Why does starch paste thicken when stirred?

Starch paste thickens when stirred due to the mechanical agitation that breaks down the starch granules, causing them to swell and release amylose and amylopectin into the liquid. This process, known as gelatinization, increases the viscosity of the mixture as the starch molecules absorb water and form a gel-like structure. The stirring action enhances the distribution of heat and moisture, further promoting the thickening effect.