There is an old saying that you should only eat oysters in months with the letter R in them – that is, September through April. This advice dates back centuries and originates from concerns over the safety of eating oysters during the warm summer months.
What’s the reason behind the “R” rule for oysters?
The basis for this recommendation has to do with the spawning season for oysters. Oysters spawn during the warm summer months, from May to August. Spawning refers to their reproductive cycle, when they release eggs and sperm into the water.
Here’s why this makes summer oysters less appetizing:
- Spawning depletes the oyster’s glycogen reserves and nutrient stores. This can make their meat slimy and less plump.
- With their energy focused on spawning, their filter-feeding action is reduced. This means they pump less water through their systems and may accumulate bacteria and contaminants.
- Higher bacteria levels in warm waters also increase the risk of spoilage.
In the past, eating oysters during summer months posed significant food safety risks. While modern refrigeration and handling practices reduce that risk today, the old adage remains popular wisdom.
What happens to oysters when they spawn?
Oysters are broadcast spawners, releasing eggs and sperm into surrounding waters where fertilization occurs. This results in a significant reduction in the size, yield and quality of the meat.
A single female oyster can produce as many as 100 million eggs in a season! This tremendous reproductive effort means their bodies must conserve energy and divert resources away from the muscles and flesh that we eat.
Other effects of spawning include:
- Change in appearance – from plump to shriveled and thin
- Meat takes on a mushy, milky consistency
- Altered flavor – metallic taste
- Lower glycogen content, resulting in less sweetness
- Less juice released when shucked
These changes make summer oysters less appetizing. While not dangerous, the decline in quality led to the old recommendation to avoid them during spawning season.
When exactly do oysters spawn?
Oysters typically spawn when water temperatures reach 68-77°F (20-25°C). This happens during summer months in most oyster harvesting regions.
The exact spawning period can vary depending on:
- Geographic location – latitude and water temperature
- Species of oyster
- Environmental factors like tides, sunshine, turbulence
As a general rule, oysters spawn from late spring through early fall when waters are warmer:
| Months | Northern Hemisphere | Southern Hemisphere |
|---|---|---|
| January | No spawning | Peak spawning |
| February | No spawning | Peak spawning |
| March | No spawning | End of spawning |
| April | Start of spawning | No spawning |
| May | Peak spawning | No spawning |
| June | Peak spawning | Start of spawning |
| July | Peak spawning | Peak spawning |
| August | End of spawning | Peak spawning |
| September | No spawning | End of spawning |
| October | No spawning | No spawning |
| November | No spawning | No spawning |
| December | No spawning | No spawning |
As you can see, months without an “R” correspond with peak spawning activity in most locations.
What health risks exist with summer oysters?
Traditionally, there were two main health concerns with eating summer oysters:
- Higher bacteria levels – Warm waters enable bacteria like Vibrio vulnificus to multiply faster. This bacteria can cause serious illness or death. Proper refrigeration helps control bacteria.
- Spoilage – Higher water temperatures also accelerate spoilage. Spoiled oysters can cause stomach upsets.
Modern transportation and refrigeration have made summer oysters safer. However, some key tips for buying summer oysters include:
- Look for oysters farmed in approved waters and harvested under strict regulations.
- Buy only fresh live oysters on ice, with tightly closed shells.
- Avoid oysters with broken shells or gaping shells that don’t close.
- Keep oysters cold at all times, below 40°F (4°C) for storage.
- Discard any oysters that die or don’t open when cooked.
When buying from a reputable source and following safe handling tips, modern summer oysters pose minimal health risks. But their declined quality and flavor during spawning season still makes the old “R” months advice valid.
What do oysters taste like in months with vs. without R?
The most notable differences between oysters in “R” vs. non-“R” months involve flavor, texture and juiciness:
Oysters in months with R:
- Plump, firm meat
- Natural sweet and briny flavor
- Higher glycogen content, more juice released
- More full-bodied
Oysters in months without R:
- Smaller, thinner meat
- Mushier texture
- Muted flavor, sometimes metallic
- Less juice, drier
- Less sweet due to lower glycogen
These differences are subtle. Oysters are still edible during non-R months, but many oyster aficionados say they are less satisfying. You’ll get the best taste and texture in fall through early spring.
Are there any exceptions to the “R” rule?
There are a couple exceptions where you can enjoy good oysters during non-R months:
- Aquaculture oysters – Farmed oysters can be conditioned and manipulated to spawn less. Look for brands that use spawning control methods.
- Southern hemisphere oysters – The seasons are reversed below the equator. Australian and Chilean oysters spawn December-February, so they are in prime condition during our summer.
- Colder waters – Some northern regions, like Canada and Scotland, have prolonged cold waters so oysters spawn later. Peak months may be July-September.
With aquaculture advances and imported southern hemisphere oysters, you can now find good quality oysters year-round. But for peak flavor and texture from local oysters, it’s still best to follow the traditional R months rule.
Conclusion
The old recommendation to only eat oysters in months with the letter R has its roots in legitimate concerns over spoilage, bacteria and declined quality during summer spawning months. But modern handling practices mean summer oysters are safe to eat, though they may still lack the plump texture and sweet flavors of fall-spring oysters.
Following basic food safety practices like buying live oysters from reputable growers, keeping them chilled, and discarding dead ones enables enjoyment of oysters all year long. But for oyster aficionados seeking peak flavor and experience, the tastiest oyster months remain those with an R.
