Oyster varieties are often listed with parts per thousand ratings, which indicate their salinity level. Below 12 ppt is considered low salinity, 12 to 20 ppt is medium and over 20 is high. Oysters can survive in water that contains 5 to 35 ppt (0.5 percent to 3.5 percent salt by volume).
Low-salinity oysters tend to be milder and creamier and have fewer mineral tones than high-salinity oysters. The Chesapeake Bay area is in a mid-zone geographically and climate-wise; water temperatures fluctuate between hot and cold more than in, say, Canada and Florida, and the influx of fresh water from the rivers of the watershed is frequently unpredictable.
Shifts in temperature, current and environment affect an oyster’s salinity and overall flavor. That is what defines an oyster’s merquoi, the sea version of terroir, and explains why oysters grown not very far from each other can have markedly different characteristics.
Here’s how some Chesapeake Bay area oysters measure up, from low to high salinity:
Hayden’s Reef: 11 to 13 ppt
Parrot Island: 12 to 18 ppt
Rappahannock River: 13 to 17 ppt
Dragon’s Creek: 14 to 15 ppt
Stingray: 17 to 22 ppt
Snow Hill: 28 ppt
Olde Salt: 28 to 33 ppt