Anderson's Moonshine

Whatever the Anderson Brothers made their moonshine out of, it seems to have the ability to resurface suppressed memories about the Dark Presence if one gets drunk off of it. It is implied that Walter has been getting drunk off of it for this purpose and Alan remembers what happened between him arriving at the cabin and its disappearance after blacking out drinking it. Considering the Anderson Brothers are aware of the Dark Presence, they could have brewed it specifically for this purpose.

Example of:
Higher Understanding Through Drugs