All though some of you feel that buttermilk is NOT a brine, it is just a different method, with the same results.
It is now known that calcium in dairy products triggers “aging” enzymes within muscle and connective tissues, which, in turn, degrade certain proteins that hold bundles of muscle fibers together. The meat industry is now experimenting with genetic selection for these enzymes, increasing dietary levels of Vitamin D (involved in calcium absorption and metabolism), electrically shocking carcasses after slaughter, and injecting meat with calcium chloride solutions. I would rather just brine mine in buttermilk, thank you very much.
I personally believe that brines are the most effective and reliable method of flavoring meat, poultry and seafood at home. Acid and oil marinades remain popular in spite of the fact that they simply don’t work. Marinades do not penetrate, thus they can flavor and tenderize only the surface of meats. Strong acids, such as vinegar and lemon juice, can actually toughen muscle fibers. Enzymes in plants, such as papaya and pineapple, often added to marinades to tenderize, actually do too good a job and can make the surface of meat mushy without affecting the interior. Brines, on the other hand, are salt based and can actually penetrate muscle tissue through osmosis, taking dissolved flavor components and tenderizers deep into tissues. Contrary to popular belief, salt in brines actually adds water to meat and aids in moisture retention during cooking. I always add some sugar, to my brines and dry rubs. Sucrose reduces the salty taste, helps retain moisture and improves flavor. Buttermilk can replace part or all of the water in a brine, depending upon the characteristics of the meat. Mild meats, such as turkey, chicken and lamb, benefit from a mixture of 25% buttermilk, while strong flavored, tough or gamey meats require higher levels - up to 100% for goat and venison. Acid in buttermilk is not strong enough to toughen muscle fibers. Enzymes and calcium, with the osmotic assistance of less salt, can penetrate tissues to flavor and tenderize even large cuts of meat, it is buttermilk brined, frozen or slowly cooked on the pit. The larger cuts of meat, additional is salt is needed.