How do you know when oysters go bad?

Whether steamed, stewed, sautéed, baked or broiled, oysters provide a light and fresh flavor and a powerful pack of nutrients. They are low in calories and fat and high in calcium, copper, manganese, phosphorous, potassium, protein, vitamin A, vitamin B12 and zinc. While eating raw or undercooked oysters can be dangerous, oysters that have been cooked to an internal temperature of 140 degrees F are generally safe. But to ensure your safety and prevent food-borne illness, make sure you can identify good oysters from bad oysters.

1. Inspect the shell for broken or damaged areas. Discard any oysters with shell damage. The shell should also be glossy white in color, although a few pink or grey streaks is acceptable.

2. Tap the shell with your finger. The shell should close tightly with no gaps. If the shell does not close, discard the oyster as the animal is likely dead and may harbor bacteria.

3. Inspect the oyster meat. Healthy oysters are plump with a glossy tan color. Bad oysters are dry and withered with a cloudy appearance. Contaminated oysters tend to be grey, brown, black or pink in color.

4. Smell the oyster meat. Healthy oysters smell fresh and mild. Bad oysters have a strong, offensive or pungent fishy smell.

And how to spot warning signs that should convince you to send them back.

Unlike when you broil, bake, or fry them at home, when you order a dozen oysters on the half shell at an oceanfront bar or your favorite seafood restaurant, you don't have a chance to choose and inspect the mollusks yourself. How can you tell if the oysters you're served are good quality-and, more importantly, if they're safe to eat? If you haven't eaten many raw oysters before, you should expect a certain aroma, texture, and for them to be served in what looks like "a pool of their own juices," says Frank Proto, director of culinary operations at the Institute of Culinary Education. "You have to be a little fearless. Be prepared for an admittedly 'slippery and slimy' profile."

His first piece of advice is to order oysters a la carté the first time you eat them in a restaurant instead of ordering a full dozen or even a half dozen. This is also a good way to scope out the oysters being served that day. The freshest oysters are likely to be local varieties, Proto says. "If you're on the coast, you can pretty much bet that they're going to be decent [and safe]. But, as people say, don't go to a steakhouse and order the fish-ask yourself where you are and consider the locale." Proto adds that oyster farmers have invested in shipping processes that start with an ice bath to preserve quality. In fact, oyster farming allows for many streamlined processes that make farmed oysters much safer than wild oysters that once were harvested in less than optimal conditions. Eating oysters from the West Coast, the Pacific Northwest, New England, or Canada when not in these areas doesn't mean the oysters won't be fresh. "There was a time where you couldn't vet when oysters had been shipped, which is why people used to say avoid eating oysters in the months without 'r' in their spelling-that's where that old adage came from," Proto explains. "Today, [farmers] are very on top of what oysters should be, and each bag sold to restaurateurs comes with tags and info about where the oysters came from, and when exactly they came out of the water."

Beyond choosing local varieties, Proto says there are a few ways you can instantly grade an oyster when it's served to you-no matter how far it had to travel to reach your plate.

What Good Oysters Look Like

Before eating an oyster, you should pick it up and take a sniff: The smell should be "like the ocean breeze," Proto says, and they should feel ice cold to the touch. If they feel warm or if they give off an odor that makes you recoil, that's a major red flag. Inspect the bottom of the shell for broken or damaged areas, as this outward sign of trauma could mean the oyster was damaged in transit. Additionally, the best oysters are never wrinkled or dried out. Other positive visible cues that illustrate they were just harvested include firmness and plumpness.

How Oysters Should Be Served

Raw oysters should always be plated on a bed of shaved ice-and they should be served in their original shells. "Oysters should be whole. You'll know if you're at a place where they are educated about serving fresh oysters because they won't 'scramble' them," Proto says. "If they get the knife in there and [the oyster] is all beat up, it wasn't opened with care. It doesn't affect quality and taste so much, as long as there's no shell in the oyster, but it's a red flag for me. Oysters should be served without any toppings or accompaniments-at least, initially. Our expert believes you should taste an oyster on its own first. A sauce can disguise the true flavor and quality of the oyster. "At reputable restaurants and established oyster bars, [chefs] won't spend too much time putting stuff onto your oysters," Proto says. "When I serve oysters, I'll have dressings on the side-some chefs will finish theirs with a sorbet of some sort, or a cucumber jus… But it won't always reflect on the quality. Now, if you're at an oyster bar and they're pouring dollops of dressing over the oysters, could that reflect poor quality? Sure."

How Good Oysters Taste

When you slide the first oyster in your mouth, you'll know immediately if it's fresh-that's true even for those who have never enjoyed raw oysters before. They should taste briny, of seawater, but not overwhelmingly so. They'll feel velvety smooth in your mouth, and while good oysters tend to be soft in nature they aren't mushy and there's a bit of a bite to them. "You'll taste all the complexity of the ocean," Proto says.

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