Experimental cookery

Uses. Starch, either alone or in flour, of which it may compose as much as 75 per cent and averages 65 to 70 per cent, is used in cookery : for thickening, as in soups and sauces; to form molded gels, i.e., cornstarch puddings and similar desserts; and, because hydrated starch has adhesive qualities, as a cementing or binding material for holding pieces of food together in the sauce base of croquettes and in the framework of such baked products as muffins, biscuits, cakes, and breads. Hence its charac- teristics of special interest in food preparation are its gel-forming properties. Alsberg (Wheat Studies) has given an excellent review of the role of starch in bread making. Sources of starch. Most of the starches and starchy foods used in food preparation are obtained from the cereals : rice, barley, rye, corn, and wheat. Starch is also obtained from tubers, potatoes and sweet potatoes being the principal sources. In addition tapioca, arrowroot, cassava, and some other starches are used to a limited extent. Starch from different sources varies in size, shape, and properties. Some starches are more suitable for some purposes than others. Some of these differences are in thickening capacity, adhesiveness, ease and rate of hydra- tion, and rate of hydrolysis by diastase. Samec states there are two possible explanations for these differences. ( 1 ) It may be supposed that starch is a homogeneous substance existing in many different colloidal conditions and (2) it may be assumed that starch is a heterogeneous system built up from a polysaccharide (or several kindred polysaccharides) together with inor- ganic or organic substances which accompany it. Under the first condition the properties would result because of different colloidal conditions and under the second condition the components with the starch would modify its properties. Size and shape of starch granules. Sjostrom has published excel- lent photomicrographs of the natural and gelatinized starch granules. Butcher gives excellent descriptions, and Scott gives both descriptions and illustrations. Starch is laid down as discrete particles called granules. Many SIZE AND SHAPE OF STARCH GRANULES 403 granules are compound, i.e., composed of aggregates of 2 to 25 or more granules. Some starch granules have a characteristic black spot called the hilum, which is an air space visible microscopically as a black spot. The hilum, even in varieties in which it is a definite characteristic, is not always present in all granules. In some starches distinct concentric markings or striations occur which are visible because certain portions of the granules contain less water and thus are denser than other portions. Naturally the size and to a certain extent the shape will vary with the growing condi- tions, so that sizes reported in the literature vary considerably. Fig. 43. — A photomicrograph of flour with enough water so that it will stick to the slide. Note that the starch granules are both oval and round. Magnification approximately x 100.