Tuesday 18 August 2009

Taking down a large fish without water

Okay, so maybe you're thinking you're not too likely to need to take on a whole tuna and convert it into pieces that are recipe-ready. Even if you or people you know go tuna fishing it will almost always be the case that someone else (like the deckhands) will cut the catch into large chunks free of bones, skin, guts, etc., and pack them into plastic bags for the trip home. I mean, isn't it worth the minor expense to do this and avoid the substantial hassle of icing down the fish whole and encumbering the kitchen with blood and guts and flying scales?

Well, no. It's not. The problem is that even the loveliest skinless loins of tuna cut on the boat will have been exposed to a lot of water and air—enemies #2 and #3 after elevated temperature when it comes to keeping your fish in impeccable shape. By comparison, a tuna kept whole and under refrigeration from the time it was boated will have been continuously chilled and protected (by the fish's skin) from water and air. Meat that is cut off of a whole fish closer to the time of preparation will be in better shape than fillets that are cut early.

Unless you're going to cook the fish right away, rinsing the fillets with water is just a really bad idea. Seawater bears a very high density of microbes, most of which are innocuous but will all the same contribute to the degradation of the fish. The rinsing water is never as cold as the chilled fish, so by rinsing, you're actually warming the fish and speeding up the spoilage process.

Even when cutting the fish at home, rinsing with tap water will have the same warming effect, and the fresh water will put the fish cells into osmotic stress, which does absolutely no good for the preservation of fish quality.

My solution to the problem is to leave the fish whole in the boat's refrigerated hold, and when I get back to land pack it directly into a chest full of ice. I do the "taking down" of the fish under dry conditions, i.e., no water, at home. The fish should be kept in the ice chest up until you're ready to work on it, and just before cutting its skin should be wiped off with a paper towel.

Albacore tuna, about 10 kg each. Yes, they have very long pectoral fins, which need to be hacked off. This is the "white flesh" tuna that is most highly prized for canning, though it is also excellent fresh. Note I've wrapped my table in plastic—this helps a lot at clean-up time.


Eviscerate the tuna by making a "careful" cut along the belly. "Careful" means you don't cut into the intestines, stomach or gall bladder, any of which can taint the fillets with their contents, requiring you to rinse with water. But work quickly. You're cleaning the fish, not dissecting it for a biology class. I cut close to but not actually starting at the vent (anus). This way I can cut the intestine close to the vent from the inside, then strip out all of the "taint risks" of the digestive organs at once. In a larger fish like the tuna, I need to cut the esophagus just behind the mouth cavity (back of the head). With this, the viscerae come out with almost no blood.


The heart may have already come out together with the digestive organs, but maybe not. Besides the heart itself, the area just above the heart (sinus venosus) and the gills are going to contain most of the fishy's blood. Once these are removed, packing a paper towel or two into the area where the gills had been will contain the small amount of blood that would be leaking back from the dorsal aortae.


Now quickly onwards. A cut just behind the head (on the side that you are filleting) all the way to the vertebral column will be important later when it comes time to free the fillet from the center bone.


Cutting both forwards and backwards from the vent just to the side of the center bone will basically free the bottom half of the fillet. With a little practice you can run the knife right along the hemal spines (the spines extending downwards from the vertebral centra).


Turning the fish around and making a similar cut from the dorsal side. Cut through the skin just to the side of the dorsal midline (parts of this skin are quite tough) and run the knife right along the neural spines (in non-biologist-speak, that means staying as close to the center bone as possible). This will free the top half of the fillet. At this point the slab of fish remains attached to the central bone only at the vertebrae. If you've been using a flexible-bladed fillet-type knife so far, it might be good to switch up to a chef's knife to hack through these little bones by running the heavier knife right along the vertebrae. You'll also need to hack through three or four rib bones only, close to the front of the fish.


At this point the whole side of the fish should detach from the central bone in one big thick piece, and there should be no meat left along the frame (this takes some practice). Only the skinny end near the tail needs to be freed and this is done with another cut. Now do the same thing but on the other side of the fish.


Each side consists of an upper loin, a lower loin, a belly, and a collar. The only parts that should be considered "waste" are the skin, the line of little side-bones, and the dark muscle. I don't remove the skin or trim the dark muscle until just before final preparation, so once the loins are separated from each other and the side bones and the belly and collar are cut, the loins get wrapped in plastic and go immediately into a large pan that is already chilled in the fridge. The bellies and collars go in their own wrappings and into the fridge as well.


Are you still reading? Would you actually do this in your kitchen? Note the color and "togetherness" of the loins. There's no separation of myotomes or oily sheen, like what you get in store-bought albacore or fish that is filleted on the boat. My fish is way, way better than what the other folks who fished with me are eating. I figure that if I allow anyone else to cut my catch, there is no way that person will be as careful or as picky about quality as I am. [There are a couple of exceptions, like Jeanine, who gave me some seabass earlier this summer, and Kirby, who blessed me with some lingcod as well as an outstanding abalone.]


It took almost an hour, but the two tuna gave way to a big pile of wrapped loins, bellies and collars. There was very little waste—just the head, gills and innards. The bones went into a stockpot (actually two stockpots) for tuna broth. Why would I make so much tuna broth? No, it wasn't for tuna soup. Details to follow.

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