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Question on air flow in Heat gun
DanN
Guys,

This is my first post and I am excited to be part of this group!

I have been roasting coffee for the last 1.5 years and used all the below methods. HG/DB, ( heat gun dog bowl), flour sifter with heat gun and Hg/BM. Lately I watched Joe Marocco with Cafeimports do a video on Yemen coffee's and I wanted to introduce his philosophy in my roasting, though my setup is very rudimentary .

His advice was to use lots of conductive heat( during drying) and as the coffee's density reduced , he suggests to reduce conductive heat and introduce "air flow" aka convective heat. He says that using lot of convective heat in the beginning aids in removing moisture too early and the steam exiting out of the bean prevents heat entering the bean core.

So I now use the same concept of Heat gun dog bowl , but use a heavy terracota/clay pot instead of the dog bowl and a whisk. Can heat gun's air flow be used in place of air flow which Joe is talking about or the so called "air flow" which is being used in all the expensive roasters not the same as heat gun airflow. I preheat my clay pot to 300F and roast for the first 5-6 mts with NO heat gun and after yellow start using heat gun heat and use lot of heat gun heat during development and the results are ok. Coffee is all evenly roasted, but I feel its not sweet, though the development time is only 3 mts for a overall roast time of 12 mts. But one thing to admit is though this setup is very rudimentary , stove top heat and heat gun heat presents a setup which is super responsive. Just wanted some help and suggestions as I am ready to apply them and report back . Thanks !

Dan
 
oldgearhead
A typical heat gun blower is usually 20-25 cfm. I use a 1550 watt heat gun element in a fluid-bed roaster. I use the 40-60 cfm range of my two-stage, flow-through, vac motor to roast the coffee and 75 cfm to cool it. I roast, cool, and separate the chaff in one Bake-A-Round Pyrex tube...
I spent 10 years in the grain drying industry. Drying field corn from 28%M to 10%M is pretty much the same as drying wet-processed coffee to 8%M. Based on what I know the conduction-convection theory doesn't hold water (pun intended).
The time it takes to dry grain can be shortened by increasing either the air-temperature or the air-flow. In other words if your air temperature is above 100C you product will dry 20% quicker if you raise either the air-temperature or the air-flow by 20%
.
No oil on my beans...
 
DanN
Your explanation makes sense and packs a lot of wisdom.
So if I understand you correctly , both conductive and convective forms of heat are the same in removing moisture regardless of its coffee or corn and the coffee bean reacts to both forms of heat pretty much the same. Higher the air flow lesser the roast time and vice versa. My mistake was in assuming that applying convective heat initially during drying phase was detrimental as supposed to conductive heat and now your explanation makes lot of sense. Thanks a lot !Grin
 
oldgearhead
Another thing is your coffee beans may arrive somewhere between 5%
and 13% moisture. So home coffee drying is somewhat of a crap-shoot.
However, %moisture below 10% is more difficult to remove so that helps even things a bit.
What I do is determine a 'test weight'. When I get a new bag of beans I weigh a level-full quarter cup of them and classify them as normal, wet, or dry. I also have a capacitance-based moisture meter, but I don't use it very often. In general decaf green beans, and dry processed beans are dryer than wet-processed beans, and wet-processed beans are more predictable.
All this is is rather unimportant in my coffee roaster. What I see is the wetter beans may yellow and reach second-crack a bit later but as long as you have an ever-advancing rate-of-rise throughout the roast and are able to measure the after-first-crack time, %moisture is not a factor as long as you weigh your loads.
But my fluid-bed roaster is a much different beast than your roaster.
No oil on my beans...
 
DanN
Awesome OGH for your tips . Its good to have a moisture measuring device. Helps to plan in advance I guess. By the way, whats your roast profile for wet processed and dry processed bean, once you decide on the moisture content. I understand you keep your heating element constant and control the air flow to control the roast as you wish. So do you start with low or higher air flow during drying or in other words whats your style ...is it a slow start fast finish or a fast start slow finish ?
 
oldgearhead
Most roasts start around 60 cfm and end around 40 cfm. Basically its dictated by the ever decreasing weight of the beans as they loose moisture. That's the beauty of fluid-bed roasting...
No oil on my beans...
 
DanN
Thanks again OGH Grin. So looks like you start with low heat and then slowly cruise to high heat as in your setup bean temparature in inversely proportional to airflow.

But since the bean density is really highest during the very first phase of the roasting,its only logical to start with low airflow(high heat) and end with high airflow( low temp) during development ?. In other words as the bean mass looses weight, reduce heat by increasing airflow. Just was wondering what was the significance of your approach by starting with less heat as supposed to high heat ?
 
oldgearhead
I set the wattage of my heating element at the start of the roast based on the ambient temperature and my history of the bean type, but it's the nature of all heat gun elements to deliver lower temperature at higher air flow so I really have no choice. It takes 60 cfm to float the beans during drying and 40 cfm during finish. The roaster temperature applied to the beans is 400F at 60 cfm and 500F at 40 cfm. I keep the beans moving very slowly throughout and increase the blower speed slightly if I need to slow the roast.You see 100F via the blower control is a lot of control. However, I cannot raise the starting temperature above 400F or the beans won't flow and they will burn. In the past I would adjust the wattage 3 or 4 times during each roast, but I've learned it isn't necessary because coffee, like corn will dry just fine when fed +230F air and the beans respond quicker to the blower control ...By applying hot air reclaimed from the roast chamber to the blower inlet an ever-increasing rate-of-rise in temperature is assured...
No oil on my beans...
 
DanN
Thanks again OGH. Appreciate your insights as always . So looks like fluid bed roasting is strictly a slow start - fast finish approach that is bound by the design. But still the "100F" via blower control is indeed a lot of control. I understand that your bean temp is always on the rise, but was wondering about the rate of rise(ROR). I have heard that it should always decrease as the roast progresses for better taste. Since your setup calls for low heat at the start, I was wondering what was the case with your design.

By the way if I want to make something like yours, what would be the overall average cost and is there a design template I could use to start with ?
 
oldgearhead
DanN wrote:

>skip<
I understand that your bean temp is always on the rise, but was wondering about the rate of rise(ROR). I have heard that it should always decrease as the roast progresses for better taste. Since your setup calls for low heat at the start, I was wondering what was the case with your design.

By the way if I want to make something like yours, what would be the overall average cost and is there a design template I could use to start with ?

..as the temperature exceeds ambient by a greater degree it becomes harder to maintain a high RoR and the RoR naturally decreases as the roast progresses.
..$510 US and the entire build is here. Just ignore the chaff collector..
forum.homeroaster...ad_id=2207
No oil on my beans...
 
DanN
Thanks OGH for sharing all your expertise. Much appreciated. I shall use the link you provided to start building my own.Grin
 
oldgearhead
I typical roast is at 40CFM for 3 minutes, 50 CFM for 3 minutes, and 40 CFM for 6 minutes.
Most recent RC heat map attached:
oldgearhead attached the following image:
image1-1_1.jpg

No oil on my beans...
 
oldgearhead
oldgearhead wrote:

I typical roast is at 40CFM for 3 minutes, 50 CFM for 3 minutes, and 40 CFM for 6 minutes.
Most recent RC heat map attached:


OOOps! I meant:
0 to 3 minutes = 60 CFM
3 to 6 minutes = 50 CYM
6 to 12 minutes = 40 CFM
No oil on my beans...
 
DanN
OGH .. The more I converse with you , the more I learn about coffee roasting. ThumbsUp Thanks a lot .. So with heat remaining constant(predecided based on bean type and ambient temp) and reducing the CFM, you gradually increase your heat as you coast towards first crack. I also see from your graphs that the RoR is on the decline which is awesome.

*By the way what is your usual ratio between drying phase:maillard phase:first crack and roast development phase. Does these times change with bean type(soft or hard) ?
*Does your time "after" first crack within 20-25% of the total roast time or is it different? .
*Just wondering how long you roast after first crack as it looks like you stay on 40CFM starting at 6 minutes until end of roast and I wonder if you reduce/increase CFM after first crack completes or is there no change at all ?
*Whats your average payload per batch and whats your average mositure loss ?
 
oldgearhead
The whole thing is very, very simple. As noted the blower speed is reduced at the 3 and 6 minute marks. If I have detected more than one 'pop' at the 9 minute mark the blower speed is increased for a minute, if no 'pop' detected the blower speed is left as is was at the 6 minute mark.
The roast is usually stopped exactly 45 seconds after first crack. All loads are 440-460 grams depending on expansion. I always try to fill a quart mason jar with no left over.
Exception; I have identified a few dry-processed beans that produce chaff that is too large for my system to handle. With those beans my loads are only 350 grams.
Total roast times are almost always 12 minutes..Yellowing around 3-3.5 minute mark, flat-darkening about 4-5 minute mar. I want first crack at 10 minute mark..
Edited by oldgearhead on 10/02/2015 3:31 AM
No oil on my beans...
 
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DanN
Thanks again OGH...and I wonder how you manage the show with only 45sec development time. Is this like a Nordic roast and does it not taste too acidic ?.
Also why are you aiming for 10mt first crack time frame regardless of the bean varietal. I read on a japanese blog somewhere , a roaster suggest to go for 10mt first crack also . But I wonder why that was the case and whats your moisture loss . I bet its in the 11-14% range.
 
oldgearhead
OOps! I meant 90 seconds not 45. I haven't bothered to weigh post-roast for years.I really don't care what the moisture loss is..I think that my be important for high temperature roasters. I have a low-temperature roaster...
No oil on my beans...
 
DanN
Thanks OGH for all your tips. I shall try to see if it makes a difference in my cup. pouring
 
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