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The perique that I have received from WLT was vacuum sealed within vapor-proof bags. It will keep that way for years. Once I open a bag, I usually shred all of it, spread it out on a baking sheet, allow it to dry down to low case, then store it in a Ziploc bag at room temperature. I suspect that it has already fermented and "matured" as much as it ever will.
If the perique is exposed to air, then stored without drying, I have, on occasion, seen the growth of some tiny yeast colonies that I assume to be Pichia anomala. That is the yeast that produces perique from cured tobacco.
Bob