23.1　Filleting fish

The order of filleting follows the same idea for every fish. First comes scaling and gutting (mizu-arai). This is the work of removing the scales, head, guts, and blood line, and washing the fish under running water. Next, you take the flesh off along the bones. Last, you cut it into saku.

The important point is this: everything up to scaling and gutting is the "dirty stage," and everything from cutting saku blocks onward is the "clean stage." The surface of a fish and the inside of its gut carry many bacteria. To keep them from moving to the flesh that goes into the guest's mouth, you wash the cutting board, knife, and hands again at the boundary between the stages (Chapter 4).

When you scale and gut the fish, insert the tip of the blade only shallowly as you remove the guts. If you damage the guts, the bacteria in the gut and the bile get on the flesh. Bile is a bitter digestive fluid. The chiai (blood line) left along the backbone is a mass of blood from the kidney, which lies under the backbone. Break the membrane over it, and wash it all away under running water. The blood line feeds bacteria. If you leave it, it becomes the starting point of bad smells and spoilage.

Finer steps of scaling and gutting: sukibiki, the head, and the blood line

To remove scales, either raise them from tail to head with a scaler, or use sukibiki. Sukibiki is a method of holding a yanagiba (slicing knife) or a deba almost flat and thinly shaving off the scales where they meet the skin. Sukibiki has two advantages. First, unlike a scaler, it does not press on the flesh. Even with a fish like hirame (olive flounder), which has fine scales and soft flesh, it does not crush the cells or split the flesh. Second, it cuts the scales off at their roots, together with a single thin layer of skin. This removes the dirt and bacteria that have worked into the gaps between the scales. Scraping with a scaler sends scales flying around the kitchen, and dirt stays at the roots (Chapter 13).

Cut off the head along the line joining the bases of the pectoral fins and the pelvic fins. Open the belly as far as the anus, and take out the guts. Break the membrane over the blood line with the tip of the knife or a sasara (bamboo brush), and wash the blood away under running water. When you finish washing, wipe off the water. At this point, wash the cutting board, knife, and hands once.

Three-piece filleting, five-piece filleting, and opening a fish flat

Three-piece filleting (sanmai oroshi) is the basic method of dividing a fish into three pieces: the upper fillet, the lower fillet, and the backbone. You can use it on any fish whose body is symmetrical on both sides of the backbone. There is one key point: always keep the blade touching the backbone as you work. If the blade moves away from the bone, flesh stays on the bone. If it digs into the bone, the blade stops.

1. Make the first cuts　Cut shallowly through the skin along the edges of the dorsal fin and the pelvic fin. Whether you start from the back or the belly depends on the restaurant and the fish.
2. Glide over the bones　Put the tip of the blade on the bones. Feel the bones as you go, and work all the way to the spine.
3. Take off the fillet　Pass the blade through at the base of the tail. Lay the blade flat on top of the backbone, and draw it toward the head. Turn the fish over, and take off the other side in the same order.
4. Look at the bones　The amount of flesh left on the backbone is your report card for filleting.

Flat fish such as hirame and karei (flounder) cannot be filleted into three pieces. Use five-piece filleting (gomai oroshi) to divide them into five pieces: two fillets from the top side, two from the bottom side, and the backbone. The long, narrow muscles along the bases of the fins are the engawa (fin muscle of flounder). They are rich in fat and have a firm bite.

Anago (conger eel) and horse mackerel are also prepared by opening from the back. You insert the knife from the back and open the fish flat, leaving it joined by the skin of the belly. Opening the fish from the belly instead is called opening from the belly. It is often said that unagi (freshwater eel) is opened from the back in the Kanto region around Tokyo and from the belly in the Kansai region around Osaka.

Finer steps of three-piece filleting, and details of five-piece filleting and opening

Here is one example of three-piece filleting. Place the fish with the head to the right and the back toward you. Cut through the skin only, along the edge of the dorsal fin, from tail to head. On the second pass, put the blade against the bones and work it down to the spine. Keep feeling the blade tip against the projections of the spine. Next, turn the belly toward you, and cut the same way from the edge of the pelvic fin to the tail. The bases of the belly bones are thick, so free them with the heel of the blade. Also use the heel to cut the thick bones that join the spine and the flesh. After you turn the fish over, change the angle at which you lay the blade, to follow the shape of the bones for the fillet now underneath. You pass if so little flesh remains that you can see through to the bones.

In five-piece filleting, place the fish with the eyed side up. Cut along the line of the backbone from head to tail. From that cut, lay the blade flat toward the fins and glide it over the bones to take off the fillet. The engawa are the muscles that move the fins, so they have a lot of fat and connective tissue. Either cut them away along the fins before you take off the fillet, or cut them off the fillet after you remove it. The top-side fillets are thicker than the bottom-side fillets, so even in the same fish you change the thickness of the slices.

When a fish is opened from the back, the skin spreads out on the outside and the flesh is an even thickness. It also keeps its shape well, whether you simmer it or grill it. A butterfly cut (kannon-biraki) is a method of cutting into the center of thick flesh and laying the blade flat to open it out to the left and right. It spreads the flesh to an even thickness. So it is used for mackerel bo-zushi (bar-shaped sushi) and to even out thick belly meat. Every way of opening a fish has one thing in common: you leave one layer of skin uncut. The skin holds the flesh together, so the fish keeps its shape.

23.2　Cutting saku blocks and using the deba

The work of turning the filleted flesh into rectangular blocks ready for kiritsuke is called cutting saku blocks. First, lay the blade flat and thinly shave away the belly bones, following their curve. If you cut too deep, you lose belly meat. If you cut too shallow, bones remain. Next, remove the pin bones that run in a single line down the middle of the fillet. With large fish such as red sea bream (madai) and Japanese amberjack (buri), cut along both sides of the line to separate it, making two saku: one from the back and one from the belly. With horse mackerel and mackerel, pull the bones out diagonally toward the head with bone tweezers. Last, remove the skin. The basic method is to keep the knife still and pull the skin instead (pin-boning and skinning are covered in Chapter 13).

Each part of the deba you use for filleting has its own job (Chapter 22). The heel is the thick part near your hand. It cuts off the head and cuts through thick bones. The front of the edge cuts skin, glides over bones, and shaves away belly bones. The spine is the back of the blade, opposite the edge. It raises scales and taps bones.

In every situation, the principle is to draw the blade, not to use force. If you use force, the blade bites into the bone, cuts away flesh, and chips at the edge. Your filleting speed does not depend on force. It depends on whether you can feel the shape of the bones with the edge.

Handling bones, and key points for each kind of fish

Pin bones are small bones in the middle of the fillet. They run at a slant from the head side, along the boundary between the back meat and the belly meat. When you pull them out with bone tweezers, follow the angle at which they grow, and pull diagonally forward toward the head. If you pull the other way, the flesh tears. When skinning, lay the back of the yanagiba flat on the cutting board, and keep the blade parallel to the board. This leaves the silver skin layer (gin-kawa) on the flesh.

When you cut through bone with a deba, put the heel on the bone. Then either press the spine with the base of your left hand, or let the weight of the blade drop. If you slam the blade down, it chips. When you glide over bones, let the blade touch the bones as part of the motion of drawing it toward you.

There are three things to remember most from this table. Fillet mackerel while checking for Anisakis with your eyes. The blood of anago is toxic, and heat destroys the toxin. The top and bottom fillets of hirame differ in thickness.

23.3　Kiritsuke: slicing by pulling

Slicing a single piece of topping from a saku is called kiritsuke. The rule is the pull cut (hikigiri). Set the heel of the yanagiba on the saku. Draw the knife toward you, using the long blade all the way to the tip, and cut the piece off in a single motion. Do not push, and do not saw back and forth.

Why pull? If you push a dull knife through a tomato, the flesh is crushed and the juice spreads. If you draw a sharp knife smoothly, the cut is clean and almost no juice comes out. Fish is the same. When you push to cut, the blade crushes the flesh before it goes in. The cells at the cut surface break, and the liquid inside flows out. This liquid is called drip. It is the umami components and the water of the flesh itself. With a pull cut, the blade slides in with little force. Only a very thin layer of cells, where the blade passed, is broken.

On a well pull-cut surface, the line where two faces meet stands sharp and shines. This is called having crisp, sharp edges (kado ga tatsu).

The science of the pull cut: why the edges stand sharp

As the blade is drawn, the fine teeth of the edge (Chapter 22) tear through the fibers one after another. The blade moves forward while sliding along its own length, so the edge enters the tissue with little pushing force. The cut surface becomes smooth, a direct copy of the line of the edge. A push cut uses only straight-down force, so it needs a lot of force. The slopes of the blade spread the tissue sideways, and the cells are squeezed before they tear, so the cell membranes break. Sawing back and forth also rubs the cut surface every time the blade moves.

The drip that flows out contains free amino acids, inosinic acid (an umami component), and water. A cut surface that has lost drip turns cloudy and whitish. Liquid is left on the cutting board, and the umami comes through weakly when the piece goes into the mouth. A topping with crisp, sharp edges looks firm, and its texture on the tongue is clear. There are four conditions for sharp edges: a sharp blade (Chapter 22), a pull cut in one motion, a cold saku, and a clean blade wiped with a wet cloth. If the edges are rounded, there is one of three causes. The blade is dull, you pushed to cut, or the saku warmed up and the flesh became too soft.

23.4　Sinew direction, thickness, and knife scoring

Sinew direction

The white lines you see in a saku of tuna are membranes that connect the layers of muscle. Put the knife in at a right angle or at a slant to these lines. The sinew is then cut into short pieces and does not stay in the mouth. If you cut parallel to the sinew, long strands remain whole, and you can chew forever without biting through.

Thickness and cutting styles

The standard for thickness is that the topping and the shari disappear in the mouth at the same time. Slice fatty toppings thinner. Slice firm white-fleshed fish thin and wide with sogigiri (angled slice). Sogigiri is a way of cutting at a slant, shaving with the blade held low. Slice lean red-fleshed fish slightly thicker. The basic way of cutting, drawing the blade held upright, is called hirazukuri (straight slice).

In words, the numbers in this table are: akami, 6 to 8 mm; toro, 4 to 6 mm; white-fleshed fish, 3 to 4 mm; and squid, 4 to 6 mm.

Decorative scoring and hidden scoring

Shallow cuts made on the top of the topping are called decorative scoring. Unseen cuts made on the underside, the side against the shari, are called hidden scoring. They cut tough fibers so the topping is easier to bite through, and they also help nikiri (simmered soy glaze) cling. The depth should be one-third to one-half of the thickness of the flesh. If the cuts are too deep, the topping tears when you shape the nigiri. If they are too shallow, they have no effect.

Myotomes and myocommata, and the reasons for thickness

Fish muscle is made of W-shaped layers of muscle called myotomes, lined up from head to tail. The thin membrane connecting the layers is the myocomma (myoseptum). These are the white lines you see in a saku. In the toro of tuna, these membranes are thicker. The basic setup is to place the saku so the lines run from lower left to upper right, and to draw the blade across them. Near the tail, the lines are close together and stay in the mouth even when cut, so use that part for negitoro (minced fatty tuna) or rolls.

If you slice toro as thick as akami, the network of fat melts more slowly than the shari falls apart. The shari disappears first, and only fat remains in the mouth. So slice it thin. With shari at body temperature (Chapter 9), the fat then melts just as the shari comes apart. White-fleshed fish is firm and chewy, so a thick slice stays in the mouth longer than the shari. With sogigiri, you widen the surface, so even a thin slice can cover the shari. Akami is sliced thicker, so its acidity and iron-like flavor are not overpowered by the shari. For toppings eaten for their texture, such as shellfish and squid, make them easy to bite through with hidden scoring rather than by adjusting the thickness.

Usuzukuri is sogigiri cut even thinner, so thin that you can see the pattern of the plate through it. It is used for fugu (pufferfish), kawahagi (thread-sail filefish), and hirame. To keep the slices evenly thin, use a thin fugubiki (fugu slicing knife), and chill the saku well to firm up the flesh. Even soft toppings such as toro will have crisp, sharp edges if you slice them while they are still firm, right out of the refrigerator.

The three purposes of decorative scoring, and scoring the skin

Decorative scoring and hidden scoring have three purposes. First, they cut tough fibers and sinew to give a clean bite. The crisscrossing collagen fibers of squid, the skin of horse mackerel and kohada, and the sinew of buri all become easier to bite through. Second, they increase the surface area. The cuts add surface, so more nikiri and salt cling to the topping. Third, the added surface widens the area that touches the taste buds on the tongue. Taste buds are clusters of cells that sense taste. As a result, you taste umami and sweetness more strongly. This is why hidden scoring brings out the sweetness of squid.

For hikarimono (silver-skinned fish) such as kohada and horse mackerel, where a whole half fillet is used, shave the thick back side thinly to even out the thickness. Score the skin side. This keeps the skin from shrinking, so the nigiri holds its shape, and it makes the tough skin easy to bite through. Restaurants have developed their own designs, such as a diagonal crosshatch on the skin of kohada or lengthwise lines on the skin of horse mackerel.

23.5　Tempering and slicing ahead

Toppings straight out of the refrigerator are too cold. It is hard to taste their sweetness and umami, and the fat of toro does not melt fully. So, right before shaping the nigiri, you let the piece you have just sliced sit for a few tens of seconds to 1 or 2 minutes, so that only its surface warms slightly. This is tempering.

Tempering is completely different from slicing ahead. Slicing ahead means slicing toppings for many servings in advance and laying them out. It exposes the toppings to room temperature and gives bacteria time to grow (Chapter 5). Keep the saku in the refrigerator, and temper only the one slice you are about to use. Taking saku out to room temperature before service to "temper them in advance" is the same mistake as slicing ahead.

Why temper: taste buds, fat, and aroma

Toppings straight out of the refrigerator are at 2 to 4°C. At this temperature, the taste buds are less sensitive, and sweetness and umami taste weak. Tuna fat is said to melt completely by about 24 to 30°C (Chapter 14). Fat that is too cold does not melt fully in the mouth and lingers like wax. Aroma compounds are released less the lower the temperature.

The target is a surface that has warmed to about 10°C. A fatty topping shows a slight sheen on its surface, and it no longer feels piercingly cold to the touch. You are not warming it all the way to the center. You warm only the surface and pair it with shari at body temperature (about 35 to 37°C). In the mouth, the fat melts, the aroma rises, and you taste the umami. The center stays cold, so freshness and texture are preserved.

Slicing ahead is banned because it means laying out toppings for dozens of pieces on the cutting board and leaving them for a long time with a food temperature above 10°C. Tempering is done "only as much as needed, right before use." You slice one piece after receiving the order, and you let it sit for a few tens of seconds to 1 or 2 minutes. In that time, you take the shari and add the wasabi. If you keep to this order, the topping spends less than a few minutes in the temperature danger zone.

23.6　Hygiene and workflow on the cutting board

During filleting, the hygiene stage changes partway through. Up to scaling and gutting, the work involves large numbers of bacteria from the fish's skin and gut, such as Vibrio parahaemolyticus and coliform bacteria. From cutting saku onward, you handle only flesh that goes directly into the guest's mouth. Ideally, keep a cutting board and deba only for scaling and gutting beside the sink, and a cutting board and knife for cutting saku on the work table. If you cannot do that, clean the cutting board, knife, and hands as soon as scaling and gutting is finished. Disinfect them with hot water or alcohol. Wipe the cutting board again before moving on to cutting saku (Chapter 4).

If the cutting board is dry, the flesh sticks to it. If it is too wet, the flesh absorbs water. Wipe the whole board with a tightly wrung wet cloth, and use it while the surface is slightly damp. Keep wet cloths and dry cloths separate. Decide that the wet cloth is for wiping the blade and the board, and the dry cloth is for removing moisture. Never wipe a saku with a cloth you used to wipe off blood.

At the tsukeba (the chef's work area behind the counter), tezu (vinegared hand water) keeps the surface of your hands mildly acidic (Chapter 6). But in the prep area, do not rely on tezu. Wash your hands with soap every time the stage of work changes. Wipe the moisture off the saku, wrap it in paper towels, put it in a tray, cover it with plastic wrap, and return it to the refrigerator. From filleting to shaping the nigiri, cut the time the fish waits on the cutting board down to the second. That awareness protects both flavor and safety.