The grain used as the base of traditional Mexican horchata is rice. Mexican horchata, often called agua de horchata, is typically prepared by soaking and blending rice with water, then adding cinnamon, sugar, and sometimes vanilla or other flavourings.
This drink belongs to the Mexican agua fresca tradition and is the most common horchata style in Mexico. The rice gives it a pale, milky appearance and a soft, cereal-like flavour even though the traditional drink does not require dairy milk. It is commonly served cold alongside tacos, grilled foods, and other dishes.
A frequent source of confusion is that “horchata” refers to different drinks in different countries. Valencian horchata de chufa is made from tiger nuts, not rice. In parts of Central America, horchata may include jicaro or morro seeds, often combined with rice. Those regional variations do not change the standard answer for traditional Mexican horchata: rice.