Why marinade meat with acid or enzymes? This might sound like a queer question, but why do we marinade meat with acid / enzymes? Given that marinading doesn't tenderize meat, it just turns the outer fibers into mush and releases the juices when cooking? Why not just go with a flavored brine instead?

In other words: Why is it customary to use such marinades, and why is it commonly said that it tenderizes the meat?

Source Shirley Corriher:

http://www.finecooking.com/articles/marinades-flavor-tenderize.aspx


  At first, water molecules are attached to and trapped within this
  protein mesh, so the tissue remains juicy and tender. But after a
  short time, if the protein is in a very acidic marinade, the protein
  bonds tighten, water is squeezed out, and the tissue becomes tough. If
  you've ever tried marinating shrimp in highly acidic ingredients, it's
  likely that you're familiar with this result.


Also


  My experience with tenderizing enzymes mirrors that of Dr. Nicholas
  Kurti, a famous Oxford physicist who tried tenderizing a pork roast by
  injecting half with pineapple juice, leaving the other half untouched.
  A noted chef, Michel Roux, was to judge on television which side was
  better. After cooking, the half treated with pineapple was total mush
  and looked like a pile of stuffing. Not surprisingly, Chef Roux
  preferred the untreated half.
Hardly a queer question.  We marinate in acidic liquids because it tastes good, really.  As Alton Brown said in the Good Eats episode, "Raising The Steaks":

"Acid doesn't tenderize meat nearly as well as enzymes.  But acids can help you tenderize your own food.  That's because acids taste tangy, and tangy tastes tell our saliva glands to do their stuff, and saliva is full of enzymes."

As that same episode shows, we generally don't marinate in enzymes, as it would turn meat to mush, and not in a good way.