Have you ever wondered how some produce and meat last so long on the shelf? Modified atmosphere packaging is the answer, and we broke down how it works.
Ever notice how some prepackaged meats, vegetables, and cheeses have an expiration date that seems surprisingly far out for such perishable foods? That's most likely because their wrapping utilizes a technology called modified atmosphere packaging (MAP) that alters the air inside the package to prolong shelf life and maintain the food's fresh appearance.
Air normally contains about 78 percent nitrogen, around 21 percent oxygen, and a fraction of a percent of carbon dioxide. The way MAP alters that composition varies from product to product. For ground beef, MAP typically replaces the air inside an impermeable package with essentially no oxygen, 20 to 30 percent carbon dioxide (to stall the growth of microbes), low levels (0.4 percent) of carbon monoxide (to turn the myoglobins in the beef from purple to a more appealing red), and the remainder with nitrogen. MAP used for produce requires a permeable membrane that allows fruits and vegetables to continue to “breathe”—that is, consume oxygen and give off carbon dioxide—during storage. The permeable package allows oxygen to be replenished (too little and the produce “dies” and rots) and keeps carbon dioxide at optimum levels to kill microorganisms such as mold.
Though MAP can dramatically impact the shelf life of food and gives you the flexibility to buy food well in advance of consuming it, be aware that once you open the package, the food will deteriorate at a normal rate.
When we opened a package of ground beef stored in MAP and rewrapped it, it turned gray and sticky in five days (left). When left in MAP, ground beef packed on the same day with the same expiration date as the package we opened continued to look fresh far past the expiration date on the package (right).