Linear Amylose and Bushy Amylopectin

The shapes of amylose and amylopectin molecules have a direct effect on their ability to thicken a sauce. The straight amylose chains coil up into long helical structures when dissolved in water, but they retain their basically linear shape. Their elongation makes it very likely that one chain will knock into another or into a granule: each sweeps through a relatively large volume of liquid. By contrast, the branched shape of amylopectin makes for a compact target and therefore a molecule less likely to collide with others; and even if it does collide, it’s less likely to get tangled up and slow the motion of other molecules and granules in the vicinity. A small number of very long amylose molecules, then, will do the job of more but shorter amylose molecules, and of many more bushy amylopectins. For this reason, the cook can obtain the same degree of thickening from a smaller amount of long-amylose potato starch than from moderate-amylose wheat and corn starches.