Assimilation theories posit that cultural change is part and parcel of the assimilation process. That change can register in the symbols and practices that individuals invoke as part of an ethnic experience. But cultural change also includes the degree to which the mainstream takes up those symbols and practices as part of its composite culture. We develop a way to examine whether cuisine, an important component of ethnic culture, is part of the mainstream’s composite culture and the contextual factors associated with the presence of ethnic cuisine in the composite culture. We begin with a comparison of 761,444 reviews of Mexican, Italian, Chinese, and American restaurants across the United States from Yelp!, an online customer review platform. We find that reviews of Mexican restaurants mention ethnicity and authenticity much more than reviews of Italian and American restaurants, but less than reviews of Chinese restaurants, suggesting intermediate mainstreaming of Mexican cuisine. We then examine Mexican restaurant reviews in the 82 largest U.S. core-based statistical areas (CBSAs) to uncover the contextual factors associated with Mexican cuisine’s local mainstream presence. We find that Mexican food is less defined in ethnic terms in CBSAs with larger and more culturally distinct Mexican populations and at less-expensive restaurants. We argue that regional versions of the composite culture change as ethnic groups come to define a region demographically and culturally.