HERMS: MLT Probe vs HERMS Return Probe

[BrewKaiser]

Just finished my first brew day on my new electric rig. I have both a temp probe in my MLT (about 3" from bottom of my Keggle) and a temp probe at the return of the HERMs into my MLT. I noticed that the two temps were consistently off from 1* to 2.5*.

I would think the MLT probe is the true mash temp, but the wort returning from the HERMs is at the intended mash temp.

I can see how using my MLT probe to control my HERMs heating element could lead to overshoot, but I'm second guessing what my true Mash temp is and trying to decide if I need to adjust in the future.

Only at the very end were they within 1* of each other.

So what does everyone else do and do others also see similar differences between MLT probes and HERMs return probes?

 

[stevehaun]

The temp in the mash is the mash temp. There will be a small gradient between the temp of wort entering the mash tun and the temp of the mash. Every system is different. You will learn your system and likely set your PID 1-3 degrees higher than your desired mash temp. Personally I control the temp of the wort as it enters the top of the mash tun. I measure the mash temp and the temp of the wort as it leaves the mash tun.

 

[Crazyeyes]

On my EHERMS system I adjust the temperature of the HLT to control the temperature of the MT, my temperature probe for my PID is in my HLT and I have an analog dial thermometer on my MT. I've got about a three degree differential between my HTL and my MT, if I want to mash at 150* I need to set PID to 153* to compensate for the heat loss in my system. I do on occasion when ramping the temperature of my mash, turn up the heat of the HLT up to 15* higher than desired to accelerate mash heating, but turn it back down when aproching the desired mash temp.

 

[BrunDog]

Just finished my first brew day on my new electric rig. I have both a temp probe in my MLT (about 3" from bottom of my Keggle) and a temp probe at the return of the HERMs into my MLT. I noticed that the two temps were consistently off from 1* to 2.5*.

I would think the MLT probe is the true mash temp, but the wort returning from the HERMs is at the intended mash temp.

I can see how using my MLT probe to control my HERMs heating element could lead to overshoot, but I'm second guessing what my true Mash temp is and trying to decide if I need to adjust in the future.

Only at the very end were they within 1* of each other.

So what does everyone else do and do others also see similar differences between MLT probes and HERMs return probes?

Welcome to the world of recirculation. Like stevehaun said, there is a gradient. The only way to mitigate it is to use an insulated vessel (you did) and recirculate as quickly as possible.

Technically, there HAS to be a gradient. There is heat transferring through the vessel, so that has to be replaced, and the only way it will be replaced is by the addition of heat. So you decide what your "real" temp is. Since the top of the grain bed is hotter than the bottom, there is a gradient, so I personally think it is best to average these two to get your "real" temp target.

My RIMS does the same thing. By the end of the mash period, they are about 0.5 - 1 degree apart. At the start they are 2.

 

[BrewKaiser]

Technically, there HAS to be a gradient. There is heat transferring through the vessel, so that has to be replaced, and the only way it will be replaced is by the addition of heat. So you decide what your "real" temp is. Since the top of the grain bed is hotter than the bottom, there is a gradient, so I personally think it is best to average these two to get your "real" temp target.

Kinda what I figured. Good to know that misery loves company

I'll adjust accordingly. I have my Mash Process currently programmed as:

Dough-in: PID Set to Mash Strike Temp. I re-circ strike water volume until both temps somewhat normalize at strike temp then dough in. Manual exit to next state

Vorlauf: PID set to mash temp. Exit after 30 sec

Check Mash Temp: PID to Mash Temp. Exit is checking if Temp is below Mash target then exit back to Vorlauf. If Temp is above then Exit to Mash 1.

Mash 1: PID at Mash temp. Exit to Mash 2 at end of 20 min timer
Mash 2: PID at Mash temp. Exit to Mash 3 at end of 20 min timer
Mash 3: PID at Mash temp. Exit to Mash Out at end of 20 min timer

Mash Out: PID at 168

Since I use my MLTRtn Temp probe to control the HEX element I'm thinking setting Vorlauf, ChkTemp, and Mash1 temps at 3* higher than intended Mash temp. Mash2 at 2* higher, and Mash 3 at 1*.

I'll have to give this a try and monitor on my next brew day.

Thanks again for the feedback and advice.

 

[BrunDog]

You find with automated brewing that you are constantly making adjustments. I made at least one programming change with each brew.