The cherry-red color that you are use to seeing when you purchase a fresh roast is the result of myoglobin and oxymyoglobin, two pigments that when combined with oxygen turn bright red. Continued exposure to oxygen and bright store lighting results in the formation of metmyoglobin, a third pigment responsible for turning the pleasing cherry-red color of the roast to a more unappealing brown. This pigment change does not necessarily mean that the roast is bad.

Green and iridescent rainbow hues also tend to make consumers wary of the freshness of a piece meat. Iron, fats and other compounds are often benign causes for such color changes, which is why it is important to check for additional hints that may spell spoilage. If brown or other color changes are present, smell the meat to check for rancid or off odors. Fresh meat does not have an overwhelming smell. If it does, the roast may be spoiled. After smelling the meat, pick it up with your hands. Fresh meat feels moist, yet firm. If the roast feels slippery or slimy, it may be bad.

Meat is a perishable item and should always be stored at temperatures of 40 degrees Fahrenheit and below. If a roast is stored outside the refrigerator -- cooked or raw -- for two hours or more, it is no longer safe to eat, brown or not. In temperatures of 90 F and above, the same roast is no longer safe to eat after one hour. Bacteria on the meat grows to dangerous levels after this time and may cause serious foodborne illness.

Roasts only keep for a short while in the refrigerator. This is because bacteria on the meat does not die during refrigeration, but merely slows. Roasts have a shelf-life of three to five days in the refrigerator. After that time, do not cook or eat the roast. Instead, throw it away. Freezing gives you a bit more leeway, keeping roasts safe to eat indefinitely because bacteria is unable to grow. Safety aside, roasts keep for four to twelve months before the quality of texture and taste begin to breakdown.