How packaging changes the colour of (red) meat

Any time I’m cooking, or baking I think about my recipes and why I have to do what I do. So, when unwrapping a pack of meat before cooking I noticed all the different colours of this formerly red piece of meat. I saw brown, purplish and red/pink! Was anything going wrong here? Was my meat going bad? No, it wasn’t these colour changes are perfectly normal for meat and all depend on the way the meat is packed. So today: a first deep dive into meat colour and how it changes because of the packaging.

Packaging meat

Let’s start at the basics, how is most of our meat packed? In my shopping world, there are roughly three options:

  1. Vacuum sealed, in other words, all air has been pulled out and the plastic sits tightly around the meat.
  2. Modified atosphere packaging, you might not recognize this immediately, but just about all the meat in supermarkets packed in a plastic tray with a sealed plastic layer have been packed this way. It means that the air in which the meat lies does not have the same composition as the air around us does. More on this later.
  3. Hand wrapped in a bag or tray by a butcher.

What’s important in this story is the composition of the air. As we will see, the air composition highly influences the colour of the meat. More or less oxygen influences how the meat looks like. So how does that look like for our packages?

  1. Vacuum sealed: there is no air, thus no oxygen
  2. Modified atmosphere packaging: it all depends on the product that’s inside, the producers can put whichever gas is best for the product. In the case of red meat this generally means there’s quite a bit of oxygen, more than in regular air.
  3. Hand wrapped: this pack contains the same air as the one around us, thus roughly 20% oxygen, a little carbon dioxide and roughly 80% nitrogen.

Hand wrapped meat

After buying a piece of meat at the butcher, who hand wrapped it in a little tray I left it in the fridge for a while before using it. When taking it from the container I saw that it didn’t have a consistent color everywhere any more! When cutting into the meat there were three different colour layers which slowly started disappearing after cutting into the meat.

Meat different colours

These three layers can be grouped by their oxygen content:

  • Top: this sits in an oxygen rich air (our normal air around is)
  • Middle: there’s no oxygen inside the meat
  • Bottom: there’s very little oxygen at the bottom, but the meat has been in contact with the oxygen before packing

Myoglobin, Colour and Oxygen concentration

Before delving deeper into this we have to take one step back: what causes the colour of meat? The colour of red meat (e.g. beef) is determined by the molecule called myoglobin. Myoglobin is a protein. Inside the proteins iron ions sit. This construction of protein + ion causes it to be able to bind oxygen. Whether it has bound oxygen determines the colour of the myoglobin.

There are roughly three colours the molecule + ion can be as determined by oxygen concentration:

  1. No oxygen present: the myoglobin does not bind any oxygen and turns a purple colour (the form of the molecule is then called: deoxymyoglobin).
  2. Little oxygen present: the meat will turn brown (the state of the myoglobin is now called: metmyglobin).
  3. Plenty oxygen (e.g. in the air): the meat turns red (oxymyoglobin is present, the red variant).
Red meat from supermarket MAP
A fresh piece of meat from a recently openend ‘modified atmosphere pack’, notice the bright red meat colour.

What about carbon monoxide?

Commonly the main impact on colour is caused by the presence or absence of oxygen. However, industry has found out that also the presence of carbon monoxide influences the colour of meat. If there is enough cabon  monoxide present, the meat will turn a lighter pink colour. Adding some carbon monoxide ot meat will thus make it look more appealing.

Relating pack with meat colour

So let’s turn back to that first observation of the hand wrapped meat. The top layer which is pink/red is clearly the part that has come into sufficient contact with oxygen and thus is a nice red. The bottom however seems to have had some oxygen, but not enough, causing it to turn brown. In the center however, no oxygen sits at all, thus it remains purple.

After leaving the meat on a counter for a couple of minutes it could be seen that the whole piece of meat had turned to red again. All pieces from the fresh cuts had been able to get into contact with oxygen again and thus the myoglobin transferred to red again.

What’s the best packaging technique for red meat?

So based on these phenomenon there are clear advantages and disadvantages of the different types of packaging of red meat. Vacuum packed meat will make meat look a very dark red, sometimes even purplish which not all consumers might appreciate. Hand wrapped meat has the disadvantage that it will turn brown over time. Modified atmosphere packaging however can be used in such a way though that the meat remains a beautiful red over time. It can do so by either eliminating oxygen or by strongly increasing the oxygen content.

Unfortunately, the packaging world isn’t as easy as that. The air composition of a pack of meat doesn’t only influence the colour, it also influences shelf life. Generally speaking, a vacuum packed piece of meat keeps a lot longer than the other two packs and hand wrapped keeps for the shortest amount of time. Also, adding too muxh oxygen to a MAP piece of meat can increase the growth rate of bacteria, thus causing the meat to spoil faster. What’s more, different cuts of meat tend to react slightly different to different packaging methods.

 

So next time you look into buying meat, have a look at the pack and how it affects the appearance of the meat!

Also, if you’re a meat packer, consider these different options when packaging your products. They greatly affect how consumers perceive the products.

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