I don't have a problem, I'd just like to understand this phenomenon a little better.
I mashed 20 LBS grain at 2 qt/lb. Fill 15 gallon stainless steel boilermaker with the approppriate water, raise to dough in temp, kill gas, add grains to Voile bag, place sensor in the top of the mash and stir vertically until the temp falls to the upper level of the mash range. Cover and walk away. No insulation on pot. After about 40 minutes the temp sensor indicates an INCREASE in temp of 4-5 degrees. The sensor is still on the top of the mash, right where I put it. I understand that as I mash the temp tends to stratify, but I would expect the increases to be offset by the loss at the perimeter of the pot. FYI i also did a mash on another batch with 10 lbs at 1.25 Qt/gallon in a 7.5 gallon SS turkey pot with no such increase. I had to add heat and stir at 45 minutes to offset the temp loss of about 4 degrees. Is this a real issue I should be addressing by stirring or should I just leave the larger mash alone and let it do its thing?