Myoglobin. Denaturation. Meat. And the science behind how you want your steak done.
Go to a restaurant, order a steak, and the server will ask how you would like it done. Very often, you might choose anything from rare to well done. But what exactly is rare, or well done, or medium well, or any combination in between? And what’s the science behind them?
The science starts with the oxygen-storage protein myogloblin, which is found in muscle tissue. It plays an important role when a piece of meat goes from raw to cooked. You can read the details in the 1-Minute Marvels “Oxygen, you turn me(at) red”, but here’s a summary (for those who are impatient!):
1) On its own, myoglobin is dark purplish and is the reason freshly cut raw meat looks that way.
2) Once a piece of meat has been exposed to oxygen, myoglobin will turn into oxymyogloblin. This gives the meat we see in supermarkets its bright red.
3) When the meat is cooked, at about 60°C/140°F, myogloblin denaturates, giving us metymyoglobin, which is gray (or grayish-brown?), a color we see in cooked meat.
The last chemical and biological change is particularly interesting. Because of conduction (read all about how this works in the 1-Minute Marvels “Pleased to heat you“), the heat takes time to be transferred from the surface of the steak to the insides. Hence the surface temperature would be higher than the inside.
This means that the surface may be denatured already (i.e. the temperature is above 60°C/140°F) and look gray, while the inside would still be red (i.e. below 60°C/140°F).
These different colors are the visual cues — take a look at the featured photo at the top of this post again — to what restaurants are referring to when they ask if you want your steak rare, medium, or well-done. And it’s also how you can tell, when your steak is served, whether the restaurant got your order right.
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