Mash Temp Spike question

Howdy,

I have a quick question... I just started AG and I used my new 51000 BTU 30 quart turkey fryer the other day for my mash. When I was monitoring my temps everything seemed fined and then bam the temp would spike like 15F. I would stir it and then it would drop quickly. Anyone have any idea on why this happens.

The mash consisted of:
11.25 lbs grain
14.63 L of water
Mash ratio 1.3
Absorption loss 5.11 Liters

I Was shooting for about 154F for 60 min. I dropped the flame down to almost off when I got it to the strike temp of about 159F. Added the grain which dropped it about 6F. Everything was good for about 15 minutes but it was a little low so I increased the flame to bring it up a bit but it didn't change much and them BAM temp spike to almost 170F! Did it just store the heat at the bottom of the mash and then it spiked when it hit my thermometer? I'm using the 12" dial thermometer that came with the fryer. Here is a picture of the mash I was doing at the time and my fryer:

With direct fired MLTs you get a lot of temperature deviation through the mash b/c the bottom is getting heated a lot faster than the top, you really need to stir a lot when heating to maintain even temperatures, you will get more consistent readings that way. The spikes you are seeing are just local temperature fluctuations from one area to another.

cool thanks... next time I'll try and keep the temp changes to small increments and stir it more frequently to ensure a good reading. Hopefully all is good with this batch. We will see in a month

Get a frictionless themometer.

How thermonmeters work: heat makes stuff expand. Mercury (silver colored) and alcohol (red, blue) thermometers are direct reading, as the fluid expands, it gets bigger in the tube. You read it. Dial thermometers use the same expansion to push a piston up the tube. The piston has a spiral on the upper end. The rising spiral turns the needle. Accuracy falls if there is any stickeness in the mechanism. Plus, mechanisms have some free clearances that allow the needle to lag the actual temp. Good dial thermos work acceptibly, cheap ones are crap.

also once you hit the right temp, wrap your kettle in a heavy blanket, or towels, or sleping bag to reduce heat loss. Keeping mash temps with direct heat is a PITA, thats why I got a cooler system now.