we caught crab at Waldport Oregon Sept. 1 2 and 3. Cleaned and cooked them and quickly cooled them and put them on ice. Yesterday some of the crab had turned blue and the meat and even the shells looked bruised.Why? We threw them away.
Blueing is sometimes seen in canned crab that is canned without a lined can. The corrosive metal reacts with the crab and turns it blue. Doesn't sound like you pressure canned it, so possibly a corrosive metal came in contact with the meat, through juices, etc... Another possibility is the butchered crab sat too long and the juices or blood of the crab stained the meat. Probably was safe to eat. Butchered crab should be held on ice and cooked almost immediately. If the sections were boiled in water say 10 minutes, there were probably cooked sufficiently, you can always tell of course, they turn white. Again, blueing is often related to exposure to corrosive metals, it is also seen in canned shrimp.
Thank for your question about crab cooking issues, and congratulations on getting your crab catch. Here is a long answer for you. First, you did the right thing by not eating the crab that’s meat had turned blue for unknown reasons. Seafood poisoning is serious. After consulting with an Extension agent and researching online, other than metal contamination, we think at least three other things could have happened:
1) the meat actually may not have been cooked fully, so remember larger crab take a bit longer than the smaller ones. Crab blood can turn blue/black soon after being cooked if not at a full boil long enough, first in body meat and follows veins down into leg meat. The blue comes from hemocyanin, a copper-containing protein that transports oxygen in the blood. You need to start cooking timing AFTER it reaches a boil and maintain a steady boil, during the process.
2) putting crab on ice too soon can create a condition similar to an ice cave, where the heat from the cooked crab creates pockets of insulation within the ice, actually keeping it warm longer. And
3) a few crab themselves may have started to die and decompose prior to cooking. This happens rather quickly as crab don’t “travel well” and need oxygen and cold (not freezing) temperatures between catching and cooking. September is one of the warmest months on the Oregon coast. But even cool crab don’t do well after the first day in captivity, many die.
“Crab meat deteriorates rapidly after the death of the animal predominantly because of the action of enzymes in the white flesh and in the hepato-pancreas, the brown meat. While the crab is alive, the enzymes are under natural biochemical control but, on the death of the crab. They work indiscriminately to degrade the quality of the meat. Digestive enzymes break down the flesh, reducing yield and imparting off-flavours to it. Other enzymes in the flesh break down the compounds which impart the sweet, creamy flavours typical of fresh crab meat resulting in a lack of flavour. These enzymes are inactivated by heating. And the best flavoured meat of the highest yield is obtained from crabs which have been cooked alive or very soon after death.” From: INFOFISH Marketing Digest No 4/84.
So for others reading this too, the best way is to thoroughly boil fresh-caught crabs for the correct timing immediately after killing. Dungeness crab are usually boiled for approximately 20 minutes total. Then rinse in cold water and “keep” at cool temperatures for a while before proceeding – refrigerate crab before freezing or packing. And finally, as you know, any crab that die before cooking must not be eaten.
As a kid, I have fond memories of taking our crab right out of the boat and boiling it on the beach in sea water for the best taste. Note that Alaska fishers do not recommend eating the internal organs including the "crab butter" (hepatopancreas). Here are some references. I hope this all helps you in some way.
Happy future crabbing!