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Hong KongThermometers: which type, where to put it, how to calibrate it
Food thermometers must be accurate to ±1°C (±2°F) and calibrated using the ice-point method - an ice slurry at 0°C (32°F). Thin foods need a thermocouple or thermistor, because a bimetallic stem averages across its sensing area.
Three of the eighty questions sit under maintaining temperature measuring devices, which is more than the whole of pest control. It is a small topic with a good return.
The types
| Type | Good for | Not good for |
|---|---|---|
| Bimetallic stem | Thick foods, roasts, large volumes | Anything thinner than about 5 cm |
| Thermocouple | Thin foods, fast readings, surfaces | Being cheap |
| Thermistor | Thin foods, fast digital readings | Rough handling |
| Infrared | Surface checks, receiving deliveries fast | Internal temperature - it reads the surface only |
| Maximum registering | Dishmachine final rinse verification | Food |
The infrared row is the one worth carrying. It reads surfaces, so it is excellent for scanning a delivery quickly and useless for deciding whether a chicken breast is cooked.
The bimetallic problem
A bimetallic stem thermometer senses across a length of the stem, usually marked with a dimple about 5 cm from the tip. It reports the average temperature over that whole span.
Put it in a burger and most of that span is in air. The reading is meaningless. That is why the Code expects a thin-probe thermocouple or thermistor for thin foods, and why the sensing dimple exists as a thing to know about.
Calibrating
Ice-point method: fill a container with crushed ice, add water, stir, wait, insert the probe without touching the sides, and adjust to 0°C (32°F).
The boiling-point method exists and is altitude dependent, which is why the ice point is the one to learn and the one that appears in questions.
Before each shift, after dropping it, after a large temperature change, and whenever a reading looks wrong. That last one is the professional habit - a thermometer that disagrees with your judgment is either telling you something or broken, and both are worth resolving.
Taking a reading properly
- Thickest part of the food, away from bone, fat and the pan.
- Stir liquids first; the top of a pot is not the middle of it.
- Wait for the reading to stabilize rather than taking the first number.
- Clean and sanitize the probe before and after each use.
- For packaged food in a delivery, put the probe between two packages rather than piercing them.
That last point catches people. Piercing a sealed package during receiving contaminates it, so the between-packages technique is the correct answer.
Accuracy
±1°C, or ±2°F. A thermometer outside that is not a marginal thermometer, it is a broken one, and every temperature record made with it is unreliable.
Which is the real point of the topic: temperature control is only as good as the instrument, and the exam asks about the instrument because kitchens tend not to.
Common questions
How do you calibrate a food thermometer?
The ice-point method. Fill a container with crushed ice, add water, stir, insert the probe without touching the sides, and adjust the reading to 0°C (32°F).
How accurate must a food thermometer be?
Within ±1°C (±2°F). One reading outside that is not marginally wrong, it is broken, and every record made with it becomes unreliable.
Can you use an infrared thermometer on food?
For surface checks only, such as scanning a delivery quickly. It cannot read internal temperature, so it never confirms whether food is cooked.
Why is a bimetallic thermometer wrong for a burger?
It senses across a length of the stem, usually about 5 cm, and reports the average. In a thin food most of that span is in air, so the reading is meaningless. Use a thin-probe thermocouple or thermistor.
How do you check the temperature of packaged food at delivery?
Place the probe between two packages rather than piercing them. Piercing a sealed package contaminates it, and that distinction appears in receiving questions.