to knowing which ones need a marinade. More than anything, you need to make sure the beef is of good quality. Perhaps you've already followed these steps but are now discovering that expensive cut of steak you spent a pretty penny on has turned gray or a brownish red. It leaves you wondering if you've been storing your meat the wrong way or if those steaks are still safe to eat. The answer depends on a variety of factors.

Beef is actually purplish in its natural state and not red, like we may assume. The red color comes from a protein called myoglobin, which binds to oxygen in muscle cells. So, when myoglobin is exposed to oxygen for the first time, the steak turns a brighter red as it forms oxymyoglobin, a lighter, fresher-looking pigment. That slimy, pulpy, red liquid you see after removing it from the packaging? That's actually myoglobin, not blood. Leave the meat exposed to oxygen a little longer and it begins to turn brownish red or gray due to oxidation. 

Think of it like that silver jewelry you wear, which darkens as it tarnishes over time, or the rust that forms on iron grills — same chemical process, different surface. But this doesn't necessarily mean your steak has gone bad. While the color can be a warning sign, it has to show up alongside a few other indicators before you decide to toss those steaks.