Two fish traditions that look similar and are not
India has two large fish-eating regions and they are usually discussed as one. The coasts cook sea fish, generally with a firm acid — tamarind, kokum, raw mango, vinegar — and often with coconut. The river plains of the east and northeast cook freshwater fish, and the acid is far less prominent while mustard, in one form or another, is everywhere.
The difference isn’t a matter of preference passed down. Freshwater fish is a different material with a different set of problems, and the river plains’ cooking is a set of solutions to them rather than a regional accent applied to a dish that’s otherwise the same.
The flesh is softer and the bones are worse
The carps that dominate river cooking have flesh with weaker connective tissue than most sea fish, and it flakes apart readily once cooked. That is why so many of the classic preparations begin with a turmeric and salt rub and a hard fry on both sides before the piece ever meets a gravy. The fry firms the surface and gives the piece enough structure to survive being simmered and served.
Salt does part of that work chemically, drawing water from the surface and altering the proteins there so they set more firmly, and the turmeric contributes colour and a little antimicrobial help on a fish that may have been sitting in the heat since morning.
The bones are the other structural fact. River carps carry a great many fine intramuscular bones, which is why the fish is cut across the body into steaks rather than filleted, and why it is eaten slowly and with the fingers. A cuisine that had tried to fillet these fish would have given up.
Muddy flavour is a real thing with a real cause
Freshwater fish sometimes carries an earthy, muddy taste that has nothing to do with freshness, and it comes from compounds produced by certain bacteria and algae in the water that the fish absorbs and stores in its fat and skin. The human nose detects them at extremely low concentrations, which is why a faint problem is so noticeable.
The traditional handling addresses it head on. The fish is scaled and cleaned thoroughly, the skin and the dark lateral flesh get particular attention, and the pieces are rubbed with turmeric and salt and often left to sit. Strong aromatics — mustard, chilli, ginger, and the pungent seed mixes of the region — then sit on top of whatever remains. Sea fish rarely needs any of this.
Mustard does a job that acid does elsewhere
The mustard paste that defines so much eastern fish cooking is doing several things at once. Its pungency is generated when the seed is broken in water, and it is sharp enough to cut through a fatty fish and to sit over any residual earthiness. The paste itself thickens the sauce. And the oil pressed from the same seed brings its own pungency and a distinct aroma.
Its pungency is also short-lived, which shapes when it is added and how the dish is finished. The compounds responsible are destroyed by prolonged heat, so a mustard gravy that is boiled hard for twenty minutes loses the sharpness that was the point of it, and the traditional method keeps the cooking after the paste goes in deliberately brief.
What it does not do is preserve. Sea fish on the coasts was frequently handled with acid partly because acid keeps, and a fish landed at a distance from where it would be eaten needed that. River fish was generally bought alive or within hours of being caught, in a region where ponds and rivers were everywhere, so the preservation problem was smaller and the acid never became central.
Which is why the two traditions do not transplant
Cooking a firm sea fish in a mustard gravy tends to give something that tastes correct and feels wrong, because the mustard was calibrated for a softer, more delicate flesh and it overwhelms a fish that has its own character. Cooking a river carp in a coconut and tamarind curry sends it to pieces, since the long simmer that a firm fish tolerates is more than the flesh can take.
The parts that do travel are the techniques. The turmeric and salt rub, the preliminary fry and the practice of cutting across the bone are all useful with any soft-fleshed fish, wherever it came from. The gravies are more local than that, and it is worth treating a regional fish recipe as being about a particular fish rather than about fish in general.
Common questions
Does soaking fish in curd or lime remove muddiness?
It helps somewhat, mostly by masking rather than removing, since the compounds responsible are held in the fat and skin. Thorough cleaning, removing the dark flesh along the lateral line, and a proper turmeric and salt rub do more. A badly affected fish is difficult to rescue entirely, whatever it is soaked in.
Why is the fish always fried before it goes into the gravy?
To firm the surface so the piece holds together, to develop browned flavour that the simmering will not produce, and to deal with any surface moisture. It is a structural step first. Preparations that skip it usually handle the fish very gently and serve it in the same vessel it cooked in.
Is mustard oil essential to these dishes?
It is characteristic rather than strictly essential, and its pungency and aroma are a large part of what the dishes taste like. Cooking one in a neutral oil gives a recognisable dish with a piece missing. Heating the oil until it just loses its raw sharpness is the usual practice and it changes the flavour considerably.
Reporter, Wah Taste
Gautam covers everyday cooking, street food, spice & pantry and the questions readers actually send in and is unreasonably interested in the detail nobody else checks.
