I’m glad you asked this. Aztec hot chocolate should not be confused with Mayan hot chocolate or any other hot chocolate for that matter. The Aztecs preferred their beverage cool, so their drink was not necessarily “hot chocolate” at all, but quite often referred to as “chilcacahuatl” when chilies were added. In both Mayan and Aztec society, there were basically two types of chocolate beverage: one “pure” version consumed by royalty and warriors (simply cacao and water); then one gruel-like version that had various cacao extenders added, such as maize. Because they did not add sugar to the beverage, other ingredients were added to mask the bitterness.
Also, cacao (as a drink) was used as a medicine and was most often mixed with other ingredients, such as rhubarb water, vanilla, various nuts and seeds, roots, and many other things. The Mesoamerican medicine system operated through concepts of hot/cold and wet/dry in which all diseases were perceived as either hot or cold, wet or dry. All available foods were likewise perceived as such, with hot diseases treated using cold foods/medicines and dry diseases treated with wet foods/medicines. Cacao itself was regarded as a cold ingredient and when heated was referred to as hot, and when mixed with various ingredients, it was also hot. So in this respect, this could be where the concept of “hot chocolate” stemmed. Cool, huh?