Floating oyster bags at Forth North Oyster Farms

Oyster Grow-out: How to Get the Prettiest Oyster of Them All

What goes into that perfectly cupped oyster nestled on your plate?

As it turns out, oysters certainly have their own natural beauty, but generally a uniform, strong-shelled, aesthetically pleasing oyster has been molded that way by a farmer’s hand. Whether or not an oyster achieves a particular look depends largely upon the farmer’s grow-out method.

You may recall that oysters enter the grow-out phase after they leave the nursery. This usually happens when the oyster is about 20 mm in length. The oyster leaves the protected confines of the nursery, and must now fend for itself in open water. In about 1.5 years, the oyster will grow to market size, or it may take even longer for slow-growing species.

There are two main types of oyster grow-out: bottom and off-bottom. Essentially, bottom grow-out means the oyster is touching the seafloor. Beach culture is one of the most popular methods of bottom culture. You simply take the oyster seed and spread it along the beach, where the oysters are periodically submerged and exposed as the tides move in and out. This means the oysters will develop hard shells and strong adductor muscles to keep their shells clamped shut during dry periods. This technique is best for protected areas with firm mud bottoms, where currents and waves are not too strong. It’s low maintenance, involves little equipment, and doesn’t require as much investment.

Off-bottom grow-out means the oyster is above the seafloor. Typically, this means the oyster is placed in a mesh bag or cage, so that there’s ample water circulation into the bag. Rack and bag culture refers to a system of polyethylene bags that are tied to racks raised several inches above the seafloor. This protects the oysters to an extent from predators and prevents them from being buried in mud. Every few weeks, the bags are turned to reposition the oysters and make sure they have equal access to food.

Floating culture involves suspending bags along ropes with buoys, so that the oysters are floating well above the seafloor. Being near the water’s surface means the oysters will capture more food, the water will be a bit warmer to encourage growth, and it’s easier for the farmer to monitor and check on the oysters.

Tumbling is a technique used by farmers to grow stronger, more uniformly shaped oysters. Similar to the way a gardener prunes a tree, you can tumble an oyster to chip its shell and encourage it to “cup up,” or grow a deeper cup with a larger meat. It’s like asking the oyster to do high-impact exercise, strengthening the oyster’s shell to make it less brittle and easier to shuck, and shaping it into a more rounded figure. Tumbling can be done by putting the oyster into a mechanical tumbler, a cylindrical roller that tumbles the oysters. Or, a more natural way to tumble oysters is to put them in floating bags which flip in the water. As the tide goes in, the bag flips one direction, and as the tide goes out, the bag flips the other way. This method of tumbling is used with the Shigoku oyster, which results in a smooth, deep-cupped oyster with a large meat.

In the end, there is no right or wrong way to grow an oyster, it just depends on the location and conditions of the harvest area. Some oyster growers move their oysters from area to area depending on size, and may move oysters closer to the ocean right before harvesting to give them a saltier finish.