Before wax became widely available and at a relatively inexpensive price, many candles were made of tallow — rendered fat from beef and lamb. Tallow worked as a fuel for candles because of a simple rule: fat burns. Which is why you should not pack raw pistachios too tightly when shipping them.

If you do, they may spontaneously combust.

Pistachios contain very little water and need to be kept that way. In shipping, the nuts need to be kept free of moisture, in order to prevent them from getting moldy or rancid. So they need to be stored, so to speak, in a cool, dry place.

Unfortunately, there’s a not-so-great problem caused by this. Pistachio oil, due to the nut’s high fat content — 45% of the nut, by mass, is fat — is highly flammable. If packed densely enough, the pistachio oils can self-heat, causing spontaneous combustion. As the German Marine Insurer’s handbook notes, this can happen without an external heat input — and certainly, without a flame to kindle the fire. Similarly, the German Transport Information Service advises that pistachios “not be stowed together with fibers/fibrous materials as oil-soaked fibers may promote self-heating/spontaneous combustion of the cargo,” and for that matter, the fibrous materials may act as a wick.

To prevent this outcome, pistachios have to be shipped in specific conditions — not too dry, not too hot, not too densely packed — and monitored throughout transit. With a large percentage of pistachio production in the Middle East (Iran is the largest grower of the nut, followed by the US, but Turkey and Syria round out the top four), transit typically requires a cargo ship. Thankfully, to date, no such ships have been deep-sixed by an errant pistachio fire.

Bonus fact : Extinguish a candle and bring a new flame slowly into the smoke of the extinguished one. Get close to, but do not touch, the wick of the extinguished candle. What will happen? If you do it right, the smoke will catch fire and re-ignite the wick, as seen here. This happens because the smoke contains wax from the recently extinguished candle; the wax is highly flammable, and creates a pathway back to the wick upon which the new flame may travel.

From the Archives: Mystery Food: This food isn’t explosive, but it also is not what you think it is.

Related: A candle making kit. $79.99, designed for beginners, and four stars on 4 reviews.