What do you think of this fact?
Pistachios are the ultimate couch snack: crack, nibble, collect shells. Hard to imagine anything more harmless. But in large quantities, stacked in sacks in the belly of a cargo ship, they become a problem. Pistachios can heat themselves up and, in extreme cases, catch fire on their own.
Too much fat, too much moisture
The reason is the nut itself. According to the Transport Information Service run by the German insurance industry, pistachios contain about 45 to 55 percent oil, depending on the source. At the same time, they’re supposed to be shipped very dry, with only a few percent water.
If they get damp, things get tricky. Enzymes kick in that break down the fat. Fat can also break down through oxygen. Both processes release heat, and according to the Transport Information Service, damp spots in a cargo can start heating up within hours. In big stacks, the heat can barely escape, so it keeps building. In the worst case, that’s enough for a fire.
A case for the dangerous goods rules
Because this can happen, experts take the nut very seriously. According to the Transport Information Service, pistachios may behave like substances in Class 4.2 of the IMDG Code. That’s the international rulebook for dangerous goods at sea, and Class 4.2 covers substances liable to spontaneous combustion.
Packaging matters too. According to the Transport Information Service, high stack pressure and oil collecting in jute bags encourage self-heating. That’s why shipping is mostly about keeping the cargo dry and cool.
According to HuffPost UK, other high-fat nuts and seeds can also self-heat under the wrong conditions, including walnuts, cashews and sunflower seeds.
No danger on your couch
The bag of pistachios in your cupboard won’t suddenly burst into flames. This is about tons of goods, packed tightly and gone damp, where heat can build up over a long time.
A snack that officially counts as tricky cargo in the right amounts: not every nut can say that.