I did my first BIAB and found the same thing... it was accurate on ramp up and boil, but it showed a 10 degree drop over about 15 minutes. I think that on a mash since there is no fluid movement, the area around the TC port cools and gives false reading since a good 1-1.5" of temp probe is in the TC port. Initially I freaked, but grabbed a extra stainless thermowell and tossed my inkbird probe in there. It showed 149° and held for the hour (I blanket wrapped the kettle)
I have one brew in this kettle and tried to treat is just like my old kettle:
- Full volume BIAB.
- Over heat the strike water by a few degrees, cut the flame and bag it.
- Wrap in reflectix insulation. This kettle gets two layers top and bottom (12" wide roll). Old kettle used to get 5 or 6 layers in a spiral.
- Dough in when the temp is right.
- Measure temp with an instant read handheld from an open lid (about 6" probe).
- Put the lid on with reflectix.
- Cover the whole thing with a moving blanket.
- Open up at 15 min to grab a sample for ph meter and cover back up.
I used to get a drop of 2-3 degrees F with the old kettle. No worries.
This brew, this kettle, I got a drop of 8 degrees F!
My thoughts are:
- less layers of reflectix
- major increase in headspace (8 gallon kettle to 12). basically no headspace to 4 gallons headspace.
- pump and 10' of silicone hose attached during mash is not insulated. it's enlightening to watch the hoses turn color after only 10 minutes into the mash.
I'm thinking it may not be worth chasing the insulation headspace losses, and just put that money into a RIMS tube.
I have an auber PID that I can borrow from my smoker for the RIMS.