Tacos Al Pastor, literally meaning "Shepard Style" is made from marinaded pork cooked in a spit grill. Each taco vendor has his or her own marinade containing a combination of chiles and anatto, which gives the pork its color. It is cooked on the spit or rotisserie. A chunk of pineapple is placed on top during the cooking process, which contains an enzyme that helps tenderizes the meat. The influence comes from the Lebanese shawarma and is considered a "must try dish" whenever visiting Mexico DF. Wars of words go on each and every day about who serves the best variation of this classic taco.
The picture above, is a meal that I had at El Charco de Las Ranas in Pedregal. It was delicious, but pricey (25 pesos each taco), since I can eat about 10 of these in one sitting.
The great taco debate still goes on!