Pistachios are so delicious that people are willing to suffer the indignity of breaking their shells apart, like a little squirrel. In fact, we love them so much we're willing to risk them spontaneously combusting on their journey to our nut bowls.
Before we go any further, pistachios are of course "drupes" rather than nuts, being a fruit that contains a shell, which in turn contains a seed, and should go in the drupe bowl with the almonds and cashews. Or maybe not, if you don't want them to catch fire.
It turns out that shipping these vegan clams (as well as other drupes and nuts) is a lot more dangerous than you'd think. For a start, as the fats decompose they produce carbon dioxide and remove oxygen, and need to be kept in a well-ventilated area.
Pistachios are pretty good fuel, given their oil and fat content.
But the real danger, according to Reddit, comes when the pistachios get moist.
"If the critical water content of the pistachio nuts is exceeded, this promotes hydrolytic/enzymatic fat cleavage," the German Transport Information Service (TIS) explains. "The free fatty acids formed are consumed by respiration processes in the pistachio nuts to form carbon dioxide and water, a process which is associated with considerable evolution of heat."
As the reaction gives off water, this can trigger a chain reaction as it reaches other nearby pistachios.
"Self-heating of pistachio nuts is an extremely vigorous process, as the consumption of fatty acids by respiration processes is associated with a considerably greater evolution of heat than is the case with the respiration equation for carbohydrates," TIS continues. "The spoilage process proceeds in a type of chain reaction, because heat and water are formed by the fatty acids consumed by respiration, which in turn contribute to an intensification of the process."
The self-heating of pistachio nuts requires only a small amount of moisture, so that within just a few hours, heating may occur at moist points for which weeks or months would be required in goods dry on shipment.
So, should we give up on pistachios and switch to a safer, less delicious drupe? Not so fast. Though Reddit posts and others on the internet attribute this spontaneous combustion to the pistachio alone, all nuts are high in fat and are capable of spontaneous combustion in moist conditions. A Wikipedia article that only listed pistachios as doing this is likely the root of pistachios being singled out like this.
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