It is said that dead crabs cannot be eaten, so why do supermarkets still sell frozen crabs?

Today is the Mid-Autumn Festival. What delicacies have you prepared to treat yourself and your family? For autumn, one delicacy is crab. Mr. Liang Qiushi said: "Crab is delicious, and everyone loves it, regardless of north or south, elegant or vulgar." The "Book of Jin: Bi Zhuo Biography" also records: "Holding a wine glass in the right hand and a crab claw in the left hand, floating in a wine boat is enough for a lifetime." This shows how much everyone loves crabs.

Source: A shopping website

I wonder if you have a doubt when buying crabs, that is, "crabs/seafood cannot be eaten after they die". Why is this? On the other hand, sometimes we still see some frozen, thawed, or even disassembled crabs in supermarkets. Why is this?

The Mid-Autumn Festival is coming soon. Are the crabs we bought in the market still edible? Don't worry, let's talk about it today.

1

Why can’t we eat dead crabs?

Whether or not to eat dead crabs depends not only on the species of crab, but also on the cause of death. Only then can we decide whether to eat them or not. What is going on?

In fact, in the Chinese context, when we talk about "crabs", on the one hand, we refer to all crabs, that is, various animals of the order Brachyura , and sometimes even "crabs" that are not crabs, such as the relatives of hermit crabs belonging to the order Heterocura , such as the king crab (Paralithodes camtschaticus and several other species of the family Paralithodes), coconut crab (Birgus latro), etc. On the other hand, in some areas in southern China, "crabs" often refer specifically to the Chinese mitten crab (Eriocheir sinensis), which is the "hairy crab" we are most familiar with. The problem of "crabs cannot be eaten after they are dead" is caused by them.

Hairy Crab

Source: Wikipedia

Chinese mitten crab (hereinafter referred to as "hairy crab") belongs to the family of Archegonidae. It is a crab that lives in freshwater environments such as rivers and lakes, but needs to return to the ocean to reproduce. Earlier, we mentioned that "the autumn wind blows, and the crab's feet itch", which means that when autumn comes , the reproductive glands of Chinese mitten crabs mature, and they return to the ocean in groups driven by instinct to reproduce . This is the best time to taste the delicious hairy crab.

We have all seen on TV the environments where hairy crabs are farmed, usually in freshwater environments such as ponds, lakes, and rice fields. Wild hairy crabs not only live in the water, but also come to the shore at night. I believe everyone has an impression of the scene of hairy crabs covered in mud crawling on the ridges of the fields. Here I want to mention their feeding habits. Although the digestive system of hairy crabs is very developed and they can digest all kinds of corrupt food, they prefer to eat fresh food in artificial breeding, such as small fish, snails, and formula feed.

Chinese mitten crab in rice field

Source: China Township Network

There are many bacteria in the environment where hairy crabs live, and the hairs on the crab's body, the grooves and gaps in the shell, and the gills of the crab are very suitable for bacteria to hide (not only hairy crabs, but also the body surfaces of other fresh aquatic products may carry various bacteria, including various pathogens). So once the crab dies, the bacteria on its body surface will quickly invade the crab's body. In addition, the crab's body tissue is rich in protein, which makes the whole crab quickly become a bacterial culture medium within a few hours. Various bacteria quickly decompose its body tissue and produce toxic histamine (even if the crab is cooked, this toxin is not easy to be destroyed. If the human body ingests more than a certain amount of histamine, it will cause poisoning. Common symptoms include nausea, vomiting, abdominal pain, diarrhea, and in severe cases, dehydration, convulsions, and even shock) and other toxic substances, so it is naturally not edible.

This situation of more bacteria on the body surface is not only found in hairy crabs, but also in many crabs living in freshwater and incomplete saltwater environments, such as mud crabs (Scylla sp. The meat crabs in the meat crab pot usually refer to mud crabs), "weed crabs" (mainly species of Sesarmidae, sometimes also refers to other small crabs on mudflats), stream crabs in streams (mainly Potamidae), etc. Therefore, it is recommended that you must eat these crabs fresh and thoroughly cooked when tasting them.

Blue Crab

Source: Internet

Knowing the reason why hairy crabs cannot be eaten after they die, combined with the fact that some areas call hairy crabs "crabs", in many contexts the concept has evolved into "all crabs cannot be eaten after they die", which is actually a bit of a misunderstanding.

2

Why can we eat dead crabs?

In fact, the statement that "sea crabs can be eaten after they are dead" is not absolute.

The sea crabs we eat (those available in markets and supermarkets as well as restaurants) almost never live in environments such as mudflats that contain a large number of bacteria. The few exceptions, such as the blue crabs and weevil crabs mentioned earlier, will not be elaborated here.

Caught swimming crab

Source: Internet

Sea crabs caught in deeper waters with nets or crab cages, such as the three-spotted swimming crab (Portunus trituberculatus), the sea swimming crab (P. pelagicus), the Japanese crab (Charybdis japonica), the rusty crab (C. feriatus), etc., will be transported alive to the market and dining table; on the other hand, when conditions are not suitable for live transportation, they will be quickly frozen on board or at the port before the crab dies, to ensure that no bacteria will grow after death, thus avoiding corruption and deterioration. This is why we see freshly chilled sea crabs sold in supermarkets.

In this case, once the frozen dead crabs are thawed, they must be eaten as soon as possible, otherwise there is still a risk of spoilage. Dead crabs in supermarkets and markets are generally either transported alive to the market and died, and are frozen or chilled for emergency treatment, or frozen crabs are thawed and sold. However, although frozen crabs can be eaten, the taste and flavor will become worse as the freezing time increases , so relatively speaking, fresh crabs are more suitable for consumption than frozen ones.

Cooked frozen king crab, it is not real crab

Source: Internet

Another type of dead crabs is "cooked frozen". After the crabs are caught, they are quickly cooked while they are still alive, and then frozen at low temperatures. The crabs treated in this way are already cooked, so they can be eaten directly after thawing. This method is more common in imported shrimps and crabs, such as snow crabs (Chionoecetes sp.), king crabs , brown crabs (Cancer pagurus), Arctic shrimps (Pandalus borealis), etc. Similarly, they cannot be kept for a long time after thawing and must be eaten as soon as possible.

What Arctic shrimp look like when alive

Source: Wikipedia

3

Can other seafood be eaten after it dies?

Many seafood products have high protein and fat content. When the environment is suitable (seafood dies, temperature rises, etc.), bacteria will multiply in a short period of time, causing seafood to quickly spoil. In particular, seawater also carries halophilic Vibrio parahaemolyticus , so for fresh seafood, you should try to choose fresh and alive ones. Even if it is chilled, frozen or cooked and frozen sea crabs and other seafood, you must ensure that they are fresh before eating.

If you search for "seafood" and "food poisoning" on CNKI, you will find that many articles and cases are related to Vibrio parahaemolyticus.

Source: Screenshot from CNKI

Take snails and shellfish as an example. The fresh snails and shellfish we see in the market are usually transported alive after being caught to the stalls. Generally speaking, snails and shellfish are more resistant to transportation than shrimps and crabs, but they may still die on the way, which means that there may be dead individuals mixed in with the snails and shellfish on the stalls.

Therefore, we must be extra careful when selecting. Rotten snails and shellfish will produce a strong odor. If you smell the odor of rotten protein at the stall, try not to buy them.

Red snails on the market

Source: Internet

Therefore, if you buy seafood in the market or supermarket, try to choose fresh and vibrant ones. If you find that some of the seafood is dead or even rotten after you get home, you must pick it out and throw it away.

Finally, let me highlight the following key points: river crabs (hairy crabs), blue crabs, and other freshwater crabs (including crayfish) cannot be eaten after they die; ordinary sea crabs can be eaten frozen or chilled; cooked and frozen shrimps and crabs can be eaten; snails and shellfish cannot be eaten if they are dead; no matter what seafood, it must be eaten fresh, and if any signs of corruption are found, never eat it.

I hope everyone can enjoy the delicious crabs with peace of mind and have a healthy and pleasant Mid-Autumn Festival~