Molecular recognition is doubtlessly one of the most important steps for scientists working in the field of flavors and fragrances, since it represents the primary link between an odorant and the full perception process [1]. At a molecular level, only some favored conformations of the odorant and flavor molecules will induce an activation of the receptor protein. To understand the structural preferences and molecular properties of such biologically active molecules, a joint approach using highly accurate theoretical and experimental techniques is required. On the experimental side, molecular beam Fourier transform microwave has emerged as an extremely powerful tool to perform conformational analyses of isolated molecules in the gas phase [2]. This method is especially interesting, when the systems of interest exhibit large amplitude motions that cause difficulties for the prediction of theoretical geometries. On the theoretical side, previous benchmark calculations showed that explicitly correlated coupled cluster technique with single, double and perturbative treatment of triple excitations (CCSD(T)-F12) in conjunction with the aug-cc-pVTZ or the cc-pVTZ-F12 basis sets lead to geometrical and spectroscopic (rotational, vibrational) parameters and energetics of small molecules close to those obtained using the costly standard CCSD(T) extrapolated to the complete basis set limit. In comparison, semi-empirical approaches are usually inadequate to sample the conformational space of such medium-sized molecules, as the energetically lowest conformations may easily be overlooked, which would subsequently strongly complicate the assignment of the microwave spectrum. Consequently, explicitly correlated schemes are viewed as the methods of choice for effective and accurate predictions for rigid, semi-rigid and weakly bound small and medium-sized molecular systems, and for the mapping of their multi-dimensional potential energy surfaces close and far from equilibrium getting access to full consideration of anharmonic effects [3,4,5]. Here, we applied a scheme using a mixture of first-principle and explicitly correlated coupled cluster methods to characterize the lowest energy conformations of the sulfur-containing odorant Cassis mercaptane in their electronic ground states. The microwave spectrum was recorded in the frequency range from 9000 to 14000 MHz and we successfully assigned the spectra of the three of the lowest energy conformers, obtaining three sets of highly accurate rotational and centrifugal distortional constants. This well-defined balance between state-of-the-art ab initio calculations and high-resolution spectroscopy technique allows to assign the structures of the observed conformers under molecular beam conditions and to push forward the development of new methodologies to improve computational predictions at affordable computational costs.