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temperature drop / ramp up question

Hi everyone,

After a couple of my first cooks on my large BGE, I keep seem a behavior with the temperature I don't quite understanding and nothing I've searched in forums makes any mention of the behavior I see.

The rule of thumb seems to be to close down the vents to where you think it should be when within 25-50 degrees of target temp. Lets say I'm targeting a dome of 250 and I close the vents at 225.  Based on everything I've read, after closing the vents I would expect the temperate increase rate to decrease and climb slowly toward my target temp.  However what I see is that my temperature drops 100+ degrees first and then climbs back up but at a gradual pace.  I've see the same thing happen on a 375 target cook today where I closed down the vents to the approximate final location (and this time leaving the top open) and the temp still dropped from 325 down to under 200.

Is this the behavior others see or am I doing something the wrong way?  If this is normal, why wouldn't I just close the vents down at a higher temperature (25 degrees over target temp) to reduce the ramp up / stabilization time?

Comments

  • TjcoleyTjcoley Posts: 2,961
    Are you doing anything besides just closing down the vents, like putting in a platesetter or big hunk of meat?  Both of those can cause the drop you are describing.  
    __________________________________________
    It's not a science, it's an art. And it's flawed.
    - Camp Hill, PA
  • Tjcoley said:
    Are you doing anything besides just closing down the vents, like putting in a platesetter or big hunk of meat?  Both of those can cause the drop you are describing.  
    I put the plate setter in immediately after the coals are lit and then close the dome for the first time. I have not put in any meat yet and I'm closing it down to approximately an inch to inch & half opening.
  • lousubcaplousubcap Posts: 5,036
    @sppatel-I'm not seeing this first-hand so please factor that into the following:  When you first light the lump, once you shut the dome the thermo will see direct radiant heat from the burning lump; depending on the time for direct fire creation, at the time the dome is closed, this "direct cook" environment can significantly impact the dome thermo reading.  Open it again to insert the PS and other things (drip pan, grid etc) to create the indirect setup will drop the temp by many (few hundred degrees..) on the dome thermo. FWIW-and it may be nothing!
    Louisville
  • TjcoleyTjcoley Posts: 2,961
    sppatel said:
    Tjcoley said:
    Are you doing anything besides just closing down the vents, like putting in a platesetter or big hunk of meat?  Both of those can cause the drop you are describing.  
    I put the plate setter in immediately after the coals are lit and then close the dome for the first time. I have not put in any meat yet and I'm closing it down to approximately an inch to inch & half opening.
    How long after closing the dome are you seeing the temp going up and start closing the vents?  
    __________________________________________
    It's not a science, it's an art. And it's flawed.
    - Camp Hill, PA
  • Tjcoley said:
    sppatel said:
    Tjcoley said:
    Are you doing anything besides just closing down the vents, like putting in a platesetter or big hunk of meat?  Both of those can cause the drop you are describing.  
    I put the plate setter in immediately after the coals are lit and then close the dome for the first time. I have not put in any meat yet and I'm closing it down to approximately an inch to inch & half opening.
    How long after closing the dome are you seeing the temp going up and start closing the vents?  

    this is a rough guess ill time it exact tomorrow but temp starts to go up in about 2 min and then after that mabye 5-10 I close vents
  • twlangantwlangan Posts: 285
    I have had this happen. My theory on the cause is with the vents wide open, the fire is getting plenty of air and creating flames. The flames artificially raise the temp on the dome thermometer, causing you to want to close vents as you think you are approaching target temp. Your ceramic temps have not really come up close to your target temps though. You then cut the air flow down, causing the flames to die down and you are left with glowing embers that eventually will bring the Egg to the temp you want, but takes awhile. I mostly see this with pizza cooks where I am looking for high temps. With the bottom vent wide open and nothing on the top, one can look into the top and see flames rising around the platesetter and licking at the thermometer. The temp readout will be rather high. Due to my dough recipe, I want to limit temps to 6-700, so I will close the bottom vent down a little, causing flames to die down as well. I often see a considerable initial drop on the dial before it will recover again in time.
  • @twlangan thats interesting.  But I always wait for the flames to die and only have coals burning before I close the lid for the first time.  Next time I think I'm going to cut back the vent only 50% initially see the dome temp react (hopefully not drop as much), and then slowly close it down.
  • gdenbygdenby Posts: 4,229
    sppatel said:
    @twlangan thats interesting.  But I always wait for the flames to die and only have coals burning before I close the lid for the first time.  Next time I think I'm going to cut back the vent only 50% initially see the dome temp react (hopefully not drop as much), and then slowly close it down.
    From what you said, I'm supposing you may be using starter cubes. If so, here is a possible explanation. Something i noticed when I used starters was that at the point the stopped flaming, there was still quite a bit of the parafin soaked into nearby coals. Perhaps what is happening is that while the vents are wide open, that residue continues to burn, but when the vents are shut to low temperature settings, the fire is smothered, leaving only a small amount of lump fully kindled.

    Also, perhaps a modification of your method would produce more predictable results. When the dome therm reads 200, shut the vents half way. At 225, vents to 1/4. At 240, down to the slim openings that should get to 250. Its a bit fussy to do that, but it should get the fire where you want it.

    You can shut the vents to low temp settings immediately. You will be assured of a low temperature fire, but it can take quite awhile to get to temperature, and then an equal amount of time to burn off the "bad" smoke.
  • twlangantwlangan Posts: 285
    I don't use starter cubes. I use paper towels that my wife has saved, used for soaking up bacon grease. Same concept could apply though, I suppose.
  • Just a thank you to everyone for all the great input... ,hopefully by this time next year i'll be an expert and be able to provide guidance to others from my experiences as well.
  • mimaulermimauler Posts: 119
    We're not experts we just think we are.
  • Greeno55Greeno55 Posts: 348
    I don't use starter cubes often. Only when I want a small amount of coals for a low and slow. I tend to bounce back and forth between the electric starter and my overkill propane torch. But regardless of starter cubes or napkins, I've realized when the flames die down, there is still a ways to go before enough coals are burning to close the lid. Depending on what temperature I'm shooting for, I'll continue to leave the lid open another 5-10 minutes to let more lump ignite. Then as @twlangan points out, much of the temperature on the thermo is from the flames. I have had recent luck overshooting my temp by 50 or so degrees, then choke back and as the flames die down, the ceramic is closer to my desired tempt. Good luck!! I've been Egg'n since April, and while a lot of the learning curve is quick, I'm still figuring things out thanks in part to trial and error (and the odd fail), but more importantly, this forum.
    LBGE + others I hope - Sudbury, Ontario
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