Sinner’s circle of heat, time, mechanical action and chemical action is a well-known way of analysing the effectiveness of any cleaning process.

The Sinner’s Circle describes the four key factors that determine the effectiveness of a cleaning process: time, temperature (heat), chemical action and mechanical action. The principle is that these elements are interdependent - if one factor is reduced, another must be increased to maintain the same cleaning effectiveness.

However, in food processing, cleaning alone is not enough. Cleaning removes visible soils such as fats, proteins, and food residues, but it does not necessarily eliminate harmful bacteria. To ensure surfaces are truly safe for food contact, a second step, sanitising, is required.

This short article looks at the four elements that go into an effective sanitising process and the equipment necessary to achieve each element.

What is sanitising?

First let’s remember what sanitising actually means. Sanitising reduces bacterial pathogens to safe levels, typically aiming for a 99.999% (log‑5) reduction in organisms like Salmonella and E. coli. This can be validated by swab tests. For some high risk areas we might want a 99.9999% (log-6_ kill rate). In the UK, this is often achieved using chemical sanitisers that combine cleaning and disinfecting properties. Because of this, the term “sanitising” is commonly used in industry practice to describe the full process of cleaning and microbial reduction, even though technically, disinfection is a stronger process aimed at killing most microorganisms.

It is worth nothing that sanitising is not about achieving a total kill of all pathogens. That would be sterilisation. It is about getting to a generally agreed safe level to allow food to be processed and prepared.

The Four Elements

To make sanitising truly effective, it helps to look at the process in four essential elements. Each element plays a critical role in ensuring that surfaces are not just visibly clean, but microbiologically safe. By understanding and controlling these four factors, food processors can consistently achieve the required pathogen reduction and maintain compliance with hygiene standards. 

1. Surface preparation

If the surface being sanitised is not cleaned properly then it is very unlikely that enough pathogens will be killed to achieve the log5 kill rate. Fats, grime or mineral deposits will shield bacteria from contact with sanitising agents and so many more will survive. As such it is essential to remove as many hiding places as possible by cleaning the surface properly.

2. Coverage

Once the surface is prepared it is essential to deliver the sanitising chemical to the whole area. If bits are missed then, obviously, pathogens can survive. In order to achieve this, it is essential to equipment that gives an even and consistent spray pattern.

3. Dosing

Even if the surface is perfectly prepared and the sanitising liquid or foam covers the whole area,  it is all for naught if not enough chemical is delivered to achieve the required kill level. Sanitising sprays, fogs and foams will be generated by mixing water with a chemical concentrate.

4. Dwell time

The final element of effective sanitising is the contact time the sanitising fluid has with the target surface. The more contact time we can achieve, the better the pathogen kill rate will be. Required dwell time can be reduced by increasing the concentration of chemicals used but this is often wasteful and can create secondary problems such as unacceptable residues being left behind. It is, therefore, often more sensible to look at delivery systems that will improve dwell time.

Equipment selection and advice for each element of the sanitising process

Below are some practical recommendations for how equipment can support each stage of the sanitising process:

Surface preparation

• Use high impact cleaning jets for greater mechanical action
• Ensure the detergents used are suitable for the residue being removed i.e. they are of the right type and mixed at the right dose
• Use heat to help remove strongly adhered residues

Coverage

• Use finer sprays with low pressure to achieve better coverage in easy to reach surfaces
• Consider foaming systems to give a visual indicator of complete coverage
• Consider fogging systems for complex geometries like pipe systems

Dosing

• Use inline Venturi mixing stations that mix concentrate directly with mains water as it is used
• Consider centralised dosing pumps for even greater accuracy
• Use Venturi mixing stations to premix chemicals for use in mobile sanitising system – this will give more accuracy than mixing concentrate in a bucket

Dwell time

• Consider using finer sprays or mists that will spread more evenly and produce less run off
• Consider foam to increase dwell time and possible air assisted foam to produce even longer lasting dwell time

Conclusions

Once we break down the four elements that make up an effective sanitising system we can see that there are many potential implications for equipment choice. As with the 4 elements of Sinner’s circle for cleaning, increasing any one of the 4 elements of sanitising will improve overall effectiveness. This can mean we can reduce one or more of the other elements which might be more costly.

For example, if we increase the dwell time by using a foaming system then it may well be the case that we can reduce the amount of chemical applied i.e. reduce the dosing element of the mix. Understanding this mix and which equipment can benefit each element is essential to optimising sanitising processes.