I have a 10 gallon boil kettle and was doing a BIAB with a required mash temp of 154 F and 13 lbs of grain. About 10 minutes into the mash, most of the kettle was reading 145-150 F, but one spot was 125 F and another spot was 170 F.

I gave it a good stir and moderared the heat continually. That helped even it out nicely. But, it made me wonder. When you measure the temp, are you interested in the temp smack dab in the middle of the kettle, off to the sides, the wort itself without any grain?

Also, the OG was right where it needed to be.


  • The general procedure we use in Australia, where BIAB apparently originated, is to use a well insulated mash vessel, and turn the heat OFF when strike temperature is reached. Feb 15, 2017 at 6:03
  • To continue! In normal ambient temperatures, the mash temperature will decrease by no more than 3 degrees over 60 minutes. If you add heat, the temperature will vary unless you have an exactly calibrated temperature control mechanism. Feb 15, 2017 at 9:23

2 Answers 2


I do normal all grain procedure and the situation is the same.

The biggest heat flux will be on outer diemeter of the mash tun. The better the insulation, the smaller the heat flux will be. Usually i have one ds18b20 sensor in the middle and second one on the side of the mash tun. Then i compare readings from both sensors and if the deviation is more then a few degrees i give it a stir.


I guess in the end having small variations between different parts of mash tun/kettle at mashing doesn't really matter. I'd bet $20 that taste difference between 1) single infusion just left alone, and 2) single infusion constantly stirred -- would not be statistically confirmed at blind tasting.

Having said all that, I use a small pump throughout the whole mashing process to recirculate wort in my BIAB(asket) setup, so that all dust/crumbles would be filtered by the grain bed. That also makes temperature moreless even, even though that wasn't the primary reason. I keep a temp probe right in the middle of the grain bed.

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