How do you know if the thermometer on your brew kettle is accurate? You need to calibrate it against a known – accurate thermometer.
There are a couple different ways to calibrate your thermometer. One is by boiling point, and the other is by freezing point. I used the freezing point method here.
There are a couple different ways to calibrate your thermometer. The first is by getting water up to boiling temperature, which (while may be better for brewing), may leave you will less accuracy and will be harder to take test measurements from inside the kettle.
An alternate way is using ice water, which is a more accurate way (from what I’ve read). I used the alternate approach of ice water here.
Ensuring your valve is closed; begin by adding plenty of ice and water to pot. Let the temperature stabilize for about five minutes.
I brought my pot down to about 36 degrees Fahrenheit. I did not prepare with enough ice, so I added various frozen items from my freezer.
Near the kettle’s temperature probe or thermowall, find an open spot to check the internal temperature with a thermometer. Both readings are within a couple of degrees of each other – my internal check is at about 35.5 degrees and my kettle’s is at about 33 degrees.
After I was close to freezing temperature, I needed to adjust the adjustment screw behind my kettle’s temperature gauge to ensure accuracy, leaving my final reading at 33 degrees.
While I’m not sure if I have really gotten down to 32 degrees to call it freezing, I’m going to call it calibrated and follow what the digital probe says because both readings match.
As a side check, I pulled out a bottle I kept in the pot with ice attached to it and stuck the probe in to see how accurate my reading was. It fluctuates around 31.6 degrees so I am satisfied with my accuracy.