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Thermal Process CalculationsOverview of the General Method, Ball
Formula and NumeriCAL
IFTPS SOUTH EAST ASIA TECHNICAL OUTREACH SEMINAR
November 27, 2012
Terry L. HeyligerThermal Processing Manager
JBT FoodTechMadera, CA USA
Thermal Processing
Kill Bacteria in Food by exposing the product/container to HEAT
(at a specific temperature) for an specific TIMETIME
HEATHEAT
Process Calculations Upon completion of the heat penetration
test
one must analyze the time / temperature data and use the results
of the analysis to calculate a thermal process that will render the
product commercially sterile.
Process Calculations
A critical step in the design of a safe thermal process is the
process calculation. It is important that one understands the
calculation method employed as well as any conditions that may
restrict the use of a particular method.
Sterility (Fo value) The General Method Ball Formula Method
Process Calculations
NumeriCAL
Sterility
Death of a microorganism is defined as when it has lost the
ability to reproduce
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Commercial Sterility
1. Containers are free of viable microorganisms of public health
significance
MINIMUM PUBLIC HEALTH
2. Containers are free of microorganisms capable of reproducing
under normal conditions of storage and distribution
COMMERCIALLY STERILE
12D Concept Minimum Public Health
Minimum processes are established to reduce any population of
the most heat resistant C. botulinumspores by 10-12 or 12 log
cycles
or Reduce the probability of survival to:p y
1 C. botulinum spore in 1x1012
or
1 in 1,000,000,000,000
5 D Concept Commercially Sterile
Reduce the population of a common mesophilic sporeformer, C.
sporogenes, by 5 log cycles or 10-5
D-value
Time in minutes to reduce the population of bacteria by 90% at a
specific lethal temperature
Effect of Temperature on D-value
As exposure temperature increases the rate of bacterial death
also increases
Effect of Temperature on D-value
Temperature (F) D-Value 111.1 20.0
115.5 7.3
121.1 2.0
126.1 .63
131.1 .20
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z-Value
Reflects the resistance of bacteria to different lethal
temperatures.
Equal to the number of degrees (F or C) required to change the
D-Value by 1 log cycle ( factor of 10)
Unit of LethalityF-Value
Sterilization value F expressed as the equivalent minutes at a
specified temperature
Based on the destruction of a population of bacteria having a
known z-value
Unit of LethalityFo-Value
Represents the equivalent minutes at 121.1oC (250F) at the
slowest heating point in the container
Based on the destruction of a population of bacteria having a
z-value of 10C (18oF)
Lethal Rate Value
The lethal-rate value assigned to each temperature is
numerically equal to the reciprocal of the number of minutes
required to destroy the same population of spores in one minute at
the reference temperature, 121.1oC
L = 10 (T-121.1)/10
Lethal Rate Value
Temperature, (oC)
Minutes to Destroy Spores*
Lethal Rate Value
101.1 100 0.01
111.1 10 .1
121.1 1 1
131.1 .1 10
* Same Population of spores with know z-value of 10oC
Lethal Rate Table