All freshwater fish have delicate flesh that begins to deteriorate before the fish dies, if it's roughly handled or excessively stressed. Keeping fish lively as long as possible in a good livewell or in a keep sack before cleaning them is one step to fine-tasting fish. Stringers stress fish more than other methods, unless the water's cold. When the water's warm, it's usually best to dispatch fish immediately and surround them with ice.
After death, fish flesh deteriorates quickly if the fish isn't handled correctly. Once they die, gut them immediately when possible to do so. Don't let sour, bacteria-filled stomach and intestinal juices touch the flesh for long. Gutting fish also bleeds them: blood left in flesh speeds deterioration. Wash gutted fish in cold water to remove bacteria, then surround the fish with crushed ice to retard any bacterial growth.
In the field, icing fish is the best way to keep them fresh once they've been killed and gutted or filleted. Crushed ice works best because it packs more closely, cools more quickly, and keeps fish colder than would blocks of ice or frozen bottles of water. So, after gutting the fish, rinse them in cold water and surround them with crushed ice. Don't let fish soak for long—even in icy water.
Use the same strategy with fish at the cleaning table. Unless they're fresh and lively from a livewell, the fish should already be iced. Once a fish is cleaned, immediately immerse it in iced water. Once it's chilled, give it a quick rinse, pat it dry with a towel, wrap it with cling wrap, and surround it with crushed ice. Crushed ice keeps fish for at least five days, although the table quality of the flesh deteriorates slightly each day.
This is another method for keeping fish in the field. Super-chilled fish that have been gutted and left in the round can be kept on ice for five days and often longer. Properly stored fillets can be kept for up to five days, although, as we've said, it's best not to fillet fish until you have to.
To super-chill, line the bottom of an insulated cooler with several inches of crushed ice, leaving the drain open. In another container, mix coarse ice cream salt and crushed ice at a ratio of 1 to 20. For average-sized coolers, that's one pound of salt to 20 pounds of ice.
Packaging for the Refrigerator
The temperature of most refrigerators is set at about 40°F. The best way to keep fish in a refrigerator is to turn the thermostat down to almost freezing, but that isn't good for other things in the refrigerator, which may actually freeze.
Another option is to surround the fish with crushed ice. Partially fill a bowl with the ice, wrap the fish tightly in cling wrap, surround and cover them with ice, then cover the bowl with cling wrap, as well. Drain the melt water frequently so the fish doesn't soak in water. Proper icing lowers the storage temperature to about 34°F, which allows additional days of storage.
If you don't have crushed ice, pat the fish dry with paper towels. Moisten a clean dishtowel and line the bottom of a bowl with it. Spread the fillets on top and cover the bowl with cling wrap. This keeps fillets reasonably cold and moist but not sloppy wet. With this method, fish keep for about 5 days in the round and 3 days filleted. Again, never keep fish in a plastic bag soaking in water and bacteria-prone fish juices.
In the restaurant, Lucia's staff doesn't have crushed ice, so they use ice cubes. They place the fish on a bed of ice cubes, which they put in plastic bags to cover the fish.
Fish flesh loses its quality in the freezer through dehydration and oxidation. "Freezer burn" (whitish leather-tough flesh) is an advanced stage of dehydration. Freezer burn results from using the wrong wrap or wrapping improperly. If your wrap doesn't seal in moisture effectively, fish flesh loses its moisture and turns tough.
Oxidation is a result of poor packaging. Using the wrong wrap or failing to remove air from the package before freezing causes oxygen to combine with polyunsaturated fats and oils in the flesh. These fats turn rancid in the presence of oxygen.
Properly frozen fish keeps well and holds its flavor for months, although the quality deteriorates progressively the longer they're frozen.
The objective is to seal in moisture and hold out oxygen. Aluminum foil works, though it punctures easily. It can be used as a final wrap following cling wrap. Polyvinylidene chloride, the material in cling wraps, forms a good barrier and clings to fish, eliminating air pockets. It's the best initial wrap. Most companies make "freezer grade" cling wraps.
One simple method is to wrap fish in cling wrap, squeezing as much air as possible from the wrap, then follow with another layer of cling wrap (wrapping still tighter and forcing out more air). Finally, add a layer of wax-coated freezer wrap. Write the date frozen, fish type, size, and any other information on the outside of the package.
Zipper-lock "freezer bags" also form a good barrier against air and moisture. Layer a couple of fillets or place a fish in the round in the bottom of a bag. To remove air from the bag, zip almost completely shut and submerge the bag in a water-filled container. Seal the bags underwater. A little water may enter the bag, but that's better than leaving in air.
Vacuum sealing machines, although more expensive than the methods mentioned so far, are available and add a professional touch to the freezing process.
Freezing in Water
Commercially frozen fish often are glazed with a coating of ice to protect the flavor and table quality. It takes freezer temperatures of about -40°F to accomplish this. Water can be used to store fish in other ways.
Disagreement exists about whether or not the methods that follow are advisable. Our practical experience over the years is that lean fish like walleyes and pike retain their flavor well when a little water is used in the freezing process. We don't use water with fish like salmon and trout.
One method is to pack fish tightly in lidded plastic containers and fill the containers almost to the brim with water. Use enough water to cover the fish, but don't leave large empty spaces for water—too much water draws nutrients from the fish, causes the fish to freeze more slowly, and crushes them when the water freezes.
Pack the container with as much fish as possible, minimizing empty spaces. Then seal the remaining spaces with water. If fish portions protrude from the ice after freezing, add a little more water and refreeze.
Another method that works well is to layer fish in a freezer-grade plastic locking bag, then add just a little water. Zip up the bag, leaving only a tiny opening. Squeeze the remaining air from the bag by folding the bag over the fish, until a little water just begins to run out. Immediately seal the bag. This simple method is perhaps our favorite method for freezing lean fish fillets.
Divide cleaned fish into serving-sized portions to eliminate leftover thawed fish.
Freezing breaks down cell walls, the reason frozen fish is less firm than fresh fish and more "weepy." Don't refreeze thawed fish.
The faster fish freezes, the better. Place packages in the coldest part of a freezer and don't overload the freezer with food to be frozen. Keep the temperature at 0°F or below while the freezing is taking place.
Thawing fish at room temperature lets thawed parts deteriorate as other parts thaw. Instead, thaw frozen fish in the refrigerator, allowing 24 hours for a 1-pound package. Another option is to place frozen fish in cold water until it's thawed. Keep it in the vapor-proof wrapping as it thaws.
Cooking Tips for Frozen Fish
To pacify strong flavors added by freezing, soak fish in milk for 15 to 30 minutes before preparation—don't rinse before dusting or using other preparations.
Seasonings help frozen fish, so add dried herbs to any flour or cornmeal coatings, and consider using bacon fat to sautéd. A good wine helps when poaching frozen fish. Consider stronger sauces, especially with stronger-tasting fish like white bass and freshwater drum.
Frozen fish is never as firm as fresh fish, so it goes well with something crunchy on the plate, like sautéd vegetables, placing the fish on top of the bed of vegetables.
How To Keep Fish Fresh