Page:The American Cyclopædia (1879) Volume XV.djvu/330

318 STARCH x., p. 448.) The sizo of the granules in each plant is not uniform, but there is an average which is generally not much departed from, although sometimes, as in the potato, the dif- Fio. 8. Starch Granules of Maranta arundinacea, or West India Arrowroot, magnified 200 diameters. FIG. 4. Starch Granules of Manihot utilissima, or Brazilian Arrowroot, mag- nified 225 diameters. ference is great (see fig. 5), but then it is characteristic. It is now believed that each granule consists of two substances intimately mingled, which are alike in chemical composi- tion, having the same proportion of elements as the cellulose (CaHioOs) which forms the cellular structure of plants. These two sub- stances are called granulose and cellulose, the former being soluble, the latter insoluble in boiling water. Starch is insoluble in cold wa- ter, and in alcohol and other liquids which do not decompose it ; but when treated with about 20 parts of boiling water its granules swell, become gelatinous, and fuse into a thick opaline liquid ; this on cooling solidifies into a homogeneous paste, or hydrated starch, which when dried becomes a hard horny substance like gum. If the starch is treated with 100 or 150 parts of boiling water, it forms an opa- line liquid, which does not gelatinize, but on standing allows the cellulose constituent to form a turbid deposit, while the granulose, or soluble starch, remains in the transparent so- /ution. Starch may be converted into dextrine and grape sugar by the action of diastase, or by boiling in a dilute acid. (See DEXTRINE, DIAS- TASE, and FERMENTATION.) It may be readily distinguished in the laboratory by the deep indigo-blue compound which it forms with iodine. The test is one of exceeding delicacy, but the iodine must be in a free state, for if it is combined with almost any other substance the affinity of the starch is not sufficient to abstract it. Starch may be obtained by rasp- ing, bruising, or grinding the vegetable struc- ture to pulp, and washing the mass upon a sieve, which retains the torn cellular tissue, or the gluten, while the starch passes through with the dissolved sugar and is precipitated, when it may be collected by decantation or elutriation, and washed and dried. The fol- lowing table shows the percentage of starch in various kinds of food, according to Payen : Potatoes 20-00 Bweet potatoes 16-05 Pea* 37-80 Beans 88-00 Flaxseed 28-40 Cacao 11-00 M-ffi Wheat Bye Oata 60-89 Barley 66'48 Indian corn 6T'65 Bice . . . The size and appearance of the several differ- ent kinds of starch granules when examined by the microscope are given in the engravings. Starch is extracted from grain by two prin- cipal processes, the old or fermenting, and the new or non-fermenting process. In employing the fermenting process the grain is steeped in water till it becomes soft enough to mash easily between the fingers. It is then passed through a malt mill or between rollers, and again mixed with water. Fermentation sets in, and lactic and acetic acids are formed, which disintegrate the cellular structure and liberate the starch granules. These are collected by repeated washings and precipitations, the process being continued for several days. The gluten under- goes putrefaction, emitting a most noisome odor. The sugar and a portion of the starch are converted into alcohol, and a part of this into lactic and acetic acids, which dissolve the gluten that has escaped putrefaction. Thor- ough washing and draining remove the soluble matters, and the starch left behind is next dried in blocks about 6 in. square ; as the water es- capes from them, the masses break up into the columnar fragments peculiar to starch. The other method, introduced by M. Smile Martin FIG. 5. Potato Starch, magnified 225 diameters. FIG. 6. Rice Starch, magnified 300 diameters. of Yervins, France, consists in kneading the flour into dough with water, and then washing on a sieve of No. 120 wire in a stream of wa- ter, as long as the water passes through milky. The starch in suspension and the sugary por- tion in solution are caught below the sieve, and the gluten nearly all remains behind in a sticky mass. What passes through is left to ferment 24 hours in an oven at 68 F., and a little leaven is added, or the skimmings of a former oper- ation, to hasten the process. The portion of gluten carried through with the starch is thus separated and removed by skimming. The starch is then treated like that otherwise ob- tained. The product by this method is about 50 per cent, of the weight of the flour, while by the other process it is only from 35 to 40 per cent. Nearly the whole of the gluten also is saved in a condition suitable for food, either by mixing it with flour and making of it maca- roni and similar pastes, or with boiled potatoes, and thus making a cheap and nutritious bread, by adding to the potatoes a nutritive element in which they are deficient. Potato starch is made from rasped or grated potatoes, by & process similar to that just described. This