The salt solution passes through the permeable meat cells during the soaking process using the method of osmosis. Osmosis is the diffusion of water through a semi-permeable membrane - in this case the meat cells. Through diffusion, the salt and water within the meat cells balance with the salt and water in the surrounding brine which results in a higher concentration of salt and water in the meat. Food chemists disagree about the mechanics of this diffusion and how salt travels across membranes, but at the end of the day, the diffusion results in more water and flavor within the cells of the meat. The high concentration of salt also denatures protein strands. In their normal state, the strands are tightly wound; denatured strands unwind and tangle. During cooking, this unusual structure traps water molecules and holds onto them. The end result of this osmosis is less moisture is lost during cooking.
Are you asleep yet?
In layman's terms: Salt retains water+salt invades meat = moist, flavorful turkey
A few more key points:
1. Don't stuff your turkey. I know this is a great debate and a possible deal breaker for some of you but hear me out. Other than it being a cesspool of germs, a messy pain, and a recipe for soggy stuffing, it won't work so well with this process. You miss out on the aromatics completely, it affects the cooking process, and the saltiness could affect your stuffing. Bake it in a pan. If you want it more moist (soggy like we're used to ;) add more chicken stock.
2. You must have a probe thermometer. A digital reader with a little cord attaching to a probe that can be left in during cooking. Not only is this essential to your turkey success, it's a good investment for your roasting future. You can put it in and leave it in so you're not leaving a gaping whole for juices to spill out of (don't take it out until turkey is done resting!). Also many have alarms so you don't have to wait around baby sitting your birdie.
3. When you insert the probe make sure it's in the thickest part of the breast. Not in the dark meat. Not in the cavity. If it has a pop up thermometer ignore it but don't remove it. It would just be another gaping hole for juices to escape. And I know the temperature seems low but it will keep cooking after you remove it! Trust me. That was based on a 20 lb bird so if yours is smaller, sure cook it a few more degrees. But remember you can always put it back in if it doesn't reach 165 but you can't undo what you've already done. With all of that said, don't stress! I over cooked my bird last year and it was still the juiciest we've ever had.
4. I was going to write a whole gravy post but then I happened on the pioneer woman's site and she's got a great pictured "how to" on gravy with brined turkey that shows exactly what I would've done any how, giblets and all. So hop on over there. I may just finish mine with a little brandy and cream but otherwise she's spot on.
5. Email or text me with your questions...even on thanksgiving morning and I'll walk you through it. And please, let me know how it turns out.