We discuss a general way in which QCD can be checked in lepton-induced reactions - even with low statistics data. This is the "angular energy flow", or the average energy fraction outside a cone of opening angle 2σ about the principal jet axis. in the final state of deep inelastic reactions. We illustrate this method by a perturbative calculation of the angular energy flow in e+e- → qqg → jets. This perturbative approach can be extended to other deep inelastic reactions wit h gluon jets. At high enough energy, it should test QCD beyond lowest order in αs.