Food Safety

19.1 Microbiological data is often recorded using log numbers (see table below):
RECORDING MICROBIOLOGICAL DATA
Number
Log 10 0.1
-1: 1
0 :10
1 :100
2 :1000
3 :10,000
4 :100,000
5 :1,000,000
6 :10,000,000

; In order to record graphically the wide range of numbers of bacteria which may be encountered, and to permit statistical analysis, microbiologists customarily record results in terms of log to the base 10 (Iog10) of the number:

Number
Log 10
6: 0.8
20: 1.3
32 :1.5
63 :1.8
316: 2.5
631 :2.8
2,000: 3.3
3,160 :3.5
20,000: 4.3
An increase or decrease of log 10 1 (often referred to as 'one log') represents a 10-fold change.
Log mean results are calculated by taking the arithmetical mean of numbers for each carcase and taking log 10 of the result:
e.g. 5 carcases; 4,500, 3,400, 4,800, 800, 10,900 cfu/cttl2
Arithmetic mean
= [4,500+3,400+4,800+800+10,9001/5 = 24,400/5 = 4,880
= Log10(4880)
Log mean
'ISO' is the International Organization for Standardization (see footnote 5). UKAS (see footnote 8) (http://www.ukas.com/new_docs/technical-17025.htm)
18

You can use a scientific calculator (on most PCs - go to accessories /calculator
/view /scientific) to calculate logs (enter the number then 'log')________ or to Inverse logs (enter the number then 'inverse' then 'log').______

A result of 2.3X 10E4 = 23000 = 4.37 log
This can be calculated on a calculator using the log function. They can be converted back by the inverse log function. This as indicated above can be found on your PC calculator.