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What the “R”?

Updated: May 28

Eating Oysters in months without an “R” – what’s the deal?

the following article draws information from “the Big Oyster – History on the Half Shell” By Mark Kurlansky

Rejoice! Summer is here but consuming oysters May-August, months without an “R”, typically prompts some version of concern and a question: “I thought one should not eat oysters in months without an “R”?

This convention is steeped in history. Julius Caesar is credited for manipulating the calendar so that “R”-less months organized a season to align with Roman’s passion for oysters. “R”-less months were strung together during the spring & summer when oysters were not as desirable and in doing so, created a convention for oysters to be “out of season”. He is also believed to have set leap years to occur in February, offering one added day of oyster season for all to enjoy.

Like the produce we enjoy seasonally, the fact that breeding oysters lose their appetizing taste and appearance during this time instills an idea of an off-season. Also as a conservation measure, harvesting breeding oysters is discouraged during the warm spawning season to ensure future populations and harvests.

Fast forward to 1800-1900 American history where healthy and bountiful natural resources were set on a collision course with an expanding New World: notably the uncontested marketplace and commercial powerhouse of New York City.

The waters surrounding what is now Manhattan, similar to our Cheasapeake, were once so full of oysters that the natural resource was proclaimed infinite. Native Americans left plenty of evidence of their use of the bounty (see previous newsletter article on oyster shell middens) providing additional fuel for this misguided impression.

And while oyster “seasons” remained, NYC had a new challenge: managing its own growth. Public infrastructure was inadequate to handle the city’s urban waste. The City soon contaminated local waters and consequentially, the oysters that lived there.

The NYC Cholera outbreaks in the early 1850’s led to an “oyster panic” which prompted public officials to enforce old laws restricting oyster sales May-August in the interest of public health. By the late 1800s the prevailing medical view had also changed from blaming disease on poverty, immigration, and immortality to bacteria, sewage, and consuming contaminated shellfish.

Public health officials started to see the filter-feeder oyster as a way to measure water quality and by the turn of the century and in in the wake of a Typhoid outbreak (w/Typhoid Mary playing a key role) oysters demonstrated that NYC was producing too much sewage to dump into the sea without consequence.

Thus, what started out historically as a “season” influenced by preference in appetite and biological conservation, the seasonal idea evolved to incorporate public health themes based on water quality. This came by the new understanding that warmer months hasten bacterial growth, particularly in polluted waters, that can lead to shellfish contamination.

Hybrid oysters (aka triploids) are purchased as seed of various sizes and are grown out in gear to protect them from predators. As hybrids never spawn, they continue to grow during the warm breeding season allowing them to reach market size (+/- 3”) in half the time as native oysters.

Today, advances in breeding technology are able reproduce naturally occurring hybrid oysters that resist disease and that do not reproduce. This creates a viable year-round oyster market and renders the historical context of oyster “seasons” moot. This technology is credited with saving the oyster industry that prior to this advancement, pivoted on natural resources. As such, these hybrids alleviate harvest pressure on native oysters which are now beginning to thrive again.

During the warmer months however, all concerned remain diligent. For example, the temperature of oysters from harvest to consumption is monitored and controlled at lower temperatures between May and September. Harvest vessels are also inspected for meeting warm weather requirements to promote food safety.

The Virginia Department of Health Division of Shellfish Sanitation (VDH DSS) and the Virginia Marine Resources Commission (VMRC) closely monitor water quality, alert the industry of closures due to excessive stormwater runoff and enforce harvest regulations and laws to ensure public health.


To learn more about triploid oysters and the potential effects of increasing sea temperatures on the industry, refer to the article "So Long Triploids, Hello Creamy Oysters" by Devon Fredericksen in Hakai Magazine.

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