In-Line Thermometer (for counterflow chillers)

This type of thermometer is positioned after the “wort out” connection on a counterflow chiller and is connected on either end by vinyl tubing. The wort flows out of the chiller, through the in-line thermometer and then into a fermentation vessel. The in-line thermometer shows you temperature changes in the wort as it happens. This allows you to adjust the flow rate of cooling water going into the chiller to get the target pitching temperature you need for whatever type of yeast you might be using. Sure, you can do this with a normal thermometer by dipping it in the wort that’s already in the carboy, but this can be messy and poses a potential bacterial infection risk. Also, an in-line thermometer allows hands-free temperature monitoring.

If you have cool or cold ground water, using such a thermometer will also help you conserve water by allowing you to reduce excess water usage during cooling. Brewing is a water-intensive process, and if you can dial in the exact flow rate you need, you can potentially save several gallons of water per brew session. In addition to the cost savings, cutting your water usage is also environmentally friendly.

Commercially available in-line brewing thermometers run about $40 at retail, but you can put one together yourself in just minutes for about $10. A quick trip to your local hardware store and pet shop will get you everything you need. We’ll be using a common self-adhesive aquarium thermometer (very similar to the stick-on thermometers often used on carboys) with a temperature range from 64F to 86F (18C to 30C) as the workhorse of this project. This temperature range coincides with the recommended pitching temperatures for the vast majority of yeast strains.

PARTS LIST
• 1/2-inch x 3-inch pipe nipple, brass (Fig. 1)
• (2) 1/2-inch FPT to 1/2-inch hose barb fitting, brass (Fig. 1)
• LCD self-adhesive aquarium thermometer, small vertical style (Fig. 2)
• Teflon pipe tape
• Clear plastic packing tape

FIG 1:

FIG 2:

Before assembling this project, the brass parts should be washed with warm water and mild soap to remove any dirt and oil and then dried.
The first step is to give the threads on both ends of the pipe nipple a liberal wrapping of teflon tape (Fig. 3). It is very difficult to get a good seal with threaded metal fittings without using pipe tape.

FIG. 3:

Now screw in the hose barb connections to either end of the pipe nipple (Fig. 4). Hand-tightening may be enough to get a good seal, but you should give each connection a little extra torque with a wrench just to be safe. Even the smallest leak in your thermometer will give you a headache on brew day by adding to overall cleanup time. (Over time, temperature fluctuations can cause the metal to expand and contract, which can loosen the fittings. You should check the tightness of the fittings after every third or fourth usage).

FIG. 4:

Now that all the fittings are snugly connected, affix the LCD thermometer to the pipe nipple as shown in Fig. 5.

FIG. 5:

The small vertical LCD thermometers commonly available in pet stores are generally about three inches high, which is a tight fit on our 3-inch pipe nipple. You may have to trim a little off the bottom of the thermometer strip. When I assembled this project, I needed to trim off the name of the manufacturer in order to get it to fit on the pipe nipple. Trimming will not in any way impair the operation of the thermometer, so don't be shy about customizing it to fit your project. Since they retail for about $2 at most pet stores, go ahead and buy two of them in case you trim a little too much.

To finish off the in-line thermometer, give the pipe nipple a turn or two of plastic packing tape. The stick-on strip thermometer was designed to be used on flat glass rather than concave metal, so the clear tape will help keep it in place long after the adhesive backing wears out.