Sterilization of food in cans has been well studied both experimentally and theoretically, but little work has been done on sterilization of food in aluminum based semi rigid packaging. In this study, transient temperature and the shape of the slowest heating zone (SHZ) have been established for a uniformly heated three dimensional Alupak packaging type B 232 containing a mixture of solid and fluid food, during all steps of sterilization, through modifications to container geometry by Gambit 2.3.16. The computational fluid dynamics (CFD) code Fluent 6.3.26 was used for this purpose and governing equations for energy were solved numerically using a finite volume method. The model food was assumed to have constant properties.The measured temperature at SHZ in the container was compared with that predicted by model. Both results were found to be in good agreement and the difference was not significant at p 0.01. Key Words Sterilization, Fluent software, Semi-rigid container, Slowest heating zone, Gambit software