FOOD MATERIALS 1035 



weight than the adult. Authorities say that the needs of children are as 

 follows : 



Under 1 year 100 calories per kg. (or 45 calories per pound body-weight). 



1-2 years 100-90 calories per kg. (or 45-40 calories per pound body-weight). 



2-5 years 90-80 calories per kg. (or 40-36 calories per pound body-weight). 



6-9 years 80-70 calories per kg. (or 36-32 calories per pound body-weight). 



10-13 years 70-60 calories per kg. (or 32-27 calories per pound body-weight). 



14-17 years 60-45 calories per kg. (or 27-20 calories per pound body-weight). 



Comparison of these food requirements of the child with those of the 

 adult shows strikingly that the child needs a liberal diet) — much more in 

 proportion to his body weight than the adult. 



Reasons for Cooking Food Materials. — Food materials are cocked for 

 the purpose of developing flavor, of making foods more easily digestible 

 and of killing bacteria. Doubtless, the use of fire in the preparation of food 

 was first discovered by accident ; the flavor developed by the action of heat 

 on meat appealed to the palate, and so the action of heat on various other 

 food materials was tried gradually. Also, it was learned that some foods 

 keep better when cooked. But it was reserved for the last century to 

 explain scientifically the effects of heat on the palatability, the digestibility 

 and the keeping qualities of food. 



Effects of Heat on Foodstuffs. — One of the first lessons to be learned in 

 the cooking of foods is that all food materials conduct heat slowly — that is, 

 it takes time for heat to penetrate them. 



The proteins are coagulated, hardened by heat, and the higher the 

 temperature the more they are hardened. Hence the difficulty of cooking 

 meats "to a turn" and of cooking eggs so that they shall be tender. 

 Proteins should be cooked at a comparatively low temperature — below 

 the boiling point of water; otherwise they will be tough and indigestible, 

 i. e., not easily dissolved by the digestive juices. High heat should be 

 used at first with meats to sear the outside in order to keep the juices in; 

 then the cooking should proceed at a lower temperature. In re-heating 

 meats, the protein is much hardened. Soft-cooked eggs are best when 

 put into cold water, covered, and heated just to the boiling point. Eggs 

 may be cooked hard, and yet be tender, if put into boiling water, covered, 

 then set where water will keep hot, but not boil, for 30 to 45 minutes. 



The fats melt when heated, but otherwise seem to be unchanged except 

 at high temperatures. Then they are decomposed, and at least one of the 

 products formed is very irritating to the mucous membrane. This is one 

 reason why people find difficulty in digesting fried foods. Butter scorches 

 easily because of the small amount of protein in it. 



Of the carbohydrates, sugar is melted, but not otherwise changed by 

 heat unless heated to caramelization, or to the burning point. Starch, 

 when cooked by dry heat, changes into dextrine, a more soluble and hence 

 more digestible form of carbohydrate. When starch is cooked in the 

 presence of water, the granules swell and finally burst open. This renders 



