisture (3:30 - 4:00) and the delta BT will start to drop off quite quickly.Timing when to turn the fan on while still keeping hopper open is a fun game (not), but If I get it just right I can keep the delta BT relatively smooth. Just after EOD the hopper is closed for full air flow, which is the fixed setting I was using previoulsy.

This is by far the best coffee I have roasted to date, its sweet, full and rounded cup with no detectable roast defects. Makes my previous roasts seem weak and wispy, a bit undeveloped and baked.

I have also been using small air roaster Kaffelogic over last 6 months and have put through around 500 roasts. Nothing it does seems directly comparable or even useful to a drum roaster and vice versa. Sure, someone with far more experience may be able to get something which is a close match and possibly not detected in a blind cupping, but how that happens with regards to airflow appears to be in another realm entirely.

I will be sticking with higher conduction start for drum roasts, it's just too tasty.

interesting approach, today I tried a couple of batches using that method. Too early to tell, initial results seem good, taste will tell in a few days.
I will have to tinker with the procedure as my Huky with perforated drum obviously differs from your roaster. Flavors during the roast were clear and clean.

just ignore the last bit and the name imprinted on top, I never get around to end the log timely
This bean has a tendency to flick like few I've roasted before.