Smartphone display, dye laser, 'Tonkatini'

2 cocktails: 8 cl gin, 6 cl dry vermouth, 2 cl Maraschino, 2 lemon twist, 1 pinch freshly grated tonka bean, ice.

What do your smartphone display, a research grade dye laser and this awesome cocktail have in common? They are all built on the unique properties of coumarin, an organic substance with intriguing photophysical behaviour and captivating fragrance.

What makes coumarin and its derivatives so useful for laser- and display-engineers is its fluorescence, being short-lived as well as efficient. Countless other dye molecules have the habit of trapping energy given to them by morphing into an optically inactive 'triplet' state. Unfortunately these triplet states tend to be somewhat 'leaky' and energy is slowly wasted by being converted into heat. A good molecule in this context is one that does not trap the energy but quickly releases it in the form of light. Coumarin does exactly that because its triplet state is uncharacteristically close in energy to the optically active 'singlet' state. Trapped energy thus escapes easily and comes out as light, which is useful for both, lasers and smartphone displays based on OLEDs (organic light emitting diodes).

Surprisingly, coumarin also finds use in food chemistry. Initially the substance was extracted from the coumarou (French expression for the tonka bean). Its odour resembles sweet woodruff, newly-mown hay or vanilla beans. Unsurprisingly, it is being used in perfumes, cosmetics, tobacco-flavouring and last but not least ... in cocktails.

Like many other aromatic substances coumarin is, however, toxic in certain quantities and has been banned as flavorant food additive by the FDA. In contrast, the federally funded German BFR (Federal Institute for Risk Assessment) concluded the tolerable daily intake (TDI) to be 0.1 mg per kg of body weight. With tonka beans containing about 3% of coumarin by weight, this suggests that a person of average statue (like myself :-) ) may consume 5-10 beans a day (for her entire life!) without appreciable risk of suffering from negative side effects.

For me, this is good enough. Consuming not even a tenth of a single tonka bean per drink seems very acceptable and not really a downside. Especially considering the substantial safety margins baked into TDIs and accounting for the pleasure and quality-of-life gained from consuming this sublime drink.

Mix liquids in shaker with ice, add pinch of freshly grated tonka bean, stir and strain. Straight up or on the rocks, this one works either way. Alternatively you can also grate directly onto the drink with sprinklings of tonka decorating your ice and liquid surfaces. My impression is, that this improves the fusion of coumarin fragrance and citrus scent, an absolutely intoxicating mixture. Decorate with a fresh lemon twist and enjoy.

Zum Wohl, cheers.