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How to calculate spoilage rate in canning

Printed From: Dairy Science and Food Technology
Category: Thermal processing
Forum Name: Thermal processing
Forum Description: Effects of heat on food, enzymes and microorganisms
Printed Date: 28 Nov 2022 at 6:39pm
Software Version: Web Wiz Forums 12.03 -

Topic: How to calculate spoilage rate in canning
Posted By: Guests
Subject: How to calculate spoilage rate in canning
Date Posted: 22 Mar 2010 at 10:56pm

Good to see the Fo calculator. Tnks!

How do you work out how many canns should fail micro test. Pet food for cats.



Posted By: Guests
Date Posted: 22 Mar 2010 at 10:56pm

It is fairly easy to calculate the number of surviving micro-organisms
in a canning process. I say fairly easy since a knowledge of both the effects of heat on microorganisms and maths, probability and logarithms in particular, is required!

The critical equation has been described by Stumbo* in his well known book on 'Thermobacteriology in food processing':-

t = D(log a - log b)

D= decimal reduction time (minutes) at a reference temperature for target organism-time to reduce the population by 90%
t= total equivalent time in minutes at reference temperature
a= initial microbial load
b= number of surviving micro-organisms.

Using this equation one can predict the probability of one or more cans spoiling, this can be adjusted for 100, 1000, or whatever number you want. I have developed a simple model which shows how to do this and enables D and other values to be varied. The URL is at -

You dont say what your problem is. If the spoilage rate is in excess of the predicted one then you have a problem. This might be caused by ingress of contaminated cooling water, check residual chlorine levels; defective seams; inadequate processing; high spore loads.

*Stumbo, C. R. (1973) Thermobacteriology in food processing. Second edition. Academic Press, New York and London.

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