Calibrating food storage thermometers.


Calibrating food storage thermometers.

by tonytran2015 (Melbourne, Australia).

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(Blog No.91).

#thermometer, #household thermometer, #fridge thermometer, #food storage thermometer, #calibration, #food safety, #food poisoning,

Calibrating food storage thermometers.

Figure: A household thermometer with scale from -30°C to 50°C.

Keeping food safe for eating requires storing them at correct temperatures. This requires the use of thermometers as the difference between safe and unsafe temperatures is not easily perceptible otherwise. Household thermometers are usually of the range of -30°C to 50°C and they are made for managing the safe storage of food as well as managing the interior temperatures of houses. Any household thermometers in use must be accurate as faulty ones may cause food to be mistakenly stored in the dangerous bacterial growth zone (4°C to 60°C) resulting in food poisoning.

Thermometers can be bought at very low price (about $3 for a plastic thermometer of 40 cm, 16 inch in length, as in the photo) from general stores but they ARE NOT guaranteed to be accurate and users have to calibrate thermometers themselves before use.  The calibration is not simple to ordinary people as the ranges of these thermometers encompass only the temperature of melting ice (0 degree C or 32 degree F) but NOT the temperature of boiling water (at 100 degree C or 212 degree F).

This blog shows you how to calibrate household thermometers using no specialist instrument.

1. Required tools.

Calibrating a household thermometer requires:

a. Ice cubes to provide meting ice.

b. A large bowl to contain melting ice cubes and water.

c. One water kettle to provide boiling water.

d. Two identical cups or glasses

e. One bigger cup or glass with double the volume for mixing water from the above two identical cups.

2. Creating melting ice temperature.
Place some ice cubes in water drinking water in a glass or cup and let it melt. Stir the water thoroughly. The water is then at melting ice temperature. Dip the household thermometer into the water to verify its melting ice temperature.

The thermometer can now be used to check that some water is at the temperature of melting ice.

3. Creating boiling water temperature.
Boiling water is obtainable from the water kettle.

4. Creating half way (50°C = 122°F) temperature.
Pour one full cup of 0°C water contained in one of the identical cups into the bigger mixing cup.

Pour one full cup of 100°C boiling water contained in the other of the identical cups into the bigger mixing cup.

Stir the water thoroughly. The water is then at the temperature of 50°C. Dip the household thermometer into the water to verify its 50°C = 122°F temperature.

5. Usable thermometers 

Figure: A convenient electronic desk thermometer for home use. However being electronic does not guarantee its accuracy.

A usable thermometer should give correct readings for both temperatures of melting ice and of 50°C = 122°F.

Any error at either or both these established temperatures will lead to errors at other readings of the scale. The errors may cause dangerous consequences when applied to food storage.

The following is a dangerous food storage thermometer I have kept to prove that dangerous instruments do exist.

6. An example of dangerous fridge thermometers.

Figure: A re-calibrated, previously  faulty (dangerous) fridge thermometer.

The fridge thermometer in the photograph here was actually outrageously faulty making it a dangerous food storage thermometer. Its original markings are still visible under my re-calibration marks (Red marks are for positive including zero and blue marks are for strictly negative temperatures.).
Readers can see that the original markings are quite faulty:

Original indicated  -28°C   is actually  -10°C

Original indicated   10°C    is actually   25°C

Just imagine what may happen to any trusting thermometer owner using it to prepare for the storage of his food at indicated 0°C, which is actually 10°C. The latter temperature is actually in the DANGEROUS bacterial growth zone (4°C to 60°C).

My re-calibration has been double checked using a laboratory thermometer. The original markings were unbelievably faulty.





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