by Michael Hawkins
Short answer
If you have ever had an allergic reaction to peanuts, tree nuts, or seeds, you need to tread very carefully when it comes to eating pesto. Always read the label, and don't just assume that they all contain pine nuts because some producers substitute them for cheaper alternatives.
Long answer
Classic basil pesto contains pine nuts, which, despite their name, are in fact seeds. A small number of people have reported allergic reactions to them, but far more common are peanut or tree nut allergies. It's crucial that allergy sufferers don't just blindly assume that the pesto they are eating will have been made with pine nuts. In fact, more and more shop-bought pesto sauces have had the pine nuts switched for other nuts.
It's not uncommon in Italy for walnuts to be used in place of pine nuts, while the Sicilians prefer to use their beloved almonds. They do this for taste, of course, but they are also used because they are a lot cheaper than the super-expensive European pine nuts.
Some producers have tried to cut corners by using the cheaper pine nut variety from China. However, some diners report what has become known as "pine mouth" (or "pine nut syndrome"), where an unpleasant, metallic taste lingers for days or even weeks. Scientists haven't yet been able to conclude exactly why pine mouth happens, and although they stop short of defining it as an allergic reaction, they do believe it is a form of food hypersensitivity that affects some people and not others.
In other cost-saving measures, some large pesto companies have ditched pine nuts and replaced them with much cheaper cashews or peanuts. Others have removed nuts altogether from their pesto, not necessarily because of costs, but because there is a growing number of people reporting nut allergies and they want to be able to appeal to the broadest market possible.
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