By David Whittaker - 18 October 2019

Are you a manufacturer who applies heat to food? If so, it’s likely you’re applying a thermal process to reduce the level of microorganisms in your product, ensuring it’s safe to consume.

From pasteurisers to kettles, no matter what your thermal process is, it will need to be governed by a critical control point within a HACCP plan and, of course, it needs to be validated. This provides the evidence that ensures your thermal process is effective, repeatable and consistently produces safe products.

Having said that, chances are you have come across challenges when validating your thermal process. Many do. In fact, in our experience at Campden BRI, validation is often undertaken without a true understanding of why it is done or how to do it robustly. Lacking this understanding potentially compromises the safety of the process and prevents you from optimising it.

The challenges

We’ve compiled the key challenges of validating a process to help you overcome them:

1. Understanding what the process target is. Technical staff often target a specific temperature for a specific time. It’s usually the minimum level of heat treatment required to achieve a specific log reduction of a target organism, plus extra heating to give a margin of safety. Therefore, we recommend understanding and challenging a) the heat resistance of the organism targeted and b) the margin of safety specified. It’s possible you could reduce processing time with this understanding, or even experiment with time/temperature combinations that better suit your product.
2. Knowing the different validation techniques. Temperature measurement is the most common method to validate a thermal process. However, there are a variety of different sensors and probes/thermocouples which can be used depending on your product type and heating environment. We can provide advice as to what the best temperature measurement solutions are for your process type or we can explore other validation methods (e.g. by using surrogate microorganisms or enzymic methods).
3. Establishing where to position a probe and product sample. The exact point in the product where temperature measurement is being recorded is crucial as often within a pack, or within a unit of product, heating rates can vary (for example in a chicken drumstick heating rates by the bone are different to those in the flesh). It is a similar case with the positioning of validation samples within the heating system, for example, in a retort the top layer of a crate may heat very differently to the bottom layer, or racks of product by an oven door may heat at a different rate to those away from the door. Often extra testing is required to understand these crucial points fully.
4. Understanding the ‘worst-case’ variables of a process. When undertaking validation test runs, you need to understand how the amount of heat applied to your product may vary from day to day. This could be due to variations within the product, packaging or the cooking vessel. For example, the fill level of a drinks bottle, or the heating performance of a retort. These variables need to be controlled and set to replicate the ‘worst-case scenario’ of heating conditions during the validation run. This ensures an absolute minimum level of heat treatment will always be applied during normal production.
5. Interpreting validation data. A large amount of data is generated during a robust thermal validation. When analysing the data to calculate minimum P or F₀ values, several questions can crop up:
   • Which part of the cook program or cycle should be used to calculate the lethality?
   • If different areas of the retort or cooker vary, with large differences in temperature, what level of difference is acceptable?
   • The P/F₀ values are extremely variable, how can I be sure they will always be high enough?
   • Would it be sensible to apply a safety factor and over process the product? If so, by how much?

If you struggle with any of these challenges, or want to validate or optimise your thermal process, contact our processing support team.

Thermal validation can be a tricky subject to grasp, which is why we’ve produced two whiteboard videos to help you understand it. Head over to our videos page to watch me give a rundown on thermal process validation and optimisation.

About David Whittaker

David is a thermal and non-thermal processing specialist and has expertise across many food and beverage sectors.

David also delivers many thermal processing training courses and has a real passion for communication in this area, having spoken at several conferences and seminars on the topic, as well as contributing to Campden BRI guidelines.

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