Pan-Thai — galangal is more Central/Southern; ginger more prevalent in Northern (Lanna) preparations influenced by Yunnanese cooking
Galangal (kha, Alpinia galanga) and ginger (khing, Zingiber officinale) are not interchangeable — they are used in entirely different applications and produce fundamentally different flavour outcomes. Galangal is harder, more fibrous, with a piney, camphor-like, almost medicinal sharpness and earthy depth that anchors tom kha and green curry pastes. Ginger is softer, warmer, and sweet-spicy, used in stir-fries, nam jim, and Northern Thai preparations. Young galangal (kha on) is paler, milder, and used sliced into soups; mature galangal is denser and preferred for pounding into pastes. Neither ingredient substitutes for the other — a tom kha made with ginger becomes a Chinese-register soup.
Galangal's piney, camphor depth is one of the defining notes of 'Thai-ness' in dishes — when it is missing or substituted, the dish lacks the characteristic medicinal-earthy backbone that identifies it as Thai rather than generically South-East Asian.
{"Galangal for pastes: use mature, dense rhizome peeled and thinly sliced before pounding","Galangal for soups (tom kha): use young kha on, sliced 5mm thick — it is NOT eaten, just infused","Ginger for stir-fry: peel, julienne or slice against the grain to control texture","Fresh galangal is strongly preferred over dried or powder — substitution loses the essential oil compounds","Fingerroot (krachai, Boesenbergia rotunda) is a third distinct rhizome used specifically in cha dishes and certain pastes"}
If you can only find galangal as a dried slice, rehydrate it in cold water for 30 minutes before using in soups — for pastes, dried galangal is genuinely inadequate and fresh is worth sourcing. At good Thai grocers in the west, galangal is almost always available frozen, which preserves the volatile oils far better than drying.
{"Substituting ginger for galangal in green curry paste — produces a warm, sweet paste without the piney edge","Attempting to eat galangal slices in tom kha — the fibrous, woody texture is not pleasant","Using dried galangal powder for pastes — it lacks the fresh camphor-pine volatile oils","Confusing fingerroot (krachai) with both — it is a separate ingredient used in specific dishes like pad cha"}