Evaluation of kinetic hydrate inhibitors (KHIs) in laboratory high-pressure cells generally yields scattered results. In this work we propose a procedure that consists of characterizing the effectiveness of KHI on second hydrate formation. This procedure limits the stochastic character of hydrate crystallization using the persistence of precursory hydrate structures in water that has previously experienced hydrate formation and decomposition. It is shown that the presence of these precursors strongly increases the repeatability of results compared with systems containing "fresh water" and allows unambiguous discrimination between blank (uninhibited system) and KHI tests.