Brining the turkey before cooking is suppose to make the meat really tender, less dry.
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Brining is a pretreatment in which the whole turkey to placed in a salt and water solution known as brine. This pretreatment produces a wonderfully moist and well-seasoned bird. Brining should be done in the refrigerator or in a cooler with 5 to 6 ice packs to keep the turkey and brine at 40 degrees or below during the entire brining process. Brining is more manageable with a rather small turkey from 12 to 14 pounds.
Table salt or kosher salt can be used to make the brine. Crystal kosher salt is recommended since table salt contains additives such as anti-caking ingredients, iodine and other additives. Table salt is also very finely ground and more is required to produce good results.
1. Start the brining method the day before you plan to cook the turkey. Start with a fresh or completely thawed turkey. Wash the bird inside and out and remove the giblet bag and neck.
2. In a large stockpot, plastic tub or cooler dissolve 4 cups kosher salt or 2 cups table salt in 2 gallons cold water. Add 1 cup sugar. Stir until the salt and sugar are completely dissolved. Water will look clear, not cloudy.
3. Herbs and spices may be added to brine to enhance the flavor. Add several crushed bay leaves, several sprigs of dried thyme, or other dried herbs, if desired.
4. Place the turkey in the brine solution, breast down. Cover and chill for 6 to 8 hours. Or use the overnight method by reducing the salt and sugar amounts by 1/2 so the turkey does not retain too much salt.
5. Remove the turkey from brine, rinse inside and out under cold running water. Pat dry with paper towels. Place on a shallow pan and refrigerate overnight. This allows the skin to dry out so it becomes crisp during roasting. This step may be omitted if desired.
http://www.urbanext.uiuc.edu/turkey/techniques.html