In this paper, we consider the b‐family of equations on the torus ut−utxx+(b + 1)uux=buxuxx+uuxxx, which for appropriate values of b reduces to well‐known models, such as the Camassa–Holm equation or the Degasperis–Procesi equation. We establish a local‐in‐space blow‐up criterion. Copyright © 2016 John Wiley & Sons, Ltd.