Uh?
Posted on 11/25/2001 8:38:06 AM PST by Jhoffa_
I have a question regarding pasteurization that no one has (thus far) been able to answer.
In a production environment, pasteurization units (Pu's) are the standard for determining pasteurization effectiveness. A pasteurization unit is equal to one minute @60° C. Depending of which bacteria you wish to kill each product is pasteurized to a specified number of PU's. The total number of Pu's are a product of both Time and Temperature.
My question is: How is the total number of PU's calculated over a production run where the times and temperatures vary?
What is the formula for accurately determining total Pu's when you have the time/temperature available?
I had thought that it was a simple matter of raising the Lethal Rate to the power of (Tempurature-base)
Example: Pu's per minute = Lt ^ (Temp - 60)
So if the Lt were, say 1.235 And the Temp were 62° You would be pulling down 1.52 Pu's per minute.
But I now have a Chart from a major manufacturer of Pasteurization Equipment and while this formula is dead accurate in the middle of the chart, error creeps in as you near the high and low temperature extremes.
So, what is the formula for calculating these Pu's accurately, regardless of temperature?
ANY HELP you can provide will be greatly appeaciated.
Thank You.
Uh?
I personally know an ex-quality manager who has no idea what the answer is.. and the Present Quality Manager has no idea either (she makes seventy grand BTW)
A large majority of their products are pasteurized and they refer to the chart to determine if the product has been pasteurized properly.
Aside from that, production would cease.. because no one can accurately calculate these PU's.
No one can calculate this themselves without the Pu chart. And it's a huge company making millions a year.
I would be willing to bet you have consumed one of their products at some point..
Correct, you are targeting specific organisms..
And there is a "D" value which effectively gives you a list of organisms which die after a certain time/temperature
The Lethal Rate, is calculated from this "D" value.
Assuming the Lethal Rate to be fixed. (pick a number, 1.393 works.. very close to that of beer)
How can I calculate this?
Honestly, No one can answer this.. If you need more information I will do my very best to provide it.
The variables are: Time, Temperature, Lethal rate (use 1.393) And the sum (sigma) of total Pu's accumulated over a given period.. (delta, a change in)
And, don't sweat the paper.. Lot's of guy's look sexy with no eyebrows.. Honest!
(Have I ever lied to you?)
My microbiology work on milk products goes back to the late 1950's. Can't remember a lot of specifics. I do remember that there were a couple of different ways of pasteurizing. One [the 'flash' method] involved bringing the product up to a high temperature for a very short period [perhaps a minute]; the other involved holding the product at a somewhat lower temperature for a lengthier period of time.
As I recall a critical point was the cream line . If you got milk held too long long at too high a temperature the cream turned an interesting color and was aesthetically unappealing.
My microbiology work on milk products goes back to the late 1950's. Can't remember a lot of specifics. I do remember that there were a couple of different ways of pasteurizing. One [the 'flash' method] involved bringing the product up to a high temperature for a very short period [perhaps a minute]; the other involved holding the product at a somewhat lower temperature for a lengthier period of time.
As I recall a critical point was the cream line . If you got milk held too long long at too high a temperature the cream turned an interesting color and was aesthetically unappealing.
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