When Should You Not Eat An Oyster?

Many oyster lovers have suppressed their craving for this delicacy at some point based on the time of year. All because of a recommendation believed to have been uttered by William Butler (1535-1618). It also appeared in an English cookbook, “Dyets Dry Dinner,” published in 1599. But is there any merit in following this age-old wisdom and avoiding raw oysters for certain parts of the year?

There is a belief that you should not eat raw oysters in months without an “R,” which is May, June, July, and August (i.e., summertime). Oysters are indeed at their best during winter, but oysters farmed in healthy waters and handled properly can be eaten any time of the year. 

The saying that you should avoid raw oysters in summer dates back over 400 years, before the days of refrigeration and when people harvested oysters solely from the wild (sea). Although there is a rationale behind this rule of thumb, the reality is that it is now entirely possible to eat oysters during the summer. Quick research into their farming and harvesting methods will confirm whether they are safe to eat.

When Can You Eat Oysters?

Since the 16th century, oyster farmers have developed more advanced farming and harvesting techniques and processes to offer a safe, more sustainable option for consumers year-round. People still harvest wild oysters from the ocean, but they grow slower than their farmed counterparts, and you should consume them with caution.

Farmed Oysters

The more modern practice of farming oysters in controlled environments means that people no longer rely solely on wild oysters. Some farmed oysters flourish in conditions that are not usually conducive for wild oysters, and cold-water farms can produce edible oysters year-round. You can, therefore, safely buy farmed oysters any time of the year, including the summer months.

Some farmers also breed triploid oysters in warm water farms. Triploids are sterile oysters, like seedless fruits and vegetables, which means they never spawn. This breed of oyster, therefore, does not suffer from the lower quality and sub-par taste that often comes with summertime spawning.

Wild Oysters

The peak season for wild oysters is during the winter months or in months with the letter “R” (October to March). During the colder months, the taste and quality of wild mussels are at their peak, just before they begin spawning. Spawning happens during the spring and summer.

The summer months cause an increase in water temperature. This warmer water induces oysters to spawn, releasing the contents of their largest organ, the gonad (part of the oyster’s reproductive system that produces and releases eggs or sperm). The gonad makes up 30-40% of an oyster’s mass, so when it loses this weight, it leaves the oyster small and watery with an unpleasant taste.

Polluted water is also a problem, with certain types of bacteria being more prevalent in summer. You can become fatally ill if you consume an oyster harvested from the wild that contains these bacteria. It is, therefore, safer to consume raw, wild oysters during the winter months.

Winter also offers less chance of raw oysters spoiling, which can happen in summer heat if they are not correctly refrigerated (or iced). Even though the National Shellfish Sanitation Program (NSSP) enforces strict icing laws in summer to ensure they are safe for human consumption, many oyster farm owners still refrain from transporting oysters in warmer months to avoid potential spoiling.

Another reason wild oysters harvested in winter are considered safer and better is that Red Tide often occurs in the summertime. Red Tide is when algae grow and reproduce fast enough that it causes a toxic buildup of organisms in the sea. You can get shellfish poisoning if you consume oysters that have absorbed the toxins released in the water during Red Tide.

Considering all of this, the old saying to avoid oysters in the summer months might have some merit. But times and oyster farming techniques have changed since the 16th century.

The U.S. has made significant attempts to ensure the sustainable harvesting of wild oysters. Oyster fishermen and various agencies in America now monitor each step in the harvesting process, including checking the water quality and tracking safe transportation. By U.S. law, fresh oysters must also contain labels outlining the specific time and place where oysters were harvested.

Even if you are still hard-set on the belief that oysters have a particular peak period, it is always oyster season somewhere in the world. Thanks to the global import and export industries, the U.S. can thus source oysters from other countries, making it safer for you to consume them anytime. If unsure, you should enquire about the origin of the oysters you purchase at a restaurant or from your fishmonger.   

Signs That An Oyster Is Not Good To Eat

Oysters are typically enjoyed raw, so it is vital to keep them fresh and alive until they are ready to be consumed. They should, preferably, not be more than four days old. If you are buying oysters, it is perfectly acceptable to ask your local fishmonger when they were harvested. Oysters are also best stored (or displayed on a fish counter) on ice to preserve freshness.

No matter the time of year, when buying fresh oysters, it is also essential to use your senses.

The first thing to look at is the shell of an oyster. The shells of raw oysters should be tightly closed with no gaps. If it is open, test it by gently tapping the outside with your finger, a knife, or the back of a spoon. If the shell does not close, you should discard it. The opposite is true when cooking oysters: fresh oysters will open up. If they remain closed after cooking, it would be best to discard them.

Avoid oysters with chipped, broken, or damaged shells since this can signify a bad oyster. The shell of a fresh oyster should also be glossy white but can sometimes have a few pink or grey streaks. The shell should also feel cold to the touch. Do not consume the oyster if the shell feels warm and is damaged.

In terms of their aroma, fresh oysters will smell like the sea: Mild, salty, and fresh. Do not buy oysters with a strong, unpleasant, or overly fishy odor.

Look carefully at the meat of the oyster when opened. Fresh, healthy oysters should be plump with glossy tan color. Oysters that are off will look wrinkly and dry and will have a cloudy appearance. Contaminated oysters tend to be grey, brown, black, or pink.

What Happens When You Eat Bad Oysters?

Some raw oysters, especially those commonly harvested from the Gulf of Mexico, can contain a bacteria called Vibrio vulnificus. This bacterium is found in higher concentrations during the summer when the water temperatures rise. The problem is that you cannot identify a contaminated oyster by merely smelling or looking at them. Even fresh oysters can contain bacteria.

It will take 12-48 hours for symptoms of the Vibrio vulnificus bacteria to appear, lasting between 1-7 days. Symptoms can include:

People who show symptoms of the Vibrio vulnificus bacteria should get plenty of rest and drink a lot of water to curb dehydration due to diarrhea. If the symptoms continue for several days or if it worsens to include ear or wound infections, you should see a doctor who will prescribe a dosage of the necessary antibiotics.

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Who Should Not Eat Oysters?

Certain people are more at risk of falling seriously ill or dying within days from eating raw oysters contaminated with the Vibrio vulnificus bacteria.

People who drink 2-3 alcoholic beverages daily might suffer from impaired liver or liver disease without showing symptoms. This liver damage can put them at risk for contracting an infection from Vibrio vulnificus. Those with diabetes, cancer, stomach disease, an iron overload disease, or any illness or medical treatment that weakens the body’s immune system are also at a higher risk of infection.

How To Safely Eat Oysters

Even if you get your oysters from reputable sources with the promise that they harvested the oysters from clean waters, it does not mean that you are fully protected. The Vibrio vulnificus bacteria is not a result of polluted water. Hence, its presence in cleaner water and the fact that it can go undetected means that you could still be at risk of falling ill.

Some people believe that putting lime juice or hot sauce on raw oysters before eating them will kill all the bacteria. The truth is that this method does not kill bacteria at all. It would be best if you thus refrained from using this technique as a safety measure.

The only way to ensure that your oyster is bacteria-free is by applying heat to raw oysters. Therefore, if you want to steer on the side of caution and avoid any infection from eating raw oysters, order them fully cooked when you are at a restaurant. If you purchase oysters to cook yourself at home, make sure their shells are tightly closed.

How To Cook Oysters For Safe Consumption

Once you have shucked the oysters, boil or steam them in simmering water for at least four minutes or until the edges curl. If you are unsure whether they are adequately cooked, you can allow the oysters to continue boiling or steaming for another couple of minutes. You can allow a total cooking time of around nine minutes.

Baking your oysters is also an option. Do this at 450°F for about 10 minutes. You can also pan-fry oysters for 3-4 minutes or use your oven and broil them for the same duration.

When you cook oysters, always use a large pot or pan, or cook them in batches to ensure that the ones in the middle cook through completely. Remember to discard any oysters that do not open during cooking.

How Long Can Fresh Oysters Last Before They Go Bad?

Preparing and cooking fresh oysters within two days after buying them is vital for the best result. Shucked oysters (i.e., opened oysters) will only last five days in the fridge. They will, however, keep it in a refrigerator overnight for up to seven days.

If you want to store live oystersin the fridge, lay them on a tray or baking sheet, cupped side up, and cover them with a damp tea towel, cloth, or paper towel. Do not store them in freshwater since they can get contaminated after a few days. Also, avoid putting the oysters in an airtight container. The oysters need to be able to breathe while in storage.

If you want to store shucked oysters in the fridge, put them on ice or in an airtight container for 4-5 days. Some people believe their shelf-life can extend to two weeks, but this is not advisable. The sooner you eat raw oysters, the better! Always ensure your fridge’s temperature is between 34-35°F (1°C). Shucked oysters need a frigid environment to maintain their freshness.

How To Know When Other Types Of Shellfish Are Safe To Eat

Some tests to determine the freshness of oysters can also apply to other shellfish. For example, open clams and mussels can also be tested by gently tapping their shells. If the shells close, then it is safe to consume. You should throw them out if they do not respond and remain open.

Like oysters, living mussels and scallops will also have a fresh sea odor and intact shells, which means they are safe to eat. If scallops smell overly fishy or have damaged surfaces, you should discard them. 


The longstanding adage that you can only eat oysters in months that contain an “R” might no longer apply with modern farming techniques. Still, consuming oysters in colder months will always be safer and yield oysters that are at their very best.

Regardless of the time of year, you must first buy fresh oysters from reliable, reputable sources that take the necessary precautions and monitor the entire process – from harvesting the oysters to transporting them safely to the consumer. The next thing to do is always use your senses to determine whether the oysters are safe to eat. Once you know it’s fresh, it is a delicacy very few can resist!