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Big Joe Vent settings and charcoal burning.


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Hey everyone. I've had my KJ big joe for a couple of months now and while I'm having many successful cooks, there's a couple of issues I'm dealing with. 

 

1. Vent settings: I like to generally shoot for around 275 on most of my cooks. My last cook I shut down the vents around 200. The top vent was slightly before the first white line and the bottom vent was maybe finger width wide. The first 45 min it seemed to stabilize around 250 which was fine but then over the next 2 hours it increased up to 300+. This seems to be a common theme with me. Do I need less width in the bottom vent? Should I shut down even sooner and just always expect it to increase that much over a few hours? 

 

2. Charcoal management: I used to have a large BGE and charcoal would burn evenly and I could easily cook for 15+ hours. On the big joe, because of the wider bowl, I find when I light in the middle of the charcoal stack it will burn straight down and leave charcoal unlit on either side and can only get around 8-10 hours. Maybe I'm just not filling it up enough? Maybe I should light in 2 spots instead?

 

Any help would be appreciated. Thanks!

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There are so many variables involved in lighting and managing a fire that there is no simple answer.In my experience, there are times when there may be more humidity present in left over lump and it is more sluggish to start. Anyway, regarding the temps, you are just going to have to monitor a little more closer and adjust the vents as appropriate. Regarding charcoal- there is no reason why you should not have longer burns. I had similar type issues with a BJ Classic prior to obtaining a Kick Ash Basket. I was more inexperienced then and it propbably had to do the a combination of not sufficiently stirring the lump to remove ash before the cook and the presence of extremely small pieces of lump that we blocking the holes in the grate.

 

I am curious to know which model you have.

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20200723_161422.jpg

 

I have been playing around a LOT with using a smaller basket inside the grill to keep my charcoal together.  When charcoal is spread out over a wider area, it will not burn as efficiently.  In this photo, I am using a kick ash basket for the small Big Green Egg inside of my Kamado Joe Classic.  This definitely gives me a more efficient burn.  I also get the most efficient burn possible by using a fan controller.  That helps tremendously as well.

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44 minutes ago, CentralTexBBQ said:

There are so many variables involved in lighting and managing a fire that there is no simple answer.In my experience, there are times when there may be more humidity present in left over lump and it is more sluggish to start. Anyway, regarding the temps, you are just going to have to monitor a little more closer and adjust the vents as appropriate. Regarding charcoal- there is no reason why you should not have longer burns. I had similar type issues with a BJ Classic prior to obtaining a Kick Ash Basket. I was more inexperienced then and it propbably had to do the a combination of not sufficiently stirring the lump to remove ash before the cook and the presence of extremely small pieces of lump that we blocking the holes in the grate.

 

I am curious to know which model you have.

 

I have the Big Joe 2. It's possible the lump had some moisture to start and that's why it didn't get up to temp as quickly. I'm honestly probably just nitpicking because the food is coming out amazing, and that's the important thing. 

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8 minutes ago, John Setzler said:

20200723_161422.jpg

 

I have been playing around a LOT with using a smaller basket inside the grill to keep my charcoal together.  When charcoal is spread out over a wider area, it will not burn as efficiently.  In this photo, I am using a kick ash basket for the small Big Green Egg inside of my Kamado Joe Classic.  This definitely gives me a more efficient burn.  I also get the most efficient burn possible by using a fan controller.  That helps tremendously as well.

 

That's a good idea. I also thought about using the divider to concentrate the charcoal to one side only. Not sure if that's a good idea or not. I am getting a KJ basket tomorrow, so that could change things as well.

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Just now, StlBBQDan said:

 

That's a good idea. I also thought about using the divider to concentrate the charcoal to one side only. Not sure if that's a good idea or not. I am getting a KJ basket tomorrow, so that could change things as well.

 

The divider would work but it might unbalance the heat above the heat deflector a little.  It would not be a show stopper though.

 

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2 hours ago, John Setzler said:

I have been playing around a LOT with using a smaller basket inside the grill to keep my charcoal together.  When charcoal is spread out over a wider area, it will not burn as efficiently.  In this photo, I am using a kick ash basket for the small Big Green Egg inside of my Kamado Joe Classic.  This definitely gives me a more efficient burn.

 

This is a welcome modification, John, if it continues to provide the results you want without a major downside.  Please keep us apprised.

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4 hours ago, StlBBQDan said:

... the bottom vent was maybe finger width wide. ...

Which finger? I use fingers for both vents (old-style top). My index finger is about twice as wide as my pinkie finger, which is half as thick across the nail bed as it is at the joint.  "Half-pinkie" is the smallest I go when I'm looking for a smoke ring. 

 

I have used fingernails to get repeatable at smaller openings, but found that I need excess air to get a smoke ring. If I leave the top vent open and control temperature using the bottom vent, there's no smoke ring. 

 

4 hours ago, StlBBQDan said:

...  it seemed to stabilize around 250 which was fine but then over the next 2 hours it increased up to 300+. This seems to be a common theme with me.

Yep, I see this too. Over many cooks, I noticed where the vent settings eventually ended up, give-or-take a little. Now I put food on as soon as I have a mature fire, always use a water pan, and set the vents when I add food. That means I start the cook at lower temperature than I want long-term, but the cold food doesn't seem to care as long as it's stable after a couple hours. 

 

Eventually you will find the temperature starts to rise. The odds are the water pan will be dry, too. Keep it wet. Converting water to steam provides negative feedback to control the fire. 

 

Stay well,

Frank

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27 minutes ago, fbov said:

Which finger? I use fingers for both vents (old-style top). My index finger is about twice as wide as my pinkie finger, which is half as thick across the nail bed as it is at the joint.  "Half-pinkie" is the smallest I go when I'm looking for a smoke ring. 

 

I have used fingernails to get repeatable at smaller openings, but found that I need excess air to get a smoke ring. If I leave the top vent open and control temperature using the bottom vent, there's no smoke ring. 

 

Yep, I see this too. Over many cooks, I noticed where the vent settings eventually ended up, give-or-take a little. Now I put food on as soon as I have a mature fire, always use a water pan, and set the vents when I add food. That means I start the cook at lower temperature than I want long-term, but the cold food doesn't seem to care as long as it's stable after a couple hours. 

 

Eventually you will find the temperature starts to rise. The odds are the water pan will be dry, too. Keep it wet. Converting water to steam provides negative feedback to control the fire. 

 

Stay well,

Frank

Index finger. Probably about a 1/2 inch or so. That's for the bottom vent. Top was opened to just under first line. I cooked a brisket and a had a great smoke ring. Maybe I just have to be used to the KJ taking a few hours to fully come up to temp. 

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I'll add that in my experience there's not a nickels worth of difference between 250°F and 300°F.  Unless you've calibrated the dome thermometer, you really don't know what you're cooking at.  With that said, I try to smoke at 275°F dome temp, plus or minus 25°, with an uncalibrated thermometer.  As long as the temp holds steady and doesn't rise above 300°F I don't worry about it.

 

My vent settings on my Big Joe are nowhere near an inch open, top or bottom, for maintaining 275°F.  More like 1/8 inch top and bottom.

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On 7/27/2020 at 5:37 PM, pmillen said:

I don't get it.

We've been through this, I think. Water expands by a factor of 1,800 when converted to steam. This affects the top and bottom vent air flow. 

- a hotter fire makes more steam, which increases back-pressure at the lower vent. This reduces fresh air.

- a cooler fire makes less steam, reducing intake back-pressure. This increases fresh air. 

 

Negative feedback drives a response in the opposite direction of any change, increasing stability. A hotter fire makes more steam which reduces air to the fire causing it to make less heat which reduces the amount of steam allowing in more air to make the fire hotter. 

 

Stay well,

Frank

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8 hours ago, fbov said:

We've been through this, I think. Water expands by a factor of 1,800 when converted to steam. This affects the top and bottom vent air flow. 

- a hotter fire makes more steam, which increases back-pressure at the lower vent. This reduces fresh air.

- a cooler fire makes less steam, reducing intake back-pressure. This increases fresh air. 

 

Negative feedback drives a response in the opposite direction of any change, increasing stability. A hotter fire makes more steam which reduces air to the fire causing it to make less heat which reduces the amount of steam allowing in more air to make the fire hotter. 

 

Stay well,

Frank

 

And I wonder why I drink. LOL

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I wondered if the amount of steam being generated from a pan in a Kamado is enough to even make a difference to the air pressure beyond the expansion of gases due to burning the charcoal.

 

Does anyone have any idea how to test this or has this already been done?

 

OK, so I did some digging....

 

With the Classic II, I typically can fill the fire box with about 5 lbs of charcoal. 5 lbs of coal generates roughly 10 lbs of CO2. 1 lb of CO2 fits into a square of roughly 24.6". Therefore 5 lbs of lump produces 80 cubic feet of CO2. Since a 5 lb burn at 275 will generally take let's say 12-13 hours, the Kamado in theory should be throwing out 7 cubic feet/hour or 0.11 CFM of CO2 through a 1" square opening.

 

With these rates, I don't see why there should be any effective back pressure inside the Kamado due to steam since the top opening looks like it can easily handle the CFM. The flow is in reality higher due to the open vent at the bottom.

 

Sorry, hope I'm not rubbing anyone the wrong way, but my theory is that the heat rising out of the top vent is most likely pulling the pressure out of the Kamado faster than pressure can build in it unless the top is almost totally closed.

 

Cheers.

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