So, as the title explains this has become my biggest foe in brewing. I started doing 1.5 gal batches to test new recipes and cut the cost of doing so. I adopted the BIAB method, although I'm using a three gallon cooler for my mash.
Anyway to the brew this morning. I preheated the cooler with Boiling water for 10 minutes. Dumped out the water right before adding the calculated 166 Strike water (1.02 gallons) for a rest at 151. This is for 4.27 lbs of grain. I doughed in and shut the cooler for five. Came back and the water was 161!. I stirred it around again and moved the thermometer to a couple of places and it read 155. So I start thinking I just need to let it set and let the temperature settle. So I closed it and came back in 10 minutes. This time it's back to 161. (I left the glass lab thermometer in the cooler). I stirred and checked a few more places. It was all 152 or 151, except one corner I had know I stirred up at 158.
What's going on? I have the lab thermometer submerged up to a point while it sits in the closed cooler. I bring it up so the tip is half the depth of the total mash when I check several places of the mash. Just frustrated. I don't think I've ever been able to hit a temp right on but maybe once. Is my calculation wrong (double checked it with a phone app and beer alchemy)? Or is my method of reading the temp wrong? Or something else that's not right?