Freezing by spraying with Freon 12. — 



A spray nozzle head was attached to the copper 

 tubing carrying liquid Freon from Dewar I 

 (Fig. I-l) . The Freon was sprayed in a sway- 

 ing action for about 6 min onto a crab meat 

 sample placed on a stainless steel screen. After 

 the meat was covered with another stainless 

 steel screen, it was turned over and sprayed 

 from the other side until completely frozen. 



Freezing by immersion in liquid nitrogen. 



— The same procedure as used in freezing by 

 Freon immersion was applied, using in this 

 case liquid nitrogen in the Dewar flask II (Fig. 

 I-l). The crab meat was dropped into the 

 nitrogen piece by piece. Since the meat sank 

 to the bottom, no cover screen was necessary. 



Freezing by intermittent dipping in liquid 

 nitrogen. — The crab meat was spread as loosely 

 as possible in the wire basket and then the 

 basket was immersed in the liquid nitrogen. 

 However, the liquid nitrogen immersion was 

 interrupted in short intervals to allow the in- 

 side of the sample to equilibrate in temperature. 

 This was done by dipping the sample 10 times 

 in 30 sec, with an immersion time of 2 sec each 



time. This procedure prevented cracking of 

 the frozen meat samples. 



Freezing by nitrogen gas blast. — An "Ultra 

 Freeze Simulator Freezer" of National Cyl- 

 inder Gas (NCG) Division of Chemetron Cor- 

 poration, Chicago, 111., was used to demonstrate 

 the effect of fast freezing in a low-temperature 

 nitrogen gas atmosphere. Freshly picked, reg- 

 ular blue crab meat was placed on a wire screen 

 (Fig. 1-3) and exposed to a blast of nitrogen 

 gas at a temperature of — 150° F. This tem- 

 perature was maintained by injecting controlled 

 amounts of liquid nitrogen into the gas which 

 was circulated by a high-speed fan. 



Slow freezing of blue crab meat. — The 



blue crab meat was packaged in a double wall 

 polyethylene bag, then wrapped by aluminum 

 foil and a paper bag. The different samples 

 were then placed in a — 20° F freezer room. 



Other Methods of Preservation 



Pasteurization of blue crab meat. — Vac- 

 uum-packed pouches (6.5 x 10 inches) con- 

 taining 95 g of crab meat were submersed into 



Figure 1-3. — Crab meat spread on 

 the screen of an "Ultra-Freeze 

 Simulator Freezer". 



