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Pasteurisation F values

Printed From: Dairy Science and Food Technology
Category: Thermal processing
Forum Name: Thermal processing
Forum Description: Effects of heat on food, enzymes and microorganisms
Printed Date: 02 Dec 2020 at 4:14pm
Software Version: Web Wiz Forums 12.03 -

Topic: Pasteurisation F values
Posted By: Admin
Subject: Pasteurisation F values
Date Posted: 17 May 2010 at 8:23pm

I have had an interesting series of Emails concerning the determination of the F value of a product which received an in pack pasteurisation heat treatment. I am summarising these discussions and making them as generic as possible to avoid any confidentiality issues.

Companies processing e.g.  sous vide type-products must ensure that they are safe. This means subjecting the product to a time / temperature treatment that will reduce the probability of the presence of viable pathogenic or spoilage organisms by the requisite number of D-values. Lets say that regulatory authorities in a particular country specify that manufacturers must ensure that their products are subjected to a lethality equivalent to say 65°C for 10 minutes. The F value must be determined using 65°C as the reference temperature; every minute at this temperature will give a value of 1.   During the heating and cooling period of the product  some microbial destruction will take place and this needs to be calculated.  As a consequence the lethality  calculated during heating and cooling must be added to the lethality experienced at the reference temperature. The methodology for doing this is described on this site and the F value can be calculated using the - calculator or e.g. an - Excel spreadsheet.

Posted By: Jennie
Date Posted: 09 Aug 2010 at 1:34am

Dear Dr. Michael,

Thank you so much for your post. I still have a question. If a process authority said our process needs 79.4 C for 5 minutes. In order to calculate least sterilizing value, I have set 79.4 C as reference temperature. Shceduled process is fill and hold process. Can filling temperature be some where below 79.4C, let say it's 69 - 72.2 C? Would this be possible? Or filling temperature needs to be above reference temperature?
Please kindly advise.
Thank you very much in advance.


Posted By: Admin
Date Posted: 09 Aug 2010 at 11:08pm
Dear Jennie
First and this is important. Will your regulatory authority accept a process that gives a lethality equivalent to 79.4 C for 5 minutes? Or do they require you to hold a product at 79.4 C for 5 minutes and to evidence this using temperature / time data?
Assuming the former is true then you can obtain a lethality equivalent to 79.4 C for 5 minutes by holding at a lower temperature than the reference temperature say 69 or 72 for the appropriate time. Note that extended holding times will be required. You will also need to add the "come up" and "come down" times.  You can use the spreadsheet at -  to quickly do the calculations assuming a Z value of 10C or the free lethal rate calculator at -  . 

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