Some people are left with a metallic taste in their mouths after having eaten pine nuts, making all subsequent food or drink taste metallic and bitter. This bitter sensation usually occurs some time (mostly one day) after having consumed pine nuts and can last for up to two weeks. It will go away without medical treatment.
This phenomenon – also dubbed “pine mouth” – has been described on the internet by individuals affected since 2001 and has been acknowledged and looked into by many European food authorities in recent years.
The German Bundesinstitut für Risikobewertung (BfR) issued a statement on this subject in April 2010. It states that the consumption of pine nuts, in particular the seeds of the so-called Korean pine (Pinus koraiensis) from China and Pakistan, may lead to an impairment of a person’s sense of taste in individual cases. The BfR believes that there is generally no acute toxic potential and, thus - except for an impairment of the sense of taste – no danger to the consumer.
First suspicions that the pine nuts were contaminated with heavy metals, pesticides or other substances that caused the bitter taste could not be confirmed. A scientific article from Switzerland in 2010 describes a new method that can help find out which species of pine (in a botanical sense) are in a pine nut sample using chemical analysis. The scientists could confirm the following pine species in the commercial samples taken: P. pinea, P. koraiensis, P. gerardiana, P. armandii and P. massoniana.
The Food and Agriculture Organization of the United Nations (FAO) keeps a list with edible pine nuts. Pinus armandii and Pinus massoniana are not on this list, while P. pinea, P. koraiensis, P. gerardiana are. Thus, the assumption that the pine mouth phenomenon is caused by the contamination of edible pine nuts with non-edible pine seeds is clear. This has also been confirmed by manufacturers’ statements that name unripe pine nuts of the Chinese white pine (Huashan pine – Pinus armandii) as the main cause of the bitter taste.
The Swiss Federal Office of Public Health released a statement in July 2010 calling on retailers and producers to carry out self-monitoring and only put pine nuts safe for human consumption on their shelves.
There are about 100 different species of pine worldwide and their seeds have been used for human consumption for centuries. The most popular pine nuts in Central Europe are the seeds of the Italian stone pine or umbrella pine (Pinus pinea), also known as “pignoli” in Italy. They have an elongated oval shape. The nuts of the Asian pine are shorter and wider than those from Italy or Turkey.
The chemical substances responsible for the impaired sense of taste have not been identified to date and even the physiological processes in the human body involved in this phenomenon are not yet understood. Experts believe that the substances could cause a so-called taste conversion (known for miraculi, which causes a sour taste) or that chemical compounds could form in the blood after consumption that have this effect on the taste buds.