I have to inform you -in order for future expanding of the article- that there sometimes was a secret ingredient to the pulque, named ocpatli or ocpantli (depending Nahuatal or Tehuana language). Oc stand for October and the secret ingredient was added at the October festivities. The flowering of that secret ingredient is in October. Al the scrolls have been destroyed by the Church, so no-one knows what plant it is. Some language books say it was "resinosa"; sticky. One would think about marihuana flowers, but according to a Oaxacan anthropologist, that plant was not available in teh America's at that time. Furthermore almost the same letters as in ocpatli, are in Copal; a sticky juice from a specific tree. When hardened, they're used as a burning smelling stick in churches and should take away bad spirits. No idea if and what made the language connection with copal, but its a candidate. 
 Sources: library of the botanic garden of Oaxaca MM