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Writer's pictureValeria Hirvonen

Oyster season and the “R”rule

Updated: May 25, 2023

To be perfectly honest, I didn’t plan for this blog to be about dispelling oyster-related

misconceptions. Oyster lovers already seem to be well-versed in claires and

creuses. If people like to think that oysters squeak, have a jelly-like consistency,

become inedible during summer because they accumulate toxins and radiation, that

farmed oysters are artificial and synthetic, and that oysters can only be eaten where

they’re grown, then they’re free to do so; more oysters left for us.


But friends are telling me it’s got to be done. Fine. I looked at the calendar and

decided that now is the best time to talk about the “R” rule. 


Traditionally, the oyster season in our Northern hemisphere is from September to

April. Remember this line in Remarque’s Heaven Has No Favourites: “She reached

her hotel. Her present room was again on the first floor, so that she would have only

the one flight of stairs to climb. The shellfish seller was standing at the door of the

restaurant. “Wonderful shrimp today,” he said. “Oysters are almost past. They won’t

be good again until September.”




“Oysters are not in season, but they have been replaced by peaches.”

Any person wishing to try some bivalves in the summer months is bound to be

reminded about the “R” rule. It states that oysters must not be eaten in May, June,

July and August—aka, the months without the letter “R” in their name.


Now listen here, we’re living in the 21st century, but some people still fall back on the

rule that was a thing already back in Ancient Rome. Cicero pondered upon the

dangers of eating oysters in his De Ostreis in first century BC, and about instilling the

“R” taboo.


Well, since the rule has such deep historic roots, I shall explain the meanings of the

old taboos and the truth of what is happening to oysters in the r-less months with the

help of Neptune, the Ancient Roman God of the seas.



His symbol of power over the seas, the trident, has three points. There are also three

reasons for restricting oyster consumption in the summer months, remember those.


1. The nature was so clever in designing the oyster that the mollusc can easily

survive for several days of transport or storage just with the water within the shell it

managed to retain at the time of harvest. The most important thing is the

temperature. The optimal temperature for the oyster is from +1 to +4 degrees.

Naturally, in the past, it was nearly impossible to transport a load of oysters while

keeping that temperature. The oysters went bad during transport and became an

actually dangerous foodstuff.


2. In the Northern Hemisphere, many molluscs spawn during summer. The warm

water serves as a signal for the mollusc to start this important process. During that

period, oysters produce eggs, turn a milky colour and change in taste. Oyster sperm

may make the mollusc bitter, and the flesh becomes softer. In addition, warm water

causes algae blooms, changing the chemical content of the water inhabited by the

oysters. That, too, changes its taste, and not for the better.


3. Uncontrolled oyster harvesting caused a rapid decline in oyster populations on the

coast of France, as well as East Coast of the US in the 18th century. In 1762, the city

council of New Haven, Connecticut, aiming to prevent a complete and irreversible

destruction of oyster colonies, banned oyster harvesting during the time of their

spawning, from 1 May to 1 September, and instilled strict fines for breaking it. France

introduced its own temporary bans on oyster sales from May to September in order

to preserve the oyster population with the Royal fishery edict of 1771.


Got it memorised? Now take a look at the oyster fork. It has three points, too. Each

of these represents a reason to forget about those old taboos and happily eat

oysters in a restaurant far from the sea any time of year.



1. Technology has progressed enough to guarantee a swift, careful transport of

oysters and their storage at the necessary temperature.


2. The oysters served at restaurants are grown on farms that strictly monitor all

processes in the mollusc’s life. The water temperature and chemical contents are

under the strictest control. Oyster sperm isn’t poisonous, and you can’t get poisoned

from eating a fresh “milky” oyster. I even know some people who actually like the

taste of these summer oysters. In addition, a technology of producing all-season

oysters that never turn milky was invented in 1980s. These oysters are sterile, and

their taste remains good in any time of the year. And as soon as normal oysters

upon finding themselves in warm waters, begin producing eggs, the farmers pause

the harvest of these oysters. Only the “4 seasons” oysters are sent to restaurants

and shops.


3. Seasonality of molluscs in Southern and Northern Hemisphere is different. Most

Australian and New Zealand oysters reproduce from November to March, and the

peak season for them is actually the months without “r” in them. Unfortunately, for

reasons unconnected to oysters, restaurateurs and suppliers, Russian gourmets are


unable to enjoy Australian oysters since 2014. However, New Zealand oysters will

doubtlessly delight our mollusc-lovers with their excellent taste this summer.


The only rule you really must remember is that you shouldn’t even try an oyster that looks

and smells bad. A fresh oyster should smell of the sea, have a glossy and plump

appearance, contain colourless transparent liquid that experts call oyster liquor. And eat

oysters in reliable places, that have professionals guaranteeing their quality.


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