As you approach Mina street, just south of the 20 de Noviembre market in Oaxaca, the smell of chocolate fills the air. There are several chocolate grinding shops along this street. One of the most popular is Chocolate Mayordomo, where you can almost always see cocoa beans being ground to make the Oaxacan chocolate that is frequently consumed here.
The shop attendant puts the cocoa beans along with some cinnamon sticks and almonds in the top of the machine and out the bottom comes a thick, rich paste, which he mixes with sugar. This is the very simple process by which Mexican chocolate is made. It creates a somewhat gritty product which is more suited to making hot chocolate than to consuming on its own, but since they're giving out free samples, you may as well have a few pieces while you decide what kind you want to purchase to take home with you.