The container is then evacuated and sealed. In order to minimize the production of off-flavors the product would be frozen before it was irradiated. The container might be some type of flexible pouch or a metal can. The dose received is related to the flux rate of the source and the distance of the product from the source. If the product was not cooled it would increase in temperature as the radiation was absorbed, but the temperature increase would be small compared to the increase observed during conventional cooking.
Irradiation kills microorganisms by different mechanisms than does conventional heating.
The gamma rays have enough energy to break DNA molecules when a direct hit occurs. Once this happens the bacteria are unable to reproduce. There is also a secondary effect in unfrozen products where highly reactive free radicals produced by the gamma rays can kill the bacteria. The most promising applications of irradiation are not sterilization treatments but are pasteurization treatments where a milder treatment is used. Low dose treatments can be used to eliminate insect infestations in food products.