Sirloin follows the same path to spoilage as any other cut of steak. Steak keeps a few days longer than minced meat in the refrigerator and can be safely stored in a freezer for months. The U.S. Department of Agriculture recommends checking the colour, texture and smell of meat before cooking.
Look at the colour of the steak. Colour changes alone do not indicate that the sirloin has gone bad; according to the USDA, colouring simply indicates whether or not a protein called myoglobin has been exposed to oxygen. However, fading or darkening meat often indicates that the steak may have begun to spoil.
Touch the sirloin. The USDA reports that a spoiled steak feels either tacky or slimy.
Smell the steak, carefully. If the steak smells sour, "off" or makes you gag, throw it out.
For maximum longevity, do not keep the sirloin in the store's packaging, as most meat packers cover meat with a plastic film that allows oxygen to get in, interact with myoglobin and turn the meat red. Remove the steak from the store's package and place in a dry, airtight container.