Typically, digital thermometers are easy to use and quick to respond. They generally consist of a probe, a display and an electronic means of converting the data received from the probe detector into a displayed reading.
However, despite being easy to use, there are a few things you need to be aware of when using one to measure the temperature of food.
The Thermometer Itself
The first thing to remember is that a thermometer measures its own temperature as well. This means that the probe must be allowed to reach the temperature of the substance or object of which you are measuring.
Inside the probe is a detector which relays information to the electronics of the thermometer. When you insert the probe into a substance, for example hot soup, the probe will start to heat up.
If the probe is large and thick, it will take longer to heat up and the detector will therefore take a long time to react. In this instance the display will show a slowly increasing temperature. This makes the determination that the thermometer has reached the final temperature more difficult.
A thin probe will react more quickly, reach the appropriate temperature, and remain steady if the temperature of the substance is steady.
Where to take the Reading
It is very unlikely that the whole of an object or substance will be the same temperature throughout. You need to decide therefore where to insert the probe to take the temperature.
In a pan of soup on a stove, the bottom of the pan and the soup immediately adjacent to it will be very hot, whilst the middle of the soup could be cold. This is particularly true when reheating frozen liquids.
To get a better reading, the liquid should be thoroughly stirred and the temperature taken whilst the pan is stirred. This will then give the average temperature of the whole content. Remember though, if the probe touches the bottom of the pan, your reading will tell you the temperature of the pan, not that of the soup.
When cooking food in an oven, generally it is being heated from the outside and therefore the temperature must be taken in the centre of the object.
It may be that the item being heated has different densities and different thicknesses, which will take different times to heat. As an example, the bones and thickness of meat in a turkey leg can be a problem and therefore the temperature probe should be inserted into the thickest part of the leg.
Similarly when cooking joints of meat of varying thickness, it is the thickest part should be tested.
If you are reheating food in a microwave, the item can often be heated in different areas, thus resulting in the development of hot-spots. It is essential that resting time is allowed for in the process, to allow the heat to even out, and accurate temperatures to be taken.
Infrared is not Ideal
The development of infrared thermometers has revolutionised temperature monitoring – but it must be appreciated that an infrared thermometer only measures the surface temperature that it sees i.e. the outside of an object. The ideal combination therefore is an infrared thermometer with a probe facility.
The Length of a Reading
A digital thermometer may show temperatures at 1°C or 0.1° intervals. If the reading does not change for 20 seconds on a 1°C instrument or 5 seconds on a 0.1°C instrument you can be confident that a satisfactory reading has been achieved. Obviously this will require a longer time if you need a more accurate reading.
The probing of foods can involve cross-contamination. Probes should be wiped clean after each measurement with an anti-bacterial probe wipe, and ideally different probes should be used for highly contaminated foods such as raw poultry.
Temperature requirements for commercial preparation of foodstuffs can be found in the Food Safety (Temperature Control) Regulations, England & Wales.
Temperatures should be monitored and recorded on a regular basis to show due diligence. To save time and effort, dataloggers are a useful tool for keeping a record of storage temperatures.