They started going downhill when they caved and removed beef tallow from their frying oil.

The new fry didn’t stack up. As it turns out, the beef tallow had added more than just cholesterol to the signature french fry. To compensate for the loss of meaty flavor, McDonald’s added “natural beef flavor.” Even worse, the fries lost much of the contrasting soft and crunchy texture that Kroc loved, and the new fries weren’t exactly healthier. As the public later learned, the trans fats in hydrogenated vegetable oil posed serious health threats, forcing McDonald’s to change the recipe again.