In this work we investigated the influence of solid particles on the heating of canned foods. A numerical model for natural convection heating of liquids developed by Datta and Teixeira in 1987 was used for predicting the values of temperature and velocity inside a can filled with liquid and grain. The solid particles influence the buoyancy that drives the flow during the heating of the can, and this problem has not been solved until now. As a first attempt to solve it, we assumed a radical simplification and treated the system composed of liquid and particles as a porous medium. FIDAP (Fluid Dynamics Analysis Package) was the finite-element-based software used for simulating the fluid and heat flow. The plots of distribution of temperature and velocity in the cans showed that the qualitative behavior of both cans (liquid and liquid+grain system) was the same: the liquid near the hot wall becomes lighter and rises, there is radial flow near the top and uniform flow near the centerline. In conclusion, we observed that the solid matrix reduces the magnitude of the velocities by approximately 10% and slows down the distribution of temperature in the can filled with liquid and grain.