For many years, a culinary myth dictated that oysters should only be eaten in months containing the letter ‘R’—from September through April.

This left the summer months, May through August, as an oyster-less period. However, this ‘R-rule’ has become outdated and it’s time to unshell the truth about summer oysters.
The ‘R’ month rule originated from a time before refrigeration, when warmer months could cause oysters to spoil more rapidly, posing a risk to consumers. The onset of modern technology and advancements in food safety, however, have made this rule largely redundant. Thanks to controlled harvesting and strict regulations, it’s now perfectly safe to enjoy your favorite shellfish in summer months too.
This leap in food safety is primarily a result of two key advancements. The first is modern refrigeration and rapid cooling techniques, which effectively limit bacterial growth and reduce foodborne illnesses. And the second, remarkably, lies in the very biology of the oysters themselves.

Enter the world of triploid oysters.

Oysters, like most organisms, usually have two sets of chromosomes and are hence termed ‘diploid.’ However, in the 1990s, scientists developed a method to create ‘triploid’ oysters, which have three sets of chromosomes and are sterile. This sterility is the game-changer.
In warmer months, diploid oysters reproduce, causing them to become soft and less flavorful, which is another reason people avoided them in summer. Triploid oysters, however, do not reproduce and therefore remain firm and tasty all year round, including in those ‘R’-less months.

Triploid oysters are not genetically modified organisms, but are created through a process that involves manipulating the temperature and pressure of oyster larvae to create an extra set of chromosomes. Today, triploid oysters are widely cultivated and their popularity continues to grow globally.
In conclusion, there’s no longer a reason to miss out on your favorite bivalves in the summer. With stringent safety regulations, advanced refrigeration techniques, and the scientific achievement of triploid oysters, you can now safely savor your cherished shellfish throughout the year.

Bon appétit, oyster lovers!

Sources: Harvard Health, Word Health Organisation, Smithsonian Magazine