A thermometer is one of the most important tools used when brewing and distilling. Thermometers are inexpensive and simple tools, yet people first getting into the hobby often overlook their importance. A properly calibrated thermometer is necessary to ensure the correct mash temperature, a safe pitching temperature for yeast, and used during the distillation process too.

If a thermometer is not calibrated correctly, the intended outcome (whatever that may be) may not happen as planned. A variety of things could cause a thermometer to require calibration. Not only should a thermometer be checked if it is dropped, kicked, or mishandled, it should also be checked before the initial use.

Before we get to calibration we will look at the various types of thermometers used for brewing and distilling.

Types of Thermometers

Floating Brewing Thermometer:

Floating thermometers are often sold at homebrew supply shops. They are inexpensive, accurate, and a good low-cost option for measuring mash temperature. The floating thermometer’s use is simple—it’s placed into the mash—but it can be tricky to read, especially if the mash is hot. These thermometers work well but are vulnerable to breakage, and they can’t be calibrated if they are not reading correctly. If you have one, keep using it until you break it; once it breaks, replace it with a thermometer that can be calibrated and is not made completely of glass.

Dial Thermometer With Clip: 
Some dial thermometers have a clip that attaches to the side of the pot. These thermometers are easier to read than the floating thermometers. They are often sold with starter homebrewing kits, and they work pretty well. They can sometimes be difficult to read because they often fog up when the lid of the still is opened for a temperature reading. Make sure that the dial thermometer has a calibration screw; these thermometers need to be calibrated periodically, especially if they are dropped or mishandled.

Digital Thermometer:
Digital thermometers are a great option. If you use a digital thermometer, it is important to get one that is well made and can be calibrated. Good digital thermometers will be extremely accurate; they often feature 2-point calibration instead of 1-point calibration. Digital thermometers are great for measuring mash temps because they read the temperature in a few seconds and are extremely reliable. It is important to calibrate them periodically to make sure they are measuring correctly. They are great for taking quick temperature readings during a mash, but good digital thermometers can be pretty expensive.

Boiler Dial Thermometer:
These are the best thermometers, in our opinion, for both brewing and distilling. Using a mash vessel with a built-in thermometer gives the ability to read the temperature of the mash with a quick glance.

When distilling we recommend at least having a thermometer in the boiler, but we prefer to have one in both the boiler and the column of the still. They are extremely accurate, but it is important to periodically calibrate these thermometers because they can drift over time. If you have not read our article on “Distillation Temperature,” check that out for more information on thermometers and distilling.

Equipment Needed to Calibrate a Dial Thermometer:

• A thermometer that can be calibrated
• Mason jar (1 quart)
• Ice
• Water
• Spoon

How to Quickly Calibrate a Thermometer:

1. Fill the Mason jar to its top with ice.
2. Top off the jar with water.
3. Stir the ice water with a spoon and let sit for 5 minutes.
4. Hold the probe of the thermometer in the ice water while giving it a couple of good swirls. Make sure the probe is fully submerged for 30–60 seconds and not touching the sides or the bottom of the container.
5. While the probe is submerged, check the reading on the thermometer. The thermometer should read 32 degrees Fahrenheit or 0 degrees Celsius. If the thermometer reads 32F or 0C, it is perfectly calibrated and does not need any adjustment. If it does not read 32F or 0C, adjust the calibration screw on the back of the thermometer until the reading is 32F or 0C.

You can also calibrate a thermometer using boiling water, but instead of adjusting to 32 degrees Fahrenheit, adjust to the boiling point of water at the elevation. See chart below