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Pasteurisation Units and the relevance to 70°c for 2 minutes


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#1 dzabhi

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Posted 03 December 2019 - 05:22 PM

Hello

 

Would anyone be able to explain some details of pasteurisation units to me?

 

We are currently cooking protein products through a steam oven with the objective of achieving a core temp of 70°C for 2 minutes (as per BRC and Campden guidelines). We validate the process using temperature data loggers that monitor the core temperature of the product throughout cooking and chilling.

 

When we come to assess the data, we use a z value of 7.5°C, as this is what Campden says is necessary to achieve a 6 log reduction of Listeria Mono - someone please correct me if I am wrong here.

 

The software we use then calculates the pasteurisation units based on the the below criteria:

  • Tmin = 60°C
  • Tref = 70°C
  • Z = 7.5°C
  • tref, seconds = 60

 

Please can someone with more thermal processing knowledge and experience than me explain what pasteurisation units results we should be looking to achieve and if any of the above criteria/logic is flawed?

 

Apologies if i've not explained this very well, if you need more info then please do ask.

 

Thanks in advance,

Danny



#2 pHruit

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Posted 03 December 2019 - 06:47 PM

IIRC there is a formula in the Campden guide (I don't have a copy of it at home so can't check it) that is probably the one to use if you're citing that as a reference source, and indeed in general they are widely acknowledged as an authority on thermal processing, at least in the UK.

From memory the formula is something like PU=t*10([T-Tref]/z)

So in your case you'd put your values in and get:
PU=60*10([70-60]/7.5)=1292.7

 

I'm not sure about your t value though - this is the (core) treatment time so would be 120 seconds for two minutes?

You should definitely check my working in any case, as you don't want to rely on what I can/can't remember without the relevant formula in front of me.

The other key item to check is the z value, as this will depend on the specific matrix (material/food) you're looking at - I know the Campden book has a reasonable selection in there, but it certainly isn't exhaustive and if there isn't a good match then you may need to do a literature search and/or give Campden a call. Again I'd recommend reading the Campden guide, as from memory it goes into quite a bit of detail on the basis for the calculation and it's much better to get to grips with it that way if possible.

 

Generally PU is useful for comparing thermal processes - for example, if you want to reduce temp for organoleptic reasons you can work out how much you have to increase time, or vice versa. As you'll see from the structure of the formula, temperature has a significantly greater impact on lethality than time ;)






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