Indirect heat/direct heat

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BRBBQ

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:idea:I always hear that indirect heat such as an offset smoker is the best for smoking/cooking. I think 225-250 degrees is 225-250. I use a UDS smoker and I think there's no differance in cooking temps (225 is 225]. If a offset smoker cooks at 225 degrees at the grate and my UDS cooks at 225 degrees at the grate, then whats the differance?
 
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So what you are telling me is that there is no difference if I am smoking above a bed of coals in my large Egg without a plate setter as there is with a plate setter? I may have to do a comparison analysis of side by side cooks on my 2 large eggs and see if it so. I am guessing the direct heat will give a crustier bark on the bottom of the meat but that might be good if it is a brisket!
I guess this would be considered food for thought!:biggrin:
 
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There are reasons that offset and indirect are used for smoking. It is used to do long low-temp cooks without drying out the meat and causing it to be shoe leather.

Let's try this on for size. Would you want to be cooked in the sun at 250 degrees for 18 hours and have the blistering or cooked in the shade at 250 degrees and still be moist & plump? (This is not meant as sarcasim just an example)
 
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Are you kidding, UDS cooks low and slow, if it got any slower I would have had to post this question yesterday. My question is whats the differance between 225 degree vs 225 degrees? Direct cookers (such as BGE or UDS or offset smoker). I say if the grate temps are the same then there's no differance. 225 degrees is 225 degrees.
 
225 degrees is 225 degrees.

But I know that a brisket and/or butt cooks faster in my UDS than my Bandera. Don't know the science behind it, but there is a difference.
 
trp1fox, I wrote this post because most articles say offsets are the best cookers since they are indirect heat. My opinion is 225 grate temp is 225 grate temp. Your right though the UDS cooks faster, I like my UDS. Easy cooking. I had an offset and I got tired of feeding the fire.
 
i really tried to answer this.. but cant...

All i know is 225 direct is very different than 225 ambient. One will have a direct radiant heat effect, the other is swirling air. A UDS is direct/radiant and will cook faster than the convection effect in an offset.

I am going to try to get Jim Minion here to see if he can answer.
 
BRBBQ said:
trp1fox, I wrote this post because most articles say offsets are the best cookers since they are indirect heat. My opinion is 225 grate temp is 225 grate temp. Your right though the UDS cooks faster, I like my UDS. Easy cooking. I had an offset and I got tired of feeding the fire.
Click to expand...

I think at that low of a temp the distance from the direct source may play a role as to cooking faster than drying out a piece of meat much like having a rottisserie.
Direct is more for grilling than smoking in my opinion.
 
BBQchef33 said:
All i know is 225 direct is very different than 225 ambient. One will have a direct radiant heat effect, the other is swirling air. A UDS is direct/radiant and will cook faster than the convection effect in an offset.
Click to expand...
Exactly right-

UDS is radiant and convection heat
Offset is just convection heat
 
I don't believe it's the temp in the smoker as you are saying. 250* is 250* but the size of the smoker and the environment created by the temp is what makes a difference. A UDS, cabinet smoker, or an egg creates a moister cooking atmosphere inside because it seals better which helps in the faster cooking than say in an offset which doesn't seal as well. The grate temp and air temp is 250* in both but to average 250* somewhere the temp has to be hotter and that will be right in front of the fire. Distance from the fire or offsetting from the fire eases the radiant effect and then the created environment takes over. JMHO
 
I want to play..........

Put a thermometer an inch above the coals - the air coming off of them is much hotter than 250. So, in a direct method, you have much hotter heat source rising up to the meat, then getting diffused and averaging out to 250 at the grate.

In the indirect, the diffusion occurs prior to the heat getting to the meat, so the air touching the meat is never above 250.

Maybe?
 
To add to this.. I have this thing i discovered years back playing with my WSM without a water pan trying to crispy chicken up on the top shelf. I called it a 'heat shadow'. Maybe a real name for it.. but thats how I described it.

Its the spot UNDER the meat at the grate.. its was about 20 degrees hotter than the ambient air in the pit and even more of a difference from the spot directly ABOVE the meat. Think like this.. A brisket set on a grate 18 inchs above the coals in a UDS is actually doing the same thing as as a diffuser plate or heat shield when it comes to something on a rack above it. Its trapping heat below it, and diffusing it around the sides and up. That heat shadow is trapped heat, and thats where the radiant heat effect comes in that cooks the meats faster.
 
I'm surprised no one has mentioned the effect of the meat dripping on the coals.

MA
 
There is that, the drippings and I think they add to the flavor but don't really affect the cooking time. My guess is that most offsets have big variances in the grate temp next to the firebox as compared to the far end at the exhaust stack. I know it was around 50* in my Bar B Chef and I could not even it out. I tried water pans below the cooking grate, one on top of the cooking grate next to the fire box, added a heat deflector to try and push more heat towards the far end before it rose to the meat.

Some offsets I am sure don't vary that much especially for the comp guys, but for the average backyard guy you gotta do alot of smokin to fix that problem. In the UDS I think the temps are not so varied. I also agree that having the meat 24" from the heat source must have something to do with it but not being a scientist don't know what it is but know it works.
 
You would be suprised at the difference in temps on a UDS. How are you measuring the temp? A gauge on the side is not what the temp is center grate. Too many variables. On a larger offset you have a bigger mass. On a drum that is 16 gauge metal a little breeze will affect the temp as it will rob radiant heet off the metal. The main reason the UDS cooks faster is it is running hotter than most think it is.
 
there are alot of factors going on in a UDS that make the temperature question hard to answer

keeping in mind that thermal energy can be transported via conduction, convection, radiation or by a combination thereof, along with effect of latent heat. the only factor that can be left out is pressure, since effectively the pressure is constant, with intake and exhaust in a fixed state ( air in = air out).

latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), – also called a phase transition.

With some moisture being driven out of the cooked food and fat rendering they both absorb the heat. fat or water dripping onto the coals once again absorb heat as they are vaporized. drippings and fat can also extinguish areas in the coals which can diminish the available heat for a period of time. fat can become fuel and enrich the available heat

your temp gage only reads the "dry bulb" heat in the chamber, while all the other forms of heat energy are left unmonitored. The moist air in the chamber is more like steam than the hot air your temp gage reads.

Radiant heat travels from the heat source to the target with out heating the air in between , your gage may register some of this radiant heat due to it's stem being a small "target" . the 'heat shadow' effect that BBQchef33 mentioned can be thought of like an eclipse. Radiant heat travels like a beam of light, so anything that is hidden from the beam will NOT receive radiant heat.

convection heat can be described like holding your hand in front of the heater vent in your car, blowing heated air transfers more heat to items they are passing by, your hand gets warmer faster than the car. Again your gage may not register this heat.

Conduction heat, well in its simplest form ... think frying pan. the food in the pan will absorb the heat directly conducted from the pan. if there is a source of heat below the pan the food will eventually reach the temp of the pan. in the UDS the conductor is the smoky moist air. this is what your gage reads.

Sooooooooo 225 degrees is NOT 225 degrees. its only the average temp of the conducted heat in the air plus a small amount of the radiant heat. the rest of heat energy is totally ignored by the temp gage.

and yes the convection heat source ( the air) is 225 but it conducts more heat energy. The Radiant heat may be more or less than 225 - but odds are good that it is higher.

Practical experiment - take a non radiant heater thats has a fan and directed it to a chair, then take a radiant heater and aim it at the same chair. try the heaters on with the fan and radiant heat going - then reconfigure to no radiant no fan - you will get the idea in a hurry
 
Good science lesson hook. Dispite what my Spam eating friend Larry said, heat is not heat. Anyone who has cooked in a convection oven knows this. The food will cook faster due to convection. Convection is when the heat is transfered by air or liquid. Think of your forced air heating system or your car. They use convection.

Radiation is what things like the sun does. You can feel the heat the most when you are in direct exposure to it.

Conduction happens when you actually touch something. Browning food in a fry pan is a good example. Only the stuff touching the pan browns.
 
I use both type but using any type barer betweeen the heat and the food isnt' actually direct heat.
 
Hook_Line_and_Sinker said:
there are alot of factors going on in a UDS that make the temperature question hard to answer

keeping in mind that thermal energy can be transported via conduction, convection, radiation or by a combination thereof, along with effect of latent heat. the only factor that can be left out is pressure, since effectively the pressure is constant, with intake and exhaust in a fixed state ( air in = air out).

latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), – also called a phase transition.

With some moisture being driven out of the cooked food and fat rendering they both absorb the heat. fat or water dripping onto the coals once again absorb heat as they are vaporized. drippings and fat can also extinguish areas in the coals which can diminish the available heat for a period of time. fat can become fuel and enrich the available heat

your temp gage only reads the "dry bulb" heat in the chamber, while all the other forms of heat energy are left unmonitored. The moist air in the chamber is more like steam than the hot air your temp gage reads.

Radiant heat travels from the heat source to the target with out heating the air in between , your gage may register some of this radiant heat due to it's stem being a small "target" . the 'heat shadow' effect that BBQchef33 mentioned can be thought of like an eclipse. Radiant heat travels like a beam of light, so anything that is hidden from the beam will NOT receive radiant heat.

convection heat can be described like holding your hand in front of the heater vent in your car, blowing heated air transfers more heat to items they are passing by, your hand gets warmer faster than the car. Again your gage may not register this heat.

Conduction heat, well in its simplest form ... think frying pan. the food in the pan will absorb the heat directly conducted from the pan. if there is a source of heat below the pan the food will eventually reach the temp of the pan. in the UDS the conductor is the smoky moist air. this is what your gage reads.

Sooooooooo 225 degrees is NOT 225 degrees. its only the average temp of the conducted heat in the air plus a small amount of the radiant heat. the rest of heat energy is totally ignored by the temp gage.

and yes the convection heat source ( the air) is 225 but it conducts more heat energy. The Radiant heat may be more or less than 225 - but odds are good that it is higher.

Practical experiment - take a non radiant heater thats has a fan and directed it to a chair, then take a radiant heater and aim it at the same chair. try the heaters on with the fan and radiant heat going - then reconfigure to no radiant no fan - you will get the idea in a hurry
Click to expand...


um

yeah...

thats what I meant. :biggrin:
:tongue:











(Great post there HLS)
 
Hook_Line_and_Sinker said:
there are alot of factors going on in a UDS that make the temperature question hard to answer

keeping in mind that thermal energy can be transported via conduction, convection, radiation or by a combination thereof, along with effect of latent heat. the only factor that can be left out is pressure, since effectively the pressure is constant, with intake and exhaust in a fixed state ( air in = air out)....
Click to expand...

WOW! I'm impressed. No, really I am.
 
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