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Advance Charcoal Science thread


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I have been BBQing on Charcoal exclusively for almost a year now and have many questions I need answered to help take my cooking to the level.

 

Regarding the relationship between Charcoal and Oxygen:

1. What is exactly happening from a thermodynamics/energy standpoint when Oxygen is drawn into charcoal?

2. What happens when charcoal is "red hot", the vents get shuttered, and the oxygen in the trapped air is exhausted? Is there some store of oxygen or energy from some intermediate process left in the charcoal besides the energy already turned to heat?

3. At what point is the charcoal "out"? I will define "out" as: given unlimited non-forced airflow, not being able to generate sufficient heat to restart the chain reaction leading to redhot coals.

4. Assuming I want to get all the charcoal going, and then back off the temperature real low (say 180 for smoking Salmon), what happens when I start closing the vents? I notice that red hot coals will go out if over-choked. The same level of Choke is sufficient to carry on a chain reaction starting at lower temperatures! What is the technique to lower as fast as possible, but without choking out the coals?

 

Thanks! will be more questions based on these answers.

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I respectfully beg to differ that any of this will necessarily take your cooking to the next level. Except perhaps, avoiding #4 at all costs. Since you understand the concept of choking a fire, you know that it is counterproductive to get all of the lump lit solely for the purpose of choking it.

 

You start small fires for low temps and bigger fires for higher temps– setting the vents so that the amount of air drawn will maintain the target temp. Excess air will force temps upward. Insufficient air reduces the temp.

 

I just smoked 10 pounds of Salmon today for our Resurrection Sunday Fellowship. Got the fire up to 155° and it help there simply by opening the vents until the fire started to approach 140°ish and then reducing the vent openings as it crept up toware the 150's.

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1) C + O2 -> CO2, Heat of formation = -393.5 kJ/mol

 

2) Once the oxygen in a closed kamado is used up, it's gone until the vents or hinge are opened to allow more in. The thermal energy generated during combustion will in part stay in the unburned charcoal, serving as a source of the activation energy needed to begin combustion once oxygen is reintroduced, or until normal thermodynamic equilibrium is established with the surroundings (i.e. it cools down).

 

3) It's out once it no longer has the activation energy.

 

4) Answered above. Try not to overshoot.

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1 hour ago, MD_Ag said:

1) C + O2 -> CO2, Heat of formation = -393.5 kJ/mol

 

2) Once the oxygen in a closed kamado is used up, it's gone until the vents or hinge are opened to allow more in. The thermal energy generated during combustion will in part stay in the unburned charcoal, serving as a source of the activation energy needed to begin combustion once oxygen is reintroduced, or until normal thermodynamic equilibrium is established with the surroundings (i.e. it cools down).

 

3) It's out once it no longer has the activation energy.

 

4) Answered above. Try not to overshoot.

Activation energy.... I had so much trouble with that in college...

 

great explanations!

 

heat + fuel + oxygen. All are required. Remove one, fire stops. Add it back while the other two are ready to go, and there’s a strong likelihood that it’s coming back. 
 

As for temperature surfing, the best way to have good clean burn is to have a small amount of fuel burning hot instead of a lot of your fuel smouldering because it’s just barely getting air. Start in one spot, it will favour itself before spreading because it has to convert the solid fuel to gas before consuming it. 

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6 hours ago, CentralTexBBQ said:

I respectfully beg to differ that any of this will necessarily take your cooking to the next level. Except perhaps, avoiding #4 at all costs. Since you understand the concept of choking a fire, you know that it is counterproductive to get all of the lump lit solely for the purpose of choking it.

What about this idea I heard about charcoal burning off a nasty tasting smoke when first lit? and that once charcoal has turned red and then cooled down the bad stuff is already burnt out so its fine to just light and go? Ive mostly ignored this idea, but its in the back of my head to understand what was meant, and what circumstances it applies in.

 

4 hours ago, MD_Ag said:

3) It's out once it no longer has the activation energy.

What temperature approximately is the threshold for having charcoal light itself again when adding oxygen? obviously the temperature of the air makes a difference, so lets just say on an 80ish f degree day. Am I correct in assuming that there is a temperature below which something happens, but there is not enough energy to make the charcoal hotter, just generate some heat and prolong the cooldown time? or is it an activation/no activation equation without an in between?

 

3 hours ago, Webber_Grills said:

As for temperature surfing, the best way to have good clean burn is to have a small amount of fuel burning hot instead of a lot of your fuel smouldering because it’s just barely getting air. Start in one spot, it will favour itself before spreading because it has to convert the solid fuel to gas before consuming it. 

This sounds like it answers my question RE bad smoke above, its generated from a low burn temperature, not from anything in the charcoal that needs to be burned off?

 

Also, good explaination! The C + O2 form a gas, which spontaneously combusts in the presence of enough heat?

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6 hours ago, CeramicTool said:

Also, good explaination! The C + O2 form a gas, which spontaneously combusts in the presence of enough heat?

Nope. The C02 is the product of combustion. CO2 doesn't burn (at least at BBQ temperatures) - hence why it's used in fire extinguishers. It's the Carbon that is burning in the air.

 

 

 

 

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8 hours ago, CeramicTool said:

What about this idea I heard about charcoal burning off a nasty tasting smoke when first lit? and that once charcoal has turned red and then cooled down the bad stuff is already burnt out so its fine to just light and go? Ive mostly ignored this idea, but its in the back of my head to understand what was meant, and what circumstances it applies in.

 

What temperature approximately is the threshold for having charcoal light itself again when adding oxygen? obviously the temperature of the air makes a difference, so lets just say on an 80ish f degree day. Am I correct in assuming that there is a temperature below which something happens, but there is not enough energy to make the charcoal hotter, just generate some heat and prolong the cooldown time? or is it an activation/no activation equation without an in between?

 

This sounds like it answers my question RE bad smoke above, its generated from a low burn temperature, not from anything in the charcoal that needs to be burned off?

 

Also, good explaination! The C + O2 form a gas, which spontaneously combusts in the presence of enough heat?

Basically, but it’s just as important to understand which different compounds are burning because each is a part of the flavour profile.

 

If there is not enough air for the volume of fuel gas being released by the solid fuel, you are tasting those gasses. If it is burning efficiently, you are tasting the fuel “post burn” which is entirely different 

 

This here is a good deep dive

 

https://barbecuefaq.com/thin-blue-smoke/

 

 

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12 hours ago, Webber_Grills said:

This here is a good deep dive

 

https://barbecuefaq.com/thin-blue-smoke/

 

 

Very cool. More for Woods, but the science remains the same. Again, this only introduces more questions ;)

 

Like, I already own a Thermapen IR (and MK4), BUT, if I fork out for a high temp Thermoworks IR gun, is it as simple as pointing the gun at the charcoal? Does the white ash layer interfere with readings? I assume yes, the glowing red is the hottest part!?!?

 

I'm thinking this is a viable path to perfection. I've asked myself before the relationship of bottom damper to top damper, and come up retarded. 

 

This article articulates that there is a proper temperature:

 

"Thin blue smoke is the result of a equilibrium (fuel, oxygen, heat) being achieved and the burning process being deemed efficient. In this state the fuel in the woods carbonize or caramelize which results in thin blue smoke."

 

So Im thinking out loud and asking for rebuttals and corrections when I say: the airflow relationship between the top and bottom vents should be used to produce the best smoke flavor. Many positions can hold a grate temperature, but only one optimal position holds a grate temperature AND allows for optimal smoke.

 

Thoughts? This gets into another area entirely, airflow and dampers, which I really don't understand, so please school me by correcting my thoughts.

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2 minutes ago, CeramicTool said:

Very cool. More for Woods, but the science remains the same. Again, this only introduces more questions ;)

 

Like, I already own a Thermapen IR (and MK4), BUT, if I fork out for a high temp Thermoworks IR gun, is it as simple as pointing the gun at the charcoal? Does the white ash layer interfere with readings? I assume yes, the glowing red is the hottest part!?!?

 

I'm thinking this is a viable path to perfection. I've asked myself before the relationship of bottom damper to top damper, and come up retarded. 

 

This article articulates that there is a proper temperature:

 

"Thin blue smoke is the result of a equilibrium (fuel, oxygen, heat) being achieved and the burning process being deemed efficient. In this state the fuel in the woods carbonize or caramelize which results in thin blue smoke."

 

So Im thinking out loud and asking for rebuttals and corrections when I say: the airflow relationship between the top and bottom vents should be used to produce the best smoke flavor. Many positions can hold a grate temperature, but only one optimal position holds a grate temperature AND allows for optimal smoke.

 

Thoughts? This gets into another area entirely, airflow and dampers, which I really don't understand, so please school me by correcting my thoughts.

 

 

That's a rabbit hole I've found myself down many times, and definitely is going to be different between wood, charcoal kettle, Kamado...

 

My thoughts? Keep a small spot hot in the fire. Feed enough air on the intake for it to be clean but not enough to encourage it to spread. Keep the top damper as open as you can without getting too hot or closing the bottom completely (you still want an upwards flow) 

 

For me, that's open a knats testicle on the bottom and all the way open on top, but sometimes, I end up closing the top to 3/4 or so. Not the usual 1-finger many others recommend. I want my smoke to kiss the meat and get out without ever lingering. But that's a matter of taste.

 

You can go nuts measuring charcoal temp on an IR, but it would likely work (ish). I prefer to think concept, and see it as an explanation why a small hot fire is better than a larger cooler one - despite the overall pit temp being the same

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What are the pro's and cons of choking out completely a fire, and then heat gunning just a small spot in the middle to life again?

 

It seems like a pretty easy move, the ceramic is presoaked, and the most effective way to bring the temp down is to choke it off till dead, then open it up and let the heat escape. Then because the charcoal is already warm, a quick 30 seconds with the heatgun will have a small optimal fire going.

 

Is the smoke from the choke going to nastify my food? I figure not if its been cooking for a while dryish on the outside?

 

Practical example: Im thinking for things like Chicken wings where I want to get some cooking done around 350, and then drop the temp down to 200ish to let all the tendons and ligaments or whatever they are simmer and break down and flavor the wings while the moisture slowly leaves and I pull them off at the right consistency.

 

When first starting the Kamado, Im thinking with the proper application of timing I could just leave the BBQ open for a longer period of time, close it completely and let the heat dissipate into the ceramic while choking the fire. Then Light a small portion back, throw the meat on right away, hook the Signals and Billows up, and let them stabilize the temp where I want it. How fast could I be perfectly heat soaked and cooking with a method like this? With the added bonus of a smaller more efficient fire during the critical phase of smoking while there is a coating of moisture to absorb.

 

I guess the answer is how long does it take to use all the oxygen in a Big Joe? Because the ceramic is cool, it will suck out the heat from the charcoal for me after the oxygen disappears.

 

I'm going to try it to see how fast I can be heat soaked above 275 and Roasting a chicken at 275 grate temp. Perhaps a pointless endeavor, but will be fun and informative

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