Amyloid fibrils offer the possibility of controlling their contour length, aspect ratio, and length distribution, without affecting other structural parameters. Here we show that a fine control in the contour length distribution of β-lactoglobulin amyloid fibrils, achieved by mechanical shear stresses of different levels, translates into the organization of tactoids of different shapes and morphologies. While longer fibrils lead to highly elongated nematic tactoids in an isotropic continuous...