How to Calibrate a Food Thermometer

How do you calibrate a food thermometer?

Put the probe in a glass of crushed ice and cold water. Keep it in the center. Wait 30 seconds; it should read 32°F. Adjust it if not, or replace it. Calibrate once a day before you start, and after a drop. A food thermometer must be accurate to within 2°F (FDA Food Code 4-203.11).

A thermometer that reads wrong makes every temperature check wrong.

Which thermometers does a kitchen need?

A food thermometer accurate to within 2°F, handy wherever food is cooked, held or cooled.
A thin-tip probe for thin foods like burger patties and fish fillets.
A thermometer inside every fridge, freezer and cooler, in the warmest spot (near the door).
Never glass or mercury thermometers around food.

Sources: Food Code 4-203.11 · Food Code 4-302.12 · R392-102-8(15)–(16)

How often should you calibrate?

Before using a new thermometer
On a schedule: the source protocol says once a day; CleanCleaver asks once a week (Essentials and Standard) or at each opening (Thorough). The Food Code itself sets no interval (4-502.11(B): as the maker says, as needed)
After it is dropped or damaged
Whenever a reading seems wrong
After a suspected foodborne illness, before relying on those logs

Record every calibration.

Sources: Source protocols: calibrating thermometers (when to calibrate)

How does the ice-water method work?

Fill a large glass with crushed ice, then add cold water to the top. Stir.
Put the probe in the center, not touching the sides or bottom. A dial thermometer goes at least 2 inches deep, past the dimple.
Wait 30 seconds, or until the reading stops moving.
It should read 32°F. If not, adjust it (dial: turn the nut under the head with a wrench; digital: press reset per the maker). Replace it if it can't be adjusted.

Do not use boiling water in Utah. Water boils at about 198–206°F here depending on elevation, not 212°F, so it can't confirm accuracy.

Sources: Source protocols: ice-point method; do not use the boiling-point method in Utah

Where do you probe, and how do you clean it?

Digital thin-tip probe: best all-around tool. Probe the thickest part.
Dial thermometer: senses in the first 2–2½ inches; wait 15–20 seconds. Too thick for thin patties.
Infrared (laser) reads only the surface, never the inside of food.
In large items, probe two spots and use the lower reading.
Wash, rinse and sanitize the probe (sanitizer dip or 70% alcohol swab) between foods, and always between raw and cooked.
Don't soak a digital thermometer unless it's waterproof. Store it in its sleeve.

Sources: Source protocols: thermometers (types and use); sanitizing thermometers · Food Code 4-602.11

The rules behind it

Accurate thermometers. Food thermometers accurate to ±2°F; calibrate by ice point (32°F); not boiling water in Utah. Food Code 4-203.11, 4-302.12; R392-102-8(15)–(16)