Impact of the method chosen for measuring temperatures on the efficacy of rapid cooling of foods in catering facilities

Cooked dishes must be cooled rapidly after cooking to avoid significant growth of Clostridium perfringens. French regulations require that produce be cooled from 63 degrees C to 10 degrees C in less than 2 h. Cooling is a critical phase for central cooking facilities that need to cool large quantities of food. The food is cooled in blast-chillers before being placed in cold storage. We observed that in France the blast-chiller is usually switched off by operators as soon as a measured temperature is equal to or below 10 degrees C. This temperature measurement may be taken at any place in the batch. We studied the consequences of this procedure on the distribution of temperatures at the time when cooling is stopped. We did this by monitoring the core temperatures of the foodstuffs during 52 cooling operations carried out in seven central cooking facilities for hospitals or schools. The data allowed us to estimate the characteristics of the distribution of temperatures within batches. Simulations suggest that, when the blast-chiller is switched off after cooling, there can be significant differences between random temperature readings in the batch and the highest temperatures. For 5% of simulations, the difference could be greater than 17 degrees C. We propose alternative rules to reduce this discrepancy. If such a single measurement was replaced by three measurements, with each of them taken at the centre of a container, this difference would be less than 3.8 degrees C in 95% of the simulations. The improvement of methods for measuring temperatures is necessary to achieve the cooling durations recommended by the official organizations. (C) 2011 Elsevier Ltd. All rights reserved.