1. Data on the maximum temperatures of growth of certain organisms, on the rate of toxin production by Cl. botulinum and the rate of multiplication of certain Salmonellas, is given, as a basis on which to define the time and temperature of dehydration in the preparation of dehydrated foods.
2. It is concluded that 50° C. is the minimum temperature below which dehydration should not be carried out. Where some heating below this temperature is unavoidable, the period of such heating should not exceed 4 hr.
3. Data on the microbial changes in dehydrated foods equilibrated at various humidities indicate that bacterial growth is not expected below about 15 % water content. Some experiments on the death of bacteria at water levels below this are discussed.
4. Details are given of the general bacteriological examination of the process of dehydration on a commercial scale for dried soup, dried minced beef, dried carrot, cabbage and potato.
This work was carried out under the joint auspices of the Food Investigation Board of the Department of Scientific and Industrial Research, and the Ministry of Food, and is published by permission. The authors are indebted to Professor H. R. Dean for the provision of facilities, and to him, Professor G. S. Wilson, Dr A. W. Downie, and various other members of the Emergency Public Health Laboratory Service for help and advice.