To understand the concept of freezing it is necessary to remember the fact that the meat consists of up to 75% of water. When water is placed in a freezer it freezes but also increases in volume.
Bottle of water is placed in a freezer. Water becomes ice and expands by about 10%.
Expanding ice puts pressure on the bottle and ruptures the glass. The ice remains in one solid block but the glass shattered into pieces although it still clings to the ice.
The same applies to meat – it contains water everywhere, inside the muscle cells, in sarcoplasm, in connective tissues of membranes and in smaller amounts in fats.
The water inside of the meat, like the water inside of a bottle, will become ice and because of its increased volume will expand and do damage to the meat protein, resulting in a loss of elasticity and its ability to hold water. How much damage is created depends directly on the temperature and speed of freezing.
When freezing is slow, water molecules that get frozen first are the ones that reside between individual muscle fibers. Water inside cells contains more salt, it is under higher pressure and lower temperature. As a result water molecules leave muscle cells and diffuse towards connective tissues. Crystals grow large, mainly outside the cells and damage the structure of the meat, membranes included.
When freezing at very low temperatures water has no time to leave cells and move into areas with lower pressure. Freezing is almost instantaneous, the formed ice crystals are very small and there is no damage to the internal meat structure. The crystals are formed inside and outside the cells, water in myofibrils is the last to freeze.
It shall be noted that the curing process progresses somewhat faster in meat that was previously frozen due to the disrupted cell structure that was created by ice crystals. Meat freezes at 28° F (-2° C) but to freeze all water present inside of the meat we have to create temperatures of -8°-22° F (-22°-30° C), which is well beyond the range of a home refrigerator.
The temperature of a home freezer is set to 0° F (-18° C) which fits into the slow freezing process described earlier. A butcher’s freezer -25° F (-32° C) is more effective but to really fast freeze the meat an industrial unit is needed. They freeze meat by blasting fast moving cold air over the product that drops the temperature to -40° F (-40° C). Freezing prevents the spoilage of sausage, however, keeping it in a freezer for longer than 6 weeks will lower it’s flavor, though it will still be nutricious and safe to eat. Fish contains more water than other meats and its cells are more susceptible to damage by ice crystals. This means that it is wiser not to freeze fish that would be subsequently cold smoked, for example cold smoked salmon which is usually thinly sliced.
Curing process progresses somewhat easier in meat that was previously frozen due to a swollen and ruptured structure of meat cells, what creates an easier path for the salt to follow.
|Storage time of some meats|
|Method||Refrigerated at: 28-32° F (-1.5-0° C)||Frozen at: -22° F (-30° C)|
|Pork halves||1-2 weeks||12 months|
|Beef quarters||4-5 weeks||18 months|
Color of Frozen Meat
The color of frozen meat depends on the size of the crystals that formed during freezing. Fast freezing rate creates small ice crystals which scatter most light leaving the meat looking opaque and pale. Of course color of the meat is influenced by the species and the amout of myoglobin they carry. In frozen meat, light accelerates discoloration. Meats kept in freezers should therefore be covered.
Freezer burn is the appearance problem that affect meat in frozen storage. The problem occurs in unwrapped or poorly covered meat which is stored at low humidity. Such meat starts to dry out fast leaving unattractive spongy layer. Meats kept in freezers should therefore be covered as a pracaution against freezer burn.