Melilot

Freshly turned hay in the summer sun, sweet and warm with woodruff and tonka, over a herbal, faintly honeyed undertone.

• In the 1920s, whole herds of cattle in North America died of a mysterious bleeding disease caused by mouldy sweet clover hay. Moulds had converted the coumarin into dicoumarol, which researchers at the University of Wisconsin isolated and which later became the model for the rat poison warfarin.

The key odorant is coumarin, which in the living plant is almost entirely bound as a glucoside of cis-o-hydroxycinnamic acid. Only when the tissue is damaged or dries does the enzyme beta-glucosidase release free coumarin, which is why sweet clover only develops its hay scent as it wilts.