Osmosis. Diffusion. Concentration. And how salt makes roast chicken succulent and crispy.
Yums. One of the big pleasures of a roast chicken (or turkey) is when the skin is crispy and the meat is succulent. But wait, how did they manage to make it both crispy and juicy at the same time?
It has to do with salt, and the wizardry it wields with osmosis and diffusion. Roast chicken recipes often call for salt to be rubbed into the surface of different parts of the chicken and left in the refrigerator for several hours (or a day or more).
These parts of the chicken where the salt concentration is higher will start to draw water from the rest of the chicken. This process is called osmosis, which is the movement of water from an area of high concentration of dissolved substances (in this case, the salt) to one of low concentration.
The water drawn out forms a salt solution. At the same time, when the chicken is cooked, water evaporates from the surface, leaving behind a highly concentrated salt solution.
This is where diffusion kicks in. Diffusion is the movement of molecules from an area where there are a lot of them (i.e. concentrated), to an area where there are fewer of them. Because the surface of the chicken now has such a high concentration of salt, the salt starts to diffuse into the chicken.
Then osmosis kicks in again. As the salt concentration increases inside the chicken, water is now drawn back from the surface into the meat, in a reverse of what we started out with at the beginning.
The drier exterior gives us a crispier skin, while the water drawn back in results in a juicier meat. This interplay of osmosis and diffusion and osmosis again is what produces such a delicious salted roast chicken. Yums. (p.s. you can also find out more about the all-important role of water in cooking in the 1-Minute NomNom “Water you cooking?“!)
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