Apparent viscosities of dispersions of swollen cornstarch granules

Cornstarch granules were dispersed in water at various concentrations and heated to 65, 67, 70, 75 and 80.degree. C for various times. Viscosity shear-rate plots for these dispersions were then determined at 60.degree. C and a shear-rate range of 3-500 s-1 using a rotational viscometer. A variety of viscosity shear-rate curves was observed that varied with concentration, cooking temperature and cooking time. A very sharp transition in the apparent viscosity behavior occurred between 65-67.degree. C with, for example, a viscosity of 2,000 cp observed both at 26% concentration when cooked at 65.degree. C for 15 min and at 15% concentration when cooked at 67.degree. C for 15 min. All apparent viscosity-concentration plots for temperatures from 65-80.degree. C could be superimposed by plotting .eta./CQ vs. CQ, where .eta. is the viscosity, C is the concentration in grams of dry starch per grams of dispersion and Q is the grams of swollen starch divided by grams of dry starch. The quantity CQ is equivalent to volume fraction of swollen starch in the dispersions.