How deep should the food probe thermometer go in water when testing?

When testing a probe thermometer in water, it should be submerged at least 2 inches deep. Make sure the probe isn't touching the sides or bottom of the pot as this can give false readings. The probe needs enough space to get an accurate reading of the water temperature.

Common misunderstanding: It's unnecessary to immerse the probe thermometer deeply because modern thermometers are highly sensitive and can measure accurately with just a touch of the water surface.

While modern thermometers are indeed sensitive, they still require proper immersion to provide accurate readings. The sensor, which is typically located at the tip of the probe, must be fully submerged at least 2 inches into the water to ensure the reading reflects the actual temperature of the water and not the ambient air or surface temperature.

Common misunderstanding: Touching the sides or bottom of the pot with the probe won't affect the temperature reading as long as the water is very hot.

Even with hot water, touching the sides or bottom can lead to inaccurate readings. The material of the pot can conduct heat differently than water, which may skew the thermometer's reading, resulting in incorrect temperature measurements. Always ensure the probe is free-floating in the water for the most accurate results.

Do I need to stir the water while testing?

For cold testing in an ice bath, you should gently stir to keep the temperature even throughout. However, be careful not to let the probe directly touch any ice cubes as this will affect the accuracy. When testing in hot water, stirring isn't necessary - just ensure the probe remains steady and submerged while taking the reading.

Common misunderstanding: Stirring is only necessary for cold water, not an ice bath, as the ice will naturally cool the water evenly.

In an ice bath, stirring is crucial because it prevents thermal layering, where water near the ice is much colder than water further away. Stirring ensures a uniform temperature throughout the bath, leading to more accurate calibration of the thermometer.

How long should I wait before taking the temperature reading?

You need to wait until the temperature reading stabilises. The temperature must remain static for at least ten seconds before taking your final reading. This ensures you're getting an accurate measurement rather than a fluctuating temperature as the probe adjusts.

Common misunderstanding: Once the thermometer displays a temperature, it's ready to be recorded immediately, as digital thermometers are instant.

Even digital thermometers require a few seconds to stabilise and provide an accurate reading. It is crucial to wait until the temperature remains constant for at least ten seconds. This practice ensures that the reading reflects the true temperature, avoiding fluctuations that may occur as the probe adjusts to the food or liquid's heat.

Common misunderstanding: A rapid fluctuation in the reading is acceptable as it indicates the thermometer is responsive.

While a responsive thermometer is beneficial, rapid fluctuations in temperature readings suggest that the probe has not yet stabilised. An accurate reading is achieved only when the temperature display remains consistent for a period, confirming that the thermometer has adequately acclimated to the environment's temperature.

UK Official Guidance

• UK Food Standards Agency guidance including food probes

USA Official Guidance

• FDA guidance including including food probes