Tonka bean is native to Venezuela and parts of the Amazon Valley.
Originally it was borne only on three kinds of Coumarouna, giants of the forest, and the only ones to furnish the big seeds which are in world-wide demand.
This bean yields coumarin, a crystalline substance with many uses; as an odour-enhancer and as a blood thinner.
Because its fragrance suggests vanilla, the coumarin is also used to flavour cigarettes, cocoa, confections, perfumes, sachets, and cosmetics.
The chief of the tonka bean trees is C. odorata, which can reach 100 feet or more in height, but substantially less than that in cultivation.
This genus is one of the few among legumes whose pods do not open at maturity and contain only a single seed. The fruit resembles that of an almond; but, inside, a fleshy, oily covering surrounds the lone, black, elongated seed. Although shaped like an almond, it is much longer and highly aromatic.
The bean mature in June and July, about nine months after flowering.
It is rather poisonous to eat as it contains alkaloids that react on the heart and are often used as a poison for rats.
The beans are cured after the ripe fruit falls to the ground, gathered up, and dried out in the sun, and turned daily like the cacao.
After drying, the pods are carefully cracked, and the chestnut-coloured bean is removed. They are further dried to become ready for curing.
The dried beans are placed in casks filled to about a foot from the top with a strong alcoholic substance, usually containing 45% alcohol; and the cask is covered with a thick cloth.
Two days later, the unabsorbed liquid is drained and the beans removed and again spread out to dry for about a week. The alcoholic substance can be used as many times as needed, as long as its strength does not go below the 45% level.
As this curing takes place, the beans become coated with a white deposit of coumarin.
Until shortly after WWII, they were in considerable demand for flavourings; but the use of coumarin in food was banned in the US in 1954.
Since then, the use of tonka beans has been restricted to perfume. In other countries, they have been replaced by synthetic coumarin and vanilla.