Rapid cooling is essential to prevent multiplication of microorganisms in potentially hazardous foods. This requirement is frequently not met with viscous foods in large containers. The time required to cool an 8-gal container of white sauce from 105 to 57 F was 25 hr. Similarly, a 14-gal container of beef stew required 84 hr to cool from 115 to 50 F. Under some conditions, cooling times are directly proportional to the square of the shortest dimension of the food sample. For example, if the shortest dimension is doubled, cooling times are increased by a factor of four. The effect of most plastic containers on cooling rates of foods is generally insignificant. Thermal properties of polyethylene, nylon, and Teflon are similar to thermal properties of foods, and a 1/8-inch-thick container will have about the same effect as an additional 1/8-inch thickness of the food. Polystyrene, however, has a very low thermal conductivity and will significantly delay cooling of most foods.