A fire is built iside the oven, and when the adobe is heated, the distiller rakes out the coals, seals the mouth of the oven, drops in the agaves through a hole on the top, and seals that hole too. The agaves bake inside for a couple of days. This means a mezcal (raicilla) without the characteristic smoky overtones from pit- oven roasting: more true to the agave itself
There are plenty of raicillas made using pit ovens. The ovens tend to be smaller because of smaller batches. Las Perlas adds water on the 2nd day.