Thai basil (horapha, โหระพา) has narrow, pointed leaves on purple stems with purple flower buds and a bold anise-licorice flavor that survives heat. Holy basil (kra pao, กะเพรา; tulsi in India) is a different plant: smaller, fuzzy, jagged leaves with a peppery, clove-like taste—it is the basil in pad kra pao. Italian sweet basil is soft and sweet and wilts to nothing in a wok. Thai basil goes into green and red curry, pho, drunken noodles and Vietnamese bún; holy basil belongs almost only to pad kra pao and Thai stir-fries.

How to buy

Thai basil is sold in bunches at Vietnamese and Thai grocers, H Mart and 99 Ranch, and at many US supermarkets in summer (Whole Foods, some Krogers). Look for perky leaves, purple stems, no black spots and a strong licorice smell. Holy basil is hard to find outside Thai grocers and farmers' markets, where it may be labeled 'tulsi' or 'hot basil'; it grows easily from seed on a sunny windowsill.

How to store

Both basils bruise and blacken in the cold. Stand the bunch in a glass of water on the counter, loosely covered with a bag, for 4–5 days; in the fridge, wrap the dry leaves in paper towel inside a bag and use within 2–3 days. Wash only just before cooking. For longer storage, blend the leaves with a little oil and freeze in ice-cube trays for 3 months; whole frozen leaves turn black and mushy. Discard once slimy.

Substitutes

  • Italian basil + a pinch of ground anise or a few tarragon leaves: 1:1 for Thai basil, added only at the end. Close in aroma, but it wilts faster and darkens in the pan.
  • Holy basil for Thai basil, or vice versa: 1:1. Both work in stir-fries; pad kra pao with Thai basil is sweeter and less peppery, curry with holy basil more pungent.
  • Mint + Italian basil, half and half: 1:1 for pho, spring rolls and salads. Fresh and cooling; the licorice note is gone.

How to use

Add Thai basil at the very end: stir a big handful of whole leaves into a curry or stir-fry after the heat is off so they wilt in the residual heat and stay green; minutes of cooking turn it black and dull. Use it generously: a curry for four wants a full cup of leaves, not a garnish. For pho and bún, serve whole sprigs on the side so each person tears leaves into the hot broth. Flower buds and tender tips are edible; strip leaves off thick stems. Holy basil is the exception that tolerates a few seconds of high heat: toss it into pad kra pao in the last 15 seconds so it flash-wilts and releases its pepper.

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