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Fast food sauces are not immutable; they have undergone various modifications over the years. McDonald's Special Sauce, for instance, evolved throughout its history, even reverting to its original recipe after customer feedback prompted discontent with a revamped version in the 1990s.
Though today's signature sauces may not be marketed as "secret" as before, they play a significant role in building brand loyalty. As nearly every franchise promotes some sort of house sauce, they provide a sense of uniqueness in the fast-food landscape, even leading to numerous online imitation recipes from enthusiastic fans.