Sterilization of food in cans has been well studied both experimentally and theoretically, but little or no work has been done on sterilization of food in pouches. The food pouches have only been recently introduced to the market. In this study, transient temperature, velocity profiles and the shape of the slowest heating zone (SHZ) have been established. for a uniformly heated three-dimensional pouch containing carrot orange soup, using saturated steam at 121 degreesC. The computational fluid dynamics (CFD) code PHOENICS was used for this purpose. The liquid food used in the simulation has temperature-dependent viscosity and density. From the simulations, the maximum axial velocity of the soup was found to be 10(-2) - 10(-4) mm s(-1), which was due to the small height of the pouch and high viscosity of the soup. The SHZ was found to migrate into a region within 30-40% of the pouch height above the bottom and at a distance approximately 20-30% of the pouch length from its widest end. The experimental measurements were conducted at Heinz Watties Australasia based in New Zealand. The measured temperature at different locations in the pouch was compared with that predicted. Both results were found to be in good agreement. The results of a simulation done for the same pouch geometry and material considering pure conduction mechanism were also presented for the purpose of comparison. (C) 2001 Elsevier Science Ltd. All rights reserved.