Stresses and cracking in freezing spherical foods: a numerical model

Thermal stresses during the freezing of a spherical food were simulated with an elastic model, using realistic thermal and mechanical properties. It was found that to explain observed cracking patterns, both expansion due to phase change and thermal contraction subsequent to it must be taken into account. During freezing, the unfrozen core is always under uniform isotropic tensile stress, but that is unlikely to explain the cracking pattern. Cracking during cryogenic freezing is more likely due to tensile tangential stresses caused by thermal contraction, with vitrification at the surface possibly playing a role in crack initiation. The calculations suggest that once a crack forms at the surface it will propagate towards the centre, as has been observed experimentally.