For almost a decade now there have been anecdotal reports of people suffering from disturbed taste sensations after eating pine nuts. The symptoms take a day or so to develop, and are usually described as persistently bitter, metallic sensations that spoil the taste of all foods. In most cases they go away after a week or two.
Several European investigations have failed to find a cause for pine-nut mouth, but the Danish food ministry may have cracked the case.
The components responsible for "cacogeusia," as one medical report names the taste disturbances, have yet to be identified. But the European Commission has now banned any further imports of these unapproved nuts.
Until the pine-nut story is clarified further, it seems advisable to choose nuts from European, American, or Korean sources, and to avoid small rounded nuts from China.