Cook king crab correctly!
When boiling king crab the core temperature in the muscle should be at least 90 ºC. The crab must then be chilled rapidly and frozen in brine or nitrogen. This achieves the best possible quality and meat utilisation, a recently completed research project at Nofima shows.
The objective of the project was to increase the value of king crab through better control of the processing conditions which affect the quality and quantity of crab meat. The project was funded by the Fishery and Aquaculture Industry Research Fund (FHF).
Cooking temperature and time
Today several methods are used to process king crab, such as different cooking methods, temperature regimes and chilling techniques. The choices that are made can influence both the quality and quantity of the meat. In light of this there is a significant need for knowledge linked to charting the consequence of different processing techniques such as the significance of bleeding, cooking time, cooking medium, chilling and freezing on the quality and quantity of the crab meat.
The project involved the implementation of four different experimental research designs, each with 2-3 kg male crab. The cooking time and core temperature in the crab legs influence both the meat utilisation (weight) and quality. Prolonged boiling after the core temperature has passed 90 °C resulted, for instance, in significant quality reductions of sensory qualities, such as taste, smell and consistency.
“This result has been demonstrated in crab legs that were boiled at a high temperature for a long time. They have significantly less meat utilisation compared to legs cooked at the core temperature of 80-90 °C for approximately 12 minutes,” says Senior Scientist Sten Siikavuopio.
On occasions it is reported that frozen crab can develop discolouration, particularly in the shoulders, which can be quite disfiguring. This is called “blueing” and is most likely an enzymatic reaction linked to the crab’s blood, which produces a discolouration of the crab meat and an extremely poor visual impression of the product. Such discolouration after processing can be a major quality problem. In particular in 2009 this was a significant problem for the crab producers.
Factors such as not bleeding the crabs, poor quality and boiling conditions have been mentioned as possible causes of blueing. The experiments show a clear connection between the core temperature during boiling and the proportion of the crab that develops blueing. Blueing was not detected in crab boiled at a core temperature of 90 °C.
Freezing, meat quantity and quality
Freezing trails pointed to the fact that crabs with high quantities of meat more easily developed cracking in the shell. This can occur when the freezing is so rapid that it creates a shell on the surface of the product that cracks when the inner core expands. Further, the trials show that the choice of the type of chilling medium during the freezing process influences the formation of ice crystals in the tissue. Freezing the crab meat in brine appears to produce smaller ice crystals compared to tunnel freezing, which produces relatively large ice crystals in the muscle.
There were large differences in the meat quantity in the crab legs of crabs that were still intact compared with those in damaged crabs. Whole, undamaged crabs had significantly higher meat quantity, on average 10 % higher than damaged crabs.
“These injuries can originate from earlier handling or from fights between the crabs and can lead to, for instance, them having only one claw and not being so good at getting food,” believes Senior Scientist Sten Siikavuopio.