How does a brine work?

Quite a few readers out there have written in asking whether a salt crust gives a result similar to a brine when it comes to roast chicken. It’s a good question. Both methods surround the bird with a salty medium. Intuitively, they should produce a chicken that’s about the same in terms of taste and texture. But in fact that isn’t so.

The critical difference is water. A solution of just 3% salt will penetrate chicken muscle much more readily than the salt in a salt crust will, even though there’s a lot more salt in the crust. Which begs the question: why?

Most kitchen scientists answer the question with one word: osmosis. That’s correct, but only up to a point. For osmosis is the process by which water from a region of low salt (or other dissolved substance) concentration moves into a region of higher concentration through a semi-permeable membrane. Which means that by osmosis, when you place a chicken in a brine the bird will actually lose moisture, since the water in the chicken will move out of the muscle cells and into the brine. How does that help circulate flavors and/or make my bird juicy?

It’s doesn’t, but that’s only half the story. What happens next is the important part. For as water flows out of the muscle cells, salt flows in. And that does serious damage to the cells, dissolving protein structures both within the cells themselves and in the muscle fibers. The brine then gets literally sucked into the muscle as a result of capillary action (by which water can move — even against the forces of gravity — through very narrow passages as a result of the pull that molecules exert on one another).

Thus the muscle tissue takes in about twice as much water as it loses, and with that water comes not only salt but other flavoring components from the brine. So the meat becomes both flavorful and moist. The added benefit is that because the proteins in the muscle fibers have been structurally compromised, they can’t contract as much as they normally would when they’re exposed to heat. Which means the meat is more tender when it’s cooked.

Pretty neat. But this week we’re doing salt crust. So let’s stay focused, shall we people?