11 



Boiling also brings about another form of thickening. It is common 

 knowledge that all starchy grains, such as rice, sago, tapioca, oatmeal, or 

 macaroni, must be cooked in boiling water, otherwise they remain hard and 

 indigestible. When well " boiled " they become soft and glutinous. The reason 

 for this change is found in the fact that the groundwork of every part of 

 plants, whether hard or soft, is a fibrous substance called " cellulose," a tough 

 and indigestible material, though often of marvellous delicacy. 



Starch of a Potato when changed by cooking. 



If a piece of potato or a few grains of arrowroot or rice be looked at 

 under a microscope, they will be seen to consist of numbers of little round 

 bags (or "cells," as we call them), of which the outer covering is comi>osed 

 of cellulose. The nutritive starch is enclosed in these cells, and can only be 

 released when their covering is softened by boiling. Under the influence of 

 heat, too, the starch swells and bursts its envelope. Thus when a sauce 

 thickens or rice softens, it means that the envelopes have burst and the 

 contents of the cells have become soft and fit for food. 



All cereals, green vegetables, and most roots must be boiled, or their 

 cellulose framework remains tough and indigestible. Meat and poultry or 

 fish, on the contrary, must only be boiled just long enough to seal their pores, 

 when the cooking process must be continued at a lower temperature; for they 

 contain considerable amounts of a substance closely resembling white of egg. 

 called "albumen." The difference between a ''lightly boiled" and a "hard- 

 boiled " egg is familiar to us all. Fresh foods also become tough and leathery 

 when cooked too fast or at too high a temperature. 



Haw albumen is quickly and easily digestible, and so it is when heated 

 to 134 Fahr.. when fine threads of white appear in the clear, sticky liquid. 

 If the temperature is raised another 30 the albumen becomes a tender, white 

 jelly, when it is still quite suitable for the most delicate digestion. Kggs 

 placed in boiling water and then stood on one side of the stove for twenty 

 minutes, so that the water cools very gradually, are cooked to just this 

 digestible degree. The tough condition of the "white" of a hard-boiled egg 

 is common knowledge. It can be digested, but at a greater expenditure of 

 time and energy. There are occasions when it is advantageous to be provided 

 with hard-boiled eggs, as, for instance, when a long interval before the next 

 meal is inevitable; but under ordinary circumstances the albumen in meat. 

 eggs, fish, or poultry should be so cooked that its tender and digestible 

 qualities are preserved. 



