12 replies to this topic

[Tran Lam Thanh]

Hi All,
I am also not clear about how to calculate the Fo Value for UHT process.
Example: my product is Ready To Drink Tea
pH : less than 3.5
UHT Condition: 116oC & holding time : 20sec.
How i calculate the Fo value for this process. I don't have info about Heating step (embient temp. to 116) and Cooling Step (116 oC to 88oC) for filling. Do theses steps contribute to Fo Value ?

Thanks

[Charles.C]

Hi All,
I am also not clear about how to calculate the Fo Value for UHT process.
Example: my product is Ready To Drink Tea
pH : less than 3.5
UHT Condition: 116oC & holding time : 20sec.
How i calculate the Fo value for this process. I don't have info about Heating step (embient temp. to 116) and Cooling Step (116 oC to 88oC) for filling. Do theses steps contribute to Fo Value ?

Thanks

Dear Tran Lam Thanh,

I doubt that 116degC is classified as UHT.?

As you say, you are missing some data for a complete analysis for F0.

Data points below 100degC can usually be neglected for the times involved in this case.

One approximation is to neglect the heating / cooling periods. The error will be small if times are rapid. Result will be a minimum value for F0.

Formula for uniform temperature period (ie 20secs) is –

F0 = (t/60) x 10 ^ [(T-121.1)/z]

Symbols
F0 is the number of minutes of equivalent sterilisation at 121.11°C.
^ = (to the power)
t = sterilisation time in seconds at T °C
T = sterilisation temperature in °C
121.1degC = sterilisation reference temperature
z = a value expressing the increase in temperature to obtain the same lethal effect in the 1/10 of time. The value varies with the origin of the spores (10 – 10.8°C) and can generally be set as 10°C. (ex milk handbook)
(If the formula is expressed in °F, the reference temperature is 250°F and the z value normally 18°F.)

The result for t=20sec is F0 = 0.103 min (approx).

You can also try the data out in an on-line calculator at –

http://www.dairyscie...info/uht123.asp
(the answer will probably be approx 0.1)

Rgds / Charles.C

PS Pls revert if your answer different, maybe my error.

[Mendeljev]

I agree with Charles : For UHT processes i think more in the range of 135°C and a time of 22 sec

In UHT processes there are no heating and cooling steps involved : UHT means that the product (mostly a liquid) is immediatly is exposed to high temperatures.
As the tubes passing the thermal zone are very narrow, the liquid inside is exposed to a high temparature at once.

Offcourse the pH of your product can explain the rather low thermal threatment needed : at ph < 3,5, you need to look at other microorganisms and you only require (in theory) 1 min at 60°C for safety measures; this is because low pH is icreasing the heath sensitivity (target organism = salmonella, shigella and campilobacter)
For a shelf stable product the process should be more of 3 min at 90°C (target organism = ascospores A.acidoterrestris spores)

At my factory we always combine acid foods with pasteurisation, resulting in a shelf stable product

Hope this make some sence

Kind regards
Mendeljev

[Tran Lam Thanh]

Dear Tran Lam Thanh,

I doubt that 116degC is classified as UHT.?

As you say, you are missing some data for a complete analysis for F0.

Data points below 100degC can usually be neglected for the times involved in this case.

One approximation is to neglect the heating / cooling periods. The error will be small if times are rapid. Result will be a minimum value for F0.

Formula for uniform temperature period (ie 20secs) is –

F0 = (t/60) x 10 ^ [(T-121.1)/z]

Symbols
F0 is the number of minutes of equivalent sterilisation at 121.11°C.
^ = (to the power)
t = sterilisation time in seconds at T °C
T = sterilisation temperature in °C
121.1degC = sterilisation reference temperature
z = a value expressing the increase in temperature to obtain the same lethal effect in the 1/10 of time. The value varies with the origin of the spores (10 – 10.8°C) and can generally be set as 10°C. (ex milk handbook)
(If the formula is expressed in °F, the reference temperature is 250°F and the z value normally 18°F.)

The result for t=20sec is F0 = 0.103 min (approx).

You can also try the data out in an on-line calculator at –

http://www.dairyscie...info/uht123.asp
(the answer will probably be approx 0.1)

Rgds / Charles.C

PS Pls revert if your answer different, maybe my error.

Many Thanks Charles.C
Do you have any standard about Fo Value for each kind of product (pH<3.5, pH>4.5,...) ?

[Charles.C]

Many Thanks Charles.C
Do you have any standard about Fo Value for each kind of product (pH<3.5, pH>4.5,...) ?

Dear Tran Lam Thanh,

Can try the post below, last attachment. May be others elsewhere also.

http://www.ifsqn.com...dpost__p__49275

Rgds / Charles.C

[Mendeljev]

Please find an extract out of the course i followed on F-values in relation to pH and the specific microorganisms to target
I use this quite a lot and i find this very usefull

Have fun

Kind regards

Mendeljev

Attached Files

•  Fvalues.pdf   899.02KB   233 downloads

[Fat Cat]

Dear Tran Lam Thanh,
For a UHT process, 116°C isn't UHT at all. Normally UHT starts at around 135°C.
As your product is acidic, treating at 125°C for 4s should be sufficient. Provided your system is clean.
Hope your guys do the sanitation properly and regularly.

Hope that helps.

[zhou]

Dear Tran Lam Thanh,dear all, the process whose sterilizing temperature is lower than 130oc,it is impractical  to calculate the sterilizing intensity with the reference temperature at 121oc,i suggest the reference temperature at 95oc, then the formula is  (t/60) x 10 ^ [(T-95)/z]

[Charles.C]

Dear Tran Lam Thanh,dear all, the process whose sterilizing temperature is lower than 130oc,it is impractical  to calculate the sterilizing intensity with the reference temperature at 121oc,i suggest the reference temperature at 95oc, then the formula is  (t/60) x 10 ^ [(T-95)/z]

Dear zhou,

 

No problem but it will then be necessary to designate the result as something other than F0.? And rewrite all the English language canning texts ?.

F_zh perhaps ?

 

Rgds / Charles.C

[zhou]

Dear zhou,

 

No problem but it will then be necessary to designate the result as something other than F0.? And rewrite all the English language canning texts ?.

F_zh perhaps ?

 

Rgds / Charles.C

deaar charles.c, it should be rewrite the result other than F0, and the F0 is only the sterilizing intensity at 121.1oc, also the sterilizing intensity can be write as F95 or F65, do you remember the meaning of the PU, or the P*, or the B*? otherwise should it all be write as F0? it is impractical!

[Charles.C]

Dear zhou,

 

I'm not sure I understand yr comment.

 

I have no particular objection to using any of quantities like F0, B*, C* as appropriate. Or a lethal effect referred to any other convenient temperature. My comment was only regarding the conventional use of 121.1 degC for F0 and the latter's typical use in canning  theory.

 

If you are disagreeing with the common usage of F0 in canning texts, i guess it's just a matter of opinion.

 

Rgds / Charles.C

[Marvein]

Hi All,
I am also not clear about how to calculate the Fo Value for UHT process.
Example: my product is Ready To Drink Tea
pH : less than 3.5
UHT Condition: 116oC & holding time : 20sec.
How i calculate the Fo value for this process. I don't have info about Heating step (embient temp. to 116) and Cooling Step (116 oC to 88oC) for filling. Do theses steps contribute to Fo Value ?

Thanks

[Marvein]

A few comments pretty late in the day. A product with a pH of < 3.5 wiluld not normally need a high temperature treatment to obtain commercial sterility unless you had a high count of thermally resistant spores that were capable of growth at low pH.

I note that the material on the Dairy Science and Food Technology has been updated to provide free ON Line Fo,B* and C* calculators. The article at

https://www.dairysci...processing.html provides the links