Isn’t the turkey already brined by the kashering? I thought brining was only for treif turkeys. Would a second brining help, or has the meat already absorbed all it will take?

Kosher turkeys are already soaked and salted, which, in terms of adding moisture, is equivalent to standard brining. A “flavor” brine (rather than a salt water brine) sounds promising. I guess you could just call it a marinade?

I’ve always heard you should use peanut oil, which adds a very minor nutty flavor, if one at all, rather than the “oily” flavor of corn oil.

Flavor injectors are the way to go, though, regardless. It’s not that hard, and the ingredients are basic…some herbs you like, and some moisture, voila.

Shayt has it close, but not entirely right. I’ll have to check in McGee when I get home tonight to get a full explanation for you, but osmosis works the other way — water will flow through a semi-permeable membrane from an area of low solute (in this case salt) concentration to an area of high solute concentration. You can think of it as diffusion of water, from high concentration of water to low concentration of water. If the salt concentration of the brining solution were higher than the solute concentration in the turkey cells, then water would flow out of the turkey — we don’t want this to happen. But if the salt concentration of the brining solution were a bit lower than the solute concentration of the turkey, then we’re in business. I’ll check later to get a full explanation, but didn’t want people to end up in osmotic disequilibrium

Here’s what Harold McGee has to say about brining meat in On Food and Cooking:

The tendency of modern meats to dry out led cooks to rediscover light brining, a traditional method in Scandinavia and elsewhere. The meats, typically poultry or pork, are immersed in a brine containing 3 to 6% salt by weight for anywere from a few hours to two days (depending on thickness) before being cooked as usual. They come out noticeably juicier.

Brining has two initial effects. First, salt disrupts the structure of the muscle filaments. A 3% salt solution (2 tablespoons per quart/30 gm per liter) dissolves parts of the protein structure that supports the contracting filaments, and a 5.5% solution (4 tablespoons per quart/60 gm per liter) partly dissolves the filaments themselves. Second, the interactions of salt and proteins result in a greater water-holding capacity in the muscle cells, which then absorb water from the brine. (The inward movement of salt and water and disruptions of the muscle filaments into the meat also increase its absorption of aromatic molecules from any herbs and spices in the brine.) The meat’s weight increases by 10% or more. When cooked, the meat still loses around 20% of its weight in moisture, but this loss is counter-balanced by the brine absorbed, so the moisture loss is effectively cut in half. In addition, the dissolved protein filaments can’t coagulate into normally dense aggregates, so the cooked meat seems more tender. Because the brine works its way in from the outside, it has its earliest and strongest effects on the meat region most likely to be overcooked, so even a brief, incomplete soaking can make a difference.

The obvious disadvantage of brining is that it makes both the meat and its drippings quite salty. Some recipes balance the saltiness by including sugar or such ingredients as fruit juice or buttermilk, which provide both sweetness and sourness.