Food irradiation can be accomplished in three different ways, using three different types of rays: gamma rays, electron beams, and x rays. Gamma rays are given off by the radioactive elements cobalt and cesium. Gamma rays are powerful, and can penetrate through several feet of material. As such, precautions against technician exposure to the radiation are necessary, and a special irradiation chamber is needed.
Electron beams are not as powerful as gamma rays. They can penetrate to depths of a few centimeters. Nonetheless, they are excellent for the sterilization of surfaces. Electron beam sterilization of medical and dental equipment has been routine for decades. Additionally, electron beams are not radioactive.
X-ray irradiation of food was introduced in the mid–1990s. X rays are a blend of the other two techniques, in that x rays are as powerful and penetrating as gamma rays. But, like electrons, x rays are not radioactive.
Foods such as solid meat and poultry, and fresh produce are well suited to irradiation sterilization. Not all foods, however, are as suited to the irradiation process. Eggs, milk, and shellfish, for example, should be treated by another process to best preserve their quality. Food irradiation alters the taste or appearance of some varieties of grapes, lemons, and nectarines. Irradiation is no substitute for proper cooking and storage. Even irradiated food can become contaminated if it is improperly cooked or stored.