In the Chocolate
On 16 July, Cadbury was fined £1 million, having pleaded guilty to charges that they had put unsafe chocolate on sale, had failed to alert the authorities that salmonella was in the chocolate, had breached hygiene controls, and had committed six other food safety offences at their Marlbrook manufacturing plant in Herefordshire. Essentially, Cadbury came unstuck because of bad risk-management policies. The worst was a decision they made in 2003 to introduce an ‘allowable tolerance’ level for salmonella in their chocolate. Instead of destroying contaminated product, they would let it onto the market if the number of bacteria in it was very small. This was bad science. It is very difficult to measure numbers of bacteria in foods like chocolate; underestimates are very likely. Also, the bacteria will probably not be evenly distributed, so some portions will contain more than the estimated number. Worst of all, Cadbury failed to draw rational conclusions from the evidence revealed by the study of previous chocolate outbreaks. A possible and plausible explanation is that the scientists advising Cadbury were still being influenced in their thinking by experiments done long ago. The feeding of ‘volunteers’ in US prisons in the 1950s – not with chocolate but with bacterial cultures – showed that the lowest dose that caused infection was about 125,000 live organisms. In the case of one strain, fifty million were needed. The textbooks still say that large numbers are needed to cause infection.
The full text of this essay is only available to subscribers of the London Review of Books.