Twenty things you need to know.

A decade ago, I wrote a book called A Geography of Oysters that celebrated the romance of oysters, the primal rush of slurping a raw denizen of the sea, and the mysteries of molluscan terroir. The book struck a chord, and American oyster culture has been in overdrive ever since. Where there used to be a few dozen places in the country from which you could get great oysters, and a few dozen in which you could eat them, now there are hundreds. But with every bored banker throwing a few oyster cages off his dock, and every dive bistro reinventing itself as an oyster bar, oyster know-how hasn’t kept up. I’ve never seen so many scrawny, mangled oysters going down so many clueless gullets in my life.

It’s high time for a primer. Over the past year, I’ve been visiting oyster farms and oyster bars across North America for a new site called Oysterater and a new book called The Essential Oyster. During that time I’ve settled on twenty rules for choosing—and dispatching—oysters. Use them, set your friends straight, and for God’s sake tell your servers. Viva la revolución.

1. KNOW YOUR OCEANS

The Atlantic and Pacific Oceans taste different, and oysters draw most of their flavor from the waters they live in. The Atlantic is a pure, sharp brine, while the Pacific is sweeter and more kelpy, like miso soup. Keeping that in mind can help steer you toward your oysters of preference, especially if you also:

2. KNOW YOUR SPECIES

Most of the oysters consumed in North America are either theEastern oyster (from the Eastern seaboard to the Gulf of Mexico) or the Pacific oyster (from British Columbia to Baja). The Eastern tastes like brine and broth with a sweet-corn finish. The Pacific tastes like cucumber or watermelon rind. Hugely different. Most people strongly prefer one or the other. A classic example of an Eastern oyster would be an Island Creek, from Duxbury Bay, Massachusetts. A classic Pacific would be a Hama Hama from Washington’s Hood Canal. There are also four other minor species of oysters you might encounter. Kumamotos are like baby Pacifics, and have even more of that green-melon flavor. European Flats, also known as Belons, are the native oyster of Europe and taste like a battery terminal covered in iodine. Olympias, the only oysters native to the West Coast, are tiny and taste like a Bloody Mary. Kiwas, the native oysters of New Zealand, are closely related to the European Flat and are, pound for pound, the most ferocious oyster I’ve ever tasted. They are only now becoming available in the United States. Try one if you dare.

3. SALTY PLACES MAKE SALTY OYSTERS

All day long, oysters pump seawater through their bodies, filtering out the plankton. They become just as salty as their environment—which can vary a lot. The upper section of Chesapeake Bay has only one-third the salinity of the ocean. Estuaries like Puget Sound and the Gulf of Saint Lawrence are in between. If you’re a full-on brine hound, look for oysters grown in pure ocean water, like Fishers Islands and Hog Island Sweetwaters. If you like an oyster with a fresh, mineral bite, look for oysters tucked near river mouths, like Murder Points. If you prefer balance, split the difference. Oysterater maps all the world’s oysters, so you can make a pretty good guess about salinity and water temperature, which will help you to:

4. FOLLOW THE FROST LINE

Oysters are strongly seasonal. They eat algae, which generally have a big bloom in the spring (as soon as water temperatures begin to warm), proliferate through the summer (when sunlight is abundant), tail off in the fall, and go dormant in winter. Oysters go into hibernation in the winter, when their food supply disappears, just like bears—and to survive the winter dormancy, they stuff themselves in late fall. They get plump and sweet, then live off their reserves. By early spring, they are emaciated. So: Most oysters I know are best from November through January. Far northern oysters, which have to survive the longest dormancy, can be crazy sweet around Thanksgiving or Christmas. They also suck in March and April, when southern and Pacific oysters have already been feeding and fattening for a month or two. Following these trends will lead you directly to Rule No. 5:

5. DON’T SETTLE FOR SKINNY OYSTERS

More often than not, the oysters served in raw bars look likethis—a shrunken gray ghost in a pool of seawater. That oyster is running on fumes: no fat, no glycogen, no reserves, no sweetness. It’s just going to taste like saltwater. An oyster should be plump and opaque, completely filling the shell, like these Beauregard Islands here. That photo was taken in April, when Gulf Coast oysters had been feeding heavily for months, but Northern oysters are still sleepy and starved. Among other things, this means:

6. DON’T DISS THE SOUTH

I’m so bored with northern chefs telling me they don’t serve southern oysters because southern oysters aren’t salty, firm, or safe. These chefs haven’t kept up with the times. It used to be that the last great wild-oyster harvests came from Chesapeake Bay and the Gulf of Mexico, so these were the only southern oysters most people had ever tasted. Wild oysters are dredged by the ton and sold by the sack; they get none of the pampering of farmed oysters. They tend to be gnarled, muddy, and less salty, because wild oysters thrive in brackish waters—like Chesapeake Bay and the Louisiana coast—where their many saltwater-loving predators can’t go. That’s how the South got a reputation for bland, skanky oysters. But in the past few years, growers in the Southeast and Gulf Coast have been using state-of-the-art gear to farm oysters in super-salty waters, and they are cranking out some of the briniest—and best—oysters in the country, such as Virginia’s Sewansecotts and Alabama’s Point aux Pins.

7. DON’T DISS THE FARM

Almost all oysters are farmed these days, and that’s a good thing. The debacles that are salmon and shrimp farming have conditioned everybody to think aquaculture is inherently bad, but shellfish aquaculture is actually the greenest form of protein production on the planet. Shellfish get all their food by filtering algae out of the water. You just put baby oysters in the water and take out market-size oysters two years later, leaving the water cleaner than you found it. Win-win. Also, oysters don’t move, so there’s no such thing as a free-range oyster. A farmed oyster gets much better (i.e., roomier) living conditions than its wild kin. Choose the farmed ones. Support the farmer. And forget the R rule (which suggests eating oysters only during months that have an R in them, i.e., September–April); that applied only to wild oysters.

8. DON’T SETTLE FOR SCRAMBLED OYSTERS

Most of the oysters served in restaurants have been butchered in ways that serious oyster people find completely unacceptable—and most of the people eating these oysters have no clue. The web is littered with horror shots of oysters that were apparently opened by Hannibal Lecter. Here’s a beaut fromChow.com. What the hell happened to those things? If you get served oysters that look like this, don’t go back. The muscles have been hacked and the bellies have been shredded, causing the juices to spill out into the shell. A few of these have been flopped over to try to cover up the crime scene. A proper oyster is one with its liquor still safely running through its veins, waiting to burst when you bite.Here’s a lovely Saint Simon from New Brunswick. Note the smoothly severed muscle and the unmolested belly (and the rust-tinged shell edge, classic sign of a Maritime oyster, due to the preponderance of red sandstone in the region). The mantle looks perfect. Want more oysters like this? Then:

9. GET AS CLOSE TO THE SHUCKER AS POSSIBLE

What do you do when you walk into a sushi bar? Huddle in a distant corner with your nose buried in a copy of The Tale of Genji? No, you belly up to the bar and try to mind-meld with the chef. You want his knowledge, his approval, and his best shit. Same goes for oyster bars. Sit at the counter where you can see the oysters and the shucker. Ask him questions. Suck up. He knows what’s good better than anyone else in the building. Pretty soon, he’ll be sliding you treats.

10. AVOID DILETTANTE RESTAURANTS

The corollary to Rule No. 9 is that the oysters served at places that don’t have a designated shucker are often laughably bad. That goes for very famous, high-end ones, too. These may be great chefs, but they aren’t on the front lines, chatting with the oyster growers every day, and they haven’t put in thousands of hours at the shucking station. If the restaurant doesn’t have a full-time shucker, don’t go there for the oysters.

11. GET AS CLOSE TO THE GROWER AS POSSIBLE

It used to be hard to find great, knowledgeable shuckers, but the bar was raised a few years ago when some of the best oyster growers began opening their own eateries, with Hog Island,Rappahannock River, and Island Creek leading the charge. These growers care deeply about the things that give oysters character, and they trained their staffs accordingly. Suddenly, we’re seeing oysters that are more perfect than anything we’ve seen before, presented by shuckers and servers who are incredibly knowledgeable. We’re even seeing things like species, provenance, and cultivation technique listed right on menus. Now, there’s a new wave of growers opening places like Matunuck Oyster Bar and Hama Hama Oyster Saloon, and more are on the way. This kind of vertical integration significantly shortens the supply chain, which is key, because:

12. FRESHNESS IS ALL

An oyster carries the still-living sea within it. And even though an oyster is alive until the moment it’s shucked, that marine spark diminishes with every moment it’s separated from la mer. Unfortunately, oysters can survive weeks out of the water, and many you find in restaurants (especially ones that don’t specialize in oysters) are that old. Find places that get oysters straight out of the water and serve them within a day or two. (Or, see Rule No. 19.) When you get these sparkly ones, you’ll instantly understand why it only makes sense to:

13. EAT THEM NAKED

A great oyster is truly ruined by accouterments of any kind, even snazzy ones. Lemon, mignonette, et al. are fine—they just completely cover the flavor of the oyster. All a great oyster needs is a good chaser (Rule No. 15). On the other hand:

14. KNOW WHEN TO IGNORE RULE NO. 13

Not all oysters are great. Plenty could use a little help. Honestly, sometimes it’s more fun to destroy oysters you don’t have to feel guilty for dishonoring. Standing at a bar in New Orleans, eating big, sloppy, dredged oysters right off the counter, is not the time for nude gustation. More horseradish, please!

15. THE THRILL OF THE CHASE

The drink that chases your oyster is almost as important as the oyster itself. Most oysters are quite salty and have a sea finish that goes on forever. It’s the job of the booze to stop that finish in its tracks. My general rule is that wine, sake, and martinis go better with Pacific oysters and that beer and Bloody Marys with Eastern oysters—but exceptions abound. Lots of things work well—just make sure you have something at the ready.

16. ICE IS NICE, AND WILL SUFFICE

Americans consume lots of things too cold—hard cider, cheese, potato salad—but oysters are not one of them. Cold firms up an oyster and makes it crisp and refreshing. A good oyster bar knows this, and serves its oysters nestled deep into a frosty bed of shaved ice. (Cubed ice melts too fast.) If your oysters arrive lukewarm, or sinking into a pool of meltwater, that’s a red flag.

17. NOTHING BEATS A FIRM BOTTOM

It used to be that all oysters were “farmed” on a bay bottom or an intertidal beach, as they would grow in the wild. But as growing techniques have evolved, more and more oysters are grown in off-bottom trays and cages, where life is easier and predators nonexistent. In these submerged cages, oysters can grow very quickly and easily; they get long, brittle shells and softer meats. Thrown down in sand or gravel, they’re forced to toughen up. They grow more slowly and develop rounder, deeper, stronger shells, and they get bigger bellies, firmer muscles, and richer flavor. It’s become clear that there’s no substitute for planting an oyster on the bottom and allowing it to grow naturally for its last year or two before harvest. Some of my favorite bottom-planted oysters are Colville Bays,Moonstones, Mystics, Cotuits, Pemaquids, Glidden Points, Totten Inlet Virginicas, and Kumamotos from Chapman Cove.

18. IF NATURE DIDN’T GIVE YOU A FIRM BOTTOM, TRY TUMBLING

Of course, bottom-planting works only when you have a firm and easily accessible bottom. In most places, the bottom is too muddy or too deep. Years ago, an innovative Vancouver Islander named Keith Reid discovered that if he periodically tumbled his tray-farmed oysters in a mechanical tumbler (kind of like a portable cement mixer), it would chip off their soft-growing edge and force them to “cup up.” They had to clamp shut every time they got tumbled, which gave their muscles a workout. They wound up the molluscan equivalent of elfin Olympic gymnasts with six-pack abs. As a bonus, they had beautifully polished shells. Those oysters were Kusshis, and everybody fell for the little cuties. Now many growers tumble. Some use mechanical tumblers, others let the tides do it for them. Look forChelsea Gem, Shigoku, Blue Pool, and Chunu.

19. SHUCK YOURSELF

The surest way to ensure ultra-fresh oysters is to skip all the middlemen and have them shipped directly to you from the grower. You will save a ton of money, and you will have epic parties. On Oysterguide, I keep a list of recommended suppliers who (A) grow great oysters, and (B) have the shipping part under control. Obviously, this only works if you can shuck them when you get them. But this is something every fully functional bon vivant should be able to do. You can learn in about ten minutes. After a hundred oysters, you’ll be good. Here is an excellent video guide by Canadian shucking champ Patrick McMurray.

20. GET RELIGION

You are slurping down dozens of quivering animals who have given their all for this moment. You lucky bastard. No need to fall to your knees, but a silent nod to the fates might be in order. Some days you’re the windshield, some days you’re the bug.

James Beard Award winner Rowan Jacobsen is the author of A Geography of Oysters, American Terroir, and other books, and the founder of the websites Oysterguide (for his opinions) andOysterater (for everyone else’s). His new book, The Essential Oyster, a full-color guide to the world’s best bivalves, will be published in 2016.