Oysters are typically eaten raw and seasoned with lemon juice, horseradish, hot sauce or other sauces. It is imperative that the oysters are fresh and alive until the point of serving to avoid shellfish poisoning. Eating a bad oyster can cause digestive, stomach and intestinal problems. There are several indicators for recognizing if an oyster is bad, so if you are planning on serving them, it is important to fully inspect them.
Select oysters that are no more than four days old. Ask the staff at your local fish market when the oysters were harvested to ensure freshness.
Check to make sure that oysters have been stored on ice at the fish market. This preserves their freshness.
Examine each oyster's shell to ensure it is sealed tightly. Oysters will open up as they die so confirm that all of the oysters are closed and alive. Discard any open oysters.
Discard any oysters that have broken shells as this exposure can cause the meat to spoil.
Sniff the oyster shell to check for an offensive odor. If you smell rot, the oyster is bad and should be discarded.
Open the oyster and examine the fluid and meat. The oyster should be moist and juicy. If the oyster has gone bad, the interior will be dry and wrinkled.