Temperature experiment


 
Tom_M

Tom_M

TVWBB Super Fan
I'm sure this has been done before, but I've never done it myself and thought I'd share what I found. I usually hang the Maverick ET-7probe that I'm using to measure the cooking chamber in the exhaust vent so that it's just kind if hanging in there. Tonight I smoked two small pork tenderloins and I set a block of wood with the probe inserted through a hole I drilled in it right in the center of the grate.

When they were done I took the probe that had been in the meat and hung it in the exhaust vent like I usually do. After about 10 minutes things had stabilized and I was surprised to see the one in the exhaust vent was reading 22 degrees higher than the one setting on the grate.

I let it go for a half hour and it stayed the same the whole time. I checked the thermometers before using them today and there was only 1 degree difference between them.

This was on the 18.5 WSM with the water pan removed. I assumed there would be a difference but I was surprised to see it was 20 degrees considering the water pan wasn't there to deflect the heat.

Now I'm thinking about all of the cooks I've done with the probe hanging in the vent giving me a reading that was around 20 degrees higher than what it actually was at grate level.

Anybody else ever compared the temps at these two spots and had similar results?
 
That's about my differential, 20-25 degrees from top vent to top grate. Vent vs top grate differential about the same with or without water.
Sunday cook was 275 top vent and 253-255 top grate with foiled pan.
I have also checked bottom grate vs top but that just gives me a headache since I can't control both.
Coming from an offset I have been used to stated temps being at cooking grate and also measured from end nearest firebox to far end. Everyone on here seems to use top vent temps when discussing temperature. Took some adjustment for me.

If you want to be confused further, measure top vs bottom using water and no water!
 
How did your lid probe temperature compare to the Weber mounted temperature indicator? I should add that I just got my 18.5" WSM and after doing a dry run to burn out the oils, I'm doing some cheap beef ribs tonight to check temperatures before I commit to do my Brisket tomorrow.
 
I have an older 18.5 WSM that didn't come with a factory installed thermometer. The factory mounted one on my 22.5 is usually about 25 degrees lower that what the one hanging in the vent shows, which I guess means it's pretty close to the grate temp.

Yeah, that's not confusing at all.
 
Thanks, that shows my reading was consistent with what you found.



Originally posted by J Hoke:
That's about my differential, 20-25 degrees from top vent to top grate. Vent vs top grate differential about the same with or without water.
Sunday cook was 275 top vent and 253-255 top grate with foiled pan.
I have also checked bottom grate vs top but that just gives me a headache since I can't control both.
Coming from an offset I have been used to stated temps being at cooking grate and also measured from end nearest firebox to far end. Everyone on here seems to use top vent temps when discussing temperature. Took some adjustment for me.

If you want to be confused further, measure top vs bottom using water and no water!
Click to expand...
 
Originally posted by Tom_M:
The factory mounted one on my 22.5 is usually about 25 degrees lower that what the one hanging in the vent shows, which I guess means it's pretty close to the grate temp.

Yeah, that's not confusing at all.
Click to expand...

Pretty much. Just goes to show that contrary to popular opinion, the Weber gauge isn't completely useless, after all. I'm smoking two 14lb+ briskets tomorrow and will just as likely not even mess with probes and wire, for my 22.5" OR the packers.
 
Yep, that is my experience too. Since I'm do lazy to do math while I cook, I just measure at the grate.
 
Originally posted by Jeff R:
Yep, that is my experience too. Since I'm do lazy to do math while I cook, I just measure at the grate.
Click to expand...

...but even if I remember to subtract the difference of 20* or so, my cooks usually go slower if I temp at the vent.
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ran an overnight pork butt last night. started out with full water pan (my unit leaks and gets too hot without it) digi Q II set at 250 with probe at the grate and a smoking jacket on. Didn't like the look of the smoke after a couple of hours so I pulled the jacket. The lid temp said 220 and the digi Q read 250. I stuck a thermometer thru the top vent and it read 250 so i assumed my factory therm had died. An hour later the factory lid therm and digi Q matched and stayed together all night. Cant explain that one.
 
If you measure temp at several different places on your wsm you will get several different values and will be on your way to insanity Measure in only one reasonable place, learn how to cook with that thermo location and you will turn out fine food and be able to enjoy your beer worry free
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I think you can only do that once you know the differentials between the various spots readings were taken.
 
There is no point in 'doing the math'. Neither is there anything to gain from temping in multiple places. It makes utterly no difference if there is a temp spread between grate and lid, or vent and lid, or vent and grate.

Pick one spot (I choose the vent because it is unaffected by water, waterpan, sand or ceramic, food quantity, air/heat deflection due to meat placement, etc., etc., all of which can cause temp differences in the cooker, especially at the grate) - pick one spot and just go with that. If you get used to temping at one spot you can simply work off the same spot every time. It does not matter if a different spot is 10 or 20 or 30 degrees different. Get used to one spot and forget about the notion of needing to know some actual, accurate cooktemp. It does not matter.
 
I disagree. If I wanted to cook ribs on the top grate at 230, how would I know what the grate temp was if all I ever used was the temp at the vent or the built in thermometer, if I had one? Once you know the differentials, I agree you don't have to keep monitoring at different locations.
 
I usually find the top vent runs 20° higher than the grate temp. I am moving towards just mesuring the vent temp since it is much easier to deal with than the hassle of a probe at grate level ie mods for probe placement, avoiding wire crimping, etc.
 
Probably just me, but I'm going to continue to monitor the top grate temp because that is where the meat is and the temp I am most interested in, not the top vent. Also, the Auber I just ordered will go on the top grate.
 
I disagree. If I wanted to cook ribs on the top grate at 230, how would I know what the grate temp was if all I ever used was the temp at the vent or the built in thermometer, if I had one? Once you know the differentials, I agree you don't have to keep monitoring at different locations.
Click to expand...

I don't intend for this to sound snarky so please don't take it that way. How did you decide that 230 degree grate temp is the way to go? I'm just curious because our goal is to cook ribs until they're tender. Cooking at X temp for X minutes works fine for cakes but not so much for ribs due to the variations in size and thickness. Many newcomers focus too much on time and temperature and forget to check for tenderness.
 
230-240 is the temp we use for our ribs. Some use higher, some lower. Those have worked best for us and the method we use.
Checking for tender comes at the end, after foiling.
 
230-240 is the temp we use for our ribs
Click to expand...
Or not. Just because a probe somewhere on the grate reads 230 does not mean you are cooking at 230. There is no stasis at grate level.

One can monitor anywhere one chooses, of course. I choose the lid vent (not an installed therm on the lid) because that location (as it is the exhaust) is unaffected by variations below.

Probe placement - its proximity to cold meat or to the edge of the grate - uneven ignition of fuel or smokewood, changes that occurs during cooking as meat shrinks, liquid temp and/or evaporative issues if the probe is dripped on - can affect grate probe temp, which is why I don't bother with it.
 
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