EHERMS Mash temp variation

[don_bran321]

Since ive been brewing with my Eherms system I've been faced with the difficult decision of which Tempurature reading I should trust in my MLT.

I have calibrated all of my probes and thermometers to make sure they read the same. (they do)

I have the temp probe in a 1/2 T fitting in my sparge arm and I have a thermometer through the side of the MLT.

When I'm brewing the thermometer always reads a good 10 degrees colder than the probe does. Ex: Probe 150ded thermometer 140deg.

Does anyone else run into this? And which one should I trust. I've been going mby the probe reading for fear of over shooting my mash temp.

 

[303Dan]

My eHERMS setup sounds similar to yours in terms of where you're monitoring mash temp. I have a thermometer in the Mash Tun like you do and my PID probe is at the output of the HERMS coil, just a small distance before where you have yours. During my mash, the temperature differential between those two points is 1-2 degrees F on my system. Everyone's temp loss will be a little different, but 10 degrees is an awful lot.

But if I'm shooting for a mash temp of 152, I'm looking the the thermometer in the mash tun to have that reading, while the probe at the HERMS exit would read 153-154.

How did you calibrate your thermometers and probes? Do you have one thermometer that you trust that you calibrate everything off of? Did you calibrate them in the specific range of mash temps? Or did you calibrate it closer to room temp or boiling? Sometimes thermometers can be accurate in a certain range, but not in others.

Are you constantly recirculating through the HERMS coil? If so, how fast is your flow? You definitely have to find the right balance there. Fast enough that you're recirculating the entire volume of the mash tun often enough to hold temperature, but not so fast that you're compressing the grain bed or not getting an efficient/consistent temperature transfer from the HERMS tank.

Hope I can help. My system is pretty darn consistent in that the mash temp stabilizes at 2 degrees F lower than I set my PID controller for.

If you have any questions about how I have mine set up, let me know.

Good Luck!

 

[Vale71]

Are your tuns insulated?
I have a RIMS system (same difference ) with two probes, one at the inlent of the sparge arm and one at the outlet of the mash tun. The first reads the temperature after the wort has gone through the RIMS element and is the value that is fed to the PID function, the second one reads the temperature of the wort been pulled from the bottom of the tun and is also used as a conditional value for moving the program forward to the next step.
Long story short, once target temperature is achieved and the system has stabilized the difference between probe 1 and probe 2 is no greater than a few tenths of a degree, and that's with a non-insulated tun (15 gal SSB BrewKettle). Your difference of a whopping 10°F is really out of place and cannot be explained with average heat loss alone.
Is it possible you could have severe channeling and thus you are basically circulating a smaller portion of wort, while most of is trapped in the grain bed and only very slowly warms up to target temp?
Which probe feeds the control logic in your setup? Am I correct in assuming that you control temperature by turning the pump on and off?

 

[don_bran321]

To test the calibration of my probes and thermometer I warmed up some water to about 140 degrees and placed them all in at once and read the difference between them. They were all within 1 degree of each other. (my probe, mash tun thermometer, and an external brewing thermometer)
To me that was enough to say they were all reading correctly.

My mash tun is a 10gal Home depot water cooler so definitely insulated.

My pump on the other hand is a 12v cheapo solar panel pump. I'm wondering if maybe it's not circulating fast enough. I've been meaning to get a bigger one anyway

 

[Vale71]

How are you driving the recirculating pump? More precisely, when does it get turned off?

 

[nawagner85]

I had a similar problem with my setup, not 10F but closer to 5F.

My mlt is a 10 gal kettle with reflectix or whatever it's called. Recirculation rate and mlt mixing accounted for some, but not all. Controlling on HERMS outputs caused bulk mash temp to be low by about 5F. Controlling on HLT, bulk mlt temp was about 7F low. Controlling on bulk mlt temp had way too much lag and I was never able to get stables temps. Ultimately I wrote a cascading PID on raspberry pi the inner loop controlling HLT temp, and outer loop controlling hlt setpoint based on mlt bulk temperature with some output clamping. I've brewed 3 batches with the new control and have had really stable temps in the mlt right on setpoint.

 

[don_bran321]

How are you driving the recirculating pump? More precisely, when does it get turned off?

I never turn it off. I mash in, wait 5 min for the grain to settle then recirculate the full 60 minutes.

 

[don_bran321]

I never turn it off. I mash in, wait 5 min for the grain to settle then recirculate the full 60 minutes.

Because the pump is so small I leave all the valve fully open so it's as fast as it is going to go

 

[nawagner85]

Because the pump is so small I leave all the valve fully open so it's as fast as it is going to go

One option is to have your HLT setpoint higher by ~5-10F of your mash set point and then use MLT probe to turn on and off your pump. This is similar to steam injection on commercial setups.

 

[day_trippr]

Downside with ^that^ strategy is one may bring the wort in the hex close to a rapid denaturing temperature.

I have a 24" stemmed digital thermometer for doing random mash temperature checks and the one thing it revealed was the higher the pump rate the more consistent mash temperature. I basically run my recirculation pump as fast as I can without slamming the mash shut.

Also, depending on the lautering device used, don't ignore channeling during recirculation causing large cool areas, something testing with just water can't reveal...

Cheers!

 

[303Dan]

Because the pump is so small I leave all the valve fully open so it's as fast as it is going to go

The fact that your wort is entering the mash tun at 10 degrees higher than the mash as a whole, to me, says one or more of these things:
1. Flow rate is too slow. Hard to believe this is the whole problem, though, unless it's just barely trickling back into your mash tun
2. Somehow your temperature reading is off at one of the probes
3. Temperature striation in the mash, possibly due to severe channeling.

I'm actually leaning towards 3 at this point. I just can't believe your pump would be so slow that you'd have that big of a differential, especially when your probe is at the very end of the HERMS loop and reading what it does. What exactly are you using as a false bottom in your mash tun? Does the probe of your mash tun thermometer usually reside within the grain bed or in the wort above the grain bed? If you run a full mash simulation without the grain, does your temperature differential stay the same or get better?

 

[Vale71]

Fully concur. I was assuming his control logic could be driving the pump and shutting it off prematurely, which would be a fairly obvious reason but anybody can overlook even the simplest things when dealing with complex systems. We've all been there and done that at some point...
As it is I also favor the severe channeling hypotesis. Most of the wort is probably running down the sides of the tun and the yeast cake is not warming up to target temp.

 

[don_bran321]

One option is to have your HLT setpoint higher by ~5-10F of your mash set point and then use MLT probe to turn on and off your pump. This is similar to steam injection on commercial setups.

This is an interesting idea. I don't think I can pull it off with my setup though.

 

[don_bran321]

The fact that your wort is entering the mash tun at 10 degrees higher than the mash as a whole, to me, says one or more of these things:
1. Flow rate is too slow. Hard to believe this is the whole problem, though, unless it's just barely trickling back into your mash tun
2. Somehow your temperature reading is off at one of the probes
3. Temperature striation in the mash, possibly due to severe channeling.

I'm actually leaning towards 3 at this point. I just can't believe your pump would be so slow that you'd have that big of a differential, especially when your probe is at the very end of the HERMS loop and reading what it does. What exactly are you using as a false bottom in your mash tun? Does the probe of your mash tun thermometer usually reside within the grain bed or in the wort above the grain bed? If you run a full mash simulation without the grain, does your temperature differential stay the same or get better?

I have a false bottom in my mash tun and my thermometer stem is pretty long. It reads more than through the center of mash.
I use one of those little white wort aerators as my laurtering device. It spreads the liquid pretty good across the grain bed.