Food is exposed to a carefully measured amount of intense radiant energy, called ionizing radiation. This is done in a special processing room or chamber for a specified duration. With food irradiation, radiant energy (electrons, gamma rays, or x-rays) breaks chemical bonds, leaving the food still like fresh, but with specific benefits, depending on treatment level.
The most common source of ionizing energy is cobalt 60. This radioactive material is contained in two sealed stainless steel tubes (one inside the other - double encapsulated) called "source pencils." These are placed in a rack and the entire rack is immersed in a water chamber underground when not in use.

When irradiation takes place, the rack is raised. Packaged food products move along the conveyer belt and enter an inner room where they are exposed to the rack containing source pencils. Energy in the form of gamma rays (or photons) pass through the encapsulation and treat the food.

When food is irradiated, most of the radiation passes through the food without being absorbed. The small amount that is absorbed destroys any insects, extends shelf life, and prevents fruits and vegetables from ripening too fast. Thus, food irradiation may replace chemical fumigants, sprout inhibitors, and post harvest fungicides. Higher doses can kill Salmonella and other microorganisms that can contaminate meats and poultry and cause food borne diseases.

Food irradiation is a "cold treatment" that achieves its effects without raising the food's temperature significantly, leaving the food closer to its original state. By not using high temperatures, food irradiation minimizes nutrient losses and changes in food texture, color, and flavor.

The energy used in food irradiation is not strong enough to cause food to become radioactive. During irradiation, energy passes through food much like a ray of light passes through a window. This energy destroys most of the bacteria that can cause disease by damaging the genetic material of the contaminating organisms so that they can no longer survive or multiply. Yet it allows food to retain its high quality.

Irradiation pasteurizes food by using energy, just as milk is pasteurized using heat. However, unlike pasteurisation, it can also be used on solids as well as liquids. At the level used, most harmful bacteria will be destroyed. Afterwards, surviving bacteria could start to multiply if the food were mishandled: such as, stored at an improper temperature. The level of irradiation used also does not kill certain spoilage organisms. This is for the protection of consumers. Spoilage bacteria will multiply and alert consumers not to use a product which has been improperly handled.
 

Irradiation facilities must include many safety features to prevent both environmental and worker exposure. The use and transportation of radioactive materials - including the equipment and the facilities in which they are used -- are closely monitored by the Nuclear Regulatory Commission, state agencies, and the Department of Transportation. A food irradiation plant is not a nuclear reactor. In a reactor, a nuclear chain reaction takes place, heat is generated and used to make steam which turns a turbine and creates electricity. Proper controls are needed to contain the chain reaction and maintain proper cooling. A food irradiator is completely different.

Cobalt 60 gives off rays that are absorbed by the food. Little heat is generated. Even spices which are treated for 2-4 hours remain essentially at room temperature. Since no chain reaction occurs, there is no chance of a meltdown. Although water is used to shield the cobalt when it is not in use, the water is not radioactive.
 

The Electron Beam Linear Accelerator, (E-beam)    Accelerators work on the same principle as a television tube. Instead of being widely dispersed and hitting a phosphorescent screen at low energy levels, the electrons are concentrated and accelerated to 99% of the speed of light. This produces rapid reactions on the molecules within the product. The Electron Beam Linear Accelerator machine generates and accelerates electrons to energies of 5,7.5 or 10 MeV (Million electron volts) with beam power of up to 10 kW.

Meat receiving e-beam treatment

 A Conveyer or cart system moves the product to be irradiated under the electron beam at a predetermined speed to obtain the desired dosage. Products move in and out of the irradiation area continuously. Product thickness depends on density and electron energy. For example, e-beam energy can penetrate meat a total of 3.5 inches with treatment on the top and bottom of a package.

However, as with any food, consumers must take appropriate precautions, such as refrigeration and proper handling and cooking to make sure that potentially harmful organisms do not present a problem.