A. This usually happens with homemade aioli. Extra virgin olive oil, a crucial ingredient in aioli, contains bitter-tasting compounds called polyphenols that are typically bound by fatty acids, preventing them from diffusing in a liquid. The blades of a blender or an electric mixer break olive oil into much smaller droplets than those created from hand-whisking. The smaller the droplets, the more polyphenols come off and scatter, and the more bitter the aioli will be.