Oysters have become one of the most coveted of Maine seafoods.

A true connoisseur of oysters claims he or she can discern intimate things about them simply by their look, their smell and their taste. The flavor of an oyster is determined by its merroir — the conditions under which it is grown.

In what some call the bible of oysters, “A Geography of Oysters,” author Rowan Jacobsen writes, “While it's possible to know nothing about oysters and still enjoy them, your experience will be greatly enhanced by background knowledge.”

But the whole thing begins with a tiny seed.

Marine biologist Jon Lewis, who said he's not an aficionado, though he's been studying oysters and oyster farming for the past 19 years, explained how an oyster comes to be.

“We have two oyster hatcheries in Maine,” Lewis said. “Mook Sea Farm in Walpole and Muscongus Bay Aquaculture, Inc. in Bremen.” Lewis explained that adult oysters are placed in a hatchery, and the water temperature is pumped up to 72 or 74 degrees for a couple weeks, mimicking the water temperature in Texas, Louisiana, Maryland and the Chesapeake. The adult oysters spawn and create seed.

Fertilization creates tiny larvae that swim around in the warmish water for a couple weeks, then find a hard surface to attach themselves to. “In the wild it could be a rock or an oyster shell,” Lewis said. The hatcheries, which consist of many large tanks, use ground shell, almost a powder. Each of the microscopic larva settles on these tiny pieces of shell.

Then they start to feed. In the hatcheries, the larvae are fed from giant tanks of 1,000 gallons of green and orange algae cultures. “All of the algae that the oysters like to eat,” Lewis said. Bigelow Lab provides a lot of that algae.

Then the incubation process begins. The “little guys” start to grow up, and the hatcheries will sell the still tiny oysters, or seeds, two to five millimeters, or around 1/16 inch, to oyster farmers. The oyster farmers will then place the seeds in buckets, or up-wellers, with mesh screens, to keep predators like starfish and crabs at bay. “The up-wellers give them a big kick in the pants,” Lewis said. Ocean water full of natural algae is pumped around and through the up-wellers.

Some oyster farmers opt to bypass the up-weller process and go directly to bags. ADPI, plastic mesh, bags float at the surface. “The baby oysters sit in there, the water flows through, and predators can't get at them. They start to grow.”

The oysters continue to grow in the bags while Mother Nature delivers their food — algae and detritus and anything else that floats by is filtered by them. “They're big sieves,” Lewis said. “Some farmers let them sit for two or three years, depending on the water temperature. The warmer the water, the more they filter. And the more they filter, the more they eat. In the winter, when water temperature is around 40 degrees, they stop filtering.

At that point some will drop the bags to the bottom, while others simply dump them on the ocean floor. Oyster farmers have leased areas where their oysters can be deposited, and where they will remain until they're gathered by divers. “Oysters don't move,” Lewis said. “They just sit there waiting for food to come by.” An adult oyster will filter 50 gallons of water a day.

“That’s when they stop being babies,” Lewis said. “They have to deal with the crabs and the stars, and they start to ‘cup up’: The bottom shell gets a little deeper, as it settles into the sediments.” For that reason, oysters grown in bags to maturity don't have as much of a cup as those grown on the ocean bottom.

Some farmers opt to grow them in bags at the surface from seed to market, Lewis said. That may sound like the easy way out, but it's more costly, because of the cost of the bags, and it is more work. “You have to keep the bags clean. There's stuff growing on them — algae and other things. If the bags are kept clean you don't have to clean the oysters. There's a lot of maintenance involved in growing in bags.”

After two or three years, the oysters are ready to harvest, at around three or four inches. The oysters that aren't in bags are harvested by dragging or diving.

Barbara Scully, founder of Glidden Point Oyster Co. in Edgecomb, has always used dive harvesters to gather her oysters. “None are raised entirely in bags,” she said. “They get planted directly on the bottom.” Scully recently sold a part of her business, but maintains ownership of the retail shop.

Once the oysters have been harvested, and are ready to eat, they have to be shucked. When an oyster is shucked, the flat side, or top, is removed and the oyster sits in the cupped side — an oyster on the half shell.

“What the restaurants and oyster lovers are looking for is that deep cup,” Lewis said. “It holds lots of meat, and lots of the merroir — all that flavor from the place it grew up in.”

The oysters served in restaurants and sold at retail markets are different sizes. Small ones, 2 ½ or 3-inch are considered cocktail oysters, like Glidden Point Selects. Jumbo oysters are around four inches.

The World is Mine Oyster offers oysters from areas ranging from the Damariscotta River, Southport, the Bar Harbor area and Prince Edward Island to Puget Sound in Washington State.

There are approximately 50 commercial oyster farmers and another 150 small commercial and recreational farms in Maine, where oysters are about a $3 million industry.

Lewis has been doing some of his own oyster farming, but he isn’t bragging about it. “It’s slow, slow, slow, slow ... the water in the Sheepscot is too cold for vigorous feeding. But it’s fun anyway.”

In the words of Rowan Jacobsen, “Think of an oyster as a minor work of art. Knowing something about where (the oyster) came from, how it came to be, and how it might be described will give meaning to your meal.”