Indirect heat/direct heat
 

: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?

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:

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)

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.

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.

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.

um

yeah...

thats what I meant. :biggrin:
:tongue:











(Great post there HLS)

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

While I agree with the following to some extent...

I think we are missing one very important point. Just how much charcoal is actually burning at any point in time? On my UDS, I've gotten as much as an 18 hour burn on roughly 8 - 10 pounds of lump. To me, that's saying that there cannot be all that much burning at any point and the heat is going to be disapated rather quickly throughout the cooker, unlike a grill where you go through 4 or 5 pounds in the span of say an hour.

To tell the truth, I've been known to go through 40 pounds of lump and a dozen logs on my Lang in 12 hours. Yes, it's a larger cooker and in order to keep the temps up in the cooking chamber, I need to have a good amount of heat in the fire box. Something we just don't need in a UDS.

Direct and indirect heat are radically different in terms of cooking. In this case 250 degrees direct is not the same as 250 degrees indirect.

3 types of heat,

conduction -hot solid/liquid contact, like oil, your cooking grates or water
radiant, think the warmth you feel from standing to the side of your camp fire
convection, hot air moving around the food

The above scenario of sitting in the sun is a perfect example. The air temp can be 90 degrees in and out of the shade, however your body will take up the extra radiant heat if you are sitting in the sun. Your food is the same way.

edit,
Hook line covered all of the above

the air in air theory if the heat is moving fast the meat will not asorbe as much heat the more heat the meat asorbe the better use of btu you are getting.

I suppose this smoker would be consider direct heat it work great but it have a baffle system betwenn fireboy and heat chamber with this much wood it will be on 275. Very good fuel /air ratio
http://i255.photobucket.com/albums/h...rstpork003.jpg
http://i255.photobucket.com/albums/h...trailer004.jpg
baffle /deflector over firebox heat come out in 4 points very even heat
http://i255.photobucket.com/albums/h...ing3-08009.jpg it think it a big green egg. I luck out on the baffle designe I suppose a blind hog find an acorn sometime

Convection
Radiant
Conduction
Fat Up
Fat Down
Slather
No Slather
Wood
Briquets
Lump
Pellets
Foil
No Foil
Blue Thermapen
Orange Thermapen
Green Thermapen
Egg
Off Set
UDS
Kettle

I used to think this was easy!

If it was easy, everybody would do it. :razz:

You forgot "K" orientation. :biggrin:

Up or Down? Great thread guys.

Paul

up and pointed to the left... ooppss your other left...

The important part is what color the offset is. But seriously I think back in the day it was just easier to control low and slow with an offset Now we've came up with ways to control the airflow better. I don't know why the UDS wasn't built sooner.

This is a really interesting and informative thread.

All I know is that every smoker I have ever cooked on had it's own personality.
Even a pair of WSMs or FECs may not match up.

As soon as I figured that personality out, I could cook good eats on it.
Never knew why and did not think about it.
Just different personalities I guess, and I was able to adapt.
I was lucky, I guess :oops:

TIM

Revived!!!!
 

BUMP

This is a farkin great read.
I absolutely LOVE this place. THIS is the kind of stuff I just love to find and learn here.


THIS PLACE ROCKS!!!!
:thumb::thumb::thumb::thumb::thumb::thumb:

I got more responce from this post then posting PICS of BBQ:tumbleweed:

Well I thank you for asking the question way back when. I learned about the difference between conduction, convection and radiant cooking a while back. Thought it would be a great way for newer folks to learn some of the "science" in this thing we call BBQ.

Just another way to show that there are SO many variables in cooking with fire and smoke. 225 isn't necessarily the same as 225.




The way I have learned to achieve good convection is to keep my exhaust vent(s) 100% open all the time. I control the airflow only through my intakes. What this does for me is instead of "choking" the cooker temp by limiting the airflow out (and thus airflow in), I control the intakes, thereby creating a constant "suction" of fresh oxygen to the fuel. I first learned this on my stick burner offset. Smallest fire possible, exhaust open and intakes cracked just enough to get the cook chamber where I wanted it. This creates the swirling, fresh smoke environment and keeps the air moving, thereby giving me convection, which also speeds up the cook.

Pretty wild that I had to literally start cooking with charcoal and wood outside to finally understand what really happens in a convection oven inside......:thumb: