How to calibrate a food probe thermometer (the FSA method)

Every temperature record in your kitchen depends on one cheap bit of kit. If the probe reads 3°C low, your "62°C" hot hold is really 65°C and your "7°C" fridge is really 10°C, and every log you've filled in for the last month is wrong. Checking the probe takes five minutes and a pan of water.

The short answer

The FSA's Safer Food, Better Business (SFBB) pack gives a simple two-point check for digital probes:

If it's outside either range, replace the probe or return it to the manufacturer to be calibrated.

How often: as the manufacturer says. If there are no instructions, check regularly, for example once a month.

A quick word on "calibrate"

Strictly, what a kitchen does is check the probe's accuracy. Actually re-calibrating it (adjusting it back to true) is usually a job for the manufacturer or a calibration service. That's why the FSA's instruction for a failed probe is replace it or send it back, not fiddle with it.

Why probe accuracy matters

The numbers your food safety system depends on are tight:

• 8°C: in England, Wales and Northern Ireland, chilled food must be kept at 8°C or below by law (Scotland recommends it). The FSA recommends setting fridges to 5°C or below.
• 63°C: the FSA's SFBB pack says it is a legal requirement that hot food is kept at or above 63°C.
• -18°C: frozen food should be kept at -18°C or below.

A probe that's two degrees out can turn a safe reading into an unsafe one, or the other way round. It also undermines every record you show an inspector. See fridge temperature rules and hot holding, cooling and reheating temperatures.

How to do the iced water check

1. Fill a jug or deep container with crushed ice, then add just enough cold water to fill the gaps. Mostly ice, a little water.
2. Stir and leave it a minute or two so the mix settles at its coldest.
3. Clean and disinfect the probe first.
4. Put the probe tip into the middle of the iced water, a few centimetres deep, not touching the sides or bottom.
5. Wait for the display to stabilise.
6. Read and record. Pass: -1°C to 1°C.

Tips: use crushed rather than cubed ice if you can, and keep stirring gently. A glass of water with two cubes floating in it won't be at 0°C.

How to do the boiling water check

1. Bring a deep pan of water to a full rolling boil.
2. Clean and disinfect the probe.
3. Hold the probe tip in the water, away from the bottom and sides of the pan.
4. Wait for the display to stabilise.
5. Read and record. Pass: 99°C to 101°C.

Safety: use a deep pan, keep your hand and the probe cable out of the steam, and don't let a cheap probe's plastic handle near the heat.

What to do if a probe fails

1. Take it out of use straight away. Label it so nobody picks it up by mistake.
2. Use a spare that has passed the check. Every kitchen should have at least two probes for exactly this reason.
3. Replace it or send it back to the manufacturer for calibration, as the FSA advises.
4. Record the failure and what you did.
5. Think about recent readings. If the probe was badly out and you've been relying on it for cooking or hot-holding checks, re-check the food and equipment it was used on.

How often to check

The FSA's daily opening checks also include "probe thermometer is working and probe wipes are available". That's not the full accuracy test, but it catches dead batteries and missing probes before service.

Probe check record template

Copy this into your diary or a spreadsheet.

Give each probe a number or name (a bit of coloured tape works), so you know which one failed.

Looking after your probe

The FSA's guidance on probe care:

• Clean and disinfect before and after every use. A dirty probe can spread bacteria to the food you're testing.
• Probe wipes are fine, but don't let them dry out or they won't disinfect properly.
• Don't leave a digital probe in a fridge, freezer or on a hot surface for long periods.
• Store it safely, away from extreme temperatures and liquids, in its case if it has one.
• Don't bang or drop it.
• Replace a low battery immediately.

Probe or infrared?

If an infrared reading looks high, the FSA says to confirm it with a clean, disinfected probe. Infrared thermometers need checking too; follow the manufacturer's instructions.

Who should do the check, and when

Give the probe check to one named person, usually the head chef or kitchen manager, and put it on a fixed day so it doesn't drift. If you've got more than one site, each site checks its own probes; don't assume the probe that was fine at your other venue is fine here.

Do it at a quiet time, not in the middle of prep, so nobody is tempted to rush the iced water stage. And check every probe on site at the same time, including the one that lives behind the bar or in the cellar. A probe that only gets used once a week is the one most likely to have a flat battery or a bent tip when you need it.

Common mistakes

• Testing in a glass of tap water with a few ice cubes. It won't be 0°C. Use mostly crushed ice.
• Touching the bottom of the pan. You're measuring the pan, not the water.
• Reading too soon. Wait for the display to settle.
• One probe for the whole site. When it fails, you've got nothing to check temperatures with.
• Checking but not recording. If it isn't written down, you can't show it was done.

How ShiftComplete helps

The probe check is the kind of job that's easy to forget because it isn't daily. ShiftComplete makes it part of the routine:

• A recurring checklist task for the probe check on a set weekday, or a one-off priority task each month, with every tick named and timestamped. Require a photo of the probe reading in iced water if you want proof.
• Opening checklists with "probe working and probe wipes available" every day.
• Temperature logs for every fridge, freezer and hot-hold point with its own min/max range, so out-of-range readings are flagged on the dashboard straight away.
• A 7-day rolling view of temperature records to show an EHO, plus a full audit log with CSV export.

It helps you keep the records an EHO asks to see. Free for 60 days, no card needed.