474 MICROBIOLOGY OF SPECIAL INDUSTRIES 



storage in a cold air chamber to about +2° in forty-eight hours; and 

 the meat is stored at a temperature between +1" and +2°. Under 

 these conditions the enzymes of the dead flesh continue to act and 

 bacterial decomposition proceeds slowly, bringing about a process of 

 ripening which, up to a certain point, improves the market value of the 

 flesh by making it more tender and giving to it a more desirable flavor. 

 The extent to which the slow bacterial decomposition may proceed 

 before the flavor becomes disagreeable varies with different tastes, but 

 in general the beginning of proteolytic change which follows after the- 

 almost complete fermentation of the muscle sugar may be said to mark 

 the desirable limit. This point is reached in from a week to three 

 months, depending upon the condition of the animal, skill and care 

 in slaughter and dressing, especially the extent of bacterial contamina- 

 tion at this tim!e, and the accurate control of the storage conditions. 

 In the production of frozen meat the carcasses are rapidly chilled in 

 an air chamber at — 20°, where the meat remains until frozen solid. 

 It is then kept at a tempeirature below —4°. Freezing produces a 

 marked change in the finer physical structure of the meat, as the water 

 crystallizes, leaving the protein material, with which it was formerly 

 intimately mixed, in a shrunken and shriveled state between the 

 crystals. Enzymic and bacterial activities are practically if not ab- 

 solutely suspended under these conditions, and, save for slight surface 

 evaporation, such meat remains unchanged for long periods. The 

 subsequent thawing presents certain difficulties and requires particular 

 care. If warmed very slowly the melting water crystals are imbibed by 

 the protein material and the original structure of the flesh almost com- 

 pletely restored. The warmer air must be dry and must be kept in 

 motion to avoid condensation of moisture on the exterior of the thaw- 

 ing meat. Bacterial activity is likely to gain considerable headway 

 during this process and the penetration of the microbes into the flesh 

 is favored by the diffusion currents. The more prolonged the warm- 

 ing process the greater the opportunity for bacterial decomposition. 

 Ordinarfly, in order to avoid this, the thawing is carried out rapidly 

 and the finer structure of the meat is not restored. It is softer, darker, 

 and more moist than fresh or chilled meat, and usually sells at a lower 

 market price. 



Fish and poultry are usually frozen for storage! As these foods are 

 especially subject to rapid objectionable decomposition changes they are 



