Temperature Overshoot

[R L Bagwell]

At 0445 this morning, I put two pork butts (8 lbs and 7 lbs), as well as an 8 lb brisket flat, on my 22.5 WSM. I had previously loaded the charcoal chamber to the top with K briquettes, although I DID have a 3/4-full chimney of lump that I wanted to get rid of (I hate lump, BTW - apologies to you die-hard lump fans), so it went in first; additionally, I used 4 -5 chunks of hickory. Ambient temp was 79 degrees, RH was 78%. ZERO breeze.

I started the coals using the MM, adding 12 lit briquettes to the pile. My DigiQ (DQ)DX, which I have used successfully before, was set to 225. The temp on the DQ climbed to 88 degrees, and after about 10 minutes, would not budge, although the dome temp of my WSM indicated 220. Forgot to mention in my original post that I'm using a foiled clay pan.

I unplugged the pit probe from the device, and plugged it back in. The DQ temp then jumped up to 225, and continued to climb until it reached 275; it slowed its rise a bit, although it continued to climb until it reached 310. An oven thermometer that I had placed next to the pit probe read 305. As expected, the blower fan, which was - as usual - 50% closed, never came on again once the DQ temp read 225.

In an effort to reduce the temperature, I left the lid off until the DQ temp dropped to 225, and replaced it; additionally, I closed the top vent to just a crack open (it was set originally at 25% open, as in the past.) All bottom vents were closed, per DQ instructions.

At this writing (0938, EDST), the DQ temp is down to 264, and the dome temp reads 260.

While I doubt the use of that lump contributed to the overshoot, I'm thinking that I may have used too many lit coals to begin with. I KNOW the pit probe was connected correctly, so I'm unsure as to what caused THAT particular glitch.

Any thoughts/suggestions would be appreciated.

Regards,

Rooster

 

[Steve Roxberg]

Are you sure that your pit probe wasn't touching a peice of meat?

Or connecte to the grate so close to the meat that it was reading the temp of a cold grate.

Leaving the lid off for too long can also feed the fire.

I would have almost shut the top vent and waited till it went down.

 

[R L Bagwell]

Steve:

Yes, the pit probe was situated as such that it was suspended in the air next to, but not in contact with, the meat and/or the metal grate.

I agree with your point about the lid being off causing an increase in temp, but that tactic has worked for me in the past. Moreover, ALL vents were closed, the blower damper was closed further to about 25%, and as stated above, the top vent was all but closed. That famous WSM heat retention capability no doubt played a significant role in preventing a quicker temp decline!

I should note that the temp FINALLY reached 230 F around 1300 hours, and stayed that way (thanks, DigiQ) until around 1600, when the coals were close to being spent, dropping the pit temp rapidly to around 190 F with the fan constantly blowing .

I had hoped to make this my first "foil-less" effort, but considering the meat temps had reached only 190, and I really didn't care to go to the trouble of adding more charcoal, I decided to finish everything off in a 275 degree oven.

The butts and brisket turned out great, though - tender and juicy! I'm looking forward to trying out my new vacuum sealer this morning and freeze a considerable portion of the leftovers....

 

[KeithG]

Hey RL: Did your pit probe have a smoke film on it from previous uses that was not cleaned off? The temp difference was very big and it shouldn't have been this big even with a film on it. But I have noticed that my pit probe lags my meat probe (which has not been inserted in my meat while I let the WSM come up to temp....meat is not on yet) when I have a film on it after a couple of cooks. Probably this is not your case, but something to consider in the future. Boiling or very hot water removes the film very easily.

But it really sounds like you had a bad connection or a blip with your probe in your ATC. And with your fan blowing constantly without stopping, the lump caused a big overshoot. I have another thread on here about overshoots with my Stoker and it seems to happen due to the programming keeping the fan on constantly on an undershoot vice cycling it until your setpt is reached.

Good luck,
Kg

 

[R L Bagwell]

Keith:

I clean both probes pretty thoroughly after each use, so I don't feel that smoke film was a factor.

With respect to the continuous blowing of the fan, I may not have have clear, but that was due to the fact, I feel, that the pit temp had eventually - around 1600 hours or so - dropped to 190 F, so I think the blower was functioning properly in running continuously in its effort to "stoke" the coals in order to raise the pit temp back up to the original set point of 230 F.

At the onset, with a set point of 230 F, the fan came on as it should have, but at some point, it stopped blowing (I went inside for several minutes and returned) - even though the DQ pit temp read 88 F for a considerable period of time before I recognized there was a malfunction of some sort; it was at that point that I unplugged the pit temp probe from the device, and plugged it back in. Subsequently, the temps indicated on the DQ rose, and registered closer to the dome thermometer readings, as described in my first post.

Perhaps I did NOT have the plug fully inserted in the device as I thought, but I'm pretty sure that the apparent device malfunction was not what caused the overshoot. Next time, I'll do the MM using only 4-5 lit coals (no more nasty lump, either

) and see if that has any impact on the issue....

Thanks for your replies!

Regards,

Rooster

 

[KeithG]

Hey Rooster,

I use lump with my Stoker and for the most part, it works really well. One thing I have been doing is ramping up or down to get to my initial temp setpoint. I explained this in my thread. Basically what I do is if the temp is below my desired temp (say 250), then I increase my temp setpt incrementally, say 210. Once the ATC reaches it, turns the fan off, and the temp stops rising quickly, then I increase the setpt to 220 or 225 and repeat to 235 or 240, then on to 250. This allows the fan to shutdown and not so much air lighting too many coals. Conversely if the initial temp is above my desired temp, which happens alot on my high heat cooks then I catch the temp as it is falling and make the fan cycle on to stoke the coals and prevent them from going out with a long period of no fan. (if my temp is 400 and I am trying to get to 350, then I set the ATC for 385, let the fan cycle a couple of times, then drop the setpt to 375 and repeat, then to 365, then to 350)

When I started doing this a couple of cooks ago, it really helped eliminate my initial overshoot and subsequent big over and under shoots. And if I do get a big overshoot in the middle of the cook, then I do the same thing to catch it, which really prevents a big over and under cycle.

Hope this helps and good luck.

Kg