Chew tenderness comes down to structural mechanics. Meat tissue consists of microscopic muscle filaments gathered into primary and secondary bundles wrapped in a sheath of collagen called the perimysium. During low and slow cooking, heat converts tough type-I collagen into soft liquid gelatin, a transformation that begins around 160°F and accelerates between 195°F and 205°F.
Gelatinization softens the matrix holding the muscle fibers together, but it does not dissolve the actual muscle cables. If you slice parallel to those fibers, a bite must pull across hundreds of long, unbroken filaments. The teeth encounter high tensile resistance, registering the meat as stringy and tough.
Cutting against the grain severs these bundles into cross-sections roughly a quarter-inch long. Chewing then only requires separating short fragments already loose from gelatinization, letting the slice part instantly under minimal pressure.
