Filleting and Stock
Cooking Skills: Fish and Shellfish 2
Chapter 2 · Filleting and Stock
Skill goal
Fillet a round and a flat fish, skin a fillet, and turn the bones into a quick, clear stock.
Shopping list for this chapter
The basics
Filleting is a skill of feel, not force. A thin, flexible, very sharp knife follows the backbone and rib bones, and the less you saw, the cleaner the fillet. A round fish (mackerel, trout, bass) has two fillets, one from each side. A flat fish (plaice, sole) has four, two on each side of a central bone. Cooking Skills: Knife Skills 1, chapter 8 introduces the basic cuts; this chapter goes much further.
Don't throw away the frame. Bones and heads from white fish make a light, clear stock in 20 to 25 minutes (longer makes it bitter, and oily fish makes it too strong). Use it for the chowders and stews in Cooking Skills: Fish and Shellfish 2, chapter 3, and for the soups in Cooking Skills: Soups and Stocks 1, chapter 2.
The method
- Sharpen the knife and steady the board with a damp cloth under it.
- Cut behind the gills and the head down to the backbone, then turn the knife flat towards the tail.
- Slide along the backbone in long, light strokes, letting the knife ride on the bones.
- Lift the fillet off the ribs, trimming the belly bones and pulling out pin bones with tweezers.
- Skin with the knife flat, holding the tail end with salt on your fingers and sawing gently.
| Fish | Fillets | Knife | Tip |
|---|---|---|---|
| Mackerel (round) | 2 | Flexible filleting knife | Slide along the spine; trim the belly |
| Plaice (flat) | 4 | Flexible filleting knife | Cut down the centre line first |
| Salmon fillet | Skin off | Long flat knife | Hold the tail end with salt |
| Frame for stock | - | Cleaver or large knife | Chop and rinse out the blood |
Sharp knives, raw fish and allergens
Filleting knife and slippery fish: a filleting knife is thin and very sharp, and fish skin and slime are slippery. Work on a damp cloth or non-slip mat, cut away from your hand, keep your free hand flat and clear of the blade, and never try to catch a falling knife. Wash the board and knife in hot soapy water straight after.Raw fish: keep raw fish on its own board and plate, away from food that won't be cooked. Wash your hands, boards and knives in hot soapy water afterwards, and store raw fish on a plate on the bottom shelf of the fridge so it can't drip onto other food.
Bones: even fillets can hide thin pin bones. Run a clean finger along the fillet and pull any bones out with tweezers, and warn children and anyone you serve. Whole sardines and mackerel have fine bones that are best taken out.
Allergens: fish is one of the 14 major allergens, and cross-contact is easy: it can pass on boards, oil, tongs and pans. Crustaceans (prawns), molluscs (mussels, scallops), gluten, milk and egg also appear in fish recipes. Always tell guests what is in a dish.
Try it
Level 1 · Start here
Filleting a mackerel
Mackerel is the best fish to learn on: it is cheap, fresh mackerel has a firm body, and the bones are easy to follow. Practise on two, and cook the fillets by grilling or pan-frying (see Cooking Skills: Fish and Shellfish 1, chapter 2).
Ingredients (2 portions)
- 2 whole mackerel (about 300 g each), gutted
- 1 tbsp rapeseed oil
- 1 lemon, in wedges
- 1 pinch flaked sea salt
- Lay a fish on a board steadied with a damp cloth. Cut down behind the gills to the backbone, then turn the knife flat and slide it along the spine to the tail, making one long cut. Repeat on the other side.
- Trim the belly bones in a thin strip, and pull any pin bones with tweezers. Rinse and pat dry.
- Fry skin-side down in the hot oil for 3 minutes, turn for 1 minute, season and serve with lemon.
Sharp knife, raw fish and bones
Filleting knife and slippery fish: a filleting knife is thin and very sharp, and fish skin and slime are slippery. Work on a damp cloth or non-slip mat, cut away from your hand, keep your free hand flat and clear of the blade, and never try to catch a falling knife. Wash the board and knife in hot soapy water straight after.Raw fish: keep raw fish on its own board and plate, away from food that won't be cooked. Wash your hands, boards and knives in hot soapy water afterwards, and store raw fish on a plate on the bottom shelf of the fridge so it can't drip onto other food.
Bones: even fillets can hide thin pin bones. Run a clean finger along the fillet and pull any bones out with tweezers, and warn children and anyone you serve. Whole sardines and mackerel have fine bones that are best taken out.
Hot pan and hot oil: frying fish uses a hot pan and spitting oil. Dry the fish well, lay it down away from you, use a splash guard if you have one, keep the handle turned in and keep children well back.
Level 2 · Flat fish
Filleting a plaice
A flat fish has a central bone line down the middle. Cut along it, then use short strokes to ease each fillet away over the outer fin bones. It is neater than it sounds. Dust the fillets in flour and pan-fry in butter.
Ingredients (2 portions)
- 1 whole plaice (about 600 g), gutted, head on
- 3 tbsp plain flour, seasoned
- 30 g butter
- 1 tbsp rapeseed oil
- 1 lemon, in wedges
- Lay the plaice dark side up. Cut down the central line from head to tail to the bone, then work the knife flat under the flesh, sliding outwards with short strokes to lift each fillet. Do both halves, then turn it over and repeat.
- Keep the frame for stock (recipe 4). Pat the fillets dry and dust with flour.
- Fry in the hot butter and oil for 2 minutes a side. Serve with lemon.
Sharp knife, raw fish and allergens
Filleting knife and slippery fish: a filleting knife is thin and very sharp, and fish skin and slime are slippery. Work on a damp cloth or non-slip mat, cut away from your hand, keep your free hand flat and clear of the blade, and never try to catch a falling knife. Wash the board and knife in hot soapy water straight after.Raw fish: keep raw fish on its own board and plate, away from food that won't be cooked. Wash your hands, boards and knives in hot soapy water afterwards, and store raw fish on a plate on the bottom shelf of the fridge so it can't drip onto other food.
Allergens: contains fish, milk and gluten.
Level 2 · Skinning
Skinning a fillet
Skin a salmon or cod fillet so it can be poached, cured or cut into even pieces. Hold the tail end with a pinch of salt, lay the knife nearly flat against the skin and push away from you with a gentle sawing motion, keeping the blade angled slightly down.
Ingredients (2 portions)
- 1 skin-on salmon or cod fillet (about 400 g)
- 1 pinch coarse sea salt
- 1 tbsp rapeseed oil
- 1 lemon, in wedges
- Lay the fillet skin-side down with the tail towards you. Salt your fingers and hold the tail end firmly.
- Slide the knife between flesh and skin, blade almost flat, and saw gently away, pulling the skin as you go.
- Feel for pin bones and pull them with tweezers. Cut into two portions and pan-fry for 3 minutes a side, or poach.
Sharp knife and raw fish
Filleting knife and slippery fish: a filleting knife is thin and very sharp, and fish skin and slime are slippery. Work on a damp cloth or non-slip mat, cut away from your hand, keep your free hand flat and clear of the blade, and never try to catch a falling knife. Wash the board and knife in hot soapy water straight after.Raw fish: keep raw fish on its own board and plate, away from food that won't be cooked. Wash your hands, boards and knives in hot soapy water afterwards, and store raw fish on a plate on the bottom shelf of the fridge so it can't drip onto other food.
Is it cooked?: fish is done when the flesh turns opaque (no longer glassy) and flakes easily with a fork. A probe thermometer reads about 63°C in the thickest part (general guidance). Take it off the heat a minute early, because it keeps cooking as it rests.
Level 3 · Stock
A 25-minute fish stock
Fish stock is the fastest stock there is, and it must not cook long, or it turns bitter and cloudy. Use white fish bones and heads (never oily fish, and no gills), rinse out any blood, and simmer gently. No alcohol is used.
Ingredients (about 1 litre)
- 1 kg white fish bones and heads (gills removed), chopped and rinsed
- 1 onion, sliced
- 1 celery stick, sliced
- 1 leek, sliced
- 1 bay leaf
- 6 parsley stalks
- 6 white peppercorns
- 1.5 litres cold water
- 2 lemon slices
- Put everything in a large pan and bring slowly to a simmer. Skim off any scum.
- Simmer gently for 20 to 25 minutes without boiling hard.
- Strain through a fine sieve into a heatproof bowl, cool quickly and chill. Use within about 1 day or freeze.
Hot stock and storage
Hot stock: a pan of simmering stock is heavy and scalding. Keep the handle turned in, strain it carefully into a heatproof bowl, and cool it quickly, because fish stock spoils fast: chill within about 1 hour and use within about 1 day, or freeze.Hot pot and hot steam: a heavy casserole dish or pan of hot liquid is heavy and scalding. Use oven gloves, lift the lid away from your face so the steam doesn't burn you, keep the handles turned in and never carry a full pot across a busy kitchen.
Leftover fish: cool cooked fish quickly, refrigerate it within 1 to 2 hours, and eat it within about 1 day (2 at most). Reheat only once, until steaming hot all the way through. Do not refreeze fish that was frozen and thawed unless you cook it first.
Experiments
Experiment
Sharp or blunt knife
Clean cutting.
- Fillet two mackerel, one with a sharpened knife and one with a blunt one.
Look for: The sharp knife gives smooth fillets and little waste; the blunt one tears the flesh and needs more force.
Experiment
Along or against the bones
Technique.
- Cut one fillet with long strokes along the bones and another with short, hacking cuts.
Look for: Long strokes leave a clean fillet with meat on the frame; hacking leaves jagged edges and flesh on the bones.
Experiment
Stock simmered 20 or 60 minutes
Flavour.
- Taste two stocks made from the same bones, one stopped at 20 minutes and one at 60.
Look for: The 20-minute stock is light and sweet; the 60-minute stock is cloudy and slightly bitter.
Experiment
Scales on or off
Texture.
- Pan-fry one scaled and one unscaled small fish skin-side down.
Look for: The unscaled skin is tough and gritty; the scaled skin crisps. Scaling matters.
Tasting notes
| What I tried | Method or amount | What I saw | What I thought | Will I do it again? |
|---|---|---|---|---|
| Filleting a mackerel | ||||
| Filleting a plaice | ||||
| Skinning a fillet | ||||
| Fish stock | ||||
| Sharp or blunt knife | ||||
| Along or against the bones | ||||
| Stock simmered 20 or 60 minutes | ||||
| Scales on or off |
Troubleshooting
| Problem | Likely cause | What to do |
|---|---|---|
| Fillet is ragged | Knife blunt or sawing | Sharpen the knife; use long, light strokes |
| Lots of flesh left on the frame | Knife not riding the bone | Keep the blade flat on the bones |
| Skin tears off in pieces | Knife angle too steep | Keep the blade almost flat |
| Pin bones remain | Missed by touch | Run a finger along and use tweezers |
| Cloudy stock | Boiled hard | Simmer gently; skim scum |
| Bitter stock | Simmered too long or gills left in | Stop at 25 minutes; remove the gills |
Sharp knives, stock and leftovers
Filleting knife and slippery fish: a filleting knife is thin and very sharp, and fish skin and slime are slippery. Work on a damp cloth or non-slip mat, cut away from your hand, keep your free hand flat and clear of the blade, and never try to catch a falling knife. Wash the board and knife in hot soapy water straight after.Hot stock: a pan of simmering stock is heavy and scalding. Keep the handle turned in, strain it carefully into a heatproof bowl, and cool it quickly, because fish stock spoils fast: chill within about 1 hour and use within about 1 day, or freeze.
Leftover fish: cool cooked fish quickly, refrigerate it within 1 to 2 hours, and eat it within about 1 day (2 at most). Reheat only once, until steaming hot all the way through. Do not refreeze fish that was frozen and thawed unless you cook it first.
Checkpoint: can you do this now?
- I can fillet a round fish.
- I can fillet a flat fish.
- I can skin a fillet cleanly.
- I can remove pin bones.
- I can make a clear fish stock.
Next chapter
Cooking Skills: Fish and Shellfish 2, chapter 3 is Fish Stews and Chowders: layering fish in a pot so each cooks right.