398 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



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 giv- 

 ing 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 

 contamination at this time, and the accurate control of the storage con- 

 ditions. 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 temperature 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 absolutely 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 completely restored. The warmer air must 

 be dry and must be kept in motion to avoid condensation of moisture on 

 the exterior of the thawing meat. Bacterial activity is likely to gain con- 

 siderable headway during this process and the penetration of the microbes 

 into the flesh is favored by the diffusion currents. The more prolonged 

 the warming process the greater the opportunity for bacterial decompo- 

 sition. Ordinarily, 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 

 rapidly chilled by immersion in ice water or packing in ice immediately 

 after death, and are frozen as quickly as possible. During storage in the 

 frozen condition microbic activity is suspended, but in the subsequent 



