Mash Tun HERMS Question

[priceman75]

I'm having problems with my 55 gallon SS brew system. Boil kettle, mash tun and HLT with HERMS coil. We can match temperatures in the HLT and MT pre-mash, usually around 165 degrees. We then mash in, stir and watch our temperatures. This is now the 4th batch for us and every time we see a temperature difference between wort exiting the MT and wort returning from the HERMS coil. For example, wort exiting is 152 degrees. Wort returning is 158, usually 3 degrees lower than the HLT. This has been consistent each time we have brewed. We have never had our temperatures on the control panel for the MT and HLT the same. There is always a difference. We have tried to stir the mash throughout the hour long mash. We have tried to increase the temperature of the HLT.
There always seems to be a difference in the temperature in the MT.

I’m not sure what temperature reading I should be most concerned with. Wort exiting, wort returning or surface wort temperature with a manual probe? We have a false bottom in our mash tun which holds approximately 7-10 gallons of wort. I’m not sure if that wort at the bottom is cooled down prior to exiting the MT. Is that why we are getting a lower temperature?
Should I be more concerned with the temperature returning from the HERMs? If my mash temp is supposed to be 155 and the HERMS return is reading 155, is that what I should be focusing on? Maybe switch the location of the temperature probe in the MT to the valve at the top, HERMS return?

I just don’t feel I am acheiving an accurate mash temperature. It seems to be a temperature gradient change in the MT from top to bottom. Any thoughts? I truly appreciate your insight.

We use a 1/20th HP Chugger pumps.

 

[iijakii]

What size is your HERMS coil and how much flow are you getting out of it/that pump? To me this just screams that you're losing more heat than you are gaining from the HERMS. Can you increase the flow? I'd try insulating. I always hear with that large of a batch you don't even have to worry about heat loss, but I guess that's not true.

What you want to do is set your HLT at or slightly above your targeted mash temp. So if you're wanting to mash at 155, then your HLT will be at 152-154 depending on heat loss from hosing etc. If the flow is enough it should all equalize. I'd keep the probe at the wort exit, but spot-check with a hand-held probe near the top and sides etc while you're dialing everything in.

Maybe you just need a little bit of insulation.

 

[241]

I don't know about others, but my HLT temps never match my MLT temps in my HERMS system.

I account for a 4 degree F variance in my system. For instance, if target mash temp is 152 degrees F, I set the controller (HLT water temp) to 156 degrees F.

I am most concerned with temps exiting the HERMS coil, returning to the MLT. I periodically check my temps coming back into my MLT in my return hose and it's generally dead on with my 4 degree F variance. I have a temp probe further down in my MLT, around the middle of the grain bed, as well as in a T fitting at the exit of the MLT and usually both read about 1 degree F lower than the returning hot liquor. Close enough for me!

 

[orangehero]

The most important temperature should be the temperature of the wort returning from the herms. You want that set to your desired mash rest temperature.

I'm surprised you're having such a large temperature gradient between the top and the bottom of your mash. Are you sure your thermometers are accurately calibrated? Do you have the pump fully open or is the flow throttled?

 

[itsnotrequired]

are you circulating water in the hlt?

 

[241]

I had some time at lunch so pulled some info from Kal's website for you.

MLT
http://www.theelectricbrewery.com/mash-lauter-tun?page=4

As the sweet wort exits the Mash/Lauter Tun through the ball valve at the bottom, a probe continuously sends a water temperature reading back to our control panel. This probe monitors the temperature of the mash so that we can see how fast (or slow) the temperature of the mash changes. It does not actually control anything in our process but instead provides feedback as to how the brewing process is proceeding.

HLT
http://www.theelectricbrewery.com/hot-liquor-tank?page=7

As the water exits the HLT out the ball valve at the bottom, a probe continuously sends a water temperature reading back to our control panel. The control panel then fires the heating element as required to maintain the exact water temperature we set.

Also post a pic of that 55 gal setup. It sounds rad

 

[priceman75]

Thanks for everyone's response. Still trying to figure this out. Here are some answers to your questions.

What size is your HERMS coil and how much flow are you getting out of it/that pump?
50ft. SS Coil

Can you increase the flow?
No. Pump is full flow. Its a small chugger pump, max 3-4 gallons/hr. Maybe I need to upgrade pump.

I'd try insulating. I always hear with that large of a batch you don't even have to worry about heat loss, but I guess that's not true.
All 3 vessels are insulated. MT has 2 layers of reflectix.

The most important temperature should be the temperature of the wort returning from the herms. You want that set to your desired mash rest temperature.
Is there any science or documentation to support this? Just wondering.

Are you circulating water in the hlt?
Yes

 

[priceman75]

Let me know if you guys have any questions. We ferment in 3 barrel plastic fermenters which have 50 ft. SS coils in the center. We temperature control fermentation with a sump pump submerged in a cooler. For chilling we use an air conditioning unit submerged in the cooler. For heating we have an aquarium heater in the cooler. Both are controlled with temperature controllers. The system works perfectly.

 

[orangehero]

I don't know what you mean by science supporting this, but you want to control the temperature of the wort. If you monitor at other points you will get poor control and likely to overshoot the temperature. By monitoring the output of the HEX you know you aren't overheating the wort.

If your chugger is pumping 3-4 gallons an hour I would definitely get it fixed. Mine can pump double that in a minute.

It's not unusual for the wort coming out of the HEX to be lower than the HLT temp, although it is perhaps strange considering you are using a 50 ft coil and pumping the wort wide open in a recirculated HLT. There are two ways to control the temp with a PID controller. Either monitor the HLT temp and have it a few degrees higher if you know what the difference is between HLT temp and HEX wort temp, or monitor the HEX wort temp and program the controller to respond to that. Both approaches are valid and can accurately control temp in a HERMS system.

I would suspect that the wort exiting the mash tun being 6°F lower than what is coming back in from the HEX to be an error. Have you calibrated all of your thermometers?

At the end of the day, you shouldn't be concerned with hitting some kind of mash temperature that other people tell you to use. Every brewery has to adjust their processes and parameters for their particular system. The most important thing that automation gets you is consistency and repeatability. You need to get to know the system and adjust as needed. Even if you are actually seeing a 6°F difference between the top and bottom of the mash, as long as this is consistent and repeatable then that is all you want. Evaluate the finished beer, and if necessary try adjust the mash temperature on your system.

 

[priceman75]

Sorry, that was gallons per minute. My bad!

I've done calibration on all 3 PID controllers. Auto tuned the HLT and BK.

I'll try again.

As far as the science comment, your explanation makes sense. I'm just not sure why Kal from the Electric Brewery suggests monitoring temperature at the wort output instead of wort return from HERMS.

 

[orangehero]

It's one way to do it and apparently good enough for his system. He controls his HLT temp, though, the wort probes work only as thermometers.

 

[KevinP]

My system is quite similar to yours albeit much smaller.
Keg ehlt with 50 foot stainless 1/2" HERMS coil and 5500 watt element.
20 gallon Chapman mash tun modified to all 1/2" fittings.
March 815 on hlt and March 809 on mash.
pid controls hlt temp recirculating to itself.

Process goes something like:
Add all mash water to mash tun.
Add 11ish gal to hlt (just enough to fully submerge herms coil.
Set pid to strike temp
Hlt and mash reach strike temp, turn off mash recirc, and dough in.
Lower pid to mash temp and add water to hlt to lower its temp to desired mash temp.
Hlt stabilizes to mash temp and begin mash recirc full speed.
At this point my hlt temp and mash temp are spot on equal.
For mashout I raise hlt temp to desired temp and mash come up to that temp.

My guess is you might get higher flow on your mash than me and it may not be spending enough time in the herm coil to pick up the necessary heat to = hlt temp. That bigger size false bottom has got to be less restrictive than mine giving you higher flow.
I think maybe trying to slow mash recirc speed so it spends more time in the coil. If that makes a difference then maybe installing a longer coil to re-increase the mash flow rate.

A pretty rambling response but I will be very interested in your findings as I desire a larger version of my system. ie I want your system

 

[carloski44]

I have a 22 gal automated system that monitors the mash temp under the grain bed exiting the mash tun. My M tun is insulated somewhat. I was always told the temps in or out does not matter, the important temp was the actual grain bed temp. The wort coming from the bed should be an accurate representation of your bed temp. I circulate 80-90% of the time during mashing and switch with auto valves between the HEX coil and straight feed back to the mash tun to regulate mash bed temps. My HEX coil stays a few degrees higher than desired mash temp.

 

[orangehero]

I think the more important temp is wort temp, as that's where the enzymes are. Overheating the wort in the HEX as you wait for the large mass in the mash tun to change temp is increasing the rate of enzyme denaturing.

Nonetheless, even with the various approaches to temperature monitoring and control, I doubt any of the common ones create enough of an issue to totally screw up a mash. The important thing is to get to know your personal, unique, individual system, take close observations and thorough notes, and then make adjustments as necessary.

The greatest benefit of using a PID controller to maintain temp through a HEX is precision and consistency and not necessarily accuracy. If you can maintain a relatively stable temp, and know the results from a particular temp on your sytem, that gives you an extra variable you can fairly easily control to get the results you desire.

 

[stevehaun]

I have a one barrel system. I use the temp at the herms outlet (right before it dumps into the mash) to control the temp of the HLT. I do not recirculate or stir water in my HLT. My herms coil is 25 ft long 5/8" OD copper tubing. I set my herms outlet temp 4F above my desired mash temp. I measure the temp at the top of the mash with a floating thermometer and at the temp of the wort at the outlet of the mash tun with thermowell/thermocouple. After about 5 to 10 minutes, the temp at the top of the mash is 1-2F above the temp of the wort exiting the mash tun and remains there for the rest of the mash.