Taco Bell's President, Greg Creed, issued a press release to address claims he says are "absolutely false".
Creed says that plain ground beef tastes boring and the only reason they add anything to the beef is to give the meat flavor and quality. He says their tacos consist of 88% Beef and 12% Secret Recipe.
On a YouTube video he reveals their once secret recipe stating "We start with USDA-inspected quality beef (88%). Then add water to keep it juicy and moist (3%). Mix in Mexican spices and flavors, including salt, chili pepper, onion powder, tomato powder, sugar, garlic powder, and cocoa powder (4%). Combine a little oats, caramelized sugar, yeast, citric acid, and other ingredients that contribute to the flavor, moisture, consistency, and quality of our seasoned beef (5%)."