DESICCATION, EVAPORATION, AND DRYING FOODS 455 



Many manufactured products, particularly baker's goods, as 

 crackers, biscuits, dried yeast cakes, etc., are preserved by the 

 elimination of water. 



Macaroni and vermicelli are prepared by forcing a thick paste of especially pre- 

 pared flour and water through openings of different sizes. The product is then 

 dried in the air until it is brittle and may then be kept indefinitely. 



Copra, one of the principal exports of certain of the islands of the Pacific and 

 Indian Oceans, is prepared by cutting the meat of the cocoanut into pieces and 

 drjdng them in the sun. From this copra, much of our desiccated and powdered 

 cocoanut is prepared. 



Syrups, molasses, jellies, jams, and many other carbohydrate foods 

 are preserved through the concentration of the solutes. Many of these 

 are partially sterilized by the heat used in the process of manufacture, 

 but there is usually plenty of opportunity for subsequent infection. 

 They are more frequently attacked by molds and yeasts than by 

 bacteria. An exception may be noted in Streptococcus mesenterioides 

 which sometimes causes considerable trouble by a gelatinous fermenta- 

 tion in syrups from which sugars are manufactured commercially. 



Foods with considerable quantities oifat usually contain little water. 

 Cottonseed, olive and other vegetable oils, the plant and animal fats, 

 as lard, tallow, and butter, are quite resistant to change by bacteria 

 unless water is present and considerable traces of nitrogenous im- 

 purities remain in them. With these foods the water is necessary for 

 the growth of the organism and also for the activity of the lipolytic 

 enzymes, which might hydrolyze fats and aid in the development of 

 rancidity. Butter forms an exception to the rule that fat foods contain 

 little water, as it usually has from 12 to 16 per cent. Where it is 

 necessary to keep butter-fat for long periods or under unfavorable 

 conditions, it is melted, the water and the nitrogenous impurities 

 removed, and the clear fat preserved. Bacteria, enzymes, and a few 

 molds have been described that attack fats. In the process of prepara- 

 tion or manufacture of any fat foods, sufficient heat is used to sterilize 

 the material and infection thereafter spreads to the interior very 

 slowly. The heat destroys the enzymes as well as the bacteria. 



The third class of foods preserved by drying includes those that 

 contain a high percentage of protein, in large part flesh foods and flesh 

 derivatives. 



