6.1 The Need for In-process Control
The collective experience of the international fish canning industry is generally sound: nevertheless, manufacturers can ill afford to overlook the outbreaks of botulism which in 1978 and 1932 led to the death of three consumers of commercially canned Alaskan salmon. In both these cases spoilage was the result of post-process contamination by C. botulinum (type E). The first outbreak involved only one can from a production lot of 14 600 units, yet the manufacturer inspected (visually and with a dud detector) some 14 million units. Reportedly, 3 515 cans were screened botulinal toxin and all were negative. The second outbreak was attributed to a single can from a production lot of some 24 000 cans, and led to the recall of 60 million containers from nine canneries. During this investigation approximately 1 000 cans were tested for the presence of botulinus and none was found. In addition to the logistical difficulties of implementing extensive recalls, these incidences demonstrate the impracticability of relying on large scale product recalls and quality audits as a means of detecting unsafe finished product.
In 1978 the International Commission on Microbiological Specifications for Foods (ICMSF), stated that microbiological sampling methods are inappropriate for assessing the safety of low-acid canned foods; said ”… experience demonstrates that, if present, C. botulinum would be expected to occur at such low frequency that presence." Theoretically, the probability of a single C botulium spore surviving a "botulinum cook" (Fo=2.8 min) is estimated at 10-12(see section 1.3). The probability of botulism arising through C botulinum entering containers, via post-process contamination, has been estimated to be from 10-7 to 10-10., while that due to botulism being caused by the containers failing to receive a thermal process has been estimated at between 10-6 and 10-8. Notwithstanding that these figures are estimates and difficult to validate, it is clear that when the probabilities of (or its toxin) being present in a can of low-acid food are so low, the chances of