Radhuni vs Fennel seed
The short answer
The choice of fifth seed in panch phoron. The older Bengali form uses radhuni; most commercial mixtures, and most kitchens outside Bengal, use fennel. They do opposite things to the blend: fennel adds sweetness and anise, radhuni adds a sharp, savoury celery-and-parsley note. A dal or vegetable dish tempered with the radhuni version reads as more savoury and more specifically Bengali; the fennel version is sweeter and more familiar. Neither is wrong, and a recipe that names radhuni means it.
Side by side
| Radhuni | Fennel seed | |
|---|---|---|
| Botanical identity | Trachyspermum roxburghianum (DC.) H.Wolff | Foeniculum vulgare Mill. |
| Part used | seed | fruit, seed |
| Origin | South and Southeast Asia; the species is grown and naturalised from eastern India and Bangladesh into mainland Southeast Asia. | The Mediterranean basin, where the plant grows wild and from which cultivation spread eastwards early. |
| Flavour notes | celery, parsley, herbal, savoury, sharp | sweet, anise, grassy, green, cooling, faintly bitter |
| Heat | Scoville does not apply | Scoville does not apply |
| Flavour | Savoury, green and warm, bitter only if burnt. In hot oil it gives a dish a distinctly Bengali smell that is hard to place for anyone who has not grown up with it. | Sweet and liquorice-like but noticeably lighter and grassier than star anise or aniseed, with a mild bitterness in the finish and a faint cooling quality. It is sweet enough to read as a dessert spice and green enough to work in a sausage, which is an unusually wide range. |
| Aroma | Celery and parsley, with a sharper, slightly thyme-like top note that celery seed lacks. | Sweet and anise-like with a clear green, grassy freshness underneath it, and a light warm-spicy note when toasted. |
Which should you buy?
Radhuni
Whole. Radhuni is used as a tempering seed, and the whole seed fried in fat is the use; there is little reason to buy or make it ground.
Fennel seed
Buy whole. Fennel is cheap, grinds easily, is much improved by toasting first, and is used whole in most of its traditional applications anyway — sausage, bread, tempering and mukhwas all want the intact seed. Ground fennel loses the green top notes that distinguish it from plain aniseed within months, which removes most of the reason to choose fennel in the first place.
Full detail on radhuni and fennel seed, including evidence grades and sources for every claim above.