MR. KOJO NNAMDIChristmas is fast approaching, and for many Italian-Americans Christmas Eve means a dinner involving a fish. In fact, for some families, it's a meal of seven different seafood dishes, a concept that can be intimidating to many cooks. Well, whether or not it's part of your holiday tradition, fish is one of the healthiest and most challenging things to cook. From selecting quality cuts to preparing the delicate flesh, there are lots of questions to consider. Should I choose farm-raised or wild-caught fish? Is this is a sustainable fish? Is this shellfish safe to eat? Should I boil, bake, fry? Here to help us sort through some of these questions is Harold McGee, the longtime writer of "The Curious Cook" column for The New York Times and, most recently, author of "Keys to Good Cooking: A Guide to Making the Best of Food and Recipes." Harold McGee, thank you for joining us.

MR. HAROLD MCGEEHello, Kojo. Thank you.

NNAMDILet's dive into a little anatomy and physiology before we get to the cooking questions. What is it about a fish's structure that makes it so hard to get just right in the kitchen?

MCGEEWell, it's a couple of different things. One is that fish live in a very cold environment, and so their biochemical machinery is very different from that of a cow or a pig. And what that means is that even at room -- even at refrigerator temperatures, they can spoil very quickly. So it's very important to keep them on ice from the moment they're caught until the moment you cook them. And sometimes you can't trust stores and wholesalers to do that. The other thing is that their flesh, instead of consisting of long muscles, consists of very short ones. And so when they begin to soften and become tender, they also become very fragile, and that's why when you try to lift them with a spatula, they will break up into little pieces.

NNAMDIHow do you know when a fish has gone bad?

MCGEEBy its smell and its appearance, so we all have smelled bad fish.

NNAMDII was about to…

NNAMDI...say, is there anything more technical than smelling?

MCGEEBut you can also tell, even if it's behind the case in a supermarket, if it's a whole fish and the eyes are sunken and the gill area is brown and the skin looks dull and wrinkled, that's an old fish. And you don't want an old fish. If it's a piece of a fish, then you want something that looks bright and moist. You don't want something that's brown around the edges and beginning to get that kind of rainbow iridescence to it. Those are bad signs.

NNAMDIThe first description you gave could have been any one of our producers with a hangover.

NNAMDIThat's exactly how they look. What is it about fish that make them so susceptible to carrying microbes and other health hazards?

MCGEEWell, they live in the oceans and in rivers and streams and farm fish in tanks. And lots of things will grow in water, and so they're exposed to whatever happens to be in that body of water.

NNAMDIHow do you minimize the health risks of eating fish for both healthy people and those who may be especially vulnerable to illnesses?

MCGEEWell, you want to make sure that you cook that fish to a temperature that will kill most of the microbes that might be in the fish. But it turns out, in the case of fish, that there are some things that are only killed by temperatures very, very close to the boil, which means that the fish would get just unpalatably dry. So if you're really concerned about the health of your guests, then sometimes it's best not to serve fish or shellfish.

NNAMDICan you share some basic tips when shopping for fish?

MCGEEWell, you want to look for those characteristics that we were talking about before, the signs of a fresh fish or a fresh piece of fish. And then something that many shoppers don't think of, it's really best to bring a cooler along with you in the car, with ice in it, and to ask the person who's selling you the fish to put that fish in a double bag with ice on top of it because it turns out that if you keep the flesh close to the freezing point, you extend its shelf life, the time that it's actually tasting fresh by days. It can make a tremendous difference.

NNAMDITake your cooler with ice. What a no-brainer. Why didn't I think of that before? Is it better to buy a whole fish? Because for some people, that can be pretty intimidating.

MCGEEIt can be intimidating, but it's also the best way to get the freshest possible fish, because the moment that you cut it for sale, the surfaces begin to deteriorate. And oxygen in the air is -- it's just inevitable that it's going to affect the flavor of the fish. The way you can deal with that, however, is just to make sure that you wash the fish thoroughly when you bring it home because any funny smells, any deterioration that occurs is going to be at the surface, and you can remove most of that.

NNAMDIIf we're choosing live fish, what kind of living conditions should they be in?

MCGEEWell, they should be in a clean-looking tank, and the fish themselves should look lively. They shouldn't just be sitting in a corner. You want to see them moving around. And the water should be moving around, too, and be aerated and look inviting to us, as well as to a fish.

NNAMDIBecause if the fish is not looking lively, if the fish doesn't seem to be moving around a lot, what is that an indication of?

MCGEEWell, that it's in a subprime condition and, in fact, may be in the process of dying.

NNAMDICouldn't be meditating. I just -- I don't know. I just thought of that. In case you're just joining us, we're talking with Harold McGee. He is writer of "The Curious Cook" column for The New York Times, author of "On Food and Cooking: The Science and Lore of the Kitchen." His latest book is called "Keys to Good Cooking: A Guide to Making the Best of Food and Recipes." Can we assume that the more expensive the fish is, the better the quality?

MCGEENot necessarily because it's going to depend on the market that you're buying from. Some markets are going to charge you a lot for not such good fish, and other markets are going to charge you a reasonable amount for very good quality. So what I do, for example, is go to an ethnic market, a Chinese market, where I know that the fresh -- the fish is fresh and where the prices are very reasonable. I'd be happy to pay more than what they charge for the quality of fish that they sell. So the most important thing is to identify good quality regardless of the price.

NNAMDIWhy are the ethnic markets better?

MCGEEI think probably because the customers are more demanding.

NNAMDIOh.

MCGEEI think they cook more fresh fish and more whole fish.

NNAMDIIt's cultural.

MCGEEYes. Yes.

NNAMDIYou live and learn. What kinds of fish do you recommend to people who are concerned about sustainability and the health of the oceans?

MCGEEWell, that's a story that kind of changes from year to year. So what I recommend is that people go to the Monterey Bay Aquarium website or to the NOAA, oceanic -- National Oceanic Administration's website, both of which give up-to-date information about very specific fisheries. So a given fish, for example, may be raised sustainably in one part of the world, but not in another. And so it would be a mistake to avoid that fish altogether, but you'd want to make sure that you get it from the right source. And they have wonderful resources for keeping up on that.

NNAMDIWe'll make sure that we provide links to those websites. Seafood eaters often think that good scallops should be pearly white when they buy them. True or false?

MCGEEPearly white scallops look pretty, but they're not going to cook very well. And they look pearly white because they've been treated with a solution that is designed to plump the scallops up with moisture, make them look moist and wonderful. But when you actually cook them, the scallops release all that moisture, and they end up not browning beautifully the way that they should. And they don't taste that good. So what you want to actually find in scallops is a kind of cream color to an almost orange color. Those are going to be the ones that have not been treated with the plumping solution, and they'll taste and cook better.

NNAMDISo, in this case, white is not necessarily right.

MCGEEAll right.

NNAMDIIs wild fish generally tastier than farm-raised? And is it better for us?

MCGEEWild fish generally does taste better and is firmer as well, and that's simply because those animals get more exercise.

NNAMDIReally?

MCGEEThey're out there in the open waters, and they use their muscles more and differently than animals that are in a pen and enclosed and just kind of sitting there being fed. So that does make a difference. When it comes to the nutritional value, it's a little bit more complicated because fish that are raised in a pen can be fed a special diet that makes them accumulate more of a particular nutrient or kind of fat that we might be interested in.

NNAMDIWhat about the old 10-minute rule for each inch of fish thickness? Is that a reliable measure of cooking time?

MCGEENo. In fact, I would make the generalization that no recipe can tell you how long to cook anything...

NNAMDII like this.

MCGEE...even though they try to make you feel better by giving you a precise number like that. In fact, the way heat works, you simply can't predict because there are so many other variables besides the thickness of the fish. So the best thing to do is to take that as a general guideline, but start checking the doneness long before the recipe tells you it's going to be done.

NNAMDII'm glad you brought that up because how can you check for a fish's doneness elegantly without hacking up the piece and destroying its presentation?

MCGEEWell, it does help to have a nice small, sharp-tipped knife so that you can gently pry apart a couple of the layers in the fish to see whether the flesh at the center is beginning to turn white, which is the sign that it's just perfectly done. Failing that, you can use a digital thermometer with a very fine point and stick that, not directly into the side but along the edge so that no one will see the hole.

NNAMDIIs there a particular way of cooking fish that you think is best, that is grilling, broiling, poaching, fire?

MCGEEHmm, they're all delicious. It depends on the fish and the recipe.

NNAMDIThat was my thinking exactly. By the way, what kind of fish do you most enjoy eating and cooking yourself?

MCGEEI come from San Francisco, and I love a local fish called the sanddab, which is a little -- it's like a sole...

NNAMDIYeah.

MCGEE...like a Dover sole, but it's maybe 6" long and just delicious.

NNAMDIWhere do you get it outside of San Francisco?

MCGEEYou can actually find it up and down the West Coast, but I think they're best around where I live.

NNAMDIAnd there are no possibilities of getting it here?

MCGEEThere might be people who bring it here, but it does mean putting them on a plane and flying them 2,500 miles.

NNAMDIOh, well. What temperature should fish be to be most safe to eat?

MCGEEWell, the temperature that will kill most microbes is around 140 to 150 degrees. And it turns out that you can cook to slightly lower temperatures as long as you hold the food at that lower temperature for a longer time to give that temperature the time to kill the microbes. But, as I mentioned, things that are raised in the ocean sometimes have viruses in them that cannot be killed, even by temperatures at the boil. And so it's good to be aware of that to keep your eyes and ears peeled for news of outbreaks, of problems, which usually happen in the summertime. And just be careful about what you cook.

NNAMDIThere's nothing better, at least not to me, than a good bouillabaisse, which in French, I guess, literally means to boil at a low temperature. But we don't need to take extra safety precautions or do we need to take extra safety precautions when we cook the fish in the stew?

MCGEENo, in fact, bouillabaisse is one of those wonderfully forgiving dishes where the whole point is to boil things together in order to emulsify the olive oil into the seafood broth and mix everything together. So it's -- yeah, it's a wonderful concoction and a very straightforward and simple one.

NNAMDIIt's my favorite, as a matter of fact. Can you give us any more tips on cooking at low temperatures?

MCGEELow-temperature cooking for fish is -- really isn't necessary. Low-temperature cooking for meats is a wonderful thing. But with fish, I think the best way to cook is to cook relatively quickly to a medium internal temperature but using high heat to get a nice flavor on the outside.

NNAMDISpeaking of heat, what kind of thermometer do you recommend that we all have in our kitchens?

MCGEEWell, I would beware of the old style so-called instant-read thermometers, which have a pointer and a dial. It turns out that they're not that reliable, and they're certainly not instant read. So I would look for a digital thermometer and one that has a very sharp tip because...

NNAMDIYou mentioned that earlier.

MCGEEYeah, and the sharpness of the tip determines not only the size of the hole that you make when you check, but also the quickness with which it registers the temperature. And if takes too long to register the temperature, you're going to underestimate the temperature that you have cooked to, and you're going to overcook whatever it is.

NNAMDIIn addition to which it works to help defend you against people if they don't like your fish. Stab them with your thermometer. What's the best way to store and re-serve leftover fish?

MCGEEWell, the best thing to do when you have leftovers is to get it -- get them into the fridge as quickly as possible and to put them in the coldest part of the fridge and, if possible, on a -- in a pan, on a bed of ice to keep it as cold as you can. Again, that's going to help preserve the quality of the flesh because it is very vulnerable.

NNAMDISo that's why the coldest part of your fridge.

MCGEEYes, yes. And then as for re-serving it, serving it again, I recommend serving it cold, not trying to reheat it, because when you reheat it, you end up with something called warmed-over flavors. And they're not nice.

NNAMDII have noticed that when I re-serve fish. If I eat it cold, it seems to taste better than when I reheat it.

MCGEEYes, yes.

NNAMDIYou live, and you learn. And Harold McGee is here to help us all learn. Harold McGee, thank you so much for joining us.

MCGEEMy pleasure, Kojo. Thank you.

NNAMDIHarold McGee is writer of "The Curious Cook" column for The New York Times. His latest book is "Keys to Good Cooking: A Guide to Making the Best of Food and Recipes." I'm Kojo Nnamdi.