Tonka beans are an unusual spice that you don’t see in everyday cooking, but have a very unique flavor that has won them a lot of fans. The beans are actually seeds from a type of flowering tree found in South America. They are roughly an inch high, are very firm and have a somewhat wrinkly appearance. Tonka beans taste similar to vanilla beans, but have distinctly fruity and spicy elements to them where vanilla is more floral. Also like vanilla, the flavor of the tonka bean can be very complex, but can also be very subtle when it is used in a recipe – which means that it can be difficult to pinpoint the origin of those flavors unless you know that the tonka is in there. It is not unheard of for chefs to use this ingredient in recipes (and some home chefs will find suppliers and use the beans, as well) to add another layer of flavor to something and simply not mention where some of that flavor comes from.
The beans are typically grated with a microplane and then infused into liquids or stirred in with dry ingredients. They have a strong aroma and you only need a small amount to get the flavor infused into something. Tonka beans are very popular in France, and some of my own first experiences with them came from French friends who were fans of them.
The reason that tonka beans are not well-known in the US is that they contain courmarin, a (naturally occurring chemical) that was shown to cause liver problems in rats in extremely high doses. Tonka beans have been banned by the FDA for sale in the US as a food item since the 1950s because of this, though you would have to ingest exceptionally high amounts of the tonka bean to reach these levels. The small amount of shavings that would typically be used to make a recipe don’t even come close to reaching these levels – which is why the tonka bean remains so popular in other countries, even though it is not used here often. You could also draw a comparison to nutmeg, a spice that can also contains a chemical – myristicin – that can be toxic in extremely high doses and is typically used only in very tiny amounts in recipes.
I have seen tonka beans used in candles and soaps to infuse them with a unique scent, as well as in food products. It might not be common, but you won’t forget the flavor once you’ve had it. I would keep my eye out for the opportunity to try it if you haven’t encountered it before, because its flavor is well worth a taste.