Carp: bones, muddy taste, frying

Why

The muddy or earthy taint of carp comes from geosmin and methylisoborneol, made by cyanobacteria and soil bacteria in ponds; the fish takes them up through the gills and with food, and because they dissolve in fat there is usually more of them in the fattier parts of the fish, such as the belly or under the skin. That is why carp are kept in clean water before sale, where they lose part of the taint, and at home skinning the fish and trimming the fatty belly can help; vets advise against keeping a live carp in the bath for days, and the fish is better killed professionally at the point of sale. Besides the backbone and ribs, carp has fine forked intramuscular bones that cannot be pulled out, and close crosswise scoring of the flesh down to the skin chops them into short pieces that are barely noticeable once fried. Carp portions are thick, and in oil that is too hot the coating browns before the flesh at the backbone is cooked; so it is fried at a rather lower temperature and doneness is checked at the bone, where the flesh should be opaque and flake easily, or reach 63 °C (Fish: when is it done card).

How to do it

• Buy carp killed and bled by the seller; do not keep it alive in the bath for days at home, and do not kill it without knowing how to stun it properly.
• When gutting, do not burst the gall bladder, as bile makes the flesh bitter; scrape off the scales, remove the gills and rinse the cavity and surface with cold water.
• Skinning the portions and trimming the fatty belly and the dark strip along the flank may soften the taint; then pat the flesh dry with kitchen paper.
• Score portions and fillets crosswise at 2–3 mm intervals down to the skin without cutting through it; this chops the fine bones into short pieces.
• Salt the portions, keep them in the fridge until coating and coat them just before frying, as for schnitzel (Breaded and fried card).
• Fry in oil at about 160 °C in small batches until the flesh at the backbone is opaque and flakes easily; check the thickest portion reaches 63 °C with a thermometer.

If it goes wrong

Serve carp that tastes muddy after frying with lemon or a sharp salad that masks the taint; next time skin it and trim off the fatty parts. Return a portion still raw at the backbone to oil heated only moderately, or finish it on a rack in an oven heated to 180 °C until it reaches 63 °C in the centre. An oil-soaked coating cannot be de-greased; fry the next batch only once the oil is hot again. If the feeling of a stuck bone, pain or difficulty swallowing persists after eating, see a doctor.