"Their distinctive taste does not stem from the kind of potatoes that McDonald's buys, the technology that processes them, or the restaurant equipment that fries them: other chains use Russet Burbanks, buy their french fries from the same large processing companies, and have similar fryers in their restaurant kitchens. The taste of a french fry is largely determined by the cooking oil. For decades McDonald's cooked its french fries in a mixture of about seven percent cottonseed oil and 93 percent beef tallow. The mixture gave the fries their unique flavor -- and more saturated beef fat per ounce than a McDonald's hamburger.
In 1990, amid a barrage of criticism over the amount of cholesterol in its fries, McDonald's switched to pure vegetable oil. This presented the company with a challenge: how to make fries that subtly taste like beef without cooking them in beef tallow. A look at the ingredients in McDonald's french fries suggests how the problem was solved."