Don't panic: shiny, iridescent corned beef is safe. Named for the "corns" of salt used to make it, corned beef sometimes has a colorful shine that might alarm you, but is no cause for concern.
This iridescent coloring of the beef has nothing to do with the quality or safety of the meat. Meat with this characteristic is perfectly safe to eat.
Cured meats may contain nitrites or other chemicals that can produce a colorful sheen on meat products.
Myoglobin and hemoglobin, two proteins found in beef and other meat products, can also contribute to colors on the exterior of the corned beef.
Exposure to both light and oxygen can cause these colors to become more pronounced, so make sure to tightly seal meats like corned beef to minimize this effect.
The Bottom Line
A shiny appearance or multi-colored surface is normal on corned beef. When in doubt, verify the sell-by date printed on the product.