To clean oysters, first throw out any with cracked shells and any that are open and will not close when tapped. Then scrub each shell with a stiff brush under cold running water, and shuck or cook them. Do not soak them. Storing oysters in water kills them, and none of the official guides call for purging oysters at home.
Cleaning is about the outside of the shell. Whatever is on it can be carried into the meat when the knife goes in. Cleaning does not make an oyster safe to eat raw; that depends on where it was harvested and how it was kept.
The steps
| Step | What to do | Why |
|---|---|---|
| 1. Sort | Throw out oysters with cracked or broken shells, and any that are open and do not close when tapped | A gaping oyster is dead and may have spoiled |
| 2. Scrub | Hold each oyster under cold running water and scrub the shell with a stiff brush | Keeps mud, grit, and bacteria on the shell from being carried into the meat when you open it |
| 3. Open or cook | Shuck, or cook in the shell | See the guides linked below |
| 4. Check the meat | Pick out any bits of shell; strain the liquor if you are saving it | Shell fragments are the main thing left to remove |
| 5. Clean up | Wash your hands, the knife, the board, and the counter | Raw shellfish can spread bacteria to other food |
The scrubbing instruction is the same everywhere it appears. North Carolina Sea Grant: before shucking any oysters, scrub them thoroughly with a stiff brush under cold, running water.[1] Washington's Department of Fish and Wildlife: scrub the shells under cold running water with a brush, and discard any open shells.[2] University of Florida IFAS adds the reason, which is to reduce the risk of transferring bacteria or other contaminants from the shell to the meat when the oyster is opened.[3]
For the next step, see how to shuck oysters. This article stops at the point where the knife comes out.
What to throw out
- Cracked or broken shells. The FDA's advice is to throw away clams, oysters, and mussels whose shells are cracked or broken.[4]
- Open shells that do not close. Live oysters close when the shell is tapped. If one stays open, it is dead. Washington's health department says to throw those out.[4][5]
- Anything that smells wrong. Fresh oysters have tightly closed shells and a briny, sea-like smell. A fishy smell or any off odor can indicate spoilage.[3]
- After cooking in the shell, any that did not open. The FDA says shells open during cooking and that ones that do not open should be thrown out.[4]
Sort before you scrub, so you are not cleaning oysters you will not eat.
Why you should not soak oysters
Rinsing under running water is fine. Leaving oysters to sit in water is not.
Washington's health department is blunt about it: never store shellfish in water, because they will die and may spoil.[5] Maine Sea Grant says to avoid storing oysters directly on ice or submerged in fresh water, as this can kill them.[6] Both recommend the same alternative: the refrigerator, with a damp towel over the oysters.
So clean oysters when you are ready to use them, and keep the water moving. If you scrub a batch ahead of time, drain them and put them back in the refrigerator under a damp towel rather than leaving them in the sink. Our guide to how to store oysters has the full method.
Purging and depuration
Some recipes say to soak oysters in salted water, sometimes with cornmeal, so they "spit out" their sand. None of the Sea Grant, extension, or health agency guides cited here includes that step for oysters. Their instructions are to scrub the outside, then deal with any shell or sand after opening.[1][2][3][7]
There is a real process with a similar name, and it is not something a kitchen bowl reproduces. Depuration is a commercial treatment in which shellfish are held in tanks of clean seawater under conditions that keep them filtering, so they expel their gut contents.[8] Maine's Department of Marine Resources describes it as done in land-based tank systems in sanitary seawater, only by a certified shellfish dealer, with monthly inspection of the system and testing of each lot.[9]
Even done properly, depuration has limits. A Food and Agriculture Organization technical paper says it is effective at removing many fecal bacteria, less effective against viruses such as norovirus and hepatitis A, and not consistently effective, or ineffective, against naturally occurring marine Vibrio bacteria and marine biotoxins.[8] A soak at home will not do better.
Cleaning does not make a raw oyster safe
A scrubbed shell is a cleaner shell, nothing more. University of Florida IFAS points out that harmful microbes may not change how an oyster looks, smells, or tastes.[3] What matters is the source and the cold chain: the FDA says to look for the tag on sacks or containers of live shellfish and the label on containers of shucked shellfish, which show a certified processor.[4]
Cooking is what kills Vibrio. Washington's health department gives 145°F for 15 seconds as the internal temperature to reach, and notes that barbecuing oysters only until they open will not do it.[5] See Vibrio and raw oyster safety and raw vs cooked oysters.
Cleaning oysters for grilling or steaming
Oysters that will be cooked in the shell get the same sort and scrub. Washington's Department of Fish and Wildlife describes putting scrubbed and rinsed oysters in a kettle with very little water and steaming them until the shells open.[2] Because the shell goes on the grill or in the pot, and the liquor inside is part of what you eat, a clean shell matters here too.
Our cooked oyster guide has methods and times.
After shucking
Shell and grit. The National Center for Home Food Preservation says to shuck into a strainer, save the liquor, and remove any pieces of shell or sand; the oysters can be rinsed if that is needed to remove sand.[7] Washington's Department of Fish and Wildlife says to keep as much of the liquor as possible, and, if the oysters are not being served on the half shell, to drain them and strain the juice to remove particles of shell and sand.[2]
For oysters on the half shell, that means lifting out shell fragments with the tip of the knife rather than rinsing, so the liquor stays in the shell.
Hands and surfaces. The FDA's seafood guidance is to wash your hands for at least 20 seconds with soap and warm water after handling raw food, and to wash cutting boards, dishes, utensils, and countertops with soap and hot water before they touch cooked or ready-to-eat food.[4]
Frequently Asked Questions
Do you need to wash oysters before shucking?
Yes. Sea Grant, extension, and state wildlife agency guides all say to scrub the shells with a brush under cold running water before opening them. It keeps mud, grit, and bacteria on the shell from getting into the meat.
Should you soak oysters before cooking?
No. Rinse and scrub them under running water instead. Washington's health department says never to store shellfish in water because they will die and may spoil, and Maine Sea Grant says submerging oysters in fresh water can kill them.
Do oysters need to be purged?
The official guides do not call for it. Their instructions are to scrub the shell and remove any grit after shucking. Depuration, the commercial process that clears shellfish in tanks of clean seawater, is done by certified dealers under inspection and is not something a soak at home reproduces.
Can you rinse shucked oysters?
Only if you need to. The National Center for Home Food Preservation says shucked oysters can be rinsed to remove sand. Rinsing also washes away the liquor, so for oysters on the half shell it is better to pick out shell fragments by hand.
How do you clean oysters for grilling?
The same way as for shucking. Throw out any that are cracked or will not close, then scrub the shells under cold running water with a stiff brush before they go on the heat.
Does washing oysters make them safe to eat raw?
No. Scrubbing cleans the outside of the shell. Harmful microbes inside an oyster may not change its look, smell, or taste, and it is thorough cooking that destroys Vibrio bacteria.
Sources