A guide to setting the temperature tolerance of your food storage thermometers.

This guide explains how to set appropriate temperature tolerances for food storage thermometers, taking into account the following areas:

  • Legal requirements for specific food categories
  • The type of products being stored (e.g. high-risk, ready-to-eat or low-risk foods)
  • Calibration accuracy and measurement uncertainty (included on your UKAS certificate)
  • Whether the device is monitoring a Critical Control Point (CCP) under HACCP
  • The performance capability of the equipment

Typical UK Storage Temperatures

Across the UK, standard storage temperatures are clearly defined:

  • Chilled storage: 4°C or below
  • Frozen storage: -18°C or below

Food factories must ensure compliance with any applicable maximum or minimum legal temperature limits.

It’s also worth noting that certain product categories may be subject to stricter limits under food safety legislation or specific customer standards.

Understanding Temperature Tolerances

Temperature tolerance defines how much a temperature can deviate from its target before corrective action is required. When setting the tolerance of food storage thermometers, it’s important to consider the following points:

1. Calibration Deviation and Measurement of Uncertainty

You need to account for calibration deviation (how much the device reads above or below the true temperature) and measurement of uncertainty (the small margin of error inherent in the device).

These factors affect the accuracy of every reading and must be considered when setting the tolerance of your food storage thermometers or verifying compliance with legal limits.

On your UKAS Calibration Certificate, you will find the measurement of uncertainty (e.g., ±0.13 °C), along with the true readings at different calibration points (e.g., at 0 °C or −18 °C).

Example

According to a thermometer’s UKAS Calibration Certificate, the instrument reads +0.5 °C when calibrated at 0 °C, this is the calibration deviation. The measurement of uncertainty is ±0.13 °C.

Using this information, we can work out the potential range of the true temperature:

0 °C (displayed value) + 0.5°C (calibration deviation) – 0.13 °C (measurement of uncertainty) = 0.37°C

0 °C (displayed value)+ 0.5°C (calibration deviation) + 0.13 °C (measurement of uncertainty) = 0.63°C

Therefore, the true temperature could be anything between 0.37°C and 0.63°C

Ensure your temperature monitoring is accurate, compliant, and audit-ready

Selecting the right thermometer, backed by reliable calibration and clear documentation, is key to setting appropriate tolerances and demonstrating compliance. That’s why at Klipspringer we provide:

  • Highly accurate thermometers with traceable certification
  • Online certificate portal to centralise your documentation
  • Ongoing technical support to help maintain accuracy and compliance
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2. Use Within HACCP (Critical Control Points)

When a thermometer or monitoring device is used at a Critical Control Point (CCP) under your HACCP system, the temperature tolerance must ensure that:

  • Critical limits are never exceeded in practice.
  • Combined effects of measurement uncertainty, calibration deviation, and normal operational variability do not compromise food safety.
  • Your site can demonstrate effective monitoring and due diligence to enforcement officers.

The tolerance of your food storage thermometers should be tight enough that, even in a worst-case scenario, the true temperature remains within validated critical limits. This may involve:

  • Adjusting internal acceptance criteria (e.g., requiring a slightly higher displayed temperature).
  • Factoring calibration deviation and measurement uncertainty into HACCP documentation and verification procedures.

What are the dangers of getting this wrong?

Failing to set a suitable temperature tolerance could create a food safety risk, as if the thermometer readings are artificially high, the true temperature may not meet the validated critical limit.

Conversely, readings that are artificially low could trigger unnecessary corrective actions, even when the product is actually within safe limits.

Why ±2°C Is Often Too Wide for Food Safety

In some cases, sites will apply a blanket tolerance of ±2 °C for temperature monitoring, but this approach can lead to compliance and food safety risks.

For example, if chilled storage is set at 4 °C with a ±2 °C tolerance, the upper limit effectively becomes 6 °C. This may exceed safe storage temperatures for high-risk foods.

Similarly, for frozen storage set at -18 °C with a ±2 °C tolerance, the upper limit becomes -16 °C, which may not meet expected standards for frozen food storage.

Customers, auditors, and Environmental Health Officers (EHOs) are likely to challenge tolerances that allow storage above recognised safe limits.

Top Tips for Ensuring Best Practice

1. As a general guide, it’s a good idea to set the operating target lower than the legal maximum, as this will create a safety margin.

2. The temperature tolerance needs to be tight enough to ensure legal compliance, whilst also being a realistic choice for the equipment in question.

3. Document the rationale for your chosen temperature tolerances. Reference UKAS calibration data, HACCP critical limits, product risk assessment, and legal temperature requirements.

Example

The temperature tolerance for a chiller

  • Target: 3°C–4°C
  • Tolerance: ±0.5°C to ±1°C (depending on equipment capability)

The temperature tolerance for a freezer

  • Target: -20°C
  • Tolerance: ±1°C (ensuring temperatures do not rise above -18°C)

Setting appropriate temperature tolerances for the food storage thermometers at your site not only ensures ongoing compliance with food safety requirements but also helps demonstrate due diligence in protecting consumer health.

If you require additional support in this area or would like to learn more about our wide range of thermometers and accessories, contact us on 01473461800 or sales@klipspringer.com. Alternatively, you can share your details using the contact form below. 

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