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How It's Made: Oysters

Vocab level: C1
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Oysters are a versatile shellfish.
You can bake them, boil them, smoke them, or eat them raw right from the shell.
Over the years, wild oyster stocks have declined due to overfishing and pollution.
So today, 95% of the oysters we consume come from oyster farms.
Oysters are filter feeders, meaning they draw seawater over their gills
to trap and eat the phytoplankton (microscopic aquatic organisms).
An adult oyster can filter more than five quarts of seawater per hour.
Oyster farms are located in or by the sea
because the oysters need to feed off seawater to survive.
The hatchery keeps the oysters in upwellers (mesh bottom buckets sitting in seawater).
Oysters can reproduce once they're six months old.
However, the ideal breeding age is between 2 and 10 years.
At breeding time, workers put the oysters into breeding trays,
oscillating the temperature between 68 and 86 degrees to stimulate spawning.
The females squirt out eggs, the males squirt out semen,
and 16 hours later, the fertilized eggs hatch larvae.
Right from birth, the oysters feed on a blend of the phytoplankton they'd eat in the wild.
The hatchery dilutes this plankton mix in seawater
and pumps it to the oyster containers.
Marine biologists manage the ponds in which the hatchery grows its phytoplankton supply.
The larvae are so tiny, you can't see them in the water.
They're visible only under a microscope.
Right from the time they hatch, they already have a shell and can swim.
By about the 2-week mark, they've grown to the size of a speck,
about 1/64 of an inch long.
However, now they act like miniature adults and stay put.
The hatchery keeps them in suspension in circulating water,
so they have an ample supply of food and oxygen.
As they grow, they're transferred to progressively larger bottles.
By the time they're four to six weeks old, they're ready to leave the hatchery and move to the oyster farm.
The farm floats in a harbor.
The baby oysters arriving are a tiny fraction of an inch long.
They go into upwellers.
Pipes circulate seawater, and the babies filter feed on the natural phytoplankton.
Over the next six weeks or so,
they quadruple in size to about 2/10 of an inch in length.
Workers then pack them in plastic mesh bags,
stack the bags on metal racks, and suspend the racks in the sea.
The oysters live like that for three months,
getting transferred into progressively larger mesh bags as they grow.
Halfway into it, the oysters are this big, about 8/10 of an inch long.
By the end of three months, they're double this size,
grown up enough to leave home and venture out into the real world.
Workers lay them on the sea floor and leave them for six months to reach harvest size,
which is determined not by length anymore, but by weight, just under three ounces.
To finally harvest the oysters,
they lower a custom-built machine that's part dredger, part conveyor.
It generates jets of water that blow the oysters off the seabed onto the conveyor.
They travel up out of the water into the boat.
That conveyor dumps the oysters onto another conveyor that leads to the picking station.
There, workers select the correct size oysters and put them into baskets.
Whatever they leave on the conveyor, smaller oysters, rocks and such,
continues to the end and drops back into the water.
Of course, the harvesting machine misses some 3-ounce oysters.
Those remain on the seabed, sometimes for years,
growing larger like this guy, weighing about 2.2 pounds.
Prior to sale, the harvested oysters go through a cleaning process called depuration.
For 42 hours, they sit in tanks filled with seawater, sterilized by ultraviolet light.
The oysters draw this clean water through their gills.
This flushes out all the bacteria.
Thanks to this depuration process, it's safe to eat raw oysters.
It's taken a good 18 months to grow from microscopic organism to dining delicacy,
which has a refrigerated shelf life of about a week.