RAI Legal

Dish Wash Temperatures


There is some confusion regarding the guidance on thermal disinfection. The FSA has been clear on chemical disinfection but there are ambiguities to its guidance on thermal disinfection. In essence:

  • For utensils used in prep of raw foods (chopping boards, knives etc) there is a clear standard: surfaces of utensils used in food processing areas must be thermally disinfected at 82°C and the surface needs to be at that temperature for 15 seconds (Annex III, Section I chapter II para 3 of Regulation (EC) No 853 / 2004)
  • For everything else it’s 80°C. Sort of. The FSA ‘Guidance’ – which ain’t  ‘guidance’, it’s the law enforced under HAACP – says 80. Sort of. Ish. 

What’s the temperature? Where? How’s it measured? I’ll discuss that below; the top level summary is that under the 2011 FSA Guidance (which is mandatory, not optional):

[notice]You need to disinfect food contact surfaces either using a compliant sanitiser / disinfectant or in a commercial dishwasher that achieves the correct temperature for thermal disinfection of bugs. [/notice]

Remember that ‘food’ is “any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans” and includes drink, water, ice, chewing gum and any substance intentionally incorporated into the food during its manufacture, preparation or treatment.

[important]The Devil’s In…[/important]

Thermal disinfection is one of the most reliable control measures for E. coli (and other foodborne pathogens) in a food operation but the temperature and contact time must be sufficient. And I’m sorry but it’s the FSA that are sending confused signals here, not me. I’ve just been sent the latest revision of their draft further guidance on this (that they promised three years ago) and it’s not much better.

So, what is the current standard and how is it enforced?

Page 27 of the 2011 Guidance is headed “Non-chemical disinfection – hot water and steam disinfection” and gives the standard of thermal disinfection required in commercial dishwashers.

“Properly maintained commercial grade dishwashers in which water reservoirs are maintained at a temperature of more than 80°C providing contact times of at least 15 seconds offer adequate disinfection control. The manufacturer’s cleaning and maintenance instructions must be followed and instructions typically include the removal of food debris, plastic wrapping and limescale from the water jets, filters and drains, as well as carrying out regular cleaning.”

The ambiguities which are obvious here are:

1) Relationship between reservoir temperature and temperature of utensils

Page 21 / Q46 of the FSA’s latest iteration of the guidance seems to repeat Annex III, Section I chapter II para 3 of Regulation (EC) No 853 / 2004 which requires that surfaces of utensils used in food processing areas must be thermally disinfected at 82°C. While that specific EU standard would not apply here, the FSA refer to a surface temperature of 82°C but a reservoir temperature of “more than 80°C”.

What are ‘utensils’?

One could argue, for example, that if only crockery and glassware is going through a machine this would not qualify as ‘utensils’ and so the standard would not apply. But the section of the 2011 Guidance that deals with this refers to thermal disinfection in the round, and there is a requirement to disinfect ‘all surfaces and equipment involved in food preparation’ using chemical or thermal means. On that basis any argument that plates and glasses etc going through the dishwasher are not ‘food contact surfaces’ would seem unlikely to succeed.

Is it tank or surface temperature?

Another ambiguity here is that EHOs cannot easily measure reservoir temperatures given the location of the water heater. They can measure the water as it comes out of the rinse jets but not easily or accurately.

Is there further FSA Guidance?

It’s clear the FSA is aware of this issue and Q44 of their July 2012 ‘Q&A’ publication poses the question “How will I know if my dishwasher meets the requirements of the guidance?” They say:

“The Agency has commissioned some work to examine the operation of dishwashers in relation to the requirements of the guidance. This work will examine the time/temperature combinations that can produce an adequately sanitised product, as well as the contribution to decontamination made by the chemicals within the wash cycle. Once this work has been completed, we will update this Q&A document accordingly. Until then food businesses should ensure that any dishwashers are in good working order, fit for purpose and the appropriate setting is used.”


So, can you ignore thermal disinfection requirements pending further clarification from the FSA? Of course you could, but EHOs are enforcing the 2011 Guidance now, including the requirement for thermal disinfection.

Clarifying the FSA’s Current Position

I have spoken to Enforcement at the FSA; pending the result of the independent research their position is that provided the surface temperature on plates, crockery and glassware is 71°C or higher this is sufficient for thermal disinfection and that is the standard that EHOs should be inspecting.

Current Enforcement Practice

In the absence of clear-cut published advice from the FSA, unless they have spoken to Enforcement on this issue we find EHOs are tending to conflate the 2011 Guidance with the EU standard and say that ‘all items in commercial dishwashers need to be held at >82°C for 15 seconds in order for thermal disinfection to occur’.

We have tested some by saying “>80°C?” and in almost all cases were corrected and told ‘it’s 82°C’. But do not forget that most commercial dishwashers in FBOs are used for utensils as well and not purely for crockery so you can see how this approach has arisen.

What is Tested and How?

Let’s look at what is happening in the field. Despite efforts to bring a more consistent approach to the application of hygiene regulations there is a lot of variation in how standards are applied and this will continue to be the case until the FSA publishes a standard EHOs can easily enforce – just as the FSA did with sanitisers.

In ‘real life’ almost all EHOs we speak to want to see that the machine temperature gauge reads over 82˚C and that there is a rinse contact time of at least 15 seconds. They also want to see visibly steaming crockery coming out of the machine that is very hot to the touch. By and large if they are taking a relaxed approach and see these two things combined with proper records they will be happy. If not they are likely to investigate further. If an EHO wants to check the temperature, traditionally they have had several methods available.

  • If there is a temperature gauge (as there is in this case) a relaxed EHO may simply rely on that
  • They can take a sample of the rinse water and check that – but the days of EHOs sticking their arms into commercial dishwashers are becoming ever rarer due to H&S concerns. Sampling technique also makes this erratic and under-reading can result
  • The use of probe or IR thermometers – each has its strengths and weaknesses and there are also sampling issues
  • The surface of the items being washed can be measured using melt point technology. This is fast and very accurate. The strips change colour at 65˚C (considered adequate for domestic dishwashers) 71˚C and 82˚C.

We are seeing more and more EHOs using melt strips which also give FBOs a permanent audit record.

[important]The Thermal Landscape[/important]

Our surveys using the melt point strips to compare actual temperatures reached on surfaces compared with that shown on the gauge show:

  • Only 50% of all machines tested reached or exceeded 82˚C
  • A further 38% reach or exceed 71˚C (so 88% reach 71˚C but only 50% then go on to 82˚C)
  • The remaining 12% reached or exceeded 65˚C

Interestingly a variation of 20˚C (and both under-reading and over-reading are not uncommon). We are still collecting data but there is one thing about which we can be reasonably certain: whatever requirement the FSA ends up with it is likely to be evidence-based and not based on what is currently happening in the marketplace. We await their next pronouncement with interest. Don’t forget that in addition to this key point, dishwashers should be cleaned regularly, including the removal of food debris, plastic wrapping and limescale from the water jets, filters and drains assure they function correctly.

[important]What’s the Future?[/important]

The missing bit is ‘thermo-chemical’ disinfection. No bacteria is going to survive the high pH (often >12) in the wash tank so it isn’t just thermal disinfection going on. But their mistrust of chemical disinfection – or, more accurately, their trusting food businesses to use chemicals properly – means the FSA will probably still hang their hat on thermal disinfection.

A sensible approach would be to adopt the World Food Safety Guidelines for (inter alia) airline catering which is that an 82˚C hot tank temperature relates to a final dish temperature of 71˚C and they consider 71˚C adequate for chemical / thermal (as opposed to purely thermal) disinfection. For domestic dishwashers the achievement of 65˚C is generally considered satisfactory but the cycle time is much, much longer.

[notice]How Do You Know If You Comply?[/notice]

Easy. I have some very groovy thermal strips – stick one to a plate, bung it through a wash cycle and it’ll tell you whether your machine has hit the correct temperature. If you contact me I’ll happily post one out as a thank you for reading this far!