Why can pine nuts sometimes leave a bitter metallic taste in your mouth, several days after the fact?
The reaction described is indeed bizarre—but not entirely uncommon. In fact, the condition has a Facebook page, and numerous blogs are devoted to the subject. Called “pine mouth,” the phenomenon was first reported by a Belgian anesthesiologist in 2001. Those affected report that eating pine nuts temporarily alters their sense of taste, making most food and drink (including water) taste bitter or metallic. The nuts themselves taste fine; the condition emerges hours or even days after ingestion and lingers for as long as two weeks.
While the syndrome can clearly be linked to the consumption of pine nuts, its underlying explanation remains a mystery. One theory is that the reaction stems from rancid nuts. The most recent hypothesis, from research conducted at the Nestlé Research Center in Lausanne, Switzerland, suggests that new types of pine nuts introduced to the marketplace from China (now one of the largest—and cheapest—suppliers of the foodstuff) may be to blame. According to newspaper reports, the Swiss researchers found at least two Chinese species for sale that had never previously been used for human consumption.
The good news? While the symptoms of pine mouth are downright uncomfortable, the condition is temporary and does not seem to present any long-lasting health concerns. But until the true source of pine mouth is understood, we recommend purchasing Middle-Eastern or European-grown (and more expensive) pine nuts and refrigerating or freezing them in a well-sealed container to stave off rancidity.