Remove the turkey from its packaging, also remove the neck and any gizzards or giblets inside the bird. Rise with cold water and set aside.
In a large pot bring the salt, brown sugar and 2 quarts of stock or water to a boil. Cook until salt and sugar dissolve then add in the garlic, onion, carrot and celery. Remove the pot from the heat and add the remaining ingredients and cold water to bring to room temperature, approximately 15 minutes.
Place the turkey in the brining bag and place the bagged turkey into a baking dish. Pour the cooled brining mixture over the turkey. Remove as much air as possible from the bag and tie it tightly to seal it. Place in the pan in the refrigerator for at least 12 hours but no longer than 20 hours turning it over occasionally.
Remove the turkey from the brine and rinse it off well with cool water and place it in a roasting pan and cook as desired. I recommend making my Herb Roasted Turkey recipe after brining.