The Question of Colour
Contrary to popular belief, the colour of beef is not a reliable indicator of freshness. In its initial state, beef is a deep purple colour. As it is exposed to oxygen in the air, the pigment turns cherry red. That same beef can turn purple again if oxygen is removed. The perfect example is vacuum-packaged beef.
With certain packaging types, that initial cherry red pigment will begin to take on a slightly brown hue quite quickly. The meat is still fresh and safe to eat, but just not as bright a red as when it was first exposed to oxygen. The Best Before date is still the best way to know if your fresh beef needs to be prepared and eaten right away or frozen.
Some ground beef can be brownish in the centre. This is because the small amount of oxygen present in the centre gives the meat pigment a brownish hue. However, the meat remains fresh and safe to eat up to its Best Before date.