Andrew Telzak got a great deal on pine nuts at an Asian market and whipped up a batch of pesto for friends. It tasted great. But for days afterward, nothing else did. </p><p> &ldquo;I started getting this weird taste, kind of a metallic taste, in the back of my tongue,&rdquo; said Telzak, 23, a North Baltimore resident who works for the city&rsquo;s health department. &ldquo;Everything was tasting real bitter.&rdquo; </p><p> Some of his guests had the same experience. One of them Googled &ldquo;everything tastes bitter&rdquo; and came across &ldquo;pine mouth,&rdquo; a taste dysfunction associated with pine nuts that can last for weeks. </p><p> On foodie Web sites and blogs, legions of self-diagnosed pine-mouth sufferers have concluded that Asian pine nuts, as opposed to more expensive European varieties, are to blame. </p><p> While one nut importer has dismissed the claims as &ldquo;an Internet sensation,&rdquo; the Food and Drug Administration is investigating. The FDA has received about two dozen complaints about pine nuts in recent months, said Stephanie Kwisnek, an FDA press officer. </p><p> &ldquo;Many of the complainants report an aftertaste associated with the product but no illness,&rdquo; she said by e-mail. &ldquo;Should the FDA find a public health hazard, then we will advise consumers accordingly.&rdquo; </p><p> The &ldquo;nuts&rdquo; at the center of this mystery are not technically nuts at all but the seeds of various pine trees. The United States imports 25 million pounds of pine nuts a year, 90 percent of them from China. </p><p> There is no shortage of people claiming to have been afflicted by what Food and Wine magazine recently described as &ldquo;The Pine Nut Menace.&rdquo; The phenomenon has been noted in forums ranging from Epicurious and Chowhound to the European Journal of Emergency Medicine. Researchers at a Belgian poison center investigated seven cases but found no explanation.</p><p> Accounts on Internet foodie sites tend to be as bitter as the reported aftertaste. </p><p> &ldquo;Costco knows about this&hellip;but they won&rsquo;t admit that to you,&rdquo; writes one Chowhound poster. </p><p> Craig Wilson, assistant vice president of food safety at Costco&rsquo;s Issaquah, Wash., headquarters, said the company did not think the phenomenon posed a health risk. </p><p> &ldquo;Everything&rsquo;s pretty benign at this point,&rdquo; Wilson said. &ldquo;We&rsquo;ve talked to a couple or three universities about it.&rdquo; </p><p> Asked which universities, Wilson then said Costco had, in fact, only asked one university to investigate: The University of California, Davis&rsquo; Fruit and Nut Research and Information Center. Officials at the center said they could not recall doing any pine nut research. Wilson said it took place six or seven years ago. </p><p> Andrew Rosen, an official with New Jersey-based Food Import Group, said he stopped bringing in one specific variety of Chinese pine nut three months ago because he suspected it was &ldquo;the culprit.&rdquo; </p><p> Chinese pine nuts are smaller, shaped like corn kernels and more suitable for savory dishes than for desserts. The European type is sweeter, longer and tapered on both ends like a grain of rice.</p><p> Some chefs have been forced to switch to the Chinese variety because the European ones have nearly doubled in price in recent months for reasons that are unclear even to importers.