Conflicting temps between thermometers

Hey all,

I figured I'd post this in here since I'm an all grain brewer and I assume that part of the issue has to deal with the way I'm taking temps in my mashtun with all the grain added.

I'm using a converted keggle mashtun that has a thermometer built into the side wall. I'm currently only doing 4 gallons of water with my grain in the mashtun since I'm still using a 5 gallon brewkettle (and don't have much space if I sparge out into a 5 gallon pot). Part of the issue I have right now is that the thermometer doesn't quite reach the water when only 4 gallons are in the mashtun, so I generally rely on my digital thermometer to test the initial water temp before adding grain. However, once the grain is added I'm have an extremely difficult time getting accurate temperatures.

The digital thermometer seems to change drastically whenever I stir the grain. I can only assume that there are hot/cold pockets forming with the grain in the water. Furthermore, the digital thermometer is generally reading 10+ degrees compared to the analog thermometer built into the side of the mashtun. Basically, I'm not entirely sure which temp I should be reading. I generally ere on the side of caution and go with the digital since it's higher and I'm afraid of boiling the grain at too high a heat and releasing nasty tannins. I'm not entirely sure what I have to worry about if the grain is boiled slightly under 150 (the pot thermometer reads about 140).

I'm just curious if anyone else has run into this issue and has any suggestions for me. Thanks so much!

I'm not sure if you've already done this, but it may be a case where you need to calibrate both thermometers in boiling water (adjust them until they read the water boiling point for your elevation, since you're in CO). If the mashtun thermometer is removable there is usually a nut beneath the dial that the stem comes out of. A small wrench will allow you to calibrate the reading to your boiling point once you submerge it in the boiling water.

Calibrating the digital one to match your analog should at least eliminate any suspected variance due to your equipment.

When I mash in I take 5 readings from different areas in the bed and if there are large differences between them (i.e. hot/cold pockets) I'll stir it really well until they're within a couple of degrees of each other, then seal it up.

After you stir are you giving a rest to allow the temperatures to stabilize before checking temperature? After the stir there will be pockets of higher and lower temperatures. Let everything sit for a couple minutes before checking the temperature. Also, if you add heat it will take a couple minutes, even after the heat is cut off, for the temps to stabilize. The bottom will get hotter faster and that grain will have to exchange heat with other grain, even if you stir it.

The difference between thermometers is a different problem. Have you tried boiling plain water to see which reads closer to 212F (100C)? I have two probe thermometers. One came with my burner and the other I bought at my LHBS. The one that came with my fryer is regularly 10-15F lower than the other and reads a full boil as being 200F or so. Needless to say I don't use this one for the mash.

Hey guys, so sorry for the late reply here, very busy lately.

zzARzz said:

I'm not sure if you've already done this, but it may be a case where you need to calibrate both thermometers in boiling water (adjust them until they read the water boiling point for your elevation, since you're in CO). If the mashtun thermometer is removable there is usually a nut beneath the dial that the stem comes out of. A small wrench will allow you to calibrate the reading to your boiling point once you submerge it in the boiling water.

Calibrating the digital one to match your analog should at least eliminate any suspected variance due to your equipment.

When I mash in I take 5 readings from different areas in the bed and if there are large differences between them (i.e. hot/cold pockets) I'll stir it really well until they're within a couple of degrees of each other, then seal it up.

Click to expand...

I had not considered attempting to calibrate...actually I didn't even know that was a possibility. I'll definitely look into doing so though.

cluckk said:

After you stir are you giving a rest to allow the temperatures to stabilize before checking temperature? After the stir there will be pockets of higher and lower temperatures. Let everything sit for a couple minutes before checking the temperature. Also, if you add heat it will take a couple minutes, even after the heat is cut off, for the temps to stabilize. The bottom will get hotter faster and that grain will have to exchange heat with other grain, even if you stir it.

The difference between thermometers is a different problem. Have you tried boiling plain water to see which reads closer to 212F (100C)? I have two probe thermometers. One came with my burner and the other I bought at my LHBS. The one that came with my fryer is regularly 10-15F lower than the other and reads a full boil as being 200F or so. Needless to say I don't use this one for the mash.

Click to expand...

I wasn't totally sure what I should be doing in terms of stirring and trying to get an accurate reading. When I was doing my last mash I tired to sort of shove the thermometer down into the grain bed with the stirring spoon in order to try and get a more realistic reading. I'd let it sit there and everything seemed fine. However, after I'd stir it I'd see a huge spike in temp which gave me cause for concern that I might be overheating the mash. I'd kick the heat down a bit stir as much as possible then stick the probe back in and the temp seemed to level off. However I'd have to repeat this process every 10-15 minutes when I stirred and the spikes in temperature gave me cause for concern. I'm trying to find a way to get the right, constant amount of heat without such spikes.

I also have not attempted to test or calibrate the different thermometers yet based on my location. I'm guessing that I should probably do so. I'm also considering buying a new digital probe thermometer as the one I have is somewhat crappy and doesn't work well with the receiver that I have (allowing my to monitor temp without being near the mash if needed). Do you guys have any suggestions on a solid thermometer that you like to use?

When I had only one thermometer I always knew the temperature. Now that I have several, I never know!

Junkster said:

When I had only one thermometer I always knew the temperature. Now that I have several, I never know!

Click to expand...

Haha! I have had the same experience. So true!

I usually find it convenient to check and calibrate my thermometers when I'm making starters for brews I'll be doing in the next day or two. The water is boiling anyway and I usually don't have to adjust them, but it's nice to know on brew day there's one less eff-up to deal with.