More than 76 million people get food poisoning every year, and eating spoiled shellfish is one of the more common causes. Symptoms of food poisoning can include severe vomiting and diarrhoea. Shrimp is a type of shellfish used in many recipes, and it is vital that you spot the signs of spoiled shrimp in order to keep yourself and those you cook for healthy.
Smell the shrimp before you purchase it. Since you cannot smell shrimp through plastic packaging, it is safer to buy fresh shrimp over the counter in a supermarket or from a fishmonger. Fresh shrimp should smell slightly salty, like seawater. If the shrimp smells like ammonia, or if it generally smells slightly "off," do not purchase it. The ammonia or "off" smell is caused by the growth of bacteria in the shrimp, which is likely to cause food poisoning if eaten.
Fresh shrimp have firm bodies that are still attached to the shell. They should also have clear and clean shells. If the bodies appear loose within the shell and if there are black spots on the shell, it is likely that the flesh has started to decompose inside. Also ensure that the shells are firm and glossy. If the shells are broken and slippery or slimy, the shrimp is likely to be spoiled and should not be purchased. Again, it is easier to check this by looking directly at fresh, loose shrimp rather than prepackaged shrimp.
Make sure that the shrimp are not discoloured on the heads and on the shells. If you are buying raw shrimp, they should be white and slightly transparent. If you are buying cooked shrimp, they should be pink. Any discolouration may indicate that the flesh is spoiled. Also, look to see if the shells appear yellow or gritty. This may indicate that a chemical such as sodium bisulphate has been used to bleach the shells. The chemical may have been used to disguise the fact that the shrimp are old.
Buying shrimp with their heads still on can help you to identify whether or not the they are spoiled. The eyes should be prominent and shiny. If they look shrunken or dried out or are missing altogether, you should be wary of how fresh the shrimp are. To be on the safe side, purchase your shrimp elsewhere.