Experimental cookery

Samec says that, if starch granules have been wet or soaked for some time before heating, gelatinization begins at a lower temperature. This gives at least a partial explanation for the shortened cooking period of soaked cereals. The kind of starch. Richardson, Higginbotham, and Farrow state that potato starch gelatinizes more readily than sago or cornstarch. They found that cornstarch gelatinizes slowly in water at temperatures up to 100°C. and in pastes prepared by heating for 30 minutes at this temperature the granules, although swollen, are far from completely dispersed in the solu- tion. The gel formed on cooling such a paste is quite distinct in type from that of potato, in which the granules are dispersed to a much greater ex- tent. A sago gel may be regarded as intermediate in type between those of potato and cornstarch. Alsberg and Rask report that wheat and maize starches change little until a temperature of 65 °C. is reached, when they begin to thicken slightly, thus increasing the viscosity. Woodruff and Nicoli heated 5-per cent starch suspensions by weight in a water bath at such a rate that 38 minutes were required for the paste to reach 90° and 22 minutes longer to reach 99.5 °C. They found the translucency increased quite suddenly at a temperature specific for each starch, this temperature not being sharp but covering a range of 1° to 2°. Heating a longer time to a higher temperature did not increase the trans- lucency. This temperature was as follows: Corn, 86-87°; wheat, 87-88°; rice, 84-85°; potato, 60-70°; arrowroot, 79-80°; and cassava, 74-75°C. It was necessary to heat each starch to 90° or higher for maximum gelatinization. The size of the starch granules. Alsberg states that Nageli found that larger granules of potato starch begin to gelatinize at 55°C., whereas the smallest granules do not begin to gelatinize until a temperature of 65 °C. is reached. Suggested reasons are that the walls of the larger granules may be thinner or that large granules in swelling necessarily develop greater internal pressures per unit of granule surface than small ones. The effect of large granules gelatinizing at lower temperatures and swelling more rapidly than small ones is indicated by Alsberg. Large granules in gelatinizing first swell and absorb more water which may affect the plasticity of the baking dough. *'If the average granule size is small, this effect would come later than if the average size is large." Other things being equal, the longer the dough remains plastic, presumably, the greater will be the volume of the baked loaf. The size of the starch granules might also apply to textures and volume obtained in cake. Effect of salts. In studying flocculation of starch pastes Samuel inves- tigated the effect of different metallic salts and found their action to be varied. Some lowered the gelatinization temperature considerably. VISCOSITY OF STARCH PASTES 409