Mash temp rising on it's own toward end of boil ?

[Hamner Brewhouse]

This struck me as odd and it is the first time I have encountered this. Here is my process and the observation. While heating the strike water I occasionally stir the water to get the super hot stuff mixed throughout to achieve a more uniform temp. At 144 F I stirred the water. When the temp reached 158 F I killed the flame and stirred for a minute and the water reached 159 F. Added my grains and mashed in at 152 F (room temp = 58). I put the kettle lid on and covered with blankets. The mash dropped to 151 F 3 minutes in. At 16 minutes in it dropped to 149 F. After 40 minutes I noticed the temp had increased to 150 F (room = 62). At 45 minutes it was at 151. 154 F at 51 minutes (removed blankets, room temp = 77 F). At 56 minutes the temp was 160 F (Removed lid). I was prepping stuff for the boil and ended up letting the mash go an extra 10 minutes. Ending mash temp = 170 F. WTH would cause this? I BIAB, so I don't "flame-on" to maintain mash temp.

 

[Herm brews]

How did your “room temp” rise almost 20 degrees F in less than an hour? That might provide a clue to your mash temperature increasing without flame.
If my room temp rose 20 degrees in under an hour, I would be looking to control that more than worrying about mashing grains.

 

[west1m]

Even with the house furnace raging the temp from 58° to 77° I doubt the mash temp would rise at all let alone to 170°.
Something with the temp probe?

 

[GFHomebrew]

Yep it's got to be a measurement error it just defies what is is physics?

 

[thunderwagn]

Are you stirring your mash? When I did biab, (and even now) I stir my mash about every 15-20 minutes. Biab, it really helps distribute and make even heat. One other thing, I used to use our electric stove top along with my HotRod brew stick just to add some heat and move things along quicker. I did find that if I left my pot on that burner, it would continue to heat, using up all that heat from the burner throwing my mash temps off. I don't know what you're using to heat your mash, but just throwing this out there.

 

[Bubba Wade]

Since the mash is not an exothermic reaction, there are only a couple of possibilities.

However, the first thing I would do is change the batteries in the temperature probe. As the battery voltage drops at the end of useful life, this will cause measurement drift.

Some of the other possibilities are all in violation of the 2nd law of thermodynamics, and that is one law you cannot break.

 

[thunderwagn]

Since the mash is not an exothermic reaction, there are only a couple of possibilities.

However, the first thing I would do is change the batteries in the temperature probe. As the battery voltage drops at the end of useful life, this will cause measurement drift.

Some of the other possibilities are all in violation of the 2nd law of thermodynamics, and that is one law you cannot break.

Damn engineers anyway!

 

[Hawkbox]

LIsa, in this house we obey the laws of thermodynamics!

Yeah something went wonky with your measurement or else you introduced extra heat. Weird and something to watch for more closely next time.

 

[Nosybear]

LIsa, in this house we obey the laws of thermodynamics!

Yeah something went wonky with your measurement or else you introduced extra heat. Weird and something to watch for more closely next time.

There's another possibility: If you didn't mix your mash well, you could have had "hot spots", local volumes of higher temperature that eventually cooled, warming the mash around them. I consider this to be the second most likely scenario, behind measurement error. To see if this is the issue, take the temperature at several locations and depths: The average is a good estimator of the "overall" temperature, the one the mash will tend toward. Another possibility is that you measured locally different temperatures each time: If you consider the odds of hitting a "high" temperature zone 50/50, the odds of you hitting one three times in a row are 1 in 8.

I've found my mashes are much more consistent now that I recirculate continually while mashing.

 

[Hawkbox]

I just stir the mash up real good, then move the thermometer around until it gives me the reading I want.

 

[Nosybear]

I just stir the mash up real good, then move the thermometer around until it gives me the reading I want.

That's one approach to controlling mash temperature....

 

[J A]

Without a heat source adding heat, you couldn't have gotten spontaneous temp rise in the mash tun.
You're not mentioning what type your temp probe is or whether you're using a different thermometer to determine room temp. If it's a dial-type, you can probably hold the probe stem and turn the body of it easily to change the temp reading. If it's digital, the battery may be weak or the sensor is wonky.
Maybe your ambient temp was raised by all the heating if you don't have any ventilation but it's unusual for a room temp to rise that much. Even if it did, there's not nearly enough thermal transfer to make it change the temp of the mass of the grain and water in the mash tun.

 

[Hamner Brewhouse]

My setup is a 10 gal Megapot with the thermowell at the 4 gal mark. I use a digital grill thermometer with 4 separate probes. One probe is in the thermowell checking mash temp. The other one that I was viewing room temp was on a ledge about 2 feet away from the kettle. Bubba Wade might be on to something with low batteries. After the boil when I was going to check temp of sample it kept turning off.

 

[west1m]

I think you would notice a room temp rise of 20°, I'd be sweating like a butcher!

 

[J A]

I use a digital grill thermometer with 4 separate probes.

Inkbird controllers are cheap and you can drop the probe right into the mash or boil pot. I have several that I've used for years and only once had a probe go bad. No batteries as they're plug-in but that might be a little unhandy in some set-ups.

 

[Hamner Brewhouse]

Inkbird controllers are cheap and you can drop the probe right into the mash or boil pot. I have several that I've used for years and only once had a probe go bad. No batteries as they're plug-in but that might be a little unhandy in some set-ups.

Interesting. I don't remember where I read it, probably Northern Brewer, that said not recommended for use above fermentation temps. I will have to revisit that as that would be a great idea.

 

[J A]

Interesting. I don't remember where I read it, probably Northern Brewer, that said not recommended for use above fermentation temps. I will have to revisit that as that would be a great idea.

I used one to control a hot-plate for recirculating mash in my 5 gallon set up. Works fine. And used one to check temp cooling down from flame-out to pitch temp.
Only time I had one go bad was with a sensor immersed in glycol below freezing. And that was just one of several that I've used that way.

 

[GFHomebrew]

Interesting. I don't remember where I read it, probably Northern Brewer, that said not recommended for use above fermentation temps. I will have to revisit that as that would be a great idea.

Yeah I've used in mash no probs even boil.

 

[Bubba Wade]

Interesting. I don't remember where I read it, probably Northern Brewer, that said not recommended for use above fermentation temps. I will have to revisit that as that would be a great idea.

The Inkbird controllers have slightly different ranges depending on the specific model. The ITC-308 (fairly common for homebrewing use) has a range from -40 to 248 F.