Coumarin is a substance with a sweet, pleasant odor, reminiscent of the smell of hay and naturally present in many plants. It is found in Tonka bean, Cassia Cinnamon, Ceylon Cinnamon, Pompona vanilla, honey, tea, etc.
In Cinnamon, we find it concentrated in Cassa Cinnamon (from China which is found everywhere), Saigon Cinnamon. Ceylon Cinnamon contains very little (63 times less than Cassa Cinnamon). For the Tonka bean it is present from 1 to 3% of the weight of the bean.
The Tonka Bean, however, contains less coumarin than the following plants: sweet clover, clary sage, true lavender, sweet woodruff (medieval vanilla), ash, Roman chamomile, German chamomile or matricaria, yarrow or even chestnut bark.
The cosmetic industry knows coumarin very well. It was even one of the first aromatic syntheses carried out towards the end of the 19th century (1868) by the English chemist William H. Perkin. A few years later, in 1882, Paul Parquet used this synthetic molecule to create Fougère royale, a perfume from the eponymous house founded in 1775 by Jean-François Houbigant (now H for men), then Aimé Guerlain used it for Jicky, iconic perfume in 1889. (https://fr.wikipedia.org/wiki/Coumarine)
The majority of people can consume foods that naturally contain coumarin every day without experiencing adverse health effects. However, there are a small number of individuals who are sensitive to coumarin. For these people, consuming higher concentrations than normally found in foods can lead to elevated liver enzymes and, in severe cases, liver inflammation .
It is common to hear that the use of the Tonka bean is prohibited. It is in fact only for two countries: the USA in 1954 and Belgium in 1977.
The Codex Alimentarius (international recommendation for the field of food) recommended in 1985 not to add pure coumarin as such to foods and drinks.
In 2004 and again in July 2008, the European Food Safety Authority (EFSA) recommended an acceptable daily intake (ADI) of 0.1 mg coumarin/kg body weight.
Tonka Bean and coumarin:
Regarding the Tonka bean: coumarin is present from 1 to 3% in a Tonka bean. The weight of a Tonka bean ranges between 1.2 and 1.8 g. Let's take the high value 1.8g and a high coumarin content of 3%. Which gives us, if we eat the whole bean, a weight of 54 mg. However, the daily recommendation is 0.2 mg/body weight. Thus, an assimilated Tonka bean for a person weighing 65 kg represents 54 mg while the maximum daily dose is 6 mg.
Could this be the end of the Tonka bean?
No of course, we have forgotten two main elements in this reasoning: frequency and proportion. This reasoning applies in the case where you eat a whole bean, but in your cooking you will incorporate it into a dish, a dessert or you will only eat one or two portions. Then the recommendations of food safety authorities are based on daily consumption. The risk is indeed present if you devour whole chocolate and Tonka bean fondants daily, over a long period of time.
In the end we are still on the same principle of dose. Many spices in high doses can also be very harmful (nutmeg, cinnamon, cloves, etc.).
We will remember this famous quote from the Swiss physician-philosopher of the Middle Ages: “All things are poison, and nothing is without poison; only the dose makes something not poison