To determine the F 0 value required in a particular process one needs to
know the D 121 of the target organism and the number of decimal
reductions considered necessary.w
F 121 ¼D 121 ðlogN 0 logNÞð 4 : 7 ÞIn this exercise, the canner will have two objectives, a safe product and a
stable product. From the point of view of safety in low acid canned foods
(defined as those with a pH 4 4.5)Clostridium botulinumis the principle
concern. The widely accepted minimum lethality for a heat process
applied to low-acid canned foods is that it should produce 12 decimal
reductions in the number of survivingC. botulinumspores (logN 0 log
N¼12). This is known as the 12D or botulinum cook. If D 121 ofC.
botulinum is 0.21 minutes then a botulinum cook will have an F 0 of
12 0.21¼2.52 min. The effect of applying a process with this F 0 to a
product in which every can contains one spore ofC. botulinum(N 0 ¼1)
will be that a spore will survive in one can out of every 10^12.
The canner also has the objective of producing a product which will
not spoil at an unacceptably high rate. Since spoilage is a more accept-
able form of process failure than survival ofC. botulinum, the process
lethality requirements with respect to spoilage organisms do not need to
be so severe. In deciding the heat process to be applied, a number of
factors have to be weighed up.
(1) What would be the economic costs of a given rate of spoilage?
(2) What would be the cost of additional processing to reduce the
rate of spoilage?
(3) Would this additional processing result in significant losses in
product quality?Most canners would regard an acceptable spoilage rate due to under-
processing as something around 1 in 10^5 –10^6 cans and this is normally
achievable through 5–6 decimal reductions in the number of spores with
spoilage potential (the USFDA use 6D as their yardstick). PA3679,
Clostridium sporogenes is frequently used as an indicator for process
spoilage and typically has a D 121 of about 1 min. This will translate into a
process with an F 0 value of 5–6; sufficient to produce about 24–30
decimal reductions in viableC. botulinumspores – well in excess of the
minimal requirements of the botulinum cook. Some typical F 0 values
used in commercial canning are presented in Table 4.4.
wFor pasteurization treatments, an analogous procedure is used to express processes in terms of their
P value or pasteurization units. Once again the reference temperature must be specifed. This can be
601 C, in which case: P 60 ¼D 60 (logN 0 logN).
Chapter 4 73