  We consider interjet observables in hard QCD processes given by the energy
flow E_out in a region away from all hard jets. Here the QCD radiation is
depleted (E_out << Q), and therefore these observables provide ideal means to
study non-perturbative effects. We derive an evolution equation (in the large
N_c limit) which resums, for large Q/E_out, all leading terms arising from
large angle soft emission (double logarithms are absent). We discuss the
analytical features of the result and identify universal and geometry-dependent
contributions. Our analysis confirms features found using numerical methods by
Dasgupta and Salam.
