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From the selection of potatoes to the cooking process, McDonald's fries undergo a highly standardized procedure to ensure consistent quality across locations. The fries are made primarily from locally-sourced Idaho russet potatoes, which are cured in the dry desert air for extra crispiness. After being peeled and cut into shoestrings, the potatoes are soaked to remove excess starch before being dried and fried using a specific oil blend.
Initially, that blend consisted of 93% beef tallow and only 7% vegetable oil, which contributed to the original fries' classic taste. This flavor was so beloved that it played a significant role in attracting Ray Kroc, a traveling salesman who sought to partner with the McDonald brothers in the 1950s.