How to calibrate a food probe thermometer

Why the check exists

Food business operators must run a food safety system based on HACCP principles and be able to show that it works. For many small caterers that system is the Food Standards Agency's Safer Food, Better Business (SFBB) pack: safe methods for this kitchen, and records that show the methods were followed. Temperature is one of the main controls. If the probe is reading low, a chicken that is still unsafe can look cooked. If it is reading high, sound food can be thrown away, or a fridge problem can be missed because every number looks colder than the food really is.

SFBB puts the check in the management section, under "Prove it". The pack says it is essential to know the probe is working properly so you can rely on its readings, and that a disinfected probe is how you prove cooking, cooling and hot holding methods are safe. The check is not a laboratory calibration certificate, and it is not a substitute for the daily fridge log. It is the routine that lets you trust the other records. Officers ask "how do you know that thermometer is accurate?" because a confident answer with a recent line in the diary is quick to give, and a drawer of unchecked probes is not.

The iced-water check

SFBB's method for a digital probe is iced water and boiling water. Iced water should read between −1°C and 1°C. Use a clean jug or a small pan you can spare. Fill it with ice and add a little cold drinking water so you have a slush, not a few cubes floating in a jug of tap water. Stir. Put the tip of the probe into the middle of the ice. Keep it off the base and the sides, because the container is not at the same temperature as the melting ice. Wait until the display stops moving, then write the number you see.

A reading of 0°C, 0.4°C or −0.6°C is inside the SFBB range. Write the figure, not the word "pass". A reading of 2°C or −2°C is outside it. Before you condemn the probe, repeat the check once. Too little ice, a probe resting on the jug, or a reading taken before the display settled will move the number. If the second reading is still outside −1°C to 1°C, the probe does not go back into the kitchen. That second reading is the one you keep, next to the first, so the decision is visible.

The boiling-water check

Boiling water should read between 99°C and 101°C. Bring a pan of water to a rolling boil. Put the probe into the water, again clear of the base and the sides, and wait until the display settles. Steam burns. Keep hands, sleeves and the cable out of the plume, and do not lean over the pan to read a small screen. Write the number.

Then take the probe out, let it cool, and disinfect it before it touches food. A probe that has just been in boiling water is clean from the heat, but the handle, the cable and the next surface it meets are not a reason to skip the wipe you normally use between foods. Do not plunge a boiling-hot probe into a fridge product to "see what it does". You will damage the food and you will not learn anything the iced-water check has not already told you.

Water boils slightly below 100°C as you go up. Almost every UK kitchen is close enough to sea level for the 99°C to 101°C range in the SFBB method. If you are in a high location and a careful boiling check sits just outside that range while iced water is correct, follow the manufacturer's instructions and record what you did. Do not edit the diary so the number looks like 100°C.

When the reading is outside the range

SFBB is direct about a failed check: replace the probe, or return it to the manufacturer to be calibrated. Take it out of use the same day. Label it so a busy cook does not pick it up at the pass. A spare only helps if that spare has itself been checked and the check is in date. An old probe in a drawer is not a spare until it has passed iced water and boiling water.

Some instruments have a reset or an offset in the manufacturer's instructions. If you use that adjustment, run both checks again afterwards and write the readings before and after. A screw turned until the display looks right, with no second check, is not a calibration. If you cannot bring it inside the range, it leaves the kitchen.

Look at food still on the premises that you accepted with that probe since the last good check, or at least since the start of the service in which you found the fault. Recheck it with a probe that has passed. Hot food that is still safely hot, and cold food that is still inside your safe-method limit, can stay, and you write both readings. Food you cannot show was safe is a decision to throw away or to hold for advice, written in the same note as the failed check. The corrective action guide is the shape of that note: what failed, what you did, and what will stop a repeat.

How often to check

Follow the manufacturer's instructions for that probe. Safer Food, Better Business asks you to check the probe in boiling water and melting ice and to write down how often you do that extra check. The pack does not print one national frequency. If the manufacturer is silent, choose a frequency the team will keep. Check again when the probe is dropped, when the battery is changed, when the stem is bent, when the display fades, or when readings stop matching the food in front of you. A pan that is visibly boiling and a probe that says 70°C is a reason to stop and check the instrument, not to keep serving.

Put the job on a named day and a named person, with a deputy for holidays. "Someone will do the probes" becomes a blank line. In a group of sites, each kitchen checks the probes that live in that kitchen. A certificate filed at head office for a different serial number does not cover the probe on this pass. The multi-site guide is about that split between a shared standard and the record that belongs to one address.

What to write down

The SFBB diary has a place for Prove it records. A useful line identifies the probe, the date, the iced-water reading, the boiling-water reading, the person, and the action if either reading was outside the range. If you have two probes, name them in the way the team speaks: "pass probe" and "delivery probe", or a number etched on the handle. "Probe" is not an identity once a second one exists.

Keep the sheet with the diary, not in a folder nobody opens during a visit. A printable layout is the probe calibration record. Paper is a valid record when it is filled in at the time and kept. A digital line needs the same fields. Correct a wrong entry by leaving the original visible and adding the correction. Overwriting last month's 0.2°C with a fresh number makes the history look rebuilt.

A laboratory certificate is a different document. Some businesses send probes away on a contract once a year and keep the certificate with their other papers. That certificate does not replace the monthly iced-water and boiling-water check in between. The certificate also needs the serial number or the name of the probe you actually use. See which documents to keep ready for how that file sits with pest reports and servicing records.

Disinfect the probe between foods

Accuracy and cleanliness are separate. SFBB expects a disinfected probe when you measure food. A probe that reads 0°C in ice and then goes from raw chicken into cooked rice is an accurate way to spread bacteria. Keep food-probe wipes next to the probe, not in an office drawer. Wipe before the check and after it, and between raw food and ready-to-eat food. Ready-to-eat food will not get another cook that would kill what the probe just carried.

The Food Standards Agency's E. coli O157 cross-contamination guidance is the reason this is not a courtesy. Complex equipment and cloths that touch both raw meat and ready-to-eat food are a known route. A probe is small enough to forget and mobile enough to travel the whole kitchen. Colour-coded probes help only while everyone remembers which colour may touch raw food. If you use one probe for everything, the wipe between tasks is part of the method, and the safe method should say so.

Probes, infrared guns and fridge displays

These instruments do different jobs. A food probe with a metal stem goes into the centre of food. That is the check SFBB describes for cooking and for proving a method. An infrared gun reads a surface. It can be a quick look at a delivery pack or a pan, and it will mislead you about the centre of a joint, a tray of rice, or a dense sauce. Do not record an infrared surface reading as if it were a probe in the food, and do not "calibrate" a gun with the iced-water method and then treat it as a probe.

A fridge display reads air, or a sensor the manufacturer placed in the cabinet. It moves when the door opens. It is the right tool for the daily fridge check described in the fridge temperature log guide, if that is what your safe method says you record. It is the wrong tool for the centre of a cooked chicken. When a display and a probed product disagree, write both, check the probe with iced water if you doubt it, and decide from the food. In England, Wales and Northern Ireland, food that must be kept cold is generally held at 8°C or below, and SFBB tells caterers to work colder, often at 5°C or below. Hot food held for service is normally kept at 63°C or above. Your safe method is the limit the team is trained to. A probe that has not been checked cannot police either number.

Where the probe is used in a normal day

Map the meals that depend on it. Cooking is the obvious one: the centre of the thickest piece, away from bone and away from the pan. Many caterers write 75°C into the cooking method. If your safe method uses a different time and temperature combination from the SFBB cooking method, staff need to follow that written combination, and the probe they use has to be the one you checked. Reheating is the same idea. The food is hot all the way through, not only at the edge.

Cooling is a second use. You are proving that a method you have written actually brings the food down, which is a different question from "is the oven hot?". The cooling guide covers how to speed that up and what to record. Hot holding is a third: a reading in the food, not a guess from steam on the glass. Deliveries are a fourth, when your method says you probe chilled or frozen goods on arrival. One checked probe can cover these jobs if it is wiped between them and everyone knows which drawer it lives in. Two probes with no names, and a third in someone's knife wrap, cannot.

What environmental health officers check

On a routine visit an officer may watch a probe being used before they ever ask for the sheet. They look at whether it is wiped, whether it goes into the centre of the food, and whether the person can say what the number needs to be. Then they ask for the evidence that the instrument is trustworthy. The questions are ordinary:

• Which probe is in use today, and where is the last iced-water and boiling-water check for that probe?
• Are both readings inside the SFBB range, written as numbers, with a date and a name?
• If a reading was outside the range, was the probe removed, and what happened to food checked with it?
• Is there a spare, and has the spare been checked before it is used?
• Can the cook find probe wipes, and do they use them between raw and ready-to-eat food?
• Does the daily temperature log use this probe, a fridge display, or a mixture the safe method never describes?

A perfect monthly sheet next to a dirty probe, or a probe that fails on the day while the sheet says it passed, undermines the rest of the diary. The visit itself is described in what happens during an inspection. Confidence in management, one of the three scored areas in the Food Hygiene Rating Scheme in England, Wales and Northern Ireland, is where missing checks and missing actions show up.

Worked example

A chicken shop has two probes: "pass" and "delivery". On the first Monday of the month the opener runs both checks before the lunch fry. The pass probe reads 0°C in iced water and 100°C in boiling water. Both numbers go on the sheet with the name and the date. The delivery probe reads 0°C in ice and 96°C in boiling water. They stir a fresh boil and repeat it, keeping the stem off the pan. It still reads 96°C. They label that probe "do not use", write both boiling readings, and put it in the office for return. Lunch service uses the pass probe only. A box of chilled chicken that arrived that morning is rechecked with the pass probe and is within the limit in the delivery method, so it stays, and that recheck is on the delivery log.

On Friday the pass probe is dropped on the tiles. The cook does not wait until next month. Iced water reads 3°C. They stop using it, fetch a new probe from the manager, and run iced water and boiling water on the new one before it touches food. It reads 0°C and 100°C. Chicken still in the hot hold from the last hour is probed again with the new instrument and is above 63°C, so it stays in service and both readings are written. The dropped probe does not go back on the pass "to finish the shift". When an officer asks about the two lines in one week, the sheet, the labelled probe in the office, and the hot-hold log tell the same story.

Common mistakes

• Checking a jug of cold tap water and calling it iced water.
• Resting the probe on the pan so the boiling check reads the metal, not the water.
• Writing "OK" instead of the temperature you saw.
• Keeping a failed probe in the same pot as the working one.
• Using a spare that has never been checked, because the usual probe is in a repair bag.
• Filling in three months of probe checks on the morning of a visit.
• Wiping the probe only at the start of the day, then using it on raw meat and on salad.
• Treating an infrared gun, or the fridge panel, as the probed centre of a cooked dish.

Where this comes from

The iced-water range (−1°C to 1°C) and the boiling-water range (99°C to 101°C) come from the Food Standards Agency Safer Food, Better Business extra checks: place the probe in boiling water and melting ice, and it should be within 1°C of 100°C and 0°C. The pack asks you to record how often you do that check. It does not set a single monthly rule. Hot holding at 63°C or above, and chilled food at 8°C or below, follow the temperature control rules used in England, Wales and Northern Ireland. Scottish businesses should follow Food Standards Scotland and CookSafe where that is the pack they use. The manufacturer's instructions for your own instrument still apply, and your written safe method is what the team is trained to do.

Related pages

Fridge temperature logsFreezer temperature logsFridge temperature log sheetEHO readiness quizBakeriesChilling module

Sources

Last reviewed 22 October 2026. These links are the pages this guide was checked against. They are not an endorsement of Localyn, and they do not make a kitchen compliant.

• Safer Food, Better Business for caterers (Food Standards Agency)
• Safer Food, Better Business for caterers (Food Standards Agency pack)
• Food hygiene for businesses: cooking food safely

Template, tool and hub

• Probe calibration record
• Fridge temperature log sheet
• Restaurants