18" WSM Temp Question


 
J

JerryA

TVWBB Member
Does anybody know what the temp difference is between the top rack and bottom rack on an 18" WSM?
 
Experiment. While unscientific, I used a turkey fryer therm and tried to figure it out myself by sticking it in through the top vents and the hatch. In fact, I found that the bottom grate was about 10 degrees hotter than the top grate, with the bowl in place. Most folks tend to echo Dwain since heat slips up the sides and essentially projects from the top downward. Not for me, at least not yet.
 
B Stone said:
Experiment. While unscientific, I used a turkey fryer therm and tried to figure it out myself by sticking it in through the top vents and the hatch. In fact, I found that the bottom grate was about 10 degrees hotter than the top grate, with the bowl in place. Most folks tend to echo Dwain since heat slips up the sides and essentially projects from the top downward. Not for me, at least not yet.
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Did you check the temp with meat on both grates? Empty foiled pan or with sand or clay pot base in it?

Regardless of actual temps, I find that unless the bottom grate is so crowded that the circulation of the heat up the sides is blocked to some degree, meat on the top grate always gets done a bit sooner, apples to apples. So if I put the smaller butts on the bottom, it's all done pretty close to the same time, whether there's water, nothing, or even a 16" clay pot base in the pan. Clay pot bases or sand in the pan is certainly a dynamic that can change things, based on the weather and what's going on with the fire, though, and there are certainly posters that have had the opposite experience as myself with thermal mass in the pan.
 
I've found that the dome thermometer reads about 50F lower than the temperature at the top grate and the top grate is about 10F cooler than the bottom grate.
 
See, Jerry, you can't get a straight answer to this question. :) Seriously, I think the temperature difference varies depending on how you treat the water pan...with water, empty, filled with sand, clay plate, steel plate, gold bars, etc.
 
Chris Allingham said:
...Seriously, I think the temperature difference varies depending on how you treat the water pan...with water, empty, filled with sand, clay plate, steel plate, gold bars, etc.
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I don't measure both grate temps. However, if my dome gauge and grate temps with a clay plate in the pan are any indication, the differences between the top and bottom grates are anything but constant, at least with a clay plate in the pan.

I've been using a 16" clay plate in my 22" wsm pan a lot lately, doing a lot of day cooks where I can frequently and simultaneously observe both dome gauge and grate probe measurements. Let me tell ya, the difference between the two can be all over the place! Depending on how the fire is going or how I've been monkeying with the vents, the pan seems to be either absorbing heat or releasing it, and the dome is either being cooled by cold meat or a breeze, or then again, maybe it's being warmed by the sun. It's easier to see what going on with water or nothing in the pan.
 
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As soon as the weather clears, snowing now and for the next few days, I'm going to complicate this discussion even more.

The plan is to move the lower grate on my 22 up 3" so I can get an aluminum pan on the lower grate for water during the 1st 4 hours of cooking time on briskets and butts just to add some moisture. I don't use a dome thermometer, not cooking in the dome so really don't care what the temp is, and have removed them to install an extra vent in the dome. I foil the pan and use a 16" clay plate that has 2 rolls of foil under it to create more air space then foil over the plate to keep it clean.

It will be interesting to see how the water affects the differential between top and bottom grate.

When I still had a dome thermometer I noticed the temps were all over the place with water and without water and my cookers were protected from rain and wind.
 
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J Hoke said:
...The plan is to move the lower grate on my 22 up 3" so I can get an aluminum pan on the lower grate for water during the 1st 4 hours of cooking time on briskets and butts just to add some moisture. I don't use a dome thermometer, not cooking in the dome...
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J, It's funny the stuff we all think of. You want to move the lower grate up 3" and I'd like to move mine down 3" so I can smoke a dozen butts at a time. That would also help give me more room so that a support rack wouldn't have to be as high in the dome to hang ribs from. Too funny! I don't know if or when I'll ever get to do what I'm think of, but anyhow, that wouldn't be the first time someone "cooked in the dome". I read in the Harry Soo interview somewhere that he sometime smokes an extra brisket on a BGE extender rack. I'm thinking...a few extra thighs or rib tips maybe, but I have no idea how a decent sized brisket would fit up there in an 18! :confused:

Regards,
Dave
 
So true, we can't leave well enough alone.;)

I've quit trying to do what Harry does, I think he has special powers.
 
I've never ran therms or anything on my 18. I just go by what the meat tells me, and like Dave, stuff on the top grate has more color and finishes sooner. I double stack the top grate occasionally and find the same thing, the higher up you go the food has a darker color.
Now that's with an empty foiled pan.

Tim
 
I just did four spares on my 22.5.....two on the bottom and two on the top at 275 measured at the top grate with water in the pan. I foiled and rotated them at two hours and they came out the same...excellent. Total cook time...four hours.
 
Mike, have you tried the same cook, but without water in the pan?

Don't get me wrong. I think a water pan is great for ribs, but I think it loses it's advantages if foiling. First of all, foiling evens up the cook anyway, even more so than water. Also, I like the bark better and find it much easier to target temps without water, using less charcoal in the process. You might just give it a try if you haven't yet.
 
Dave...I've done butts and some baby backs using the clay saucer method. To be honest, I couldn't tell much difference. I did think the spares turned out better than the baby backs but they are two different cuts of meat. On the other hand, my son and I do a couple of comps a year and I took 2nd in ribs (spares) out of 75 last fall using my WSM for the first time in competition with water in the pan. I'll use the saucer for most home cooks but I think I'll stick with water for competions. Maybe I'm just supertitious.
 
Mike, regarding the differences between back ribs and spares, I'll just say that a LOT of MBN cooks use water AND foil for the babybacks. Like you say, they're different from spares, and more likely to dry out than with much less fat.

On the other hand, on the KCBS circuit, st Louie's are more often cooked, and quite often without water and foiled, as Harry Soo recommends. He and other cooks that use charcoal smokers like Ray Lampe, aka Dr. BBQ, sort of make a big deal over cooking without a water in the pan for the sake of better bark when it's time to foil. Whatever works for you, though, and a win is a win. There's also regional and personal preference differences. Have you seen how folks, particularly out west, are hanging ribs over charcoal in drums, like in a UDS or in a PBC, or PIT BARREL COOKER? They don't foil them, and cook them with the small end of the slab mere inches away from the coals for about four hours, and supposedly, someone recently beat Johnny Trigg's ribs like that!
 
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