Starch


Starch -

Is one of the most important and widely diffused of the proximate principles of the vegetable kingdom, being found in nearly all plants, serving for them the purpose of reserve food. It is formed from the water, obtained by the roots from the soil, and the carbon-dioxide drawn from the air, the combination being effected by the action of the sun on the chlorophyll of the leaves and stems.

In spite of its presence in a multitude of seeds, fruits, roots, etc., frequently in large percentage and sometimes in comparatively pure state, there are only a few plants furnishing it in sufficiently large quantity and growing in sufficient abundance to be profitably utilized for its commercial production. The best known of these are CORN, wheat, rice and Potatoes. After them come MANIOC (which see), or Cassava, for both edible and industrial purposes, and Sago for the former only. The greater part of the American output is obtained from CORN; that of Europe from the potato.

There are two principal grades of starch, (1) that used for food and (2) that employed for manufacturing and industrial purposes. The latter may be roughly subdivided into (a) Laundry starch, (b) starch for the finer manufacturing purposes, and (c) starch for calico manufacture, etc.

Food starches include such items as Arrowroot, Cornstarch, Sago and Tapioca (all described under their special headings).

In this country, potato starch is considered especially suitable for sizing yarns and for some kinds of silk and wool printing, but in the textile industries generally, rice and wheat starch are preferred to the potato product because of their greater stiffening powers. CORN starch has still greater stiffening powers and is consequently the most highly esteemed for many purposes, particularly in the laundry business, because of the white, smooth, glossy finish which it gives.

Pure starch is a glistening white powder with a characteristic feeling when rubbed between the fingers. It is insoluble in alcohol, ether and cold water.

Making starch from CORN.

The CORN grain, after shelling, clearing and going through Magnetic Separators, which draw out any nails or metal fragments, is steeped in vats of warm antisepticized water for about twelve hours and is then roughly crushed in order to facilitate the separation of the hull, germ and endosperm - the last-named, the body of the CORN, containing the starch, together with a certain amount of gluten, etc. In the separator, the germs (which contain the oil) rise to the surface and the hulls sink. Both being removed for utilization in various forms (see table of products in the general article on CORN), the endosperms are ready for the extraction of the starch content.

First comes treatment with sulphur dioxide or a similar antiseptic, then grinding and agitating in "shakers." The resultant starch-milk is allowed to settle and the crude starch obtained passes to tanks where it is washed in, and mixed with, alkaline water and is then run onto the "tables" where the starch is deposited. The tables, in numerous sections, each one hundred or more feet long, are set at a slight slope and are divided into canals, eighteen inches in width. The starch goes next to the "breakers," where it is again mixed with water, and thence to the centrifugal washers, refiners, etc., finally arriving in the muslin-lined drying boxes - constructed in sets, each box five to six feet in length and seven inches deep, with a perforated bottom. The boxes are connected with a vacuum chamber which rapidly extracts the water. The blocks thus obtained are cut into 7-inch cubes, kiln-dried and broken into various sizes.

Making starch from Potatoes.

The potatoes are first carefully washed and put through machines which remove the stones, gravel and dirt. They are then ground by means of other machines and the resultant pulp is sieved under a continuous flow of water, which washes the greater part of the starch through, leaving a residue of fibrous matter, or pomace - which is in this country frequently discarded as of little value, the starch content being comparatively small, but in Germany is generally pressed for hog-feed.

The starch-laden liquid from the sieves is allowed to settle in vats, and the crude starch thus secured is put through several washing, purifying and decolorizing processes, going then to the dry-houses, where it is spread on steam-heated frames. This preliminary drying is succeeded by other processes of water-extraction by means of cloths, etc., or by air or vacuum pumps. Finally come refining, separating, bleaching, etc.

In some factories, the potatoes are sliced, steeped in water and allowed to ferment to facilitate the extraction of the starch. The starch-milk is also frequently run along sloping gutters, on which it deposits the starch.

starch from wheat.

There are several processes used for the extraction of starch from wheat. By the older methods, the grain is first steeped in water until sufficiently swollen, then, either still whole or bruised by passing through rollers, is placed in fermenting vats.

When the fermentation has been completed, the mass is, in large factories, placed in washing drums from which the starch-milk runs into tanks. When the crude starch has settled, the water is run off and the starch is mixed with clear water and passed through various sieves and then washed, refined, etc.

The fermentation greatly reduces the value of the residue, as the sour gluten is fit only for hog feed, but the process is still largely employed because it is the easiest method of loosening the especially sticky gluten of wheat.

Among the numerous methods of wheat-starch manufacture without fermentation, are several similar to that just described, except that the separation is made while the steeped grain is fresh, the sweet gluten residue having considerable commercial value.

By the most modern methods, the wheat flour is first formed into a dough or paste. If the former, it is then separated into small pieces and worked backwards and forwards by machinery over a fine sieve and under a stream of water, the starch being carried off in milk form and a glutenous mass being left. If the paste form is employed, the starch is extracted by washing without kneading. The most promising of all fresh-grain methods is by means of centrifugal machines, the action giving almost pure starch by separation from thin flour paste.

starch from rice.

rice is of all grains the richest in starch, but it is in such form that the fresh grain processes will not extract it. Instead, the rice is first steeped in an alkaline solution, then washed and ground fine and again passed into the alkaline solution, where it remains with frequent stirring for twenty-four hours. This is followed by a rest of seventy hours, during which a partial separation is effected, the gluten having risen to the surface of the liquid and the fibrous portion of the grain and the starch having fallen to the bottom. The gluten and water are drawn off and the fibre and starch deposit stirred, then mixed and washed with an abundance of water and again allowed to stand. This second settling leaves the fibrous portion at the bottom of the tanks with a second layer of crude starch. The removal of the starch is followed by various purifying, washing, decolorizing and drying processes as for other starches.


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