406 PRESERVATION OF FOOD 



gives the following periods for some : Trichinae die at or below 5 C. 

 in twenty days; Taenia saqinata, the beef tapeworm, dies in twenty- 

 one days; but Taenia solium, the pork tapeworm, may live more 

 than twenty-nine days. 



Food spoilage in cold storage is usually due to wrong temperature. 

 This is often true of the home icebox which is usually placed so as 

 to be convenient, not considering practicability, and a survey of 

 such refrigerators revealed the fact that the temperature is often 

 15 C. or higher. Such a temperature is ideal for rapid bacterial 

 growth. 



Foods taken from cold storage spoil rapidly as the bacteria in and 

 on the food have not been killed and the freezing has loosened up the 

 texture so the microorganisms can gain entrance. Moreover, the 

 enzymatic change which proceeds in the cold-storage product gives 

 rise to substances which accelerate bacterial activity. 



Drying. Nature's method of preserving foods is by drying, 

 for this is the universal principle used in preserving seeds. Bacteria 

 must have moisture to grow and multiply, and if the dessication be 

 great enough they die. Pathogens die quite rapidly when dried. 

 Furthermore, fruits, vegetables, and meats when preserved by this 

 method are usually cooked before eating; hence, the process has a 

 decided sanitary as well as economical significance. Although 

 nothing is added to the dried food and only water is lost, yet some 

 dried food loses its savor and probably at times decreases in digesti- 

 bility. 



The effectiveness of drying as a means of food preservation 

 depends upon the completeness of dessication and the specific food. 

 Those foods which are rich in soluble constituents are easily pre- 

 served by this method, for while the moisture present may be 

 considerable yet the osmotic pressure in the solution is too great for 

 bacterial growth. This is the reason grapes, apples, and prunes are 

 so easily preserved by drying, whereas meats and some fruits are 

 preserved with difficulty. 



A great variety of foods, such as meat, fruit, eggs, and even milk, 

 can be successfully kept by drying. According to Rohn's classifica- 

 tion the following groups of foods can be kept by this method : 



Group I Protein Foods 



Group II Carbohydrate Foods 



Group III Proteins + Carbohydrates 



Group IV Acids + Proteins + Carbohydrates 



Pressure. The use of pressure for the preservation of foods 

 is yet in the experimental stage. Hite and coworkers found that the 

 bacteria which cause spoilage in many fruits can be killed by press- 

 ure. Apple juice kept for five years after being subjected to a 

 pressure of from 90,000 to 120,000 pounds. Peaches and pears 

 exposed to a pressure of 60,000 pounds for thirty minutes never 



