- Smell it!
Fresh fish should smell sweet: you should feel that you're standing at the ocean's edge. Any fishy or strong flavors means the fish is past its prime; do not buy it. I still have a vivid memory of shopping in a local supermarket, watching an elderly gentleman sniff each portion of raw fish offered to him by the butcher. The gentleman rejected almost every fish because it didn't smell fresh. You can be sure that the fish he chose was moist, delicate, and delicious.
- Look at it!
Whole fish should look as they were just pulled from the water; bright eyes and firm flesh are signs of freshness. Fish fillets or steaks should be firm and bright looking, with no brown spots or discoloration.
- Freeze it!
Fresh fish should be stored in your refrigerator for only a day or two; it's very perishable. Any longer than that, and wrap the fish well in freezer paper and freeze it. Unless you live near a coast with a reliable supply of freshly caught fish, most fish that you buy will be sold frozen. Keep it frozen until you're ready to cook it. Fish can be thawed in the refrigerator, or under cold running water, or in the microwave. Be sure to cook it as soon as it's thawed.
Don wrote and reminded me of a great trick - thaw frozen fish in milk! Place the frozen fish in a bowl and cover with fresh milk, then cover and let sit in refrigerator overnight. The fish will have a wonderful fresh-caught taste. Discard the milk after the fish thaws.
- What about bones?
Many fish, including trout and salmon, have a double rib cage, so the fillets may have small pin bones. You can remove these by pressing the flesh with your fingers, and removing the bones using a tweezer. It's possible to buy fillets of these species without pin bones, but they are generally much more expensive.
Remember in our discussion about How to Cook Beef, we learned that beef is red because a cow's hard used muscles need lots of oxygen and therefore have a lot of myoglobin, the molecule that transports oxygen around the body. Fish have a much easier life. They don't need to fight gravity to stay upright, and can move long distances with just a flick of a tail. Therefore there isn't much myoglobin in fish, so it tends to be light colored and translucent.
When fish cooks, the proteins denature or unwind, then reattach to each other, or coagulate. This process squeezes out water and the molecules shrink, pressing closer together. You can see this process happening as the fish becomes opaque. Light isn't able to pass through the coagulated proteins; fish is cooked when it is opaque.
Because fish have very little connective tissue and fat, they are quite delicate when cooked. A reliable doneness test is to check if the fish 'flakes'. Insert a fork or knife gently into the thickest part of the fish and twist. The flesh should begin to separate along the natural lines.
There's a delicate balance between perfectly cooked fish and overcooked fish. First of all, remember the principle of residual heat: a pan will hold heat when it's removed from the heat source, continuing to cook the food for several minutes. For best results, cook fish until it's almost done, then remove the pan from the oven, microwave, stovetop or grill and let it stand for a few minutes to finish cooking.
Some fish, especially tuna and salmon, can be served medium rare. I myself do not enjoy fish cooked this way, and serve all of my fish well done, but the choice is up to you.
To Marinate, or Not?
Marinating fish adds flavor and moisture to the flesh, but any marinating should be very brief. If fish flesh sits in acidic ingredients for more than 30 minutes, the acid will begin to denature the delicate protein, and you'll have a mushy fish when it's cooked. Even richer flesh of salmon and tuna should only be marinated for about an hour.
Marinades include oil (extra virgin olive oil provides the best flavor) and an acidic ingredient like chopped tomatoes, red wine vinegar, or lemon juice, along with seasonings including salt and pepper. Depending on your tastes, seasonings can range from chopped jalapeno peppers and crushed red pepper flakes to fresh thyme leaves and parsley.
Go to the next page to learn about fish cooking methods.