Steriel of niet steriel, dat is de vraag

Summary This paper deals with a practical problem of sampling inspection, viz. the bacterial control of imported fishmeal (which is used in food for pigs). It was suspected that this fishmeal was often contaminated by salmonella‐bacteria, but only in about 0.5% of the samples the presence of these bacteria could be proved. An investigation by the Dutch National Institute of Public Health, at which 4 bags of fishmeal (about 50 kg) after homogenization were divided into 1000 samples of 50 grams each which were individually tested on the presence of salmonella bacteria, showed that nothwithstanding the homogenization the bacteria were very irregularly distributed. Every bag was contaminated, but only about 1.8% of the samples were infected. So the density of infection was low, but the fraction of infected bags was high. If the fishmeal were fed in a dry condition to the pigs the relevant parameter on which the condition of the fishmeal should be judged would have been the mean number of bacteria per gram of fishmeal. However, as food for pigs is mixed with water the bacteria have the possibility to increase in number so the relevant parameter to judge a batch of fishmeal is the fraction of non‐sterile bags. At the end of this paper a sampling scheme is given, including a system of penalty for producers who regularly supply contaminated fishmeal which will in a relative short time improve the quality of the imported fishmeal.