472 MICROBIOLOGY OF SPECIAL INDUSTRIES 



Changes dtjring CniLLiNG.-^The period of cooling is a relatively 

 short one, varying from a few hours to a few days in length. The chief 

 physical change is the intentional removal of heat by conduction and 

 convection, but there is usually also some loss of water by evaporation. 

 If cooled to a sufficient degree the water content of the food may 

 crystallize, altering to a considerable extent the physical structure of 

 the food substance (frozen food). Most foods are either actually 

 living when chilling begins, or they are only recently dead and various 

 chemical changes due to intrinsic enzymes continue at a diminishing 

 r^te as the heat is removed. Decomposition changes, due to microbes, 

 may also be in progress and continue during the process of chilling. 

 At this time the microbes living in the cold-storage chamber gain accpss 

 to the newly arrived food and others are added in the process of handling. 

 The extent to which these will grow and multiply depends upon their 

 ability to flourish under the storage conditions. In general the bacteria 

 which flourish at ordinary temperatures, producing the familiar decom- 

 position of the particular food, are greatly retarded in their activities 

 and other kinds outstrip them under the new conditions. The changes 

 taking place during chilling are very important in some special in- 

 stances, and often a very definite procedure must be followed to obtain 

 a satisfactory result. 



Changes during Storage. — This is often a relatively long period 

 and causes acting very slowly may ultimately produce marked altera- 

 tion. There is ordinarily some loss of water by evaporation, as well 

 as the evaporation or diffusion of other volatile constituents, some of 

 them at times important factors in the flavor of the food. Other vola- 

 tile substances may be absorbed from the air of the storage room. 

 The chemical changes of the chilling period continue at a greatly dimin- 

 ished rate, or may be entirely inhibited if the food is frozen. The 

 behavior of the microbic content of the food is the most important 

 factor to be considered during this period. Besides those already 

 present, various other microorganisms, bacteria, yeasts or molds, may 

 gain access to the food from time to time, either from the circulating 

 air or by contact with other things. The fate of the implanted microbes 

 will depend upon their nature and adaptation to the conditions exist- 

 ing in the stored food. Many of them perish, but many also survive 

 the entire period of storage, and some may actively multiply. There 

 can no longer be any doubt that some bacteria can grow at the tem* 



