40 



STUDIES OF POULTRY. 



That there may be definite criteria for the gauging of the rate of 

 decomposition, such methods as that of Folin for the estimation of the 

 ammoniacal nitrogen, and that for the determination of the acidity 

 of crude fat (see p. 12) have been adapted to the solving of the prob- 

 lems in hand. By the use of such methods gradations of quality are 

 not dependent upon the usual inspection, which consists of the evi- 

 dence of certain senses only, but are reduced to an impersonal 

 accuracy. 



The subject of refrigeration has a direct bearing on the study of 

 the comparative merits of removing the animal heat from poultry 

 by cold water and ice or by dry, cold air; and of maintaining the 

 skins of the birds in a dry condition, or of carrying them in cracked 

 ice throughout their marketing. The water cooling and ice packing, 

 keeping as it does the skins of the birds always wet, enables the 

 bacteria, which are universally present, to multiply and penetrate 

 the skin or any abrasion with but slight hindrance, since the tem- 

 perature maintained by cracked ice, when moisture is so plentiful, is 

 not very efficient in inhibiting bacterial growth ; and bacterial growth 

 in flesh means decomposition of some kind, too frequently unde- 

 sirable. A bacteriological study of skins of chickens chilled in dry 

 air and in water and ice shows a marked preponderance of organisms 

 in the latter after even a short keeping time, as marketing practices 

 go. In accordance with the fact that, for keeping, flesh should be 

 as nearly sterile as possible, chemical analyses of air-chilled and 

 water-chilled chickens show that the former change more slowly. 



As has been stated previously (p. 12), the development of acidity 

 in the fat is a delicate indication of the aging of flesh and one that 

 can be observed long before the senses can detect definite alteration. 

 Applying this test to the body fat of chickens chilled in the two ways 

 gives results as follows : b 



Acidity of fat as an index of freshness. 



Such results indicate very plainly why it is possible to maintain 

 high quality for longer periods when cold-air chilling is used than 



a Unpublished results, Food Research Laboratory, Bureau of Chemistry, U. S. 

 Dept. Agr. 



* Pennington and Hepburn, loc. cit. 

 [Cir. 64.] 



