Build a Recessed Mash Tun Thermometer

Most homebrewers who are all-grain brewing start out like I did by making their own equipment. Sometimes this is out of necessity, but if you are anything like me you do it for the satisfaction of making things yourself. Like most people who transition into all-grain brewing, I immediately needed a new piece of equipment to get started: A mash tun.

The most common option for homebrewers is to convert an insulated picnic or sports drink cooler, which is what I did.

For the first few batches I used a handheld thermometer to monitor my mash temperatures. This worked fine but I soon realized there were several things I didn’t like about it. The first is that handheld thermometers are notorious for not being the most accurate or consistent, unless you shell out big bucks for a National Institute of Standards and Technology (NIST) traceable calibrated thermometer. The second is that I didn’t like opening and closing my mash tun, letting out that precious heat every time I wanted to check the mash temperature. So I decided I needed to come up with something different.

After doing some research, I decided the solution would be to install a permanent thermometer on my tun. This would allow me to monitor the temperature of the mash without having to remove the lid. The thermometer I chose is the same as the one you would install on a boil kettle as these are accurate, reasonably priced and very durable. I purchased the 6-inch (15-cm) probe version to get deep into the mash for a good representation of the temperature, although a 3-inch (7 cm) would work fine. I recommend checking for clearance inside the tun if you use a false bottom to help you decide. I tested my thermometer by checking it in boiling water (212 °F/100 °C) and comparing it at various temperatures against the one I have on my boil kettle. I was actually surprised at how consistent these were relative to each other; each temperature check gave the same reading on both thermometers, which is exactly what I was looking for.

Since these thermometers do not have long enough attachment threads to go through cooler style mash tun walls, it would have to be recessed into the insulated wall of my tun. This was actually preferable for me. I have never been a big fan of how these thermometers stick out from my kettles and I am always paranoid that I am going to catch the thermometer on something and break it. This would also provide a nice clean looking installation. This project is based on my 10-gallon (38-L) cylindrical water cooler mash tun but it could also be applied to other cooler styles.

Materials and Tools:

Mash Tun
3-inch (7-cm) round face thermometer with a 3- or 6-inch (7- or 15-cm) probe
(2) 7⁄8-inch ID stainless steel washers
(2) silicone O-rings
1⁄2-inch NPT stainless steel nut
2-foot (0.6 m) level
Pencil/marker
Drill
7⁄8-inch spade drill bit
120 grit sandpaper
Utility knife
Blowtorch
Wrench/pliers