The same problem, solved locally four times
Fish cooked in a wet gravy is sour almost everywhere it is cooked in India, and for good reasons that predate anyone thinking about flavour balance. Acidity firms up fish protein, it cuts through oiliness in a way nothing else does, it suppresses the compounds responsible for a fish smelling strongly of fish, and it has some preservative value in a hot climate.
So every fishing coast arrived at a sour curry. What differs is the souring agent, and the pattern of which agent goes where turns out to be almost entirely a question of what grows in that soil and that rainfall rather than of anyone deciding which tasted best.
Kokum on the Konkan
Kokum comes from a fruit that grows along the western coastal strip from Maharashtra down through Goa and coastal Karnataka, in exactly the humid, high-rainfall band where it thrives. The rind is dried into dark, leathery pieces that are soaked or simmered into a dish, and it is the characteristic acid of that whole stretch.
It has qualities the alternatives do not. Kokum is sour without being fruity in the way tamarind is, it contributes a purple-pink colour, and it carries a faintly astringent, cooling quality that suits the coconut-heavy gravies of the region. Crucially it does not sweeten anything, so a kokum curry stays sharp where a tamarind one would round out.
It also keeps almost indefinitely once dried, which mattered in a monsoon climate where fresh souring agents are seasonal and storage is difficult. A fruit that dries well and rehydrates in a hot pan is a solved preservation problem.
Kudampuli further south, tamarind further inland
Move down into Kerala and the fish curry sours with kudampuli, sometimes called Malabar tamarind, a related but distinct fruit that is smoked as well as dried. The smoking is not incidental — it contributes a genuine smoky note that is part of the identity of a Kerala fish curry and that no amount of ordinary tamarind will reproduce.
Tamarind itself is the acid of the drier interior, because the tree tolerates heat and low rainfall in a way the coastal fruits do not. Across the Deccan, Tamil Nadu and much of Andhra it is the default, and it brings sugar and body along with its acid, which is why the sourness in those kitchens reads as rounder and more layered.
That difference in sweetness is not a small detail. A gravy soured with tamarind can carry more chilli comfortably, because the sugar softens the perception of heat, and it is no accident that the regions using tamarind heavily are also the regions with the most assertive chilli traditions.
Raw mango, curd and the seasonal acids
Raw mango is the seasonal wildcard and it appears wherever mango trees do, which is nearly everywhere. Unlike the dried acids it is available only for part of the year, so it tends to define particular seasonal dishes rather than an entire cuisine — and where it needed to last, it was dried into amchur or preserved as pickle.
Curd is the sour of the interior and the north, where dairying is strong and the coastal fruits do not grow. It brings acidity along with fat, protein and body, so a curd-soured dish has a different texture entirely, and it is the reason the same fish cooked in Bengal or Punjab tastes structurally different from a coastal preparation.
Green mango, curd, lime and tomato all share one property that separates them from kokum and tamarind: they are wet. A wet acid dilutes the gravy while it sours it, which changes how the dish must be built, and it is part of why northern gravies are so often thickened with something else.
Why the substitutions never quite work
People do swap these — a Konkani cook away from home will use tamarind, a Kerala kitchen without kudampuli will make do. The result is recognisable but off, and the reason is that none of these ingredients is only an acid. Each carries colour, sugar, aroma and astringency in its own proportion, and replacing one with another changes three variables to fix one.
The honest way to substitute is to name what you are losing and put it back if you can — a little sugar to imitate tamarind’s roundness, a smoky element to stand in for kudampuli, an acid that stays sharp where kokum would have. It will not be the same dish. But knowing which axis you have moved along is much more useful than pretending the swap was neutral.
Common questions
Can I use lime instead of any of these?
For a finishing squeeze, often yes. As the structural acid of a simmered gravy, no — lime’s aroma is volatile and largely disappears with cooking, leaving a thin sourness without the depth these dried fruits provide.
Why does my fish break apart in the gravy?
Usually too much stirring and too long in the pan. Fish protein sets quickly and then falls apart, so it should go into an already-finished gravy near the end, and the pan should be swirled rather than stirred.
Do these souring agents need soaking?
Kokum and kudampuli can generally go straight into a simmering gravy and will release their acidity over a few minutes. Block tamarind needs soaking and pressing to extract the pulp, though the ready-made concentrates skip that step at some cost in flavour.
Senior writer, Wah Taste
Mateo joined to cover everyday cooking, street food, spice & pantry and stayed for the awkward questions and thinks most subjects are more interesting once you know how they work.
