n8 PLANT PRODUCTS 



part, and the liquor is then run off, leaving the starch as a 

 deposit. After washing once or twice, the starch is left. 

 This method is rather wasteful, as it is not easy to get more 

 than 30 per cent, of any of the grains in the form of 

 starch. 



(2) Alternative methods consist in macerating the raw 

 material with water, and passing through a fine sieve, 

 containing about two hundred meshes to the linear inch. 

 The glutinous parts remain on the sieve, while the fine 

 grains pass through in the water. The muddy starch liquor 

 is then allowed to settle, and the liquor is poured off, and 

 the starch dried. Combinations of these processes are 

 not infrequently used, in which a certain amount of 

 fermentation is permitted, and some kind of sieving method 

 is employed. In more modern systems it is not uncommon 

 to employ sodium hydrate and sulphurous acid as convenient 

 means of dissolving the proteins and obtaining a purer 

 starch. Starch must either be dried without any heat, 

 or a very low degree of heat must be maintained, otherwise 

 the starch becomes gelatinized. Potato starch gelatinizes 

 readily, but rice starch with difficulty. The large starch grains 

 gelatinize most readily. Air-dried starch will usually contain 

 about 20 per cent, of water, and that dried with a moderate 

 degree of heat contains only 10 per cent. The starch consists 

 of very small grains, which are recognized under the 

 microscope by their characteristic form and size. Potato 

 starch grains are large and rice starch grains small. 



Wheat. Wheat constitutes one of the most important 

 of the cereals which contain a high percentage of starch. 

 Wheat is grown in almost all parts of the world, best on a 

 fairly heavy soil, and in a climate which is neither very 

 damp nor very dry. Arid regions can, however, with the aid 

 of irrigation, produce very fine wheat crops. The intro- 

 duction of irrigation into the Punjab, in India, has resulted 

 in converting some almost useless land into very excellent 

 wheat country and the growth of wheat in Egypt is 

 dependent on irrigation. Wheat is, of all the crops, the one 

 which can be cultivated for the longest period of time on 



