Starches 



65 



STARCHES 



Starch is prepared by plants in their leaves 

 and other green parts from water and the 

 carbonic acid gas of the atmosphere, under 

 conditions of sufficient warmth and sun- 

 light. The excess of starch made above 

 immediate requirements is stored up for 

 the future use of the same plant, or in 

 seeds, tubers, etc., to give a good start in 

 life to the succeeding generation. Man takes 

 advantage o± this storing habit, and appro- 

 priates the supplies for his own use in several 

 instances. Starch belongs to the large group 

 of substances known as carbohydrates, and is 

 very similar in chemical composition to sugar. 

 Plants store up starch in the form of small 

 grains or granules, which vary very consider- 

 ably in size, shape, and other characteristics 

 in different plants, so that it is easily pos- 

 sible, with the help of a microscope, to 

 ascertain the source of a sample of starch, 

 and whether it is pure or adulterated. An 

 admixture of cheap forms of starch in 

 expensive arrowroots can in this way be 

 detected with the greatest ease. • ■ • 



Photo by W. G. Freeman 

 MAIZE GROWN AS A CATCH CROP IN 



BARBADOS 



POTATO STARCH 



By far the greater part of the starch used for commercial and technical purposes is obtained 

 from potatoes. Enormous quantities of the tubers are raised on the Continent and in the 

 United States, and, besides being employed as an article of food, are used as a source of alcohol 

 and starch. 



The potato contains starch to the extent of fifteen to twenty-five per cent, according to soil, 

 climate, and manuring, and about sixty-six to seventy-five per cent, of the full amount is 

 obtained by the manufacturer. The starch is contained in the cells of the tuber as oval grains, 

 and the processes of the manufacture aim at obtaining the grains in a perfectly clean condition, 

 free from all particles of cellulose and vegetable matter. The methods adopted vary somewhat 

 in different countries, but the essential features are the same in all cases, and the processes 

 of manufacture are relatively of great simplicity. A full account of the industry in the United 

 States has recently been published by the U.S.A. Department of Agriculture, and the follow- 

 ing information has been summarised from this report. The principal states concerned in 

 the industry are Maine, New Hampshire, New York, and Wisconsin. The first process consists 

 in washing the potatoes, and is carried out in revolving cylindrical washers about twelve feet 

 long and two feet in diameter, through which water is constantly passing. The potatoes when 

 perfectly clean are submitted to the action of a cylindrical rasper turning at the rate of 

 over 600 revolutions per minute, and a stream of water passing through the machine carries 

 the starch pulp away as soon as it is reduced to the required degree of fineness. The pulp 

 falls from the rasper into a fine wire gauze " starch separator," the meshes of which are suffi- 

 ciently large to retain the vegetable debris but allow the starch grains to pass through. 

 The actual passage of the grains through the separator is effected by shaking the framework 

 in a sloping position and allowing jets of water to play upon the starchy mass. The starch 

 which is carried through by the water falls into tanks placed underneath the separators, and 



