If salt dehydrates the meat, then why would brining make it more juicy as a whole?

Question

As the title says, why does brining work?

If salting, by osmosis, pulls the water out of the meat, then why is meat considered more juicy after it's cooked?

Answer 1

Actually, it's a popular misconception that brining works because of osmosis. If it was really osmosis at work, plain water would work better than salted water. Kenji over at The Food Lab went into this a few months ago: http://www.seriouseats.com/2012/11/the-food-lab-the-truth-about-brining-turkey-thanksgiving.html

Here's the relevant bit:

To understand what's really happening, you have to look at the structure of turkey muscles. Muscles are made up of long, bundled fibers, each one housed in a tough protein sheath. As the turkey heats, the proteins that make up this sheath will contract. Just like a squeezing a tube of toothpaste, this causes juices to be forced out of the bird. Heat them to much above 150°F or so, and you end up with dry, stringy meat.

Salt helps mitigate this shrinkage by dissolving some of the muscle proteins (mainly myosin). The muscle fibers loosen up, allowing them to absorb more moisture, and more importantly, they don't contract as much when they cook, making sure that more of that moisture stays in-place as the turkey cooks.

In the article he discusses the downsides (flavor dilution) and alternatives to brining (salting). I'd check it out, it's a good read.

Answer 2

To further add to this. Here's an explanation from the Chefsteps site on brining

The Effects of Brining Charged chloride ions from the dissolved salt in a brine will repel, destabilize, and unravel various proteins within the muscle fibers of meats and seafood. This is not altogether different than what cooking with heat also does to these proteins.

The combination of dissolved salt and heat combine to increase the juiciness of flesh by drawing water in during brining and squeezing less of it out during cooking.

Brined foods that are cooked have a telltale texture because the combination of salt and heat creates a firmer, more elastic gel than heating does alone. But avoid overdoing it, otherwise the flesh can become too firm and chewy, as well as too salty.

Equilibrium Brining