When you take the meat out of the vacuum pack, the first thing that happens is oxygen reacts with pigments – and turns the meat red.
After a while, the meat starts to oxidise, and turn brown, in the same way an apple or potato turns brown when exposed to the air.
It's a perfectly normal process – in fact, it's the same process that’s used to dry-age beef.
However, meat stored in your fridge at below 4°C should remain red for a few days. If yours turns brown very quickly it could be an indication your fridge is set to the wrong temperature. Because the higher the temperature the quicker it turns brown.
Why does supermarket meat look so red?
Most supermarkets use a mixture of gasses to keep meat looking “fresh” - and to extend its shelf life.
Fresh meat, in standard packaging, only lasts a few days in a fridge – while meat packed in a gas flushed pack can last a couple of weeks. Or more.
It's called modified atmosphere packaging. And here's why it's done...
Colour and visual appeal Oxygen helps meat retain it's bright red colour. Consumers associate red with freshness – so it makes meat look fresher than it might actually be.
Shelf life Carbon dioxide slows down the the growth of bacteria and other microorganisms and extends the shelf life of meat.
Packaging Nitrogen – an inert gas – is used as a “filler”. It maintains the internal pressure of the package and helps it to keep its shape.
In a nutshell... the bright red colour you see, has little to do with freshness.
Note You can dry-age beef after it's been frozen – but it's not recommended. Especially if you're doing so at home. Dry-ageing beef is a complex and lengthy business, best left to professionals.