Build a Mash Temperature Controller

I spent a lot of time controlling temperatures on the cold side of the brewing process in my early homebrew days, including temperature control during grain, hop and yeast storage, yeast propagation and maturation, fermentation, homebrew aging and serving. Adding controls to these areas definitely made a huge impact on the quality of my brew, so recently I shifted my attention to the hot side to see what further benefits temperature control could add.

I needed a way to measure the water temperature of my hot liquor tank (HLT) and mash lauter tun (MLT) vessels and then fire the burners on and off as needed, so I bought a few temperature control switches and wired them into a relay and programmable logic controller (PLC).

I used solenoid gas valves and welded the gas lines inside the stainless steel frame back to a single propane input. I used low-pressure hurricane burners paired with hot surface ignitors (Emerson #767A-380).

Now I could program my PLC to pre-heat the hot surface ignitors and open the propane valves when a set temperature range was reached on the temperature control switch. The burners fire on and fire off. Success! Now that I had a stage set I needed a cast of characters to actually take the temperature measurements that this system is completely dependent on.

For sanitation and cleaning ease I chose tri-clamp connections throughout the system, so I wanted
a tri-clamp thermowell I could easily remove for cleaning too. Next Ineeded a sensor, but what kind? Thermocouple, thermistor and RTD are the standard varieties in the marketplace and I prefer RTD for brewing applications.

The result after installation of the RTD temperature controls was precision mashing with target temperatures hit every time. The RTDs, stainless steel braided wire and connectors all came from Omega Engineering. XLR connectors that plug into receptacles were ordered from Amazon. Weldless bulkheads were from Brewers Hardware. PLC (programmable logic controllers) and relays were from Automation Direct. Gas solenoid valves sourced from Asco Valves.

Warning: This project involves elements that are dangerous, including electrical wiring and controlling combustible gas. If you are not experienced with (and don’t feel comfortable) working with any of these elements mentioned here, do not attempt to do this project yourself. Ask a licensed professional or similarly experienced person to help you.

Parts and Tools

•Solid weldless bulkhead 1⁄2-inch MPT X 1⁄2-inch FPT
• 1.5-inch tri clamp temperature probe thermowell (5-inch)
• 1.5-inch tri clamp
• 1.5-inch tri clamp gasket
• 1.5-inch tri clamp X 1⁄2-inch FPT
• XLR female and male connector
• general purpose RTD probe (#PRTF-10-2-100-1⁄4-12-E- SB) 3-wire fiberglass insulated, fiberglass jacketed, stainless steel overbraided cable
• Insulated extension probe wire (#EXTT-3CU-26S-25)
• MFL gas and liquid quick dis- connects (threaded)
• 3-Prong Mini flat pin Connector for RTD wire
• Wire cutters/strippers
• Wire shrink tubes and flame
• Drill and step bit
• Wrench and needle tip pliers and screw drivers
• Soldering iron and solder

1. Gather the hardware

When you order multiple parts from multiple places online you can expect that not all the parts will arrive at the same time, fit together perfectly — and in my case, not all the parts even arrived. After a few adjustments in part size and some emails back and forth I finally received all the parts needed to build these RTD thermowells for my mash tun and hot liquor tank. I chose not to add a sensor to the boil kettle because I never really have an issue with my rolling boil temperature. If you wanted to add a sensor to the boil kettle then go for it. Give yourself plenty of time when working on electrical projects like this and always use caution.

2. Mount the bulkhead

I brew 5- and 10-gallon (19- and 38-L) batches in my 15.5-gallon (59-L) mash/lauter tun vessel, so I needed to mount the sensor low enough to be submerged during the smaller mashes. I filled the kettle with 3 gallons of water and marked where the top of the water hit. I used a step bit and drilled off to the side of the kettle away from the other connection valves. After sanding and smoothing down the new 7⁄8-inch hole, I mounted the bulkhead with dual gaskets. This bulkhead is computer numerical control (CNC) machined from a solid hex of 304 stainless steel. As you can see, the 5-inch thermowell reaches a few inches into the kettle for nice exposure to the mash and water temperatures.

3. Wiring

Here is where your soldering skills come in handy. I needed to connect the following: RTD probe →wire→shrink tube→3-pin connector male to 3-pin connector female←shrink tube←wire←XLR male case and connector. Easy right? The main thing to remember is to slide the XLR case and shrink tube onto the wire before making your wire to XLR connection solder. I forgot to do this and it’s not fun to redo. The quick 3-pin connectors use screws for wire connection, so they are very easy. The purpose behind the 3-pin connectors and extension wire is just for extra wire length to reach the control panel. You can get your probes with any length wire you want, but I just thought it would be nice to be able to break the connection in the middle if needed.

4. Choosing the brain (plc)

The PLC board I chose for this project was a Click Koyo (#C0-00AR-D ) paired with the stackable power supply (#C0-00AC) The PLC had 8 AC IN / 6 RELAY OUT and required 24 VDC power. I used Zettler relays (#AZ2280) to control various parts of the machine. This is an easy board to work with for newbies and it has free downloadable programming software, online help and video training if needed. Some other popular options are the Brewtroller, BCS-460 (iPhone app available) or open source Arduino.

5. Box it up

A metal box from Fry’s Electronics was used as my main control panel. I machined out some holes and mounted it on an extension arm from the main chassis. Next I popped in my Auber temperature control switches and LED pump switches. On the backside of the control panel box I mounted the XLR female connectors and a master power switch. Under the control panel, on the side of the chassis, I mounted a PVC weather resistant box to hold the PLC, power supply and relays and connected the two boxes with a plastic conduit tubing. Through this tube I was able to run the necessary control wire and power wires.

6. Connect and test

Be sure to set the Auber temperature controller to read from RTD sensors and not the default thermistors before clicking in the temperature sensors and brewing. If you don’t your readings will be off or may not even read anything at all. Next, put the probes into a glass with a slurry of crushed ice and water. Let it rest for a minute or two until the temperature stabilizes. I wrote down the temperature it was reading, then subtracted that number from 32. So if you read 42 °F then 32-42=-10. I found the Pb value in the configs menu and made it match the number I calculated. I was calibrated. Finally I tested a few batches of water through the system and was ready to brew!


Issue: October 2012